OCEAN
Explore a Watery World
LAURA PERDEW
Illustrated by Micah Rauch
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CONTENTS
Introduction
Chapter 1
Chapter 2
Chapter 3 The Intertidal Zone . . . 40
Chapter 4 Shallow Oceans . . . 52
Chapter 5 Open and Deep. . . 64
Chapter 6
and the Ocean . . . 78
Chapter 7
• Glossary
• Metric Conversions
• Essential Questions
• Selected Bibliography
• Resources
• Index
Interested in primary sources? Look for this icon.
Some of the QR codes in this book link to primary sources that offer firsthand information about the topic. Many photos are considered primary sources because a photograph takes a picture at the moment something happens —but watch out for fake ones! Use a smartphone or tablet to scan the QR code and explore more! You can find a list of the URLs on the Resources page. You can also use the suggested keywords to find other helpful sources.
Earth’s Oceans
Timeline: to come
MEET EARTH’S OCEANS
The Blue Planet. The Big Blue Marble. The Blue Sphere. Have you heard these nicknames for our planet? Why are they a good fit? Because the ocean covers roughly 70 percent of the planet! If you look at Earth from space, it looks like a bright blue dot among other, less colorful orbs, none of which have liquid water.
ESSENTIAL QUESTION
What role did the ocean play in evolution of life on Earth?
The world’s ocean takes on many different forms. Some parts are shallow and clear, teeming with colorful fish and corals. Other areas are deep and dark and mysterious. Still other parts of the ocean send waves pounding against sandy beaches or rocky shores. Sometimes, the ocean roils and twists with swells as tall as buildings. And then there are the days when the ocean is calm and quiet, lapping at our toes or slapping rhythmically against our boats.
THE OCEAN
WORDS TO KNOW
equator: an imaginary line around the earth, halfway between the North and South Poles.
erode: to wear away.
plankton: tiny aquatic organisms that drift in tides and currents of water.
larva: an organism at the beginning stage of development. Plural is larvae.
phytoplankton: tiny aquatic plant-like organisms that produce their own energy through photosynthesis.
zooplankton: tiny animals that drift freely in salt water and fresh water.
photosynthesis: the process a plant goes through to make its own food; the plant uses the energy of the sun to turn water and carbon dioxide into sugar, with oxygen as a waste product.
The ocean is both mighty and fragile. It is full of mysteries yet to be discovered. And most importantly, it is essential to all life on Earth.
Should
you use the word “ocean” or “sea?”
Use the word “sea” to refer to a smaller body of water that is part of a larger ocean.
OCEANS OF THE WORLD
You may have heard that there are five oceans on Earth: Pacific, Atlantic, Indian, Southern, and Arctic. This is true. Yet the ocean is actually one enormous body of salt water. The five oceans are all connected with no boundaries between them, like a house with no walls on the inside.
The largest and deepest of Earth’s oceans is the Pacific. At its widest point, the Pacific extends almost halfway around the planet.
Earth from space. Look at all that water!
credit: NASA’s Earth Observatory
The Atlantic Ocean is the second largest ocean. It sits between the Americas and Europe and Africa.
The Pacific and Atlantic Oceans both straddle the equator. The Indian Ocean lies south of the equator and Asia, and has mostly tropical waters. The Southern Ocean surrounds Antarctica and is the iciest, windiest, and most dangerous of the five oceans. On the opposite side of the globe, the Arctic encircles the North Pole. Most of the year, the waters of this smallest ocean are covered in sea ice— some of it stays frozen year-round.
The ocean is salty because of dissolved minerals that originated on land. During millions of years, rain erodes rocks on land and washes the minerals out to sea, where it accumulates.
Plankton
SPECIES SPOTLIGHT
Plankton are small. Most are less than an inch long and many cannot be seen without a microscope. But they are mighty! They form the base of the whole marine food web. Most plankton spend their entire life cycle drifting in the water, carried by tides and currents. Their very name comes from the Greek word planktos, which means “wanderer” or “drifter.” However, some animals are plankton in the larval stage, then mature and grow big enough to be able to swim.
There are two types of plankton: phytoplankton and zooplankton. Phytoplankton are tiny aquatic plants and zooplankton are tiny animals. Phytoplankton produce their own food through photosynthesis, just as plants on land do.
Not only do these tiny plants take in carbon dioxide from the atmosphere, they also produce oxygen. In fact, 50 percent of the oxygen in our atmosphere is produced by phytoplankton!
Zooplankton include sea snails, krill, and worms of the open ocean. Zooplankton and other small aquatic species eat phytoplankton. In turn, zooplankton are a key food source for larger species. In the ocean, giant whales including humpbacks and blue whales survive largely on krill!
Phytoplankton may be microscopic yet they are essential to life on our planet. Learn more about them on this SciShow video. Why do we owe our lives to phytoplankton?
THE OCEAN
WORDS TO KNOW
molten: made liquid by heat.
water vapor: the gas form of water in the air.
condense: the process by which a gas cools and becomes a liquid.
salinity: the measure of dissolved salts in water.
basin: a depression in Earth’s crust that holds water.
comet: a ball of ice and dust that orbits the sun.
geology: the study of the physical features of Earth including its layers.
density: the amount of matter in a given space, or mass divided by volume.
inner core: the innermost layer of Earth, made of super-hot solid metal.
outer core: a spinning mix of liquid nickel and iron surrounding Earth’s inner core.
mantle: the middle layer of Earth.
crust: the earth’s outer layer.
basalt: a black, shiny volcanic rock.
granite: a type of rock that contains many crystals. It is formed underground over a long period of time with an enormous amount of pressure.
THE OCEAN’S BEGINNINGS
The way the ocean looks now is very different from how it used to look. In fact, when Earth formed more than 4.5 billion years ago, there was no ocean at all—the planet was way too hot. It was so hot that the rocks were molten , glowing liquid. Water could not accumulate. As millions of years passed, though, the planet cooled enough for water vapor to condense. That allowed water to gather and oceans to form.
Of all the water on Earth, 97 percent is in the ocean.
We are lucky to have that water on Earth— we wouldn’t be here without it! But scientists are still not completely certain where that first water vapor came from.
One theory is that the water was already here when Earth formed. According to that theory, as the molten rock cooled, it released water vapor, which condensed into rain and eventually filled basins that became our oceans. Another theory suggests that icy comets struck our planet when it was young, bringing us water. The reality is that our water may have come from multiple sources and scientists are still investigating.
Learn more about ocean salinity from this Woods Hole Oceanographic Institution video. Where on Earth are the oceans the least salty?
Woods Hole salty
No matter the source, water accumulated on Earth and the ocean formed about 3.8 billion years ago. Earth used to be one, huge shallow ocean covering the whole planet—there were no continents.
And here we must pause for a short geology lesson. Yes, this is a book about the ocean, not rocks. But in order to understand our ocean’s past and present, we need to understand what Earth is made of.
Let’s start with the four layers of Earth. As the planet formed, layers of lighter and heavier rock separated. The denser, heavier rock—made of iron and nickel—sunk deep toward the center of Earth to make up the solid inner core. The outer core is also made of iron and nickel, but in liquid form. The next layer is the mantle , made of iron, magnesium, and silicon. This layer is also liquid, but thicker than the outer core. Finally, the lighter rock formed the crust , the thinnest layer.
The crust is made of two kinds of rock, basalt and granite. Basalt is denser than granite. Gradually, these lighter and heavier rocks in the crust also separated into layers.
THE OCEAN
WORDS TO KNOW
oceanic crust: the section of Earth’s crust that is located on the floor of ocean basins.
continental crust: the part of the earth’s crust that forms the continents.
tectonic plates: the large solid pieces of Earth’s crust that float on the mantle.
microbes: tiny organisms too small to see without a microscope, including bacteria, viruses, and some algae.
hydrothermal vents: undersea hot springs that spew mineral-rich water.
cyanobacteria: a bluegreen type of aquatic bacteria that produces oxygen through photosynthesis.
cataract: a type of waterfall with a large vertical drop.
sea level: the level of the surface of the sea.
topography: the physical features of the surface of the Earth.
Basalt formed the oceanic crust , which pushed deep into the mantle. This created basins, where water accumulated and formed the ocean. The lighter granite rose and formed the continental crust . The first continents emerged from the ocean approximately 3 billion years ago.
Now, the Earth’s crust is not one solid shell around the planet like the shell of an egg. Instead, it’s in pieces—similar to a gigantic puzzle. Those pieces are called tectonic plates , and they float on Earth’s mantle of hot, partially molten rock. Continents sit on the tectonic plates. And even though we can’t see it or feel it, those plates and our continents are always moving! The moving plates change the size and shape of the ocean basins.
Okay, geology lesson complete. While Earth’s tectonic plates were busy drifting around and crashing into each other, something extraordinary was happening in the ocean. Life began.
LIFE ON EARTH
When Earth when was a hot, roiling, gassy mess, life could not exist. But, as you know, the planet cooled. That’s when the first single-celled organisms appeared in the ocean—roughly 3.5 billion years ago. They set the stage for all life on Earth.
Learn more about tectonic plates on the American Museum of Natural History website. How have plate tectonics affected our planet?
AMNH pangaea
Those microbes survived in a harsh environment—lots of carbon dioxide and methane and almost no oxygen. Instead of using the sun, they got their energy from underwater hydrothermal vents that spewed mineral-rich water, allowing them to grow and reproduce. Millions of years later, microbes called cyanobacteria evolved.
Roughly half the oxygen in our atmosphere today is produced by plankton in the ocean.
World Records
While the ocean itself is incredible, it is also full of world-record features!
› Longest mountain range: You might guess that the longest mountain range is the Andes (about 4,350 miles long) in South America. But the longest is actually under water—the mid-ocean ridge stretches more than 40,000 miles around the planet.
› Largest waterfall: A waterfall in the ocean might sound odd, but the Denmark Strait cataract between Iceland and Greenland is the world’s largest. Denser cold water from the Nordic Seas meets warmer waters in the strait and plunges nearly 2 miles over a huge underwater drop.
› Tallest mountain: Most mountains rise above the continent on which they sit. Mauna Kea, however, rises from the ocean floor. Approximately 13,780 feet of the mountain are above sea level. But, measured from its base beneath the ocean, the whole mountain is 33,500 feet tall.
› Deepest trench: Far below the surface of the ocean is the Mariana Trench in the Pacific Ocean. This curved trench is more than 1,500 miles long and 43 miles wide. Challenger Deep is its deepest point at a depth of 36,000 feet—that’s the deepest point in the ocean.
› Largest living structure: The world’s largest living structure can even be seen from space! It is the Great Barrier Reef off the coast of Queensland, Australia, which covers approximately 133,000 square miles and is nearly 1,500 miles long.
To get a better understanding of how an underwater waterfall works, visit the NOAA website. How does the topography of the seafloor help create this waterfall?
NOAA largest underwater waterfall
THE OCEAN
WORDS TO KNOW
Great Oxygenation Event: the introduction of oxygen into the earth’s atmosphere 2 billion years ago.
biodiversity: the variety of life on Earth.
marine: having to do with the ocean.
primary producers: plants and animals that can produce their own food through photosynthesis, forming the base of the food chain.
primary consumer: a plant or animal that eats tiny plants and phytoplankton.
baleen: the tough, flexible material hanging down in some whales’ mouths to help trap their food.
Cyanobacteria can convert sunlight into energy through photosynthesis. The evolution of this microbe changed the course of life on Earth. Here’s why: During photosynthesis, cyanobacteria expelled oxygen as waste. Believe it or not, those microscopic photosynthetic organisms are responsible for the buildup of oxygen in our atmosphere! Their waste is the oxygen we breathe! This Great Oxygenation Event took place more than 2 billion years ago.
For a look at the origins of life on Earth, watch this TedEd video. How did scientists determine the most likely starting point for life on our planet?
Having oxygen in the atmosphere changed everything—thank you, cyanobacteria! More complex life forms evolved. Biodiversity increased. The first multi-cellular organisms appeared approximately 1.5 billion years ago. These were the beginnings of simple plants and animals.
Even as more complex life forms evolved, all life still lived in the ocean. Plant life gradually began moving onto land about 500 million years ago. That set the stage for the evolution of land animals. Both on land and in the ocean, life continued to evolve, becoming more diverse and more complex, leading to the plants and animals we know now.
TedEd life origins
LIFE ZONES IN THE OCEAN
Today, there are thousands of species of plants and animals living in the ocean. These include some of Earth’s smallest life forms such as microscopic algae called phytoplankton, and the largest animal ever to live on Earth, the blue whale.
The tiny phytoplankton are at the base of the marine food web. These primary producers use sunlight to make their own food. They are, in turn, eaten by primary consumers , including zooplankton, crustaceans, and small fish. Zooplankton are then eaten by larger consumers such as fish, crustaceans, sharks, and baleen whales. The ocean’s top predators include toothed whales, large sharks, marlin, dolphins, and leopard seals.
Ocean Explorer: Jacques Cousteau
Frenchman Jacques Cousteau (1910 – 1997) was a pioneer in ocean exploration and conservation. In 1943, he and engineer Emile Gagnan (1900 – 1984) invented the aqualung. The aqualung allowed people to move about freely and breathe under water for long periods of time. It was called the Self-Contained Underwater Breathing Apparatus, known today as scuba.
Jacques Cousteau spent nearly seven decades conducting research and exploring the sea, made possible by the aqualung. Through his expeditions, he not only discovered the wonders of the ocean, but also its fragility. Cousteau understood that the ocean needed protecting. To raise awareness, he brought the undersea world to the public through his films and books, believing that “people protect what they love.” Cousteau inspired millions of scientists, explorers, and conservationists to protect Earth’s oceans and its biodiversity.
Cousteau’s legacy lives on in the exploration and research of the Cousteau Society. Visit its website to learn more. Why is the work of the Cousteau Society important to the planet?
Cousteau Society
THE OCEAN
WORDS TO KNOW
ecosystem: an interdependent community of living and nonliving things and their environment.
water column: the vertical column in a body of water from the surface to the bottom, with different features at different depths.
sonar: the use of sound waves under water to measure depth and detect objects under water.
hull: the body or frame of a boat.
In today’s ocean, there are five different life zones. Each is its own unique ecosystem with organisms adapted to living there.
• Sunlit Zone: Bet you can guess how this zone got its name! This is the zone that is closest to the surface of the ocean, where sunlight reaches into the water to a depth of 660 feet. And, thanks to the sun, the water is warmer in this zone than in deeper water. This part of the water column is only about 2 to 3 percent of the whole ocean, but 90 percent of marine species live there.
• Twilight Zone: This zone is well-named, too. It is the layer of the ocean just below the sunlit zone, from 660 to 3,300 feet deep. The light is dim in this zone and because of that, there is no plant life.
Tech Talk: Mapping the Seafloor
The exploration of the ocean includes mapping the seafloor. Yet, as of 2024, just over 25 percent had been mapped in high-resolution using multibeam sonar. The sonar is attached to the hull of a ship and sends out multiple sound waves in a fan shape. The technology measures how much time passes between the sound wave being emitted, hitting the seafloor, and returning. The pings, or return sounds, allow scientists to create an image of the seafloor and the nearby land areas. These images reveal the ocean depth and the terrain of the seafloor—including mountains, trenches, and volcanoes. It also reveals shipwrecks!
This information adds to our understanding of the ocean and helps with ocean navigation, laying cables and pipelines, and mining. This knowledge also means we can make informed decisions about regulations and conservation.
• Midnight Zone: Below the twilight zone is the midnight zone, down to a depth of 13,100 feet. As the name suggests, there is no light here. Despite the lack of light, cold water temperatures, and extreme water pressure, many species are adapted to life in this zone.
• Abyssal Zone: Deeper still is the abyssal zone, which extends to 21,325 feet deep. Most of the oceans bottom out in the midnight zone at 13,100 feet deep, yet there are trenches and canyons that extend even deeper. This zone, often called the abyss, is deeper, darker, and under more pressure than the midnight zone.
This video, The Life Hydraulic, takes you on a deep dive through the layers of the oceans. How do conditions change as you dive deeper into the ocean?
• Hadal Zone: The deepest zone of the ocean was named after the Greek god of the underworld, Hades. This zone is found in deep ocean trenches that extend down to a depth of 36,000 feet. It is a world of extremes and low biodiversity.
The Scientific Method
A scientific method worksheet is a useful tool for keeping your ideas and observations organized. The scientific method is the process scientists use to ask and answer questions. Use your science notebook to make a scientific method worksheet for each experiment you do.
Question: What are we trying to find out? What problem are we trying to solve?
Research: What is already known about this topic?
Hypothesis: What do we think the answer will be?
Equipment: What supplies are we using?
Method: What procedure are we following?
Results: What happened and why?
TedEd life Hydraulic
THE OCEAN
WORDS TO KNOW
oceanographer: a scientist who studies the ocean and the plants and animals that live there.
We know a lot about the ocean, yet much of it remains a mystery. It is the least explored ecosystem on the planet. While the ocean covers more than 71 percent of our planet, only 5 percent of it has been explored.
As you read this book, you will become an oceanographer, exploring many different aspects of the ocean from the huge role it plays on the planet to the fascinating marine life found under the surface. You will also learn how we rely on the ocean for food, transportation, and recreation— and the impact humans have made on it. Plus, you will see how people around the world are working to protect our amazing oceans and how you can contribute, too.
If you’ve ever taken a deep dive in a pool, lake, or ocean and felt your ears pop, you know that the pressure increases the lower you go. Water pressure is one reason why the ocean depths have not been more fully explored.
Essential Questions
Each chapter of this book begins with an essential question to help guide your exploration of the world’s oceans. Keep this question in mind as you read the chapter. Keep the question in your mind as you read the chapter. At the end of each chapter, use your science journal to record your thoughts and answers.
ESSENTIAL QUESTION
What role did the ocean play in evolution of life on Earth?
THE OCEAN IS SALTY!
One of the ocean’s best-known characteristics is that it is salty. The ocean’s salinity affects both the water’s density as well as the temperature at which it freezes. See for yourself!
› Start by making saltwater: In the measuring cup, dissolve 3 tablespoons of salt in 1 cup of water. Stir to combine. Pour the saltwater into one of the plastic cups until the cup is about threequarters full. Fill a different plastic cup with the same amount of freshwater.
IDEAS FOR SUPPLIES
• salt
• measuring spoons
• freshwater
• spoon
• 4 plastic cups the same size (6 oz or larger)
• food coloring
• measuring cup
• small plastic jewels
› Predict whether you think a plastic jewel will float in the freshwater (NOTE: if you don’t have plastic jewels, try using a small grape or a raw egg in its shell). Place it in the water.
› Do you think the object will float in the saltwater? Place it in the saltwater. Record your observations.
› Remove the objects from the cups and put both in the freezer. For the first 2 to 3 hours, check the cups every half hour. Observe and record what you see. Did the saltwater or the freshwater freeze first? What happened after 24 hours?
› Next, make a new batch of saltwater, dissolving 3 tablespoons of salt in 1 cup of water in the measuring cup. Stir to combine. Pour the saltwater into one of the plastic cups until the cup is about one-half full. Fill a second cup half full of freshwater. Add several drops of food coloring to the freshwater and stir to combine.
› Add the colored water to the saltwater, pouring down the edge of the cup. What happens? Do the solutions mix? Which solution is denser?
Try This
Repeat the experiments using sugar (3 tablespoons dissolved in 1 cup water) and in another cup using baking soda (3 tablespoons dissolved in 1 cup water). Predict what will happen. What do your results tell you about these substances?
TEXT TO WORLD
Have you been near the ocean? What did it look like? Smell like? Feel like?
THE OCEAN IN ACTION
ESSENTIAL QUESTION
Even if you don’t live near the ocean, it plays a role in your everyday life and in the health of our planet. In the last chapter, you learned that the five oceans on Earth are just one huge body of water. Keep this in mind as we look at how the water in the ocean moves around the planet and examine its role in weather, climate, and the carbon cycle.
How is the ocean essential to life on Earth today?
Within our giant ocean, water continuously circulates around the globe in currents. These are rivers of water within the larger ocean. Some are surface currents, while others are deep ocean currents. The currents are interconnected. They mix the water from the surface with the water on the seafloor and move it all around the planet. This system of currents is called the Global Conveyor Belt .
OCEAN CURRENTS
What sets the Global Conveyor Belt in motion? Several factors control the movement of water in the ocean: tides, wind, Earth’s rotation, and differences in water density. The topography of the ocean floor also affects how water moves—the topography may slow the water down, speed it up, or cause it to change direction.
Tsunamis are a type of wave—they are long, high, dangerous waves usually caused by earthquakes below the seafloor or massive landslides into the ocean that displace huge amounts of water.
WORDS TO KNOW
carbon cycle: the continuous movement of carbon through Earth’s atmosphere, land, rocks and sediment, water, and living organisms.
current: the constant movement of water in one direction.
Global Conveyor Belt: an interconnected system of ocean currents that moves ocean water all around the planet.
tsunami: an enormous wave formed by a disturbance such as an earthquake under the water. displace: to move something from its location.
If you’ve ever built a sandcastle on the beach only to have a wave swamp it an hour later, you’ve experienced the tide. The ocean tide rises and falls two times every day due to a force that’s out of this world—the gravitational pull of the moon! Like gravity here on Earth, the gravity on the moon pulls objects towards its center. And while the moon’s gravitational force isn’t as great as Earth’s gravity, its pull is strong enough to cause the ocean to bulge on two sides of Earth—the side facing the moon and the side opposite the moon.
bay: a body of water that is surrounded by land on three sides. estuary: a body of water where a river meets the ocean, with a mix of freshwater and salt water.
These bulges cause water to rise along the shorelines in a high tide. As the planet continues to rotate, the bulge stays aligned with the moon, causing high tides in different locations. As a location moves out of alignment with the moon, the water level there falls, creating a low tide. As the tides rise and fall, they create tidal surface currents. These kind of currents are found along the shore and in bays and estuaries.
Scientists at NASA created a simulation of the ocean’s currents—you can watch it at this link. What role does physics play in ocean currents?
Goddard underwater highways
THE OCEAN
WORDS TO KNOW
gyre: a large system of circulating ocean currents associated with global winds.
dilute: to make something less strong.
Another factor that drives surface currents in the ocean is wind. What happens when you blow on the surface of a mug of tea or hot chocolate? Your breath pushes the liquid forward similar to the way wind blows over the ocean. The harder you blow, the stronger the current you create. You might even create a wave!
Wind is responsible for the ocean waves that crash at your feet at the shoreline. The wind’s energy creates the waves. The faster, longer, and stronger the wind blows, the bigger the waves.
The wind also moves surface currents in the open ocean. Predictable wind patterns have created continuous surface currents, moving water in giant rivers around our planet.
To see how the moon’s gravity causes our ocean to bulge on two sides of the Earth, watch this video from NOAA. What causes the second high tide each day?
The Bay of Fundy in Canada experiences the greatest difference between high and low tides in the world—as much as 53 feet!
The Gulf Stream is one of those powerful surface currents. Off the east coast of North America, the Gulf Stream moves warm water from the Caribbean and Gulf of Mexico into the Atlantic. The current stretches thousands of miles, all the way north and east to Iceland and the United Kingdom. In some places, the Gulf Stream is more than 60 miles wide.
Scijinks tides
While wind is the force that moves surface currents, the rotation of the Earth affects how they move. Because of the Earth’s rotation, the currents move in curvy lines instead of straight ones. The combination of wind and Earth’s rotation also creates gyres. These are ocean currents that move in a massive, slow-moving loop.
So far, we’ve talked only about surface currents, which occur on or near the top 10 percent of the ocean. The other 90 percent are deepwater currents.
DEEPWATER CURRENTS
Deepwater currents are driven by differences in the density of ocean water. Water density is affected by variations in salinity and temperature. As water gets saltier and colder, it becomes heavier and denser. When dense water sinks, it creates a forceful current that moves massive amounts of water! This movement acts like a pump, powering the Global Conveyor Belt.
You may be wondering how does water become colder or saltier? Let’s start with why it gets colder. As ocean water is transported from tropical areas to polar regions, it cools.
Salinity is a bit trickier. Tropical regions receive a lot of rain—more so than regions farther north or south. The freshwater that falls as rain combines with the ocean water to make it less salty. The rain dilutes the salt in the ocean water slightly. Have you ever added water to a cup of juice? How does it change the taste of the juice? Adding water to a cup of juice dilutes it in the same way rain dilutes the ocean water.”
The first map of the Gulf Stream was published in 1769 by Benjamin Franklin (1706–1790) and his cousin Timothy Folger (1732–1814).
THE OCEAN
WORDS TO KNOW
evaporation: the process by which a liquid becomes a vapor or gas.
nutrient: a substance that living things need to live and grow.
upwelling: a process in which deep, cold, nutrientrich water rises and displaces surface water.
phytoplankton bloom: a huge increase in in the number of phytoplanktonin an area.
weather: the temperature, wind, humidity, and precipitation conditions of an area at a particular time.
climate: the average weather in an area over time.
As you know, however, ocean water is on the move—it doesn’t stay in the tropics. As currents move water away from the tropics, the ocean receives less rain. With less rain to dilute it, the water grows saltier. Plus, with more sun, more evaporation takes place. When water evaporates, the salt gets left behind, increasing the water’s salinity.
In addition, the water in the polar oceans goes through cycles of thawing and freezing. When salt water freezes, the salt is again left behind. That makes the water below the ice saltier and denser.
The dense, salty water eventually sinks. It displaces water that is less dense, causing it to rise. Surface water flows in to replace the sinking water. And there you have your massive ocean current!
Ducky Overboard!
One of the best studies of ocean currents happened by accident and came from an unlikely source: bathtub toys. In 1992, a shipping container carrying more than 25,000 plastic bath toys fell off a cargo ship into the Pacific Ocean. During the next several decades, plastic ducks and other toys appeared on beaches around the world. How did these traveling toys contribute to our understanding of ocean currents?
Not only does the movement of water create currents, but it also transports oxygen and nutrients throughout the water column. This process is called upwelling and it occurs both in the open ocean and along the coasts. As deep water rises to the surface and replaces the surface water with cold, nutrient-rich water, it acts like fertilizer for phytoplankton, whose population explodes into phytoplankton blooms. These blooms form the base of the marine food web, providing food for marine mammals, birds, and fish.
It takes 1,000 years for water to make a full circuit around the globe!
WEATHER AND CLIMATE
Now that you know how water in the ocean moves around the globe, let’s look at the role the ocean plays in weather and climate.
Phytoplankton blooms off the Falkland Islands in the South Atlantic Ocean
THE OCEAN
WORDS TO KNOW
precipitation: falling moisture in the form of rain, sleet, snow, and hail.
tropical: having to do with the area around the equator. water cycle: the continuous movement of water on Earth, from the ground to the atmosphere and back to the ground.
First, consider the difference between weather and climate. Weather refers to the conditions outdoors at a specific time and in a specific place. Look outside. What’s it like out there? Warm or cold? Breezy? Rainy? Sunny? Those conditions are the weather in your area right now.
Climate is the average weather patterns in a place over time. Specifically, scientists look at average temperature and average precipitation in an area. If you plan to visit the Caribbean islands, you pack for a tropical climate. You can usually expect a Caribbean island to be warm or hot at any time of year, as well as humid with frequent rain. If you go to the Antarctic, be prepared for a cold, dry climate.
Oceanographer: Dr. Ashanti Jackson
Dr. Ashanti Jackson became interested in oceanography as a third grader. Every weekend, she watched the television show, The Undersea World of Jacques Cousteau She decided that, like Cousteau, she wanted a career that would allow her to travel the world exploring the ocean. Dr. Jackson earned degrees in marine science and oceanography, ultimately becoming a chemical oceanographer and researcher. In her work, she looks at the chemistry of the water in the water column to determine the health of the ocean. This research provides information on how humans are impacting the ocean and how to tackle current problems.
Dr. Jackson also works to inspire the next generation of STEM (Science, Technology, Engineering, and Mathematics) scientists and explorers. She began a mentoring program to introduce minority students to different fields of science. Dr. Jackson received the Presidential Award for Excellence from President Obama in 2009. The award recognizes her role in supporting minority students in STEM.
What does the ocean have to do with weather and climate? A lot! To start, the ocean absorbs most of the heat from the sun, as well as heat produced by human activity. And because the ocean is always circulating, it distributes heat around the globe, determining the climate in different parts of the world. For example, Europe has a mostly mild climate because the Gulf Stream brings heat up from the Gulf of Mexico and the Caribbean.
The ocean also regulates where precipitation falls, even in places far from the shore. It’s part of the global water cycle. When heated water evaporates, it rises into the air, condenses, and falls as precipitation.
THE OCEAN
WORDS TO KNOW
jet stream: a high-speed flow of air high in the atmosphere that flows from west to east.
drought: a long period of little or no rain.
sediment: solid particles of rock and minerals or the remains of plants or animals that settle at the bottom of a liquid.
carbon sink: a place where carbon is stored.
That’s why tropical areas close to the equator get a lot of rain. These places receive more heat from the sun than polar regions, so tropical water is warmer and evaporates more. That leads to more rain.
The ocean has a partner in distributing heat and water—the jet stream. Bands of strong air currents in the atmosphere move heat and moisture in a predictable pattern. That pattern shifts when seasons change. The ocean temperature affects the path of the jet stream because it heats or cools the air above it. The shift moves the air currents over different routes, which impacts local temperatures and precipitation. These changes may bring heat waves or cold fronts or drought to some places and too much precipitation to others.
Together, the ocean and jet stream create the weather you experience every day and the overall climate in your area.
Tech Talk: Buoys and Moorings
Due to the size of the ocean, studying it can be challenging. Research boats can capture information, but the data shows only a small snapshot of conditions at a certain time. With the use of oceanographic buoys, however, scientists can gather data in one location for longer periods of time.
Buoys are anchored to the seafloor with cables that can be more than three miles long. An anchor keeps the cable in one place, and the buoy keeps the cable vertical in the water column. Scientists attach instruments to the cable or to the buoy itself. Those instruments collect data about salinity, water temperature, and the speed of moving water continuously over time. Instruments attached to buoys can also collect information about the weather. The instruments are designed to withstand challenging marine conditions such as deep water pressure, salinity, and strong ocean currents.
THE CARBON CYCLE
The ocean plays another important role on Earth—it is key to the carbon cycle. Carbon, a chemical element, is vital to life on Earth. It is the building block that makes up all living things, including you! The amount of carbon on Earth is fixed—the amount of carbon now is the same as there’s always been on Earth.
The carbon cycle is similar to the water cycle—it continually moves carbon just as the water cycle moves water. Carbon moves through Earth’s atmosphere, land, rocks and sediment , water, and living organisms.
The ocean absorbs huge amounts of carbon from the atmosphere, circulates carbon between surface and deep ocean waters, and releases some carbon back into the atmosphere as carbon dioxide. The ocean is also a key carbon sink , storing carbon in coastal marine ecosystems, deep in the ocean, and in its rocks and sediments.
NOAA video illustrates the carbon cycle. How are fossil fuels created through this cycle?
This
NOAA carbon cycle
THE OCEAN
WORDS TO KNOW
biological carbon pump: the process by which carbon is moved from the surface of the ocean to the deep ocean, where the carbon is stored for long periods of time.
marine snow: the fall of organic material—feces, shed tissue or scales, dead and decaying organisms, or food scraps— through the water column from the upper zone of the ocean to deeper zones.
feces: poop.
blue carbon: carbon stored by the ocean.
greenhouse gas: a gas in the atmosphere that traps heat.
Oceans pull carbon out of the atmosphere and move it to the deep sea in a process called the biological carbon pump. Remember the phytoplankton we discussed in the Introduction? Those tiny marine plants use sunlight and carbon dioxide (CO2) from the water to make their own food through photosynthesis. Then, as larger organisms eat the plankton, the carbon moves through the marine food web. When those animals die and sink to the ocean floor, carbon is trapped in the sediment.
Your body is roughly 18 percent carbon.
SPECIES SPOTLIGHT
Sea Turtles on the Ocean Superhighways
The ocean currents not only move water, but they also move marine creatures large and small. Animals, including sea turtles, use the currents as a superhighway to help with their long-distance journey.
Numerous species of sea turtles migrate long distances to reach their feeding and breeding grounds. Several turtle species travel more than 10,000 miles through the ocean! By using the strong ocean currents, turtles conserve energy along their journey.
Some hatchlings, such as loggerhead turtle babies, use the currents to move away from the shoreline. By migrating to the open ocean, the small turtles are safer from coastal predators. In the Atlantic, these turtles use the Gulf Stream to move northward. Then, they enter the North Atlantic Gyre for several years to grow and mature. Eventually they return to the coast of North America.
Marine snow is the steady fall of bits of organic material— feces , shed tissue or scales, dead and decaying organisms, and the uneaten scraps of food left by messy eaters. The marine snow falls to the deep ocean where the carbon is stored. The process is called a pump because it pulls carbon from the atmosphere and ocean surface down to the depths of the ocean where it remains for hundreds of years.
at an underwater blizzard! Why is marine snow crucial to the carbon cycle?
The carbon absorbed and stored by the ocean is called blue carbon .
While carbon itself is essential to all life, it becomes a problem when too much of it is released into the atmosphere in the form of carbon dioxide. Some release of CO2 into the atmosphere is natural. But humans have tipped the delicate balance through burning fossil fuels, developing land, and performing other activities that add excess CO2 . Because of this, the atmosphere now has more CO2 than it’s had for more than 3 million years. The gas acts like a blanket, trapping heat in our atmosphere and driving global warming.
Here’s where the ocean comes in. The ocean absorbs heat from the sun as well as 90 percent of the heat generated by our greenhouse gas emissions. Not only that, it also captures roughly 25 percent of the CO2 that humans release into the atmosphere. Unfortunately, all the extra work that the ocean does to regulate climate has begun to affect its health. We’ll talk more about that—and the ways people are working to protect the ocean—in later chapters.
But first, let’s explore different marine ecosystems and many of the species adapted to living there. First stop—a voyage to the polar oceans.
ESSENTIAL QUESTION
How is the ocean essential to life on Earth today?
Look
Monterey Bay marine snow
MODELING OCEAN CURRENTS
One of the ocean’s best-known characteristics is that it is salty. The ocean’s salinity affects both the water’s density as well as the temperature at which it freezes. See for yourself!
› In the bottom of the baking dish, use the clay to create land masses and seafloor features such as ridges, volcanoes, and trenches. Let the clay dry completely.
› Fill your baking dish with water. Add blue food coloring to create your own ocean. Using a straw or hair dryer, blow on the surface of your ocean to simulate wind and create a surface current. How do the land masses and seafloor topography affect the current? Create wind of different strengths and make it flow from different directions. Record your observations.
› Add 2 cups of ice to your ocean. Let the ice melt for a few minutes to cool the water. While you wait, boil 2 cups of water. Add red food coloring to the hot water and carefully pour it into the corner of your ocean. What happens? Add wind and observe again.
› What currents do you see? How does the land and underwater topography affect the currents? What surprised you about the currents that formed? Add plastic animals and observe how they move with currents.
TEXT TO WORLD
Have
IDEAS FOR SUPPLIES
• large, deep clear baking dish
• clay
• water
• red and blue food coloring
• straws or a hair dryer
• ice cubes
• plastic toy ocean animals (optional)
• science notebook
Try This
Draw a map of your ocean and land masses. Choose a wind pattern and draw the ocean current on your map. Show how the coastline and seafloor features affect the current. Name your ocean and the land masses. Add a title, compass rose, and map key to your map.
WORDS TO KNOW
compass rose: a circle drawn on a map to show north, south, east, and west.
CHART AN AROUND-THE-WORLD VOYAGE
Like marine animals, humans take advantage of ocean currents for long voyages. Plan a journey around the world by boat, maximizing the use of ocean currents.
› Start your journey by doing research. Consider where you want to go and where you want to stop on your voyage.
IDEAS FOR SUPPLIES
• science notebook
• a map of ocean currents
• blank paper
• colored pencils or markers
Take a closer look at the jet stream and its role in weather. What causes the jet stream?
› Consult a map of ocean currents. Research parts of the ocean with dangerous currents, such as in the North Atlantic and the Drake Passage between the tip of South America and Antarctica. Remember, currents are stronger at different times of the year. Take time to investigate how ocean gyres might help or hinder your journey.
› Draw your own map of the world with a title, compass rose, and map key. Plot your ocean voyage on the map. Consider the following questions.
» How might different seasons affect your journey? Would you need to make a different route during a different time of year?
» How have other ocean journeys around the world been successful?
Try This
Create a diary or graphic novel of your journey. Add details as if you are on a ship or boat. What do you see? How’s the weather? What challenges do you encounter?
Scijinks jet stream
POLAR OCEANS
Polar oceans might make you think of a frozen, barren scene. And, indeed, these oceans are some of the harshest environments on the planet—often super cold, icy, and windy. Despite the harsh conditions, polar oceans are thriving ecosystems both above and below the ice or surface of the water. They play a key role in regulating Earth’s climate and in driving the global circulation of water.
ESSENTIAL QUESTION
What important roles do polar oceans play in regulating Earth’s climate?
The polar oceans are at the ends of our planet— the Arctic Ocean surrounds the North Pole and the Southern Ocean surrounds Antarctica. Both are windy and cold, even in the summer. In the winter, temperatures can plunge below -50 degrees Fahrenheit (-46 degrees Celsius) and stay there.
Polar oceans experience other extreme seasonal changes. Imagine six months of almost constant daylight in the summer, followed by six months of near total darkness! The sea ice changes dramatically each season, too. It forms in the winter and melts in the warmer months, a process that affects marine species, ocean currents, and global climate.
WORDS TO KNOW
strait: a narrow passage of water connecting two seas or two other large areas of water.
Antarctic Convergence: the place where the colder, denser, saltier water of the Southern Ocean meets the warmer, less dense waters to its north.
Look at the Arctic Ocean below. You can see that it is surrounded by land and only connects to other oceans through different straits and seas. Six countries border the Arctic: Greenland, Iceland, Norway, the United States, Canada, and Russia. The Arctic Ocean is the smallest and the shallowest of the world’s five oceans. In the winter, most of the ocean is covered in sea ice ranging from a few inches to more than 6 feet thick.
Now look at the Southern Ocean on the next page. It surrounds the continent of Antarctica. This ocean also meets the Atlantic, Indian, and Pacific Oceans in a spot called the Antarctic Convergence. It’s an invisible line where the colder, denser, saltier water of the Southern Ocean meets the warmer waters to its north.
Find out why the South Pole is colder than the North Pole in this TedEd video. What factors make the South Pole colder?
TedEd Arctic Antarctic
The Arctic Ocean
THE OCEAN
WORDS TO KNOW
Antarctic Circumpolar
Current (ACC): an ocean current that flows from west to east around Antarctica.
DNA: deoxyribonucleic acid, which is the substance in the cells of all living things that carries their genetic information.
gene: inherited material within cells that affects the traits an organism will have.
trait: a specific characteristic of an organism.
environmental DNA (eDNA): DNA shed by organisms into their surroundings.
Most of Earth’s oceans are defined by the continental land masses around them. The Southern Ocean is unique—it is defined by its currents. The Antarctic Circumpolar Current (ACC) moves clockwise around Antarctica, circulating more water than any other ocean current. It is the strongest, deepest, longest ocean current in the world and a key driver of the global circulation of ocean water.
Scientists long recognized the Southern Ocean as the world’s fifth ocean, but it wasn’t until 2021 that it was officially added to maps by the National Geographic Society.
The currents of the polar oceans are Earth’s air conditioner. As they circulate ocean water, they redistribute heat around the globe. When warm water enters a polar ocean, it is cooled and then circulated back toward the equator. This movement stabilizes Earth’s temperatures and regulates our climate.
All of Earth’s oceans are carbon sinks. However, polar oceans are much more efficient than warmer oceans at absorbing CO2 from the atmosphere and transporting it to the deep sea.
The Southern Ocean
Cold water absorbs more CO2 than warm water. As the cold, dense water of polar oceans sinks, it moves the carbon down to the deep sea.
Plus, the biological carbon pump is most effective in the polar oceans. The phytoplankton blooms are larger in polar oceans than warmer oceans. And these larger, heavier blooms sink faster than those in warmer waters. As they sink, the cold water slows their decomposition. The carbon has more time to reach the deep sea. Once carbon reaches the deep ocean, it remains trapped there for hundreds of years.
Tech Talk: eDNA
Since the North Pole is made of ice, not land, the North Pole marker is always on the move and must be relocated every so often.
DNA holds the instructions that tell cells in an organism how to grow and develop. Genes are the part of DNA that determine the traits an organism will have. All living organisms have DNA, including you.
All organisms also shed DNA—they leave traces of themselves behind in their environment. These traces are called environmental DNA, or eDNA.
Organisms shed genetic material in the water column too. Scientists collect water samples containing tissues, feces, and mucus to study the organisms living in the ocean at different depths and different locations. They separate eDNA from the ocean water and read the genetic code. The scientists enter the results into a DNA database to identify the organisms.
With this information, scientists learn a lot about the ocean and biodiversity in a particular location. They can also use the information to examine water quality. And, sometimes, they discover new marine life!
Listen to biologist Dr. Meredith Everett explain the process of collecting and analyzing eDNA in this NOAA video. What are the advantages of eDNA collection?
THE OCEAN
WORDS TO KNOW
genetics: the study of genes and how traits are passed down from parents to offspring.
turbulent: unsteady, stormy, and violent.
migration: the seasonal movement of animals from one place to another.
Ice floats because frozen water is less dense than liquid water.
SEA ICE
Ice—it’s just frozen water! That is true, but it has so many jobs. During the winter, sea ice forms in the polar oceans. In the north, most of the Arctic freezes over. In the south, the areas of the Southern Ocean surrounding Antarctica freeze. The formation of sea ice doubles the size of the Antarctic continent. In the summer, most of the ice thaws.
Why is the seasonal cycle of freezing and thawing important? For one, ice is reflective, like a giant mirror. As a result, the ice reflects most of the sun’s rays back into space, which helps keep the polar regions cool. Without sea ice, the dark ocean would absorb more heat from the sun, causing the planet to warm further.
Marine Biologist: Dr. Meredith Everett
Meredith Everett’s interest in the ocean started as a child. She later studied oceanography and marine biology in college. While she was working in a lab there, she discovered how genetics could be used as a tool to study marine life.
Since then, she has studied the genetics of a wide variety of marine organisms, including phytoplankton, salmon, and killer whales. Eventually, her work focused on deep-sea sponges and corals and the communities they live in. As a geneticist, she uses eDNA to identify different species of sponges and corals, as well as to understand the biodiversity in different parts of the sea.
Dr. Everett’s work is at the forefront of marine species exploration, and she loves that there is always something new to learn and explore.
Sea ice also impacts ocean currents. As you learned in Chapter 1, when salt water freezes, most of the salt is left behind in the liquid water. This creates denser, saltier water below the ice that sinks and drives the global ocean currents. Nutrients and oxygen then circulate throughout the ocean.
Sea ice affects the speed of ocean currents, too. In some cases, it slows the current, as when melting sea ice releases freshwater into the ocean. With more freshwater, the ocean water is less dense and less likely to sink. Without large volumes of sinking water, the ocean circulates more slowly.
In other cases, melting sea ice increases the speed of currents. In the Beaufort Gyre in the Arctic, melting ice leaves the water exposed to wind. As a result, the gyre spins faster and the water is more turbulent .
“
Sea ice is more than just frozen water. It is as essential as trees are to land, and without it many species couldn’t exist.”
—Chris Johnson, Global Lead for WWF’s Protecting Whales & Dolphins Initiative
The sea ice plays yet another important role—many marine animals depend on it for shelter, resting, hunting, and migration . Let’s look at the marine life above and below the ice.
THE OCEAN
WORDS TO KNOW
algae: plant-like organisms that turn light into energy, but that do not have leaves or roots.
habitat: an area where certain plants and animals live together.
parasite: an organism that feeds on and lives in another organism.
scavenger: an animal that feeds on dead and decaying plants and animals
adaptation: the changes a plant or animal makes to help it survive in its environment.
metabolism: the processes in an organism that convert food into energy to keep it alive.
dormancy: a state of rest or inactivity when an animal’s bodily functions slow to conserve energy and survive harsh conditions.
MARINE LIFE
The polar oceans are harsh environments. Despite that, marine life thrives there—from tiny phytoplankton and zooplankton to fish, birds, and marine mammals.
At the base of the polar ocean food web are single-celled algae that become trapped in sea ice as it forms and that grow on the underside of the ice. The algae provide a critical food source through the long, dark winter—one more reason why sea ice is so important! When spring arrives and the sun shines longer each day, the ice begins to melt. The algae are released into the water to become free-floating phytoplankton.
With the intense sun shining all day long and with nutrients stirred up by the deep ocean currents, a massive phytoplankton bloom spreads. The result is a great meal for marine organisms including krill and other zooplankton. Larger species, such as some seabirds and fish, eat these and so on, all the way up the food chain. And remember the marine snow? When organisms die, they sink through the water column and become food for deep ocean species. The phytoplankton bloom supports the entire food web for the whole year.
Explore Oceana’s Marine Life Encyclopedia, a virtual encyclopedia about a vast variety of marine species. What species do you want to learn more about?
While the underside of the ice and the water below create a vital habitat for marine species, the top side of the ice is also important. Polar bears, Arctic fox, and walruses in the north, and many species of penguins and seals in the south all depend on the ice.
Oceana marine life
add sillo of shark
Greenland Sharks
SPECIES SPOTLIGHT
Greenland sharks are enormous animals. Some grow to more than 20 feet long! They love the cold, very deep water around Greenland and Iceland, and blend into the murky darkness, which is why they are rarely seen and not much is known about them.
We do know that they move very slowly—their average speed is less than 2 miles per hour. We also know they are practically blind because of a parasite that bores into their eyes. So how do they catch food? It helps that they are not picky eaters. They will devour just about anything, alive or dead, including Arctic seals, reindeer, polar bears, beluga whales, fish, and crustaceans. They are scavengers. But they are also ambush predators, meaning they will sneak up on prey.
One of most remarkable things about the Greenland shark is their life expectancy— more than 270 years! One female found was approximately 400 years old. That means she was alive when the United States became a country, when the Taj Mahal in India was completed, and while Sir Isaac Newton discovered gravity.
POLAR ADAPTATIONS
In the Southern Ocean, an adult blue whale can eat up to 8 million krill every day during feeding season!
All the species in polar oceans have special adaptations that make it possible for them to survive there, often in water that is below freezing much of the year. Many organisms, such as the Greenland shark in the Arctic and the giant Antarctic isopod, have a slow metabolism that helps them conserve energy. They can go for long periods of time without eating. Other organisms slow their metabolism to the point of dormancy. Some organisms, such as urchins and Antarctic sea cucumbers, go into dormancy for several months at a time.
THE OCEAN
WORDS TO KNOW
antifreeze: a liquid that is added to a second liquid to lower the temperature at which the second liquid freezes.
blubber: a thick layer of fat under the skin of some animals that prevents heat loss and stores energy.
A different type of adaptation involves antifreeze! Humans put antifreeze in their cars to keep fluids from freezing when it’s cold. Arctic cod and other fish have a type of antifreeze in their bodies that produces special proteins in their blood to keep it from freezing.
Many marine mammals living in or near the polar oceans have blubber to insulate them from the cold. Walruses, seals, whales, and dolphins all have this thick layer of fat to keep them warm and store energy. The blubber provides energy to the animals when they need it, so they don’t need to eat as often. Plus, blubber helps these animals float because the blubber is less dense than the salty ocean water.
Polar bears have both blubber and a thick coat of fur. Penguins and other birds have feathers to protect them from the cold. Emperor penguins also have a teamwork approach to keeping
Dive into the frigid waters of the Antarctic in this TedEd video to learn more about survival in this extreme environment. How do some organisms grow so large in this region?
EdTed surviving coldest
A narwhal
The extreme ecosystem of polar oceans is home to many extreme species. Here are a few polar notables.
• Best tusk: Narwhals are called the unicorns of the sea because of the males’ unique spiraled tusk that can grow to 8 feet long. That tusk is actually a tooth! Scientists are still doing research to better understand its purpose.
• VIP: Antarctic krill are tiny crustaceans that feed on phytoplankton. They are an essential source of food for many marine species including whales, penguins, seals, birds, and fish.
• Noisiest: Southern elephant seals (and their northern cousins) are named for the large snouts on males. They are also loud! They inflate their snout with air to make a loud roaring noise to show off how big and strong they are.
• Best dad: Emperor penguin males are the only animals that spend the entire winter on Antarctica. The females depart after laying an egg, leaving the males to balance the egg on their feet to keep it warm.
• Longest migration: Arctic terns are named after one polar region, but they actually migrate between the two. This is the longest migration of any bird species on the planet—approximately 25,000 miles. The journey takes up to four months! The birds breed in the Arctic during the summer and then return to the Antarctic for its summer.
The next stop on our ocean journey will take us away from the cold polar extremes. There we’ll explore another complex ecosystem with its own unique features and creatures!
ESSENTIAL QUESTION
What important roles do polar oceans play in regulating Earth’s climate?
BLUBBER GLOVES
Many marine mammals living in polar ecosystems have a layer of blubber to keep them warm. This thick layer of fat is built-in insulation. See for yourself how it works.
› Put one hand into a small glove. Have a partner smear your gloved hand with a thick, even layer of shortening or lard. Put the larger glove on over the fat-covered hand. Wrap heavy tape around your wrist on the glove to keep water out.
› Next, put your other hand into the second small glove. Do not add the lard. Put the second large glove over top of it. Seal it with heavy tape. Both hands have the same gloves on, but the first one added a variable. The second hand is your control.
› What do you think will happen when you put each hand into the bucket of ice water? Remember your hypothesis to record it in your science notebook when your hands are free of gloves!
› Plunge both hands into the ice water. How long can you safely leave your hands in the water before they get too cold? What do you notice? Which hand can you leave in longer?
TEXT TO WORLD
Do you live in a cold climate? What are some ways you stay warm in the winter?
IDEAS FOR SUPPLIES
• 2 small rubber or latex gloves that fit your hand snugly
• 2 rubber or latex gloves that are larger (or 4 plastic bags large enough for your hand to fit into)
• large tub of shortening or lard
• spatula or spoon
• heavy tape
• bucket of ice water
• science notebook
Right whales live in both the Arctic and Southern Oceans. To keep warm, they have a layer of blubber that is a foot thick!
Try This
Repeat the experiment using different thicknesses of fat. Try different types of fat or insulation. Record your findings.
INVESTIGATING PLANKTON
Both freshwater and saltwater have phytoplankton and zooplankton that are mostly too small to see with just your eyes. Using a microscope to look at water samples will reveal the diverse world of Earth’s smallest species.
› With an adult’s help, collect water in a jar from three different locations—ponds, streams, wetlands, ocean, or other natural water source. Fill each jar about half full and label the jar with the location the sample was taken from.
› At home, put a few drops of water from one jar onto a slide. Look at it under the microscope. What do you see? Is there a lot of plankton? Are there different types in the one sample? Record your findings in your science journal. Draw the different types of plankton you see.
IDEAS FOR SUPPLIES
• 3 jars
• labels
• high powered microscope (if you don’t have one at home, check at your school or local library)
• microscope slides
• science journal
Learn more about the microscopic world of plankton by visiting Arizona State’s Ask a Biologist web pages. Click on the different links for photo galleries and for a video.
ASU ask biologist
› Prepare a new slide with a sample from the second jar. Predict what you think you will see and what similarities and differences you will find. Once you’ve recorded your prediction, made observations, and sketched what you see, repeat the experiment with the third sample.
› How were the samples the same? How were they different? Compare your sketches.
Try This
Take one of the jars of water you collected and separate it into two different jars. Put the jars in two different locations. Vary the locations by temperature or exposure to sunlight. After several days, compare samples from each jar. What do you predict you’ll see? Record your findings.
THE INTERTIDAL ZONE
If you’ve ever examined a tide pool , played in ocean waves, or been sprayed by the ocean hitting a rocky coast, you’ve been to the intertidal zone. It is where the ocean meets land. More specifically, it’s the area that is covered by the ocean at high tide and exposed at low tide. This ecosystem has regular cycles of being underwater and being out of the water and exposed to air.
ESSENTIAL QUESTION
What makes the intertidal zone such a complex ecosystem?
The intertidal zone is complex, with a variety of different ecosystems within it, depending on the location. Within the intertidal zone, the tides create four distinct divisions.
• Spray zone: the area that is underwater only during unusually high tides or strong storms and is exposed most of the time. It is not dry because it is regularly splashed by the ocean.
• High intertidal zone: the area that is submerged only during the peak of high tides. After the peak, this zone is out of the water for long periods of time until the next peak high tide.
• Mid intertidal zone: the area that is regularly submerged during high tides and exposed during low tides.
• Low intertidal zone: the area that is almost always submerged, except during extremely low spring tides.
SANDY BEACHES
WORDS TO KNOW
tide pool: a pool of ocean water that remains after the tide goes out.
intertidal zone: the area that is covered by the ocean at high tide and exposed at low tide.
crustacean: an animal that has a hard shell and jointed legs, such as a lobster, crab, or shrimp; most are aquatic.”
mollusk: a soft-bodied animal such as a slug, squid, or octopus that has no spine and no legs.
When you think of places where the ocean meets the land, sandy beaches might first come to mind. While playing in the sand and building sandcastles is fun for us, beaches are tough places to live. Any organism living there must be able to withstand the continual pounding of waves, movement of sand, and periods of time under as well as out of the water.
You might not think that many animals live on a sandy beach aside from a variety of sea birds pecking at the sand in search of food. Maybe you’ve dug for sand crabs or spotted coiled piles of sand created by burrowing lug worms. But what else lives on a beach? Like the sand crabs and the lug worms, many species that make their homes on sandy beaches live below the surface. They are small enough to move between the grains of sand to
THE OCEAN
WORDS TO KNOW
dune: a mound or ridge of sand that has been piled up by the wind.
bedrock: hard, solid rock below the soil.
limpet: a specialized type of sea snail with a cone-shaped shell and a strong foot for holding onto rock.
deflect: to turn aside.
anemone: an invertebrate that is related to corals and jellyfish.
mucous: containing mucus, a slimy, sticky substance
Sandy beaches are also nesting grounds for sea turtles and birds. Some species such as sea lions and seals use sandy beaches as a resting place before returning to the water.
Plants on sandy beaches grow only above the high tide line. These hardy grasses, shrubs, and flowering plants must be able to tolerate harsh conditions such as strong winds and sun, salty spray, drought, and shifting sand. Deep root systems help anchor them in place. These plants are essential to the formation and stability of sand dunes.
ROCKY COASTS
Can you guess what defines this type of shoreline? Rocks! Here, the intertidal ecosystem is made up of pebbles, boulders, or bedrock . And, like sandy coasts, rocky coasts are difficult places to live. Waves batter the rocks and sometimes water covers them and at other times they are exposed to the air. Despite that, many species thrive among these rocks. They provide food and shelter, serve as nurseries, and are safe places for young fish to grow before moving out into the ocean.
Sand fleas are not actually fleas—they are small crustaceans!
Watch this video from the Woods Hole
Oceanographic Institution to learn more about beach sand. How is sand created?
WHOI how sand crated
Marine Ecologists:
Dr. Jane Lubchenco and Dr. Bruce Menge
It wasn’t until the 1970s that scientists began to understand the complexity of intertidal zones. The two marine ecologists who made the discovery were Drs. Jane Lubchenco (1947– ) and Bruce Menge (1943– ). Their initial research centered on understanding the role of waves on the intertidal community. They selected five research sites along the northeast coast of the United States, each with different wave strengths. At these sites, the scientists observed the interactions between species of plants and animals as they competed for space and for food. They discovered that different species were present when the waves were weak versus when the waves were strong.
Their work also reinforced past research on competition between species. The fact that waves controlled intertidal communities was groundbreaking. It laid the foundation for further research on the complexity of the intertidal zone.
If you explore a rocky coast at low tide, you might spot a variety of species clinging to the rocks to avoid being swept out to sea by strong waves. Snails and limpets use a strong muscular foot to hold onto the rock. Sea stars use the suction cups on their feet to attach themselves to the hard surfaces. Mussels, barnacles, and other species produce a glue to cement themselves in place.
The structure and shape of organisms on rocky coasts also helps them survive. Many species along rocky shores have strong shells to protect them from the pounding waves. Limpets not only have a strong shell, but those shells are also cone-shaped, which deflects the waves. Species such as anemones are flexible so they can bend with the waves instead of breaking.
What happens to these creatures during low tide? The species found among the rock have developed adaptations that keep them from drying out. For many species, their shells serve as both armor against the waves and a way to hold water in. Other species create a mucous layer— like a slimy blanket—around themselves to prevent them from drying out. Some cluster together to avoid drying out. And some species hide in rock crevices or among seaweed or take shelter in tide pools.
THE OCEAN
WORDS TO KNOW
invertebrate: an animal without a backbone.
holdfast: the specialized root-like system of a marine plant such as seaweed that helps it attach itself to rock and not be swept away by the tide.
lichen: a plant-like organism that grows on rocks, trees, soil, and human-made structures.
brackish: somewhat salty, as in the mix of freshwater and seawater found where rivers meet the ocean.
Canada has more than 125,567 miles of coastline, more than any other country.
Some species—jellyfish, crabs, and fish— swim and move freely in the tidewater along rocky coasts. One of those fish is the wellnamed rockfish. Others include sculpins and blenny eels that hide in beds of mussels or under rocks.
You can find leafy algae, otherwise known as seaweed, on rocks where small fish or invertebrates find food and shelter. True plants cannot grow on rocky shores because the rocks do not provide places for roots. The seaweeds, though, have holdfasts that keep them anchored to the rock. Different types of lichen grow on rocks, too.
Tide pools are sanctuaries for marine life and mini ecosystems in the intertidal zone. They form in depressions in the rock—like bathtubs! During high tide, they fill with water. At low tide, the water remains in the tide pool and recedes from the surrounding rock. The cycle of the tides brings in new water twice a day and sometimes brings new residents!
Animals in tide pools are often well-camouflaged. But keep watch and you’ll see tiny crabs or fish moving around. A few tide pool residents, such as barnacles, are permanent. Others, such as crabs, shrimp, and fish, roam the shoreline at high tide looking for food and then retreat to the tide pool during low tide. Some animals—octopuses or eels—sometimes get stranded in tide pools as the tide recedes. They must wait for the water to return before they can escape.
ESTUARIES
Estuaries are places where freshwater from land meets the ocean. The species that live in estuaries are uniquely adapted to living in brackish water. Freshwater has almost zero salt. When it mixes with the salt water of the ocean, the waters have a range of salinity. Weather, tides, freshwater input, currents, and other factors affect the water’s salt levels. Any species living in an estuary must be able to tolerate the changes in salinity. These unique wetland ecosystems are important breeding, nursery, and feeding grounds for dozens of species of birds, fish, crustaceans, shelled mollusks, and other wildlife.
Learn more about sand crabs on the Monterey Bay Aquarium website. What do you think is most interesting about sand crabs?
Monterey sand crab
Peek inside a tide pool!
THE OCEAN
WORDS TO KNOW
mangrove forest: a specialized saltwater forest that grows in the intertidal zone in tropical and subtropical areas.
mudflat: a flat area of mud in estuaries that is left exposed at low tide.
lagoon: a pool of shallow seawater separated from the ocean by a narrow strip of land.
hydrogen sulfide: a colorless gas that stinks like rotten eggs.
turbine: a device that uses pressure on blades to spin generators and create electricity.
Read this article about the role of mussels and sea stars in the intertidal ecosystem. Why are ochre sea stars considered a keystone species?
Frontiers mussels
Estuaries have several distinct ecosystems. Mangrove forests are made up of trees and shrubs. Around 80 species of mangroves grow in the salty, muddy places where most plants could not survive. But mangrove roots have a specialized system that filters out most of the salt from the seawater. Their dense, tangled roots anchor the trees in place and hold the main part of the tree up above the water so they can withstand the changing tides and moving sediments.
Mangrove forests create a unique habitat for animals in and near the water. Many species in mangrove forests stay put in the water among the dense, crisscrossed roots, safe places for crabs, anemones, and others.
Above the water you’ll see birds, monkeys, lizards, snakes, frogs, and more among the mangrove trees. One species of crab even climbs the trees— the mangrove tree crab! Mangrove tree crabs spend most of their time in the trees, to avoid being eaten by fish. But, they drop into the water when threatened by birds or other predators.
And if you thought a tree-climbing crab sounded odd, what about a treeclimbing fish? Yes! Mudskippers are a species of fish that spend more time out of the water than in it. They can breathe because they store water in their mouths and gills. Not only that, but they can also breathe through their skin.
Mudflats are another type of ecosystem in estuaries—like their name implies, they are flat, muddy places. They form when fine sediments from rivers and tides settle in an area, creating sticky, thick mud. They usually form in sheltered areas—bays and lagoons —and are exposed at low tide and flooded at high tide.
Have you been near a mudflat at low tide and noticed the smell? Mudflats stink like rotten eggs! That’s because they are full of the remains of dead animals and plants. Microbes thrive in this environment, breaking down the organic material. In the process, the microbes release hydrogen sulfide , a smelly gas. This gas creates bubbles on the surface of the mud—and the stench.
Despite the smell, mudflats are full of life, although few plants live there. At the base of the food web are the microbes in mudflats. Plus, oysters, worms, snails, crustaceans, and other invertebrates thrive there. Do you like fried clams? Those clams might have come from a mudflat! This muddy life prevents the animals from drying out when the tide recedes. Mudflats are also important nursery sites for many fish. And shorebirds love mudflats because of the buffet of food just below the surface!
Tech Talk: Tidal Energy
As you know, tides rise and fall in predictable patterns. During the 1900s, engineers developed special generators that capture the energy of moving tides. These generators convert tidal energy into electricity, making tides a reliable source of renewable energy.
How does it work? Large, underwater turbines are placed in areas that have significant differences between high and low tides. As water moves through a turbine with the tide, it causes the blades of the turbine to spin, much like the blades of a windmill. The energy in that movement is transferred to a generator that converts it into electricity.
The amount of energy produced by tides was still low compared to other renewable sources as of 2025. In addition, people worry about the impact of tidal energy on ecosystems. The turbines can obstruct marine organisms’ movements and migration, or even trap them. The turbines also create noise, which interferes with communication between animals. Some sensitive species even leave the area, affecting food chains. Engineers and scientists are improving tidal technology and working to make these systems less damaging to ecosystems.
Watch this Student Energy video. What are the three different types of tidal technology? How are they the same? Different?
Student Energy tide power
THE OCEAN
WORDS TO KNOW
salt marsh: an area of coastal grassland that is regularly flooded by seawater.
pioneer plant: the first species of plant to grow in an area.
aerate: to create channels that allow air to flow through.
Salt marshes are found in estuaries too. They are flooded and drained regularly as the tides rise and fall. What makes them different from a sandy beach or a mudflat? Good question! Salt marshes actually used to be mudflats until pioneer plants took root and created the marsh. As time passed, other types of plants took root in the peat and rich mud. All the plants in these marshes must be salt tolerant to survive in the brackish water. And like mudflats, salt marshes are also rather smelly!
Tidal power was first used more than 1,000 years ago in Europe to turn waterwheels, which turned millstones to grind grain into flour.
Salt marshes are busy places. Hundreds of different invertebrate species such as fiddler crabs, blue crabs, mud snails, marsh periwinkles, and grass shrimp crawl through salt marshes. Salt marsh grasshoppers also live in salt marshes, along with many other insect species.
Salt marshes are ideal places for birds to find food because of all the insects and small fish that live and lay eggs there. These places are important rest stops—with abundant fast food— for migrating birds.
Larger animals such as diamondback terrapins, American alligators, raccoons, and otters also take advantage of salt marshes for food.
SPECIES SPOTLIGHT
Horseshoe Crabs
Horseshoe crabs are rather prehistoric looking—and somewhat scary. But despite their appearance, they aren’t dangerous at all. Horseshoe crabs don’t have teeth and they’re not venomous. And that long, pointy tail? It’s not a weapon or even used for hunting. Horseshoe crabs use their tails to turn themselves over if they get flipped upside down on the sand!
The reason that horseshoe crabs look prehistoric is because they have been on Earth for more than 400 million years! They were alive long before the age of the dinosaurs. Today, they are remarkably similar to their ancient ancestors. Their body structure is adapted for survival in the intertidal zone, allowing them to move along the shore like a tank. They are an important part of the marine food chain and play a role in aerating coastal sediments.”.
Plus, they are important to science. Their blood is used to test medical equipment and vaccines to make sure they are safe. If you’ve had vaccines, thank a horseshoe crab!
In addition to providing food and shelter to animals, the wetland ecosystems in estuaries protect shorelines. The plants and trees slow waves, stabilize the shorelines, and prevent erosion. Pollutants and sediment in runoff from land are trapped and broken down before they reach the ocean. And these ecosystems are carbon sinks, storing carbon and keeping it out of the atmosphere.
Now, let’s move away from the shoreline into coastal waters.
ESSENTIAL QUESTION
What makes the intertidal zone such a complex ecosystem?
Visit NOAA’s Ocean Today website to watch a series of videos about horseshoe crabs. How is the blood of horseshoe crabs useful in medicine?
ocean today horseshoe crabs
POWER OF PLANTS
As you’ve read, estuaries protect shorelines from erosion. This is largely thanks to the trees, grasses, and other plants that grow there. Do this activity to see the power of plants for yourself.
› Poke holes in the bottom of both pans for drainage and fill the pans with soil. Plant seeds fairly close together in one pan. Do not plant any seeds in the second pan.
› Place the pan with the seeds in the window in the larger pan to catch draining water. Water the seeds according to directions.
› When the plants are 3 to 4 inches tall, remove the pan from the window. Take both bread pans outside. On each pan, cut along the corners of one short end so the side can fold down. Set both pans in the larger pan again, with the cut, open side facing the same direction.
IDEAS FOR SUPPLIES
• 2 foil bread loaf pans
• soil
• fast-growing seeds such as grass or peas
• a pan large enough for both bread loaf pans watering can with a rain spout
• sunny window for the plants
• science notebook
The constant movement and force of the ocean at the intertidal zone cuts, carves, and crushes rocks, creating remarkable coastal features including cliffs, arches, sea stacks, and caves.
› Fill the larger pan (with both smaller pans still sitting inside) with a ½ inch of water. Then splash water onto the open ends of the pans to simulate waves. Start gently at first, ensuring that both pans experience the same strength waves.
› What do you observe? Based on your experiment, did the plants reduce erosion? How is this similar or different from plants in the real world?
Try This
Do the experiment again in several pans with different seeds and space them at different distances. Also try the experiment with different types of soil, rock, or sand.
TIDE POOL ANIMATION
Tide pools are remarkable places that change with the tides and provide a sanctuary for marine life. Do some research to learn more about the plants and animals found in tide pools. Use what you learn to create a stop-motion animation video about a tide pool.
Stop-motion animation uses still photos to create the illusion of movement. The process involves taking a photo and then moving objects slightly before taking the next photo. When you display the photos in sequence, the objects appear to move.
IDEAS FOR SUPPLIES
• craft supplies to create a small tide pool
• miniature tide pool creatures
• miniature tide pool plants
• camera
• video editing software
› Set up your tide pool, adding both plants and animals based on what you learned about tide pools. Consider the movement you want to simulate in the pool or the story you want to tell. Set your camera in place and secure it so it does not move.
› Take a photo. Move objects slightly—only one-eighth inch or less. Larger movements will cause the animation to look choppy. Take another photo. Repeat until you have at least 50 to 100 photos.
› Upload the photos to some video editing software. Ask for an adult’s help if needed. Local libraries and schools often have the technology and knowledge to assist you. Piece together the photos and adjust how long each photo is presented to speed up or slow down your animation. Add audio or text if you can. If you can’t find video editing software, you can draw the scenes and make a paper flipbook!
Try This
Assess your video. What went well in the process of creating the stop-motion animation? What needs improvement? Consider adding different plants or animals, shooting the photos in a different way, or telling a different story. You might even want to make the video longer or create a tide pool documentary. Reshoot!
TEXT TO WORLD
Many people feel relaxed when they listen to the sound of waves. How about you? Why?
SHALLOW OCEANS
Think back to what you learned about Earth’s two types of crust, the continental crust and the oceanic crust. The continental crust is the land we stand on. Alongside the coasts, though, that continental crust extends into the ocean like a shelf. That’s why it’s called the continental shelf.
ESSENTIAL QUESTION
Why are shallow oceans vital ecosystems?
The submerged area of the continental shelf makes up the shallow oceans, up to around 660 feet deep, in the sunlit zone. The far edge of the shelf marks the separation between the shallow ocean and the deep, open ocean. Within the shallow oceans are a variety of thriving ecosystems.
CORAL REEFS
Parrotfish spend most of the day scraping algae from coral, providing an essential cleaning service so the coral can stay healthy and grow.
WORDS TO KNOW
continental shelf: the part of the continental crust that slopes gently into the ocean.
Imagine you are floating on the surface of the ocean. It is a bright, sunny day and the water is almost completely clear. You adjust your mask and snorkel. Below you is a coral reef in a rainbow of colors. Some of the large round parts of the reef look like brains. In other places, fan-like structures wave in the current. Other parts of the reef resemble stony cacti of different sizes and colors. Among and over the coral, hundreds of brightly colored fish swim in different directions. A sea turtle passes by lazily. As you float, you spot a parrotfish. If you listen carefully, you may be able to hear it scraping algae off the reef with its teeth! Other residents on the reef include angelfish, butterfly fish, sponges, crabs, and sea slugs.
polyp: a small creature that lives in colonies and forms coral.
calcium carbonate: a naturally occurring compound consisting of calcium, carbon, and oxygen.
When you look at the reef, it seems rock-like in some places and plant-like in others. Yet corals are neither rocks nor plants—they are living animals! Each tiny individual invertebrate creature is a soft-bodied polyp. As larvae, the coral polyps float through the ocean and eventually attach themselves to a hard surface—rock, sunken ship, or other structure. The polyps build a hard outer skeleton out of calcium carbonate. These stony corals live in large colonies that create entire reefs. The reefs take hundreds or thousands of years to form because corals grow so slowly—less than 0.12 inches per year to 4 inches per year!
Soft corals are also part of the reef. Similar to stony corals, they live in colonies but they do not build skeletons. Soft corals look like fans, trees, and bushes.
Watch this Smithsonian video to learn more about life on a coral reef. What is the food chain on a coral reef?
Smithsonian coral reef
THE OCEAN
WORDS TO KNOW
foundational keystone species: a species of plant or animal that maintains or creates the base on which an entire ecosystem exists.
carnivorous: describes a plant or animal that eats only animals.
mutualistic: referring to a relationship that benefits both organisms spawn: to produce and deposit eggs.
zooxanthellae: tiny, single-celled organisms that live within coral in a relationship that benefits both.
chlorophyll: a substance that makes plants green and is used in photosynthesis to capture light energy.
Most coral reefs are in shallow water in tropical and subtropical oceans, close to the equator. The reefs are important ocean ecosystems. More than 25 percent of all ocean species rely on coral reefs for some or all their lives. Because of the biodiversity they support, coral reefs are often called the rainforests of the sea. They are also considered a foundational keystone species because they form the base of the entire ecosystem.
There are about 6,000 species of coral on Earth.
Coral reefs provide a place for fish, sea turtles, seahorses, squid, crabs, starfish, octopuses, sponges, and many other marine species to find food. There’s something for everyone on a reef—from the nutrients that algae provide to the corals to prey for carnivorous species to leftover bits of food on the ocean floor for scavengers.
Coral polyps
Credit: NOAA (CC BY 2.0)
All the nooks and crannies on a reef provide shelter. These are great places for smaller species to hide from predators. They are also places for species to spawn and to raise their young.
Find out more about corals and reef ecosystems and look at a live stream video of a reef. How many different marine species can you spot?
Some species on coral reefs cooperate with one another. One example of this type of mutualistic relationship involves coral and a tiny, single-celled algae that lives in its tissue. These algae, called zooxanthellae , produce oxygen for the corals. They also contain chlorophyll and convert the sun’s energy into food for the coral polyps. In return, the zooxanthellae have a safe place to live, protected by the corals’ hard skeleton. Corals get their bright colors from these zooxanthellae.
Cleaner shrimp and larger fish are another example of a mutualistic relationship. The fish come to cleaning stations to have parasites and dead skin removed. That debris is the shrimps’ meal. Win-win!
Clownfish and anemones are yet another example of mutualism. Anemones have stinging tentacles, but clownfish are immune to the sting. Because of this, clownfish can use anemones to hide from predators. What does the anemone get in return? The clownfish fertilize beneficial algae within the anemone with their feces. Plus, the swimming clownfish sometimes drop bits of food within the anemone, circulate water, and drive away predators looking to dine on the anemones.
While most corals attach themselves to a hard surface for life, mushroom corals can walk! They pulse, roll, and slide their pincushionshaped body along the seafloor. But they’re slow—they move less than 2 inches in 24 hours.
Not only do coral reefs protect marine species, but they also protect coastlines. They are a buffer against waves and storms and reduce coastal erosion.
RMG ocean coral
THE OCEAN
WORDS TO KNOW
bivalve mollusk: a marine animal with a soft body protected by two shells hinged together. ecosystem service: the important benefit provided to people by nature., including filtering air, reducing erosion, providing food, and more.
OYSTER REEFS
Corals aren’t the only animals that build reefs—oysters do, too! Oysters are bivalve mollusks , which means they have two shells hinged together, one on top and one on bottom. The soft-bodied animal lives inside. Can you think of any other bivalve mollusks?
Like corals, oysters begin life as free-floating larvae and eventually attach themselves to a hard surface. Then, they build their own shells. As they grow, the oysters fuse together, creating a reef.
You will find oyster reefs on rocks, piers, or other hard surfaces under water. They grow in shallow, brackish, or salty water where waves don’t move very fast. They especially thrive in estuaries and bays, and some are found in the intertidal zone.
Tech Talk: Creating 3-D Models
Imagine creating a quilt. You have dozens of individual squares of fabric that you sew together into a beautiful quilt. Scientists use the same technique with photographs. Using underwater cameras, divers take thousands of photographs of reefs. Back on land, those images are stitched together like a photo mosaic to create a 3-D model of the reef.
Special software enables scientists to move around inside the model and study the 3-D reef. Traditionally, scientists’ data collection and research time was limited to the amount of oxygen in their dive tanks. With this new technology, they can collect data and study the reef for as long as they want—they don’t need to be underwater all the time! The information they gather helps with our understanding of reefs and provides information about reef conservation.
Take advantage of technological advances to take a Virtual Tour of Coral Reefs of the Pacific. What differences did you notice about the reef between 2012 and 2018?
Virtual tour coral reefs
Just as coral reefs, oyster reefs are key ecosystems for many marine species. Various organisms settle on oyster reefs, including anemones, barnacles, and mussels. The reefs provide food and shelter for species such as shrimp, crabs, and fish. If you swim near an oyster reef, be on the lookout for black drums, sheepsheads, anchovies, and urchins. If you’re able to look at the underside of an oyster shell, you might see the eggs of toadfish, gobies, or other fish attached there.
The Great Barrier reef is the world’s largest reef. It is about 20,000 years old.
Who lives on an oyster reef? Watch this Chesapeake Bay Foundation video to find out!
Not only do oyster reefs provide habitats for other species, but they also perform an ecosystem service. Since oysters are filter feeders, they help to clean the water. Each oyster can filter as much as 50 gallons of sea water every day! This service makes the water cleaner and clearer, meaning grasses can thrive.
CBF oyster reef
THE OCEAN
WORDS TO KNOW
ecophysiology: the study of how organisms are adapted to survive in their environment.
herbivorous: plant-eating.
SEAGRASS MEADOWS AND KELP FORESTS
You may think of grass as something that grows on land or maybe in swampy water. But grass can also grow underwater! The grass that grows in the ocean is adapted to being underwater all the time and to salinity. Like grasses on land, seagrasses have roots, produce seeds and flowers, and rely on sunlight for photosynthesis. They also produce oxygen during photosynthesis. The seagrasses can form vast underwater meadows and are found in shallow, brackish, and salty water off the coasts of all continents except Antarctica.
There are more than 70 different species of seagrass in a variety of sizes and shapes.
You will not be surprised that dense meadows of seagrass provide excellent habitats for marine species. In fact, 40,000 individual fish and 50 million invertebrates might live in a single acre of a seagrass meadow!
Marine Ecologists: Daniel Wangpraseurt
Daniel Wangpraseurt is a marine biologist working to protect and restore coral reefs and build new reefs. In his lab, scientists in different fields including marine biology, engineering, and ecophysiology collaborate in their research. Wangpraseurt and his team study the life cycle of corals and how they respond to stress. This knowledge will help them to discover how best to help corals as Earth’s climate changes.
One innovation from Wangpraseurt and his team involves smell. The scientists developed a method to capture the smell of a healthy reef. They built frameworks for artificial reefs underwater and released the smell of a healthy reef into the water to attract baby corals. The goal is to encourage coral larvae to attach themselves to the frameworks, grow, and increase healthy coral populations.
Listen to the NOAA Ocean Podcast about seagrass ecosystems. What ecosystem services do seagrasses provide?
Seagrass meadows make great nurseries for many species of fish and crustaceans such as shrimp and crabs. Sponges, marine worms, and anemones also thrive in these meadows. Some small fish spend their entire lives among the grasses. Because of the biodiversity of life in seagrass meadows, larger fish are on the prowl for food such as sponges, sea urchins, clams, and more.
Herbivorous species such as sea turtles visit seagrass meadows to eat
One of the larger visitors to the shallow ocean’s seagrass meadows in Florida are manatees. They graze on the grasses like cows in a field, giving them the nickname “sea cows.” These large marine mammals do not like cold and migrate south in the winter.
During warmer months, manatees are found as far west as Texas and as far north as Delaware. These gentle giants grow an average of 10 feet long and weigh more than 1,000 pounds. They survive on an exclusive diet of seagrass. They eat as much as 100 pounds of grass and other aquatic plants in a single day!
Manatees can grow longer than 13 feet and weigh nearly 3,500 pounds.
Like mangrove forests and salt marshes, seagrass meadows have roots that anchor them to the seafloor. They slow down moving water, keeping sediment in place and protecting coasts from erosion.
NOAA seagrass
THE OCEAN
WORDS TO KNOW
holdfast: the specialized, rootlike system of a marine plant such as seaweed that helps it attach to rock and not be swept away by the tide.
stipe: the stalk of algae, fungi, or plants.
frond: the leaf-like part of kelp, ferns, or palms.
canopy: the thick, dense upper layer of a forest that receives the most sunlight.
understory: the more shaded layer of a forest below the canopy.
ecosystem engineer: a species that greatly alters an ecosystem by creating, modifying, or maintaining it.
Seagrass is often confused with seaweed, but they are not the same. Seaweed is not a plant but a type of marine algae. Some seaweeds are microscopic and free-floating while some are large and grow in forests. Holdfasts anchor larger seaweed to rocks or the seafloor.
One key type of giant seaweed is kelp, a type of brown algae. It can grow to more than 175 feet tall, as tall as a tree! Like trees, kelp can grow in clusters in large, dense forests. Kelp has long stems called stipes and leaf-like fronds.
Kelp forests have other similarities to forests on land. They can consist of a single species of kelp or several different species. And just as landbased forests have layers, so do kelp forests—a canopy, shaded understory, and the seafloor.
Kelp forests grow along the Pacific coast of North America, from California to Alaska, and in other cool, shallow, nutrient-rich oceans around the world. There, they provide a place for marine species to seek shelter and food. Kelp also reduces erosion along the coast.
Above the water, many species of birds, such as egrets, terns, and gulls, rest and feed in the kelp forests. Below the surface in the canopy, you might see snails and urchins.
Sea otters use kelp as anchors—they wrap themselves in it when they are resting to keep from floating away!
Credit: Mike Baird (CC BY 2.0)
SPECIES SPOTLIGHT
Rhodoliths
Rhodoliths are not animals, nor are they plants. They look like red rocks, but they’re algae. As it turns out, algae come in many forms. In the case of rhodoliths, they build structures called redstones—they are ecosystem engineers!
Rhodoliths build skeletons in the same way corals do. Yet, unlike corals, they do not attach themselves to hard surfaces. Instead, they are subject to the movement of the water in the ocean and may roll on the ocean floor. The heavier rhodoliths settle on the floor and create large banks that become habitats for a variety of marine species. In addition, the rhodoliths protect coastlines from waves and erosion.
For a more detailed explanation of rhodoliths read this article from Frontiers for Young Minds. Why should rhodoliths be preserved?
In the understory, small species may be hiding from predators among the fronds. Shrimp and some fish spend the early part of their lives within the safety of the kelp forests before braving the open ocean as adults.
There are nearly 200 different species of kelp.
What about larger creatures? Sea lions and several whale species visit kelp forests. One famous inhabitant of kelp forests is the sea otter. Otters are so important to this ecosystem that they are considered a keystone species. Sea otters love to eat sea urchins. Sea urchins love to eat kelp. Without sea otters to prey on the urchins, kelp forests would disappear. Sea otters keep the urchin population in check to support the kelp ecosystem.
If you venture to the far edge of the gently sloping continental shelf, you will reach the edge of the shallow ocean. Beyond that, the ocean floor becomes much steeper and the water much deeper. In the next chapter, we’ll explore the open ocean and its depths.
ESSENTIAL QUESTION
Why are shallow oceans vital ecosystems?
Kids Frontiers rhodolith
COUNTING FISH
IDEAS FOR SUPPLIES
• an area on a floor or table where you can create a grid of 1-foot squares
• tape or yarn to create the grid
• a cup of rice
Scientists count fish and other marine species to learn more about their populations and to keep track of how species are doing. But how do scientists count fish in a vast ocean? They use a method called surveying. They lay an imaginary grid on the ocean floor and count fish within different squares on the grid. They then use this sample to calculate how many fish are in that area. See how it’s done!
› Mark your grid with at least 25 squares and scatter the rice across your grid. Each grain represents one fish. Make a prediction about how many “fish” you think are swimming in your “ocean.”
› Randomly choose a square (or have a partner choose one for you). That’s your sample square. Count all the fish in that square. Record the number. Count fish in five different squares.
› Add up the total number of fish you counted and divide by 5. That’s the average number of fish per square. Use that number to determine how many fish are in your total sample. For example, if you have 25 squares, multiply your average number of fish by 25.
Total ÷ 5 = Y Y x 25 = Total fish
› Compare that number to the number of fish you guessed there were before starting.
› Count all the fish in the sample (something scientists in the field cannot do!). Compare that number to the guessed number and the survey number. What do you think the benefits and drawbacks are to surveying fish populations in this way?
Try This
Repeat the count, but this time pick the squares that appear to have the most fish. Or choose only squares that are near each other, or on a border. How are the total survey numbers the same? Different? What does this tell you about the importance of randomly choosing squares to survey?
REEF BROCHURE
Many people travel to snorkel or dive on tropical reefs because of the dazzling array of biodiversity. Select a tropical reef you want to visit and research that reef. Using the information you collect, create a travel brochure.
IDEAS FOR SUPPLIES
• science notebook
• paper
• colored pencils or markers
› Research the coral reef you are interested in visiting. Take notes about its location, climate, and biodiversity.
› To make the brochure, lay a regular sheet of plain paper horizontally. Then fold it into equal thirds. Once folded, you will have six panels (three on the front and three on the back). Close the brochure to determine which panel is your front cover. Find or draw an image of your reef on the front. Include a catchy title for your brochure.
› Organize the information about the reef and plan where it will go on the different panels. Add the information to the panels. Use headings and subheadings for each section and add pictures or images.
› Consider also adding information about how coral reefs are foundational keystone species.
› Give the brochure to a friend or family member and see what questions or comments they have? Did you convey the information clearly? What else do they want to know?
TEXT TO WORLD
Have you spent time in a land forest? How might that experience compare to time in a kelp forest?
Try This
Reefs around the world are impacted by human activity, including overfishing and global warming. Visitors to reefs can do their part to protect them. Research the steps visitors can take to help reefs and add that to your brochure.
OPEN AND DEEP
At the edge of the continental shelf is the open ocean, with water as far as the eye can see. The farther you travel on the open ocean, the fainter the shoreline becomes until it disappears and all you can see is water in every direction.
ESSENTIAL QUESTION
Below you, the water deepens. If you were to take a ride in a submersible , you’d descend through the water column. As you descend, it gets darker and darker, until it is pitch black. The water also gets colder and the water pressure increases. The water has less oxygen.
How are species able to survive in deep ocean ecosystems?
Despite these challenges, the deep ocean is full of life. And as you near the seafloor, if you turn on a light on that submersible, you’ll see a varied landscape.
THE OPEN OCEAN
Imagine you’re a fish living in the open ocean, far from the coast and the continental shelf. You spot a predator lurking below you, but there’s nowhere to hide in this ecosystem. How do you avoid becoming someone’s dinner?
WORDS TO KNOW
submersible: an underwater vessel used for exploration and research. countershading: a camouflage adaptation in which animals are dark on top and light on the bottom. gelatinous: having the consistency of jelly. synchronous: happening at the same time.
See for yourself the marine snow falling through the water column in the open ocean! What role does marine snow play in deep ocean food webs?
Ideally, the predator doesn’t see you at all. Many marine species living in the open ocean have countershading —they are light colored on the bottom and dark on the top. When a predator looks up toward the surface of the ocean, the light color blends in with the sky, camouflaging the prey. Or, if a predator swims above the prey, its dark-colored top blends in with the dark ocean below, making it less visible. Some species, such as jellyfish, have a gelatinous , seethrough body that makes them practically invisible.
Another way to avoid becoming a meal in the open ocean is to stick with your friends. Some fish, including anchovies, sardines, and mackerel scad swim in schools. So, stay in school! There’s safety in numbers. Large schools of fish swim together in synchronous movements. This confuses predators and makes it more difficult for them to single out one animal. Plus, the school of fish may look like one huge fish, scaring off a would-be predator.
One kind of jellyfish found in open waters is called the egg yolk jelly. It looks like a giant egg that was cracked and emptied into the ocean!
If you are a flying fish, you can escape from predators by breaking the ocean surface and gliding through the air! This adaptation allows flying fish to move faster in the air than in the ocean.
EdTed marine snow
THE OCEAN
The sunlit zone of the open ocean is full of life. Phytoplankton thrive here because of the sun. These plants at the base of the marine food chain provide food for other animals, especially small zooplankton, which serve as food for larger fish. In this part of the open ocean, you can see tuna, ocean sunfish, sardines, and different species of dolphins, sharks, rays, jellyfish, and whales.
The open ocean is important to many migrating species that use it as a highway. Some ocean dwellers travel long distances to find food, to mate, or to find safe places to raise their young. Humpback whales are well-known for their epic ocean migrations. They spend summers in their feeding grounds of cool waters, including those around Alaska and the North Atlantic. Then, they migrate toward warmer, more tropical waters in the winter to mate and raise their young. Some humpback whales migrate 5,000 miles each season.
Check out this interactive infographic for more information about the massive vertical migration. What role does this migration play in the carbon cycle?
Great white sharks migrate across the open ocean too, as many as 2,500 miles between feeding grounds. Other migrators include more shark species and whales, tuna, swordfish, and some species of sea turtles.
WHOI twilight zone migration
An egg yolk jelly
Credit: Tom THai (CC BY 2.0)
DEEP OCEAN
As you descend deeper into the ocean in your imaginary submersible, you reach the twilight zone. Less light reaches the depths here so photosynthesis cannot take place and plants can’t grow. Many species in the twilight zone and below rely on the marine snow that sinks from the sunlit zone for food.
Other species in the twilight zone migrate vertically to feed each day. When the sun sets, these species move upward in the safety of darkness. Then, they descend back to the depths before sunrise. Billions of animals make this daily migration. It is the largest animal migration on the planet! Among the daily vertical migrators are squid, fish, jellyfish, mollusks, and crustaceans. The largest number of migrators are zooplankton.
Deep Ocean Explorers: Don Walsh and Jacques Piccard
The first two people to explore the deepest part of the ocean were Don Walsh (1931–2023), a U.S. Navy Lieutenant submariner, and Jacques Piccard (1922–2008), a Swiss oceanographer. Piccard designed a submersible that resembled a hot-air balloon. The top part was a float to lift the explorers back to the ocean surface. Below that was a two-man sphere designed to withstand the ocean pressure.
Walsh volunteered to pilot the submersible. “I just thought it would be fun,” Walsh said. So, on January 23, 1960, after two years of test dives and modifications to the vessel, Walsh and Piccard climbed aboard. For five hours they descended, peering out the porthole. Walsh said in an interview that there was “. . . a lot of bio-activity out there.” He also noted the bioluminescence.
Alas, when they reached the bottom, the submersible stirred up sediment that didn’t settle the entire 20 minutes they were there. Walsh said, “It was like looking into a bowl of milk.” It was 50 years before another submersible reached that depth.
THE OCEAN
WORDS TO KNOW
bioluminescence: the production and emission of light from a living organism.
For those organisms that do not migrate vertically, an unusually large mouth and big teeth aid them in hunting in the dark of the twilight zone. An example is the fangtooth fish. The proportion of its teeth compared to its body is the largest of any ocean fish. It even has special pouches so it can close its mouth without piercing its brain!
Other species have large eyes that let them see prey in the dim light. One species, the strawberry squid, has a huge eye that faces upward so it can see the outlines of potential prey in the lighter water above them. They have a second, smaller eye that faces downward so they can detect bioluminescence.
SPECIES SPOTLIGHT
Deep Sea Coral
While you might associate coral reefs with sunlit, tropical oceans, some corals survive in deep, cold, dark water! These deep-sea coral polyps are similar to their tropical cousins, but they do not have zooxanthellae, which need sunlight. Instead, deep coral polyps get their food and energy by trapping tiny organisms that float by in the ocean current.
Deep sea corals survive more than 10,000 feet below the surface of the ocean. They come in a wide range of colors—purple, orange, yellow, red, and more. They have diverse shapes, too. Stony corals build reefs. Others look like groves of trees or fans or feathers. They can grow taller than 30 feet! Some deep-sea coral colonies are thousands of years old. These deep-sea corals provide habitats that many marine species such as fish and crustaceans rely on.
TIME OUT FOR BIOLUMINESCENCE
As you descend deeper into the water column, you might notice strange lights. Another submersible? No! It’s bioluminescence! If you’ve ever seen fireflies on a warm summer night, you’ve witnessed bioluminescence in action. Fireflies, as well as many marine species, have the ability to produce and emit their own light. Bioluminescent ocean species include the shortnose greeneye fish, the jewel squid, the midwater jellyfish, lanternfish, scaly dragonfish, the cockatoo squid, and more.
Some species emit light all the time while others produce light in short bursts. They produce light for various reasons. The Syllid fireworms, ponyfish, flashlight fish, and others use the light to find a mate. Others use this adaptation to find or attract prey.
Many plankton on the surface of the ocean are bioluminescent. By day, the dense layers appear reddish brown. In the dark, the ocean sparkles with light.
The dragonfish, for example, produces a red light that it can see but prey cannot. It uses the red light to sneak up on its meal.
THE OCEAN
WORDS TO KNOW
magma: molten rock below Earth’s surface.
lava: molten rock that comes out of a volcano.
seamount: an underwater mountain.
macroalgae: large, multicellular, plantlike organisms that photosynthesize.
Visit the Monterey Bay Aquarium to learn more about species that use bioluminescence in the deep sea. Why do they refer to the red crown jelly’s bioluminescence as a burglar alarm?
Still others use bioluminescence as camouflage, or to ward off or confuse predators. One species of deep-sea shrimp uses its light in a unique way. These shrimp do not light up their bodies. Instead, if a predator approaches them, they spew bioluminescent goo. That cloud of glowing goo scares the predator away. Similarly, the vampire squid emits a glowing fluid at a predator, giving the squid time to swim away.
Around 75 percent of animals in the deep ocean are bioluminescent.
Some bioluminescent species make their own light, but others do not. A female anglerfish has a bright pouch of skin that dangles in front of her mouth like a lure to attract prey. Glowing bacteria within the pouch are the source of bioluminescence. This is one more example of a mutualistic relationship—the bacteria get a safe place to live and get nutrients from the fish, while the anglerfish gets a handy lure.
OCEAN FLOOR
When you finally reach the ocean floor, you might be surprised that it is not just a flat, barren, sandy scene. Using the bright lights on your submersible, you’ll see that the ocean floor is a varied landscape with mountains, valleys, lakes, rivers, waterfalls, canyons, and even volcanoes!
WHOI twilight zone migration
Volcanoes under water? Yes! In fact, most of Earth’s volcanoes are in the ocean. The volcanic activity in the ocean is similar to what we see on land. Magma erupts from below the ocean floor in bursts of bright orange and red. Lava oozes out and creeps along the floor of the ocean. These volcanoes form seamounts , or underwater mountains. They range in size from only a few hundred feet to thousands of feet tall. Some break the surface of the ocean and over millions of years form islands, such as the Hawaiian Islands.
Lakes form in the ocean when super salty water settles in a depression on the ocean floor. The denser, saltier water forms a lake with distinct boundaries and does not mix with the ocean around it.
The Sargasso Sea
Far out in the open ocean of the Atlantic is a unique ecosystem—the Sargasso Sea. It covers roughly 2 million square miles and is part of the North Atlantic Gyre. The Sargasso Sea is an ocean within an ocean. The foundation of this ecosystem is a type of macroalgae, a seaweed called golden sargassum, which is how the sea got its name. This seaweed floats in large mats.
The Sargasso Sea has been called a floating rainforest because of the biodiversity it supports. The sargassum mats provide critical habitat for many marine species, including birds, fish, crabs, and shrimp. The Sargasso Sea also serves as a nursery for several species of sea turtles, eels, and fish of the open ocean. Additionally, some rays, sharks, whales, and dolphins pass through the Sargasso Sea when they migrate.
Seamounts are biodiversity hot spots in the deep ocean. They provide a hard surface for species such as sponges and corals to attach to, creating a habitat for other species. Sea stars, squat lobsters, octopuses, pink sea cucumbers, and several species of fish live on and around seamounts.
Scientists have also discovered hot springs in the ocean in areas with volcanic activity. These hydrothermal vents consist of super-heated water full of dissolved minerals, metals, and gases that jet out into the ocean from Earth’s crust.
THE OCEAN
WORDS TO KNOW
chemosynthesis: a process organisms use to convert minerals and other chemicals into energy.
When the hot fluid meets the cold ocean water, chemical reactions take place, and solid deposits form. As time passes, these deposits result in towers from which water continues to flow. While the water is close to freezing in the deepest, darkest parts of the ocean, the spewing water can reach 800 degrees Fahrenheit (427 degrees Celsius). That seems way too hot for life to exist. But life has other ideas.
Hydrothermal vents are unique and thriving ecosystems. Microbes are at the base of the food web here. They use the minerals from the vents to produce energy, since there is no sunlight that deep for photosynthesis. This process of producing energy is called chemosynthesis. The microbes support hundreds of other species. If you were to explore a hydrothermal vent ecosystem, you might find giant tube worms. Some of the tube worms discovered near vents are 5 feet long! You may also see shrimp, crabs, feather duster worms, mussels, and clams.
In 2024, scientists from the Schmidt Ocean Institute were mapping a mountain range off the coast of Chile. Watch this video to see the marine life they discovered there. Why was this expedition so significant?
CANYONS AND TRENCHES
Among the mountain ranges and vents on the seafloor, are also canyons and trenches. Some of the canyons are hundreds of miles long and form a unique deep-sea habitat.
Life thrives here because the canyons influence the movement of water, funneling organic matter to these areas. As a result, marine canyons have plenty of food. They also provide places for marine life to take shelter on the canyon walls as well as places to hunt.
CNN rare species video
The deepest parts of the ocean are in the hadal zone. The trenches that make up this zone are long, deep, narrow depressions on the ocean floor. The water pressure there is 1,000 times greater than at the surface of the ocean. Most animals cannot survive this crushing pressure, but many marine creatures are adapted to living there.
The pressure in the hadal zone is like having more than 400 bricks sitting on the tip of one of your fingers.
As in other parts of the deep ocean, many creatures in the trenches are gelatinous. Their gelatinous bodies keep them from being crushed. Explorers have discovered transparent seapigs (a type of sea cucumber), hadal snailfish, and the bone-eating worm. These tube worms have colorful, feather-like plumes, and no eyes, legs, or mouths. They don’t even have a stomach! They secrete an acid that dissolves bone and then rely on bacteria to digest those bones. Some species here rely on marine snow for food. Others on chemosynthesis.
THE OCEAN
WORDS TO KNOW
whale fall: a whale carcass that sinks to the ocean floor and creates a unique deep-sea ecosystem.
As you read in the introduction, the deepest place in the ocean is Challenger Deep, around 36,000 feet deep. It is part of the Mariana Trench in the Pacific Ocean. The crescentshaped trench is sometimes called the Grand Canyon of the ocean, even though it is 120 times larger than the one on land. Two explorers first descended into Challenger Deep in 1960. Since then, several other manned and unmanned expeditions have reached this deepest point in the ocean.
What happens when a massive whale dies? It sinks to the ocean floor and becomes what is called a whale fall , a food-rich ecosystem for a wide variety of other marine life.
ESSENTIAL QUESTION
How are species able to survive in deep ocean ecosystems?
Scientists continue to explore the deep ocean. Each expedition reveals new information and new species, adding to our understanding of our blue planet. You’ll learn more about ocean exploration and discovery in the next chapter, as well as other ways people use and rely on the ocean.
A whale fall community roughly 5,500 feet below sea level off southern California
Tech Talk: Underwater Research Vessels
So much of what we know about the topography of the seafloor and life below the surface of the ocean has been thanks to underwater research technology. Modern submersibles were first developed in the mid-1900s, and their technology continues to improve. Oceanographers deploy these mini submarines from a larger ship to collect information The three main types of submersibles all have lights, cameras, and specialized equipment, but are used differently.
A human-occupied vehicle (HOV), as the name suggests, carries humans. In HOVs, small teams of scientists can personally observe the ocean depths and conduct research. They use manipulator arms and instruments to collect samples.
Remotely operated vehicles (ROVs) are robots attached to a main ship. Scientists control ROVs from a ship, directing them to capture photos and explore. Some ROVs can also collect samples with a manipulator arm that a scientist operates remotely.
Autonomous underwater vehicles (AUVs) have no people on board, nor are they connected to the ship or directly controlled by a scientist. They are preprogramed robots. Once in the water, these vehicles move on their own, collecting information and transmitting data back to the scientists..
An autonomous underwater robot
Credit: Olivier Dugornay (CC BY 4.0)
OCEAN EXPLORER’S PODCAST
You are a famous oceanographer, well-known for your exploration and research of the depths of the open ocean. You’ve been invited to be a guest on a podcast to speak about the things you’ve seen and discovered.
IDEAS FOR SUPPLIES
• science notebook
• research materials
• a recording device
How deep is the ocean? Watch this video animation to learn about the ocean depths. Based on what you learned, why do you think it is so difficult for people to explore the sunken Titanic?
› Decide on your experience as an oceanographer and what makes you well known—have you explored various depths of the deep ocean and even traveled to ocean trenches? Have you studied hydrothermal vents and the ecosystems they create? Have you specialized in a particular species? Generate 5 to 10 questions that the host of the podcast can ask you.
› Research the answers to the questions. Imagine what it would be like to be in a submersible or to use an ROV to study the ocean. Consider what experiences would be especially exciting, scary, or fun. Use your research to add details to your answers.
› Have a friend or adult be the host for the podcast, asking the questions and engaging you, the oceanographer, in conversation. Record the session.
Try This
Consider sharing your podcast with others. Beforehand, edit the recording and add a few seconds of music at the beginning. Give your podcast a title and add an introduction. Share it! Consider posting it online with an adult’s help and permission.
TEXT TO WORLD
Have you ever seen fireflies? What would it be like to spot bioluminescent creatures in the ocean?
Insider Tech deep ocean
HOW BIG IS A BLUE WHALE?
Blue whales are found in oceans around the world, except in the Arctic Ocean. Most migrate vast distances between their summer and winter feeding grounds, surviving on a diet of mostly krill. They are the largest animals on the planet. They can weigh more than 300,000 pounds and are about 100 feet long.
› Find an open basketball court playground with a hard surface. With your partner, measure 100 feet. Mark the length of the whale— nose to tail. Using your photo as a model, draw the outline of the whale in chalk.
IDEAS FOR SUPPLIES
• large, open concrete or asphalt playground
• a partner
• big bucket of sidewalk chalk
• tape measure
• picture of a blue whale
• graph paper
› Fill in the details—fins, eyes, mouth, blowhole, fluke, and more. When you are done, stand on one end of the whale and your friend on the other. Does the size of the whale surprise you? What other things can you compare the size of a blue whale to?
› Now, draw your whale to scale. On your graph paper, do the math to figure out how many boxes a blue would take up. If a whale is 100 feet long, how many feet per box should you measure so it fits on your graph paper?
› Compare yourself to the whale. How tall are you? How many boxes would you take up if you were lying beside the whale on the paper?
Try This
For more context on the size of a blue whale, research and draw a piece of krill (actual size). How many krill do you think these giant whales need to eat each day? Add other marine creatures to your drawing to scale.
PEOPLE AND THE OCEAN
When you look at the ocean, what do you see? How do you feel? Some people think the ocean is relaxing while others think it is scary or mysterious. Many indigenous cultures worship the ocean and see it as sacred. To some, the ocean is the giver of life.
ESSENTIAL QUESTION
In what ways do we rely on the ocean?
The ocean is also a place for recreation, a source of food, and a source of income. People use the ocean as a route for transportation and trade. Scientists see the ocean as a medicine chest and a place for exploration and discovery. Humans have used and relied on the ocean for thousands of years.
WORDS TO KNOW
TRANSPORTATION AND TRADE
indigenous: native to a place.
Middle Ages: a period from about 350 CE to 1450 CE.
Ever since humans built the first sailing vessels more than 5,000 years ago, we have explored the ocean. Some of the earliest voyages were not to explore the ocean itself, but made with the hope of discovering new land to settle. Some explorers went in search of trade routes. The discovery of these oceanic routes connected the world and changed the course of human history.
Early ocean voyages were very dangerous. Imagine setting sail without maps or any of the navigation tools we have today! Explorers had to rely on the sun, stars, landmarks, and their own knowledge. And when the weather turned stormy, they had no modern technology to support them–only their own skills and experience
Before people had sailing vessels, communities and cultures were relatively isolated. Once people could sail the ocean, they encountered other cultures and exchanged ideas, knowledge, customs, and foods. For instance, prior to the Middle Ages , people in Europe did not drink tea. Once contact was made with China, where people drank tea regularly, tea-drinking became common in Europe. Later, settlers to the New World brought the tea-drinking custom with them across the Atlantic. Settlers and explorers also brought apple trees, wheat, and sugarcane to the New World.
The first ship to sail around the world was the Victoria. The crew left Portugal on September 20, 1519. The journey took three years to complete.
THE OCEAN
WORDS TO KNOW
immunity: the body’s ability to withstand harmful invaders such as bacteria, viruses, fungi, and other foreign bodies.
aquaculturist: a person who farms plants and animals in water.
maritime: related to the sea, sailing, or shipping.
During the Age of Discovery (also known as the Age of Exploration) between the fifteenth and seventeenth centuries, people widely explored the oceans to find new trade routes and sources of wealth. There was also a dark side to ocean exploration. Leaders often sent explorers to other places to take over land and resources, no matter the indigenous populations that already lived there. Plus, when communities mingled for the first time, diseases had a chance to spread into populations with no immunity. For example, explorers and colonists from Europe brought smallpox to indigenous people in the Americas in the sixteenth century. In some places, the death rate was as high as 90 percent.
In 2022, the United States had more than 2 million marine-based jobs.
Ocean-Related Careers
Love the ocean? Consider making a career out of it! You could study to be an oceanographer, a marine biologist or geologist, a chemist, a climate scientist, or an aquaculturist.
Perhaps engineering is more your thing. You might design and build the next generation of submersibles or the next research habitat or vessel. Engineers also design and build specialized systems and instruments for research.
If the arts appeal to you more, you could become an ocean videographer or documentarian. Other careers include artist, photographer, writer, and journalist.
Countless port jobs are available, from boat captains and crew to fishermen and fishery managers and workers. Marinas need managers and workers and marine traffic controllers. If you love being on the water, you might find a career working on research ships or leading sea kayaking expeditions to be fulfilling.
Of course, the ocean also needs conservationists (more about that in the next chapter) and people to advocate for policies to protect the ocean!
Today, the ocean is still used for both transportation and trade. In fact, most of the world’s trade, roughly 80 percent of goods, goes by sea. This makes port cities around the world vital centers for importing and exporting goods. The maritime trade industry employs millions of people including crews on ships, dock workers, maintenance staff, those who design and build ships, those who run the ports, and businessmen.
In addition to goods, people move across the ocean. Ferries transport people and vehicles in places with many waterways or numerous islands. Sometimes, ocean transportation simply lets us get from place to place.
Other times, we use ocean transportation for tourism, recreation, and scientific discovery—more on that later! All this transportation creates jobs, generates income, and supports economies.
THE OCEAN
WORDS TO KNOW
subsistence fishing: smallscale, low-tech fishing for local consumption.
commercial fishing: the large-scale catch and sale of marine species.
The military also uses the ocean and ports. Ships often transport military personnel, supplies, and equipment. The Navy patrols the oceans to project a position of power and control to other nations, to protect shipping routes, and to stay informed about what other nations are doing. Naval ports around the world also serve as strategic posts for defense and support of military operations in times of war.
SPECIES SPOTLIGHT
Bottlenosed Dolphins
Sitting on a beach or riding in a boat on the ocean, you might spot a pod of bottle-nosed dolphins as they jump above the waves. Dolphins are incredibly playful, social, and intelligent animals. Not only do they have excellent problem-solving skills, they also use tools such as shells for foraging. Some pods have created innovative ways to hunt, showing both intelligence and teamwork.
Plus, dolphins have a sophisticated communication system that includes a variety of squeaks, clicks, and whistles. They use this language for communicating with one another and coordinating their hunting.
Dolphins jump out of the water to get a better view of their surroundings, but also just to play. They surf in the wake of a boat too, leaping and diving in the waves. Dolphins also like to play with objects. Because of their social and curious nature, they will play with people!
FOOD & MEDICINE
Seafood is an important food source around the world. Billions of people rely on food from the ocean as their main source of protein. In poor communities around the world, some people rely on subsistence fishing to feed themselves or sell in local markets. In this case, people catch only what they need. This type of fishing is usually low-tech and done on a small scale.
Commercial fishing —the large-scale harvest of fish, crustaceans, and mollusks for profit—is very different. Billions of pounds of fish are caught and sold worldwide each year. It’s an enormous industry made possible by developments in technology and fishing methods that make it easy for commercial fishing boats to catch huge numbers of fish at one time.
Searching for seashells is fun, but we should leave them on the beach. They provide homes for small organisms and nest material for shorebirds. Also, as shells break down, they provide nutrients for microscopic organisms. Shells eventually become sand!
THE OCEAN
WORDS TO KNOW
fishery: a place where fish are caught or raised as a business.
Like trade and transportation on the ocean, fisheries provide income and jobs for millions of people globally. The fishing industry also brings money to coastal communities, as well as to states and countries.
For scientists, the ocean is a medicine chest, especially around coral reefs. Many anti-cancer medications and pain relievers have already been discovered. The great biodiversity and chemical diversity in our oceans may offer possible ingredients for medicines to help people fight arthritis, asthma, dementia, cancer, heart disease, and pain.
Have you had vaccines to prevent you from getting serious diseases such as tuberculosis or measles? The safety and effectiveness of the vaccines are often thanks to horseshoe crabs! The blue blood of horseshoe crabs contains a protein scientists use to test vaccines and other medicines. It’s been key to advancements in medicine.
The HMS Challenger covered more than 68,000 nautical miles between 1872 and 1876. During this time, scientists aboard identified over 4,700 new marine species and gathered a vast amount of data on temperature, currents, and salinity.
Credit: William Frederick Mitchell
EXPLORATION & DISCOVERY
While humans have sailed the ocean for thousands of years, the scientific study of the ocean is relatively new. Italian scientist Ferdinando Marsili (1658–1730) is credited with being the father of oceanography. He used field observations and a scientific approach to investigate ocean biodiversity, ocean currents, seawater properties, and more.
During the Age of Discovery between the fifteenth and seventeenth centuries, people widely explored the oceans to find new trade routes and sources of wealth.
Scientific expeditions in the 1800s included the voyages of the HMS Beagle and the HMS Challenger, both ships of the British Royal Navy. These voyages surveyed and charted the ocean, measured ocean depths, discovered new species, and truly launched the era of modern ocean exploration. Charles Darwin (1809–1882) was the scientist aboard the Beagle who later came up with the theory of evolution by natural selection.
Tech Talk: Underwater Habitats
When scientists want to explore the ocean, they can only do so for a limited amount of time in a submersible or by scuba diving. To allow for extended research time, engineers have developed underwater habitats for humans.
The first habitat was built in 1962 by a team of engineers working for Jacques Cousteau. The small habitat was placed at a depth of 30 feet in the ocean near Marseilles, France. Two divers lived underwater for a week. During their stay, they conducted marine research. Plus, they learned more about the human body’s ability to adapt to life below sea level.
Since then, habitats have gotten larger and more complex—one has an underwater garage for a submersible! Divers have lived in them for longer periods of time. The habitats have also been placed at greater depths.
THE OCEAN
WORDS TO KNOW
bathysphere: a spherical, manned submersible made of steel that is suspended from a ship for deep ocean exploration.
sedimentation: the deposit of solid materials such as rocks, sand, and minerals in a new location.
bycatch: marine species caught accidentally as people fish for other species.
It wasn’t until the 1930s, however, that humans could explore the ocean depths. American engineer Otis Barton (1899–1992) and zoologist William Beebe (1877–1962) built a vessel of steel that also had portholes. Called a bathysphere , it was suspended from a boat by a cable. In 1934, the two men reached a depth of more than 2,900 feet, deeper than anyone had gone before. They were able to observe deep-sea marine life firsthand.
Since then, ocean exploration has expanded immensely, largely due to advancements in technology. Today, oceanography involves submersibles, sonar, communication technology, observation systems, and much, much more. Satellite observations from space also play a role in oceanography. And remember, only 5 percent of the ocean has been explored. We have a lot more to discover!
The First Ocean Explorers: Polynesians
Imagine living along the coast of southeast Asia long ago. You know the coastal ocean well and use canoe-sized boats for fishing. All you can see from your shoreline is open ocean. You have little knowledge of what lies beyond—how far does the ocean extend? Is other land out there? You want to find out! Would you board the boat?
The early Polynesians did, starting around 1500 BCE. They settled islands across the vast Pacific in an area covering more than 15 million square miles. And they did it without any modern technology. They used only the stars, sun, ocean currents, moon, clouds, and planets to guide them. Relying on their navigation skills, memory, a bit of luck, and double-hulled canoes called wa’a kaulua that were equipped with sails and an oar, the Polynesians became the world’s first ocean explorers.
Watch this TED Ed video for a deeper look into Polynesian ocean exploration. How did clouds help Polynesian explorers navigate the ocean?
TedEd Polynesia wayfinders
THREATS
Human activity has an impact on the ocean. And increasingly, we are seeing that the effects are dramatic.
Coastal Development: When people develop coastlines, they clear land for buildings and roads. This disrupts the natural flow of water and increases pollution, sedimentation , and toxic runoff into the ocean. These effects harm or destroy coastal ecosystems and impact marine species.
Overfishing: With advancements in commercial fishing technology and equipment, crews can harvest massive amounts of marine species to sell for profit. Many species, such as cod and Atlantic halibut, are so overfished that they can’t reproduce fast enough to replenish the population. This puts species at risk for extinction and causes an imbalance in marine food webs. Further, some commercial fishing results in a lot of bycatch , causing the needless death of billions of fish, turtles, sharks, and more.
Recreation and Tourism
When talking about people and the ocean, we cannot forget that the ocean is a wonderful place to play. You can do many things whether you like to be by the water or on the water or in the water!
You might enjoy sitting on the sand and building sandcastles or maybe digging for sand crabs. You might also enjoy long walks on the beach and searching for seashells. Or what about playing in the waves, swimming, boogie-boarding, or jumping onto surf boards to ride the waves? Beyond the waves you might kayak, stand on a paddleboard, or float on a raft.
Have you been out on a sailboat or motorized boat to have fun, fish, or watch wildlife such as dolphins or whales? Or perhaps you have been on a cruise? Snorkeling at coral reefs is also fun. What are your favorite activities?
The ocean provides another benefit to us—it is a source of relaxation, calm, and wonder. Scientific studies have revealed that being on, in, or by the ocean or other bodies of water improves mental health.
THE OCEAN
WORDS TO KNOW
algal bloom: a rapid increase in the growth of algae in a body of water.”
dead zone: an area of the ocean where little life can survive because the water is toxic or contains very little oxygen.
marine debris: human-made materials and trash that end up in the ocean.
microplastic: a tiny piece of plastic the size of a grain of sand or smaller.
The Great Pacific Garbage Patch is a giant floating mass of plastic debris swirling halfway between Hawaii and California in the Pacific Ocean.
Pollution: Most marine pollution is land based—it starts on land and then makes its way to the ocean. This includes sewage, trash, and chemical runoff from vehicles, agriculture, and factories. Pollution has a huge impact on marine ecosystems and wildlife. In some places, chemical runoff causes algal blooms. When algae and bacteria grow out of control, other marine animals and plants are threatened because algal blooms reduce the amount of oxygen in the water. Some algae are toxic. At times, the blooms are so severe they cause dead zones
Plastic Pollution: The majority of marine debris is plastic. Marine species often eat plastic trash, thinking it’s food. For example, a plastic bag floating in the ocean looks like a jellyfish to a sea turtle. Some marine species eat enough plastic trash that they feel full, but they haven’t eaten anything nutritious. In addition, marine animals often get tangled in nets, bags, or other plastics. This can trap, cut, or harm an animal and impede its movement.
Not only does plastic harm wildlife, but plastic also never decomposes. It only breaks down into smaller and smaller pieces called microplastics. Smaller organisms may eat the microplastics. When larger animals eat those organisms, the predators are also eating plastic. Even if an organism ingests plastic and it doesn’t harm them right away, the plastic itself is toxic. This type of pollution affects the entire marine food web, including humans.
Studies have shown that much of the seafood eaten by people contains microplastics.
Listen to a NOAA Ocean podcast about the impacts of marine debris. Why is dealing with marine debris such a huge challenge? What are people doing to meet the challenge?
NOAA marine debris
THE OCEAN
WORDS TO KNOW
seismic blast: a loud blast of compressed air used to locate oil and gas beneath the ocean floor.
ocean acidification: the absorption of too much carbon dioxide by oceans which causes the ocean to become more acidic.
Noise Pollution: Another source of pollution that people don’t talk much about is noise. With the increase in coastal development, boating, shipping, and sonar use, the oceans have gotten louder. The noise is stressful for marine animals. Some noises, such as seismic blasts , result in hearing loss. Noise pollution also interferes with animals’ ability to communicate, hunt, find mates, avoid predators, and more.
Offshore Drilling: Much of the world’s oil and gas comes from beneath the ocean floor. Offshore drilling, though, has severe impacts on marine ecosystems at every stage of the process. Seismic blasts are used to locate pockets of oil and gas. The actual drilling sometimes results in oil and gas leaks into the ocean. Metal cuttings and drilling fluid also pollute the water.
Rarely, an explosion happens on an oil rig, causing death, destruction, and pollution
An offshore oil drilling rig
Global Climate Change:
As humans burn fossil fuels, we release carbon dioxide (CO2) into the air. This greenhouse gas traps heat in the atmosphere and causes global climate change. One major effect is the increase in air and water temperature. As the ocean warms, its ability to regulate climate and weather is disrupted, leading to more frequent and intense storms, flooding in some areas, and droughts in others. Polar ice is melting too, causing the sea level to rise and increasing the risk of floods in coastal areas. Loss of sea ice also impacts marine animals that depend on the ice for part or all their life cycles.
In addition, the ocean naturally absorbs CO2 from the atmosphere, where it dissolves and forms carbonic acid. With more CO2 in the atmosphere, more is absorbed by the ocean. Because of this, the ocean is becoming acidic. This ocean acidification prevents many marine species, including corals, from producing hard, healthy shells and skeletons. The species become more vulnerable to predators and environmental stress, and marine ecosystems are altered.
Despite the threats the ocean currently faces, there is hope. Awareness of these challenges is growing. Dedicated scientists, conservationists, and individuals are working to protect our ocean. And that’s what the next chapter is all about!
ESSENTIAL QUESTION
In what ways do we rely on the
Read this TIME for Kids article to learn how marine debris is affecting whales. What is the danger of marine debris for whales as they hunt?
Time Kids deep sea danger
ocean?
OIL SPILL CLEANUP
Drilling for oil beneath the ocean floor and shipping by ocean comes at a cost—sometimes oil spills or leaks into the ocean. These spills put the ocean ecosystem at risk and harm wildlife and plants. Cleaning up oil spills is a challenging task. Try this experiment to remove oil from water.
› Fill your tray with water, about ½ to 1 inch deep. Pour a few tablespoons of oil into the water.
› Skim the water’s surface with each of the different absorbent materials. Which ones remove the oil most effectively? Do some materials pick up just the oil, while others pick up both water and oil?
› Try removing the oil with a spoon or syringe. How effective is that compared to using absorbent materials?
› Try building something in the water to contain the oil. This could be a wall of rocks, or perhaps a floating boom around your “oil spill” to keep it from spreading. What works best? Record your results in your science journal.
IDEAS FOR SUPPLIES
• a tray for water
• water
• vegetable oil
• spoon
• cotton balls or squares
• sponge
• paper towel
• syringe
• science notebook
Watch this TED Ed video about noise pollution in the ocean. How is noise pollution affecting reef fish, dolphins, right whales, and zooplankton?
Try This
Oil spills harm birds. The oil sticks to their feathers, makes them heavy, and prevents the birds from flying. One method to help birds and other animals is to give them a gentle bath in Dawn dish soap. This product is known for removing grease and oil not only from dishes, but also from animals. Try putting a few drops of Dawn in your tray. What happens? If you have a bird feather, soak it in oil and observe the feather. Then wash it with Dawn. How effective is the soap in removing the oil?
TedEd ocean louder
THE OCEAN DRUGSTORE
Scientists keep discovering substances for new medicines in marine invertebrates. Many of these invertebrates are nature’s simplest animals. Some don’t even move! Do a little research to learn more and share information about the marvelous medicines that come from marine life.
IDEAS FOR SUPPLIES
• science notebook
• posterboard
• colored pencils or markers
› Research marine species that contain substances we use for medicines. Possible species to study: sponges, tunicates, gorgonians, bryozoans, and cone snails.
› Take notes on what they are, where they’re found, and how they can be used in medicine.
› Create a poster or flyer that has a drawing of each species, information about it, and how it is important to science.
› Share this information with classmates, family, and friends.
Try This
Research medications that you or someone in your family takes or has taken in the past. Did the ocean play a role in their development?
TEXT TO WORLD
What objects in your house traveled by ocean? Do some research!
OCEAN CONSERVATION
By now you know about the incredible biodiversity in our ocean and the vital roles it plays on Earth. The ocean covers 70 percent of the planet, and decades ago it seemed too enormous to be impacted by human activity. Yet, it has been. Awareness of the damage grew in the 1960s and 1970s and launched an era of ocean conservation that continues today.
ESSENTIAL QUESTION
What can we do to restore and protect the ocean?
Conservation efforts have taken many forms. Some involve nations making laws or creating organizations to tackle problems and manage resources. In other cases, nations work together and sign treaties to protect the ocean.
Indigenous nations and conservation groups also play key roles in ocean conservation around the world.
State and local governments are often involved. At the heart of each effort are dedicated individuals who understand the need for ocean conservation and work to make a difference.
INDIGENOUS KNOWLEDGE
WORDS TO KNOW
treaty: a formal agreement between countries.
stewardship: the responsible management and care of something.
holistic: looking at the whole of something, not just individual parts.
sustainable: using Earth’s resources in a way that keeps the planet healthy now and for the future.
equitable: fair.
Imagine you have a difficult problem in your life. You are unsure how to handle it and need advice. Who would you turn to? You would likely turn to someone older and wiser, someone who has a lot of life experience. The same applies to ocean conservation. We need to learn how to better protect our ocean. Who should we turn to? Indigenous peoples.
Indigenous people have respected and cared for the ocean and land for thousands of years. They were stripped of that stewardship when they were forced off the land by settlers from other nations. In many places, Indigenous peoples were denied their fishing rights and their access to coastal areas was limited. Indigenous people were left out of ocean management, policymaking, and conservation.
Today, conservationists are increasingly turning to Indigenous people for their traditional knowledge and understanding of the ocean. Indigenous knowledge can guide policymaking and offer holistic approaches to protection and management. In this way, ocean conservation can be both sustainable and equitable.
In Canada, the inclusion of Indigenous knowledge in ocean management is called Two-Eyed Seeing. One eye sees the long history of Indigenous knowledge of the ocean. The other eye sees Western scientific knowledge. By using both eyes, ocean conservation benefits all humans, as well as ocean ecosystems and wildlife.
Marine Protected Areas (MPAs): protected wilderness areas of the sea.
THE OCEAN
PROTECTED AREAS
On land, we have parks and reserves set aside for conservation and recreation. We also have protected wilderness areas in the ocean! Around the world, these areas protect marine species, ecosystems, natural resources, and historic and cultural sites.
Marine Protected Areas (MPAs) in the United States protect coastal ecosystems, coral reefs, estuaries, the open ocean, and parts of the Great Lakes, which are freshwater habitats. President Theodore Roosevelt (1858–1919) established the first MPA at Florida’s Pelican Island Refuge in 1903. MPAs are areas that are set aside and protected, with limits placed on how we use those areas.
More than 25 percent of U.S. waters are protected by MPAs.
In some MPAs, you cannot fish or collect natural and cultural resources at all. In these “no take” marine reserves, the whole ecosystem is under strict protection. In other MPAs, regulations limit the type of fishing gear you can use, the times of year you can fish, or the areas of the MPA where you can fish. Protected areas also may restrict or prohibit development, tourism, and the use of anchors and sonar. Most MPAs, however, are open for recreational uses so we can enjoy them if we follow regulations.
Watch the Smithsonian’s video on Marine Protected Areas in the United States. How are MPAs like an insurance policy?
Around the world are more than 5,000 marine protected areas that all have similar goals.
NOTE! Fact check 25% stat and laws before publishing. https://marine-conservation.org/on-the-tide/usa-mpaguide-study-released/#:~:text=The%20good%20 news%20is%20that,marine%20life%20and%20healthy%20oceans.
Credit: John Burns/NOAA, 2017
LAWS AND PROTECTIONS
Laws play a key role in ocean conservation. In the United States, laws define and manage protected areas. In fact, the MPAs you can visit and enjoy today are largely thanks to the acts of Congress decades ago, when people began to notice the destruction of marine ecosystems and the disappearance of marine animals.
Since the ocean ecosystem is so large and complex, not just one law protects the ocean. Many different laws work together to protect it:
• The Clean Water Act (1948) prohibits ocean pollution, including releasing oil and toxic substances into the ocean and other waterways.
One of the largest protected marine areas in the world is Papahānaumokuākea National Marine Sanctuary in the central Pacific Ocean northeast of Hawaii. This sanctuary covers an area more than twice the size of Texas.
This Hawaiian green sea turtle paddles around Papahānaumokuākea.
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• The Marine Mammal Protection Act (MMPA, 1972) prohibits hunting, harming, capturing, or killing marine mammals. It does permit subsistence and traditional hunting by Alaskan natives.
• The Coastal Zone Management Act (1972) protects coasts and coastal habitats from overdevelopment. It also encourages the restoration of coastal habitats when possible.
In the United States, about half of the seafood we eat is farmed, including clams, shrimp, oysters, and several species of fish such as salmon, catfish, and trout.
• The Endangered Species Act (ESA, 1973) lists species at risk for extinction. It makes it illegal to kill, harm, harass, and trap any species (animal or plant) on the endangered species list, whether on land or in the ocean. The law also requires that steps are taken to identify and conserve the habitat where those species live.
• The Magnuson–Stevens Fishery Conservation and Management Act (1976) regulates fisheries, orders the reduction of bycatch, reduces overfishing, and keeps fisheries sustainable.
• The Coral Reef Conservation Act (2000) was established to conserve, restore, and sustain coral reef ecosystems.
Oceanographer and Explorer: Sylvia Earle
American oceanographer Sylvia Earle (1935– ) has spent decades exploring the ocean. “I was always interested in critters, and most of them were in the ocean!” she said of her childhood.
Earle has spent more than 7,000 hours diving, researching, and exploring the ocean. In 1970, she spent two weeks living in an underwater habitat with an all-female team of scientists. Her work as a research scientist has contributed greatly to our knowledge of the ocean.
In 2009, Earle founded Mission Blue. The organization is dedicated to exploring, researching, and protecting the ocean. Part of its work involves creating a network of marine protected areas around the world. Mission Blue also collaborates with other ocean conservation groups and organizations, raises awareness about the need for ocean conservation, and inspires action.
Watch this interview with Sylvia Earle to learn about her walk on the seafloor at a depth of more than 1,000 feet. How was she able to do that walk under such extreme water pressure?
PBS Silvia Earle
THE OCEAN
WORDS TO KNOW
acoustics: the way sound carries within a space.
Laws like the ESA and the MMPA offer protection for species listed as endangered. Other laws further protect specific species. Sharks, for example, are protected in the United States by the Shark Finning Prohibition Act (2000) and the Shark Conservation Act (2010).
International laws are in place to protect whales. Additional laws protect sea turtles, manatees, and other marine species.
SUSTAINABLE SEAFOOD AND MARINE FARMING
As you read in Chapter 6, many species in the ocean are being overfished. Does that mean you need to stop eating seafood? Not at all! It does mean making informed choices about the seafood you buy and consume. Sustainable seafood can be wild-caught and farmed. In both cases, the number of fish caught does not endanger species’ populations or marine food webs.
Meet an ocean farmer and learn about ocean farming in this NOAA video. Why is aquaculture more sustainable than traditional farming on land?
Tech Talk: Ocean Acoustics
Ocean acoustics is the study of ocean sounds and the behavior of those sounds in the water. A sound in the ocean travels farther than in the air. Its wave radiates through the water in all directions. Plus, the speed of sound varies depending on salinity, water temperature, and depth. Scientists learn a lot by listening!
Oceanographers use acoustics as a tool to study ocean biodiversity, as well as ocean currents and the chemistry of the ocean. As you read in the introduction, sonar uses sound waves to map the seafloor. Finally, scientists are using ocean acoustics to understand the impact of human-made noises on wildlife.
Ocean Today farming
In the past several decades, aquaculture, or fish farming, practices have grown. They are a great way to meet the demand for seafood—and they do not reduce fish populations. Just like on land, fish and other species are bred, raised, and harvested on farms. In some cases, nets are suspended in the ocean like a fence to keep the fish contained. Other times, fish are farmed in large tanks or manmade ponds on land.
Do you eat your greens at dinnertime? Some aquaculturists grow seaweed for people to consume. Because seaweed grows vertically in the water column, it requires very little space, and, obviously, no land. It also doesn’t require any fertilizer, freshwater, or food—it just grows naturally. As it does, it provides habitat for marine species and naturally filters the water, cleaning the ocean as it grows. Seaweed also pulls carbon out of the ocean. On your plate, seaweed is not just delicious, it is nutritious!
Learn how to make informed choices about seafood at the Seafood Watch website. What changes might you make in your seafood choices?
Seafood Watch
A Norwegian salmon fish farm
THE OCEAN
WORDS TO KNOW
single-use plastic: a plastic product that is designed to be used only once and then thrown away.
CLEANING UP MARINE DEBRIS
Marine debris, and especially plastic pollution, is a big problem in the ocean. The good news is that many different individuals and organizations are working to reduce marine debris.
World Oceans Day takes place every year on June 8. It is a day to celebrate our ocean and to inspire people to act to help protect it.
One solution is to reduce the amount of plastic we produce and use, especially single-use plastic . This is where laws come into play—different towns, states, and nations have banned different types of plastics. A tax on single-use plastic can also make consumers think about the plastic they use.
Proper disposal, reuse, and recycling of waste and fishing gear reduce ocean pollution as well. Organized beach cleanups keep debris from entering or reentering the ocean. Stopping trash at the mouth of rivers before it empties into the ocean is another way to reduce marine debris. One of the first trash collectors to do this was Mr. Trash Wheel. It was installed in 2014 at the mouth of the Jones Falls River where it meets Baltimore Harbor in Maryland. Since then, several similar trash collectors have been developed and installed around the world.
Mr. Trash Wheel at night
Once the debris is out in the ocean, it’s more difficult to remove. Still, some organizations are working on doing just that. Scientists and engineers have developed and used ocean cleanup systems to remove debris. The systems use a U-shaped barrier to concentrate marine debris so it can be collected and loaded onto a boat and disposed of properly. At times, artificial intelligence (AI) helps locate debris hotspots.
Explore this NOAA website to learn about ways you can help protect our ocean. Why do we all have a stake in keeping oceans healthy?
Scientists are also developing plastics that decompose and are not harmful to the environment. Many of the plastic alternatives use natural materials such as fibers from coconuts, seaweed, and bamboo. Some researchers are even coming up with ways to make edible tableware. Imagine being able to eat your utensils and your food packaging at the end of a take-out meal!
THE OCEAN
WORDS TO KNOW
citizen science: when everyday people help scientists collect and analyze data.
THERE’S MORE!
There are too many ongoing ocean conservation efforts around the world to name. And that’s a good thing! Here are a few more ways people are working to protect the ocean:
• Local Conservation: Many local communities are now leading ocean conservation efforts because they know best! This includes utilizing local and Indigenous knowledge, traditions, and practices.
• Ecotourism: Tourism may seem like an odd partner in conservation. However, when done correctly, ecotourism benefits the environment as well as the local community and visitors. Ecotourism can be a means to support ocean conservation efforts and help make people aware of issues such as overfishing and pollution.
Census of Marine Life
The Census for Marine Life took place between 2000 and 2010. During that time, more than 2,700 scientists from 80 different countries collaborated to record biodiversity in the ocean. They also looked at the distribution and populations of species. They explored coral reefs, shorelines, the deep-sea floor, open ocean, polar oceans, seamounts, and more. During the census, the scientists discovered more than 1,200 new marine species.
More recently, the Ocean Census was launched in 2023. Similar to the Census of Marine life, this 10-year project is a collaboration of scientists, organizations, and governments from around the world. As of 2025, the Ocean Census had already discovered more than 800 new marine species. In addition, a juvenile colossal squid was filmed for the first time in its natural habitat in the South Atlantic Ocean.
The work of these scientists contributes to our understanding of oceans past and present and provides information we can use to protect marine species and their habitats in the future.
• Artificial Reefs: Artificial reefs are manmade structures placed in the ocean to support marine species and boost biodiversity. Some are purposely designed to look like natural habitats. Some are 3-D printed! Others are repurposed materials such as old culverts, cages, and poles. People have even made artificial reefs by sinking old ships and a train boxcar.
Listen to this NOAA podcast for information on artificial reefs and how they benefit ecosystems. Where are artificial reefs typically placed? Why?
• Coral Nurseries: When water becomes warmer, corals can lose their color and become more susceptible to disease. can suffer. To help, people are growing coral in underwater nurseries. They attach fragments of coral to manmade, treelike structures until the coral reaches a certain size. Then, they attach the coral to a reef, with the goal that the corals will reproduce and the entire reef will become healthier.
• Reduction of Noise Pollution: Policies in some places limit noise levels, require ships to lower their speed, prohibit seismic blasts, and restrict ship travel through MPAs.
NOAA podcast artificial reefs
The United States Navy using oyster shells to create artificial oyster reefs.
THE OCEAN
WORDS TO KNOW
carbon footprint: the amount of carbon dioxide that is emitted as a result of one’s daily activities and travel.
INDIVIDUAL ACTION
Everyone, including you, can play a role in ocean conservation. If you want to get involved, participate in a beach clean-up, eat sustainable seafood, avoid single-use plastics (bags or water bottles), choose reusable straws, educate your friends and family about the ocean, or write a letter to your representatives to ask them to support marine conservation.
You can also become a citizen scientist! You might watch for whales, count seabirds, report tide levels and weather, or record the type of marine debris you see on the beach. We need this data to understand and protect species and ecosystems. Without citizen scientists, it can take scientists many years to get the information they need. Using today’s technology, people help scientists collect that data in a fraction of the time.
You can be part of ocean conservation in many other ways:
• Read the signs and follow the rules when you visit a marine ecosystem or MPA.
• Keep your distance and do not feed wildlife.
• Dispose of trash, fishing lines, nets, and hooks properly.
• Lower your carbon footprint .
• Reduce your plastic use and avoid single-use plastic.
• Before going on a wildlife or adventure tour, research companies to learn how they protect the environment.
• Use reef-safe sunscreen.
The ocean is vital to all of us, no matter where you live. To help conserve the ocean, think globally, act locally—the choices you make in your everyday life can help protect the ocean. Share what you’ve learned about the ocean with others— spread the word! Armed with knowledge, we can all make a difference.
ESSENTIAL QUESTION
What can we do to restore and protect the ocean?
OCEAN POETRY
You have learned a lot about the ocean, its roles on the planet, and its amazing biodiversity. You’ve also learned how people rely on and impact the ocean and how they are working to protect it. Use what you’ve learned to write a collection of poems about the ocean.
› Research different types of poems: free verse, haiku, ode, cinquain, limerick, acrostic, diamante, shape poem, and more. When you write the poems, try to use a different form each time.
› Pick a theme for your poems. Conservation? Creatures of the deep ocean? A particular ocean ecosystem such as a coral reef? The theme will be the thread that connects the poems.
IDEAS FOR SUPPLIES
• science notebook
• blank white paper
• colored pencils or markers
Want to learn about different types of poetry? Try this website!
Pobble poetry types
› Spend time brainstorming, drafting, and revising five poems. Use a different form for each one. Have a friend, family member, or teacher give you feedback, and revise. When the poems are ready to publish, write each one out on a piece of white paper and then illustrate it. Bind the collection with staples, yarn, or a spiral bind.
Try This
Instead of five poems, write ten. Or, have friends or family members each contribute a poem about the ocean to create an anthology. If poetry isn’t your thing, perhaps make an ABC book of the ocean or write mini essays related to your theme.
TEXT TO WORLD
What can you do today to help oceans stay healthy?
CLEANING UP MARINE DEBRIS
As you’ve learned, individuals and organizations are working to remove marine debris from the ocean. They are using science, technology, innovation, and imagination to design removal systems and methods. How would you solve this problem?
IDEAS FOR SUPPLIES
• science notebook
• a basin or bathtub
• plastic trash or small toys
• paper and pencil;
• tools, toys, and other materials to build a device for collecting marine debris
› Fill the basin or tub with water and litter it with debris. This is your ocean and your marine debris. How can you get out the pieces without picking them up one by one? Remember, the ocean is too big for that approach!
› As you brainstorm possible solutions, research what has already been done. Learn from those systems and consider what you can do to improve on them. Also keep in mind that you don’t want to harm or collect marine animals.
› Using the engineering design process, design a system or method to remove marine debris.
» Identify a challenge
» Brainstorm possible solutions
» Draw a plan
» Build the project
› Build and test your project. What worked well? What didn’t? Was removing the debris easier or harder than you thought? Would your solution be scalable to use in the ocean? After addressing these questions, redesign and tinker with your device to improve it. Then retest.
» Test it
» Evaluate it
» Redesign the project as needed
Try This
Use an online coding platform like Tinkercad to design and test your marine debris removal system.
Tinkercad
GLOSSARY
acoustics: the way sound carries within a space.
adaptation: the changes a plant or animal makes to help it survive in its environment.
aerate: to create channels that allow air to flow through.
algae: plant-like organisms that turn light into energy, but that do not have leaves or roots.
algal bloom: an abnormal growth of algae in a body of water.
anemone: an invertebrate that is related to corals and jellyfish.
Antarctic Circumpolar Current (ACC): an ocean current that flows from west to east around Antarctica.
Antarctic Convergence: the place where the colder, denser, saltier water of the Southern Ocean meets the warmer, less dense waters to its north.
antifreeze: a liquid that is added to a second liquid to lower the temperature at which the second liquid freezes.
aquaculturist: a person who farms plants and animals in the ocean.
baleen: the tough, flexible material hanging down in some whales’ mouths to help trap their food.
basalt: a black, shiny volcanic rock.
basin: a depression in Earth’s crust that holds water.
bathysphere: a spherical, manned submersible made of steel that is suspended from a ship for deep ocean exploration.
bay: a body of water that is surrounded by land on three sides.
bedrock: hard, solid rock below the soil.
biodiversity: the variety of life on Earth.
biological carbon pump: the process by which carbon is moved from the surface of the ocean to the deep ocean, where the carbon is stored for long periods of time.
bioluminescence: the production and emission of light from a living organism.
bivalve mollusk: a marine animal with a soft body protected by two shells hinged together.
blubber: a thick layer of fat under the skin of some animals that prevents heat loss and stores energy.
blue carbon: carbon stored by the ocean.
brackish: somewhat salty, as in the mix of freshwater and seawater found where rivers meet the ocean.
bycatch: marine species caught accidentally as people fish for other species.
calcium carbonate: a naturally occurring compound consisting of calcium, carbon, and oxygen.
canopy: the thick, dense upper layer of a forest that receives the most sunlight.
carbon cycle: the continuous movement of carbon through Earth’s atmosphere, land, rocks and sediment, water, and living organisms.
carbon footprint: the direct effect an individual’s actions and lifestyle have on the environment in terms of carbon dioxide emissions, which contribute to global warming.
carbon sink: a place where carbon is stored.
carnivorous: describes a plant or animal that eats only animals.
cataract: a type of waterfall with a large vertical drop.
chemosynthesis: a process organisms use to convert minerals and other chemicals into energy.
chlorophyll: a substance that makes plants green and is used in photosynthesis to capture light energy.
GLOSSARY
THE OCEAN
citizen science: the involvement of everyday people in scientific activities or projects.
climate: the average weather in an area over time.
comet: a ball of ice and dust that orbits the sun.
commercial fishing: the large-scale catching and selling of marine species.
compass rose: a circle drawn on a map to show north, south, east, and west.
condense: the process by which a gas cools and becomes a liquid.
continental crust: the part of the earth’s crust that forms the continents.
continental shelf: the border of a continent that slopes gradually underwater.
countershading: a camouflage adaptation in which animals are dark on top and light on the bottom.
crustacean: a water animal such as a lobster, crab, or shrimp that has a hard shell and jointed legs.
crust: the earth’s outer layer.
current: the constant movement of water in a direction.
cyanobacteria: a bluegreen type of aquatic bacteria that produces oxygen through photosynthesis.
dead zone: a place where no life exists.
deflect: to turn aside.
density: the amount of matter in a given space, or mass divided by volume.
dilute: to make something less strong.
displace: to move something from its place.
DNA: deoxyribonucleic acid, which is the substance in the cells of all living things that carries their genetic information.
dormancy: a state of rest or inactivity when an animal’s bodily functions slow to conserve energy and survive harsh conditions.
drought: a long period of little or no rain.
dune: a mound or ridge of sand that has been piled up by the wind.
ecophysiology: the study of how a community of plants, animals, and other organisms work together.
ecosystem: an interdependent community of living and nonliving things and their environment.
ecosystem engineer: a species that greatly alters an ecosystem by creating, modifying, or maintaining it.
ecosystem service: the important benefit provided by an ecosystem to keep the air, water, and soil healthy.
environmental DNA (eDNA): DNA shed by organisms into their surroundings.
equator: an imaginary line around the earth, halfway between the North and South Poles.
equitable: fair.
erode: to wear away.
estuary: a body of water where a river meets the ocean, with a mix of freshwater and salt water.
evaporation: the process by which a liquid becomes a vapor or gas.
GLOSSARY
feces: poop.
fishery: a place where fish are caught or raised as a business.
foundational keystone species: a species of plant or animal that maintains or creates the base on which an entire ecosystem exists.
frond: the leaf-like part of kelp, ferns, or palms.
gelatinous: having the consistency of jelly.
gene: inherited material within cells that affects the traits an organism will have.
genetics: the study of genes and how traits are passed down from parents to offspring.
geology: the study of the physical features of Earth including its layers.
Global Conveyor Belt: an interconnected system of ocean currents that moves ocean water all around the planet.
granite: a type of rock that contains many crystals. It is formed underground over a long period of time with an enormous amount of pressure.
Great Oxygenation Event: the introduction of oxygen into the earth’s atmosphere 2 billion years ago.
greenhouse gas: a gas in the atmosphere that traps heat.
gyre: a large system of circulating ocean currents associated with global winds.:
habitat: an area where certain plants and animals live together.
herbivorous: plant-eating.
holdfast: a structure that anchors kelp to the seafloor.
holistic:
hull: the body or frame of a boat.
hydrogen sulfide: a colorless gas that stinks like rotten eggs.
hydrothermal vents: undersea hot springs that spew mineral-rich water.
immunity: the body’s ability to withstand harmful invaders such as bacteria, viruses, fungi, and other foreign bodies.
indigenous: native to a place.
inner core: the innermost layer of Earth, made of super-hot solid metal.
intertidal zone: the area that is covered by the ocean at high tide and exposed at low tide.
invertebrate: an animal without a backbone.
holdfast: the specialized root-like system of a marine plant such as seaweed that helps it attach itself to rock and not be swept away by the tide.
jet stream: a high-speed flow of air high in the atmosphere that flows from west to east.
lagoon: a pool of shallow seawater separated from the ocean by a narrow strip of land.
larva: an organism at the beginning stage of development. Plural is larvae.
lava: molten rock that comes out of a volcano.
lichen: a plant-like organism that grows on rocks, trees, soil, and human-made structures.
limpet: a specialized type of sea snail with a cone-shaped shell and a strong foot for holding onto rock.
macroalgae:large, multicellular marine organisms that photosynthesize.
magma: molten rock below Earth’s surface.
THE OCEAN
GLOSSARY
mangrove forest: a specialized saltwater forest that grows in the intertidal zone in tropical and subtropical areas.
mantle: the middle layer of Earth.
marine: having to do with the ocean.
marine debris: human-made materials and trash that end up in the ocean.
Marine Protected Areas (MPAs): protected wilderness areas of the sea.
marine snow: the fall of organic material— feces, shed tissue or scales, dead and decaying organisms, or food scraps— through the water column from the upper zone of the ocean to deeper zones.
maritime: related to the sea, sailing, or shipping.
metabolism: the processes in an organism that convert food into energy to keep it alive.
microbes: tiny organisms too small to see without a microscope, including bacteria, viruses, and some algae.
microplastic: a tiny piece of plastic the size of a grain of sand or smaller.
Middle Ages: a period from about 350 CE to 1450 CE.
migration: the seasonal movement of animals from one place to another.
mollusk: a soft-bodied animal such as a slug, squid, or octopus that has no spine and no legs.
molten: made liquid by heat.
mucous: containing mucus, a slimy, sticky substance
mudflat: a flat area of mud in estuaries that is left exposed at low tide.
mutualistic: common to or shared by two or more parties.
nutrient: a substance that living things need to live and grow.
ocean acidification: the absorption of too much carbon dioxide by oceans which causes acid levels to rise.
oceanic crust: the section of Earth’s crust that is located on the floor of ocean basins.
oceanographer: a scientist who studies the ocean and the plants and animals that live there.
outer core: a spinning mix of liquid nickel and iron surrounding Earth’s inner core.
parasite: an organism that feeds on and lives in another organism.
photosynthesis: the process a plant goes through to make its own food; the plant uses the energy of the sun to turn water and carbon dioxide into sugar, with oxygen as a waste product.
phytoplankton: tiny aquatic plantlike organisms that produce their own energy through photosynthesis.
phytoplankton bloom: a huge increase in phytoplankton.
pioneer plant: the first species of plant to grow in an area.
plankton: tiny aquatic organisms that drift in tides and currents of water.
polyp: a small creature that lives in colonies and forms coral.
precipitation: falling moisture in the form of rain, sleet, snow, and hail.
primary consumer: a plant or animal that eats tiny plants and phytoplankton.
salinity: the measure of dissolved salts in water.
salt marsh: an area of coastal grassland that is regularly flooded by seawater.
GLOSSARY
scavenger: an animal that feeds on animals that are already dead.
sea level: the level of the surface of the sea.
seamount: an underwater mountain.
sediment: dirt, fertilizer, rocks, and other tiny bits of matter deposited in rivers and oceans.
sedimentation: the deposit of solid materials such as rocks, sand, and minerals in a new location.
seismic blast: a loud blast of compressed air used to locate oil and gas beneath the ocean floor.
single-use plastic: a plastic product that is designed to be used only once and then thrown away.
sonar: the use of sound waves under water to measure depth and detect objects under water.
spawn: to produce and deposit eggs.
stewardship: the responsible management and care of something.
stipe: the stalk of algae, fungi, or plants.
strait: a narrow passage of water connecting two seas or two other large areas of water.
submersible: an underwater vessel used for exploration and research.
subsistence fishing: small-scale, lowtech fishing for local consumption.
sustainable: able to be maintained at a certain level or rate without being used up.
synchronous: happening at the same time.
tectonic plates: the large solid pieces of Earth’s crust that float on the mantle.
tide pool: a pool of ocean water that remains after the tide goes out.
topography: the physical features of the surface of the Earth.
trait: a specific characteristic of an organism.
treaty: a formal agreement between countries.
tropical: having to do with the area around the equator.
tsunami: an enormous wave formed by a disturbance such as an earthquake under the water.
turbine: a device that uses pressure on blades to spin generators and create electricity.
turbulent: unsteady, stormy, and violent.
understory: the more shaded layer of a forest below the canopy.
upwelling: a process in which deep, cold, nutrient-rich water rises and displaces surface water.
water column: the vertical column the surface of a body of water to the bottom and the features of the water at different depths.
water cycle: the continuous movement of water on Earth, from the ground to the atmosphere and back to the ground.
water vapor: the gas form of water in the air.
weather: the temperature, wind, humidity, and precipitation conditions of an area at a particular time.
whale fall: a whale carcass that sinks to the ocean floor and creates a unique deep-sea ecosystem.
zooplankton: tiny animals that drift freely in salt water and fresh water.
zooxanthellae: tiny, single-celled organisms that live within coral in a relationship that benefits both.
Metric Conversions
Use this chart to find the metric equivalents to the English measurements in this book. If you need to know a half measurement, divide by two. If you need to know twice the measurement, multiply by two. How do you find a quarter measurement? How do you find three times the measurement?
RESOURCES
THE OCEAN
ESSENTIAL QUESTIONS
Introduction: What role did the ocean play in evolution of life on Earth?
Chapter 1: How is the ocean essential to life on Earth today?
Chapter 2: What important roles do polar oceans play in regulating Earth’s climate?
Chapter 3: What makes the intertidal zone such a complex ecosystem?
Chapter 4: Why are shallow oceans vital ecosystems?
Chapter 5: How are species able to survive in deep ocean ecosystems?
Chapter 6: In what ways do we rely on the ocean?
Chapter 7: What can we do to restore and protect the ocean?
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THE OCEAN
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THE OCEAN
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