In The Flow

The longest-established scuba diving magazine in North America November 2009

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In the Flow

BY JEAN-MICHEL COUSTEAU

A Goliath grouper dwarfs the film crew and the Cousteau family. The largest Goliath groupers in the Atlantic Ocean can exceed eight feet (2.4m) in length, weigh more than 800 pounds (360kg) and can live more than 40 years. For the OFS expedition team, it was a thrill to film these endangered giants. Photo: © Carrie Vonderhaar, Ocean Futures Society/KQED

Among the truly mind-boggling traits of our species is that we have extended our senses and abilities to realms beyond anything natural. We breathe underwater. We fly. We race at speeds of hundreds of miles per hour. We have taken our mechanical aptitudes and turned them into physical superpowers and there seems to be no limit to our inventiveness. But there are ways in which Nature has designed totally brilliant and sustainable means for animals and plants to accomplish the improbable as part of their life cycles.

Many of us have had the thrill of being carried along a reef by a strong current. All of us have been trained to watch for currents and not get carried where we don’t want to go. Divers struggling in these strong forces need to be smart for their own safety but also to realize that these are the highways of life itself within the sea.

One of the animals most dependent on currents is the Goliath grouper of the Gulf of Mexico, western Atlantic and the Caribbean. A behemoth that grows to over eight feet (2.4m) long and may weigh as much as 800 pounds (360kg), the grouper is not designed for fast swimming. Yet its future depends on a life cycle in which it must cross hundreds of miles of ocean, and ocean currents provide the lift.

Timed by the full moon during July, August and September, crowds of groupers gather in open water to spawn. During the filming of America’s Underwater Treasures for our PBS series, Jean-Michel Cousteau Ocean Adventures, Fabien, Celine and I experienced our own family reunion dive 10

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among an equivalent family reunion of groupers. We all gathered to witness an amazing event in the Florida Keys National Marine Sanctuary, but we almost missed it. For days we had observed massive groupers around and inside shipwrecks in the area and so we returned to observe the spawning at a ‘reliable’ site. As the full moon arrived so did we but all the groupers were gone – the shipwreck was empty – and I immediately understood why.

If the groupers spawned in the shipwrecks, their larvae would settle and die. The future of the species depends on eggs and larvae being carried – sometimes hundreds of miles – to shore to grow and mature among the brackish waters and protective architecture of the mangroves.

After being fertilized in open water, about three weeks later, the drifting eggs hatch as one-inch-long (2.5cm) larvae, equipped with the equivalent of sails to carry them efficiently in the liquid wind—long fins on their dorsal and ventral surfaces make them optimum sailors in the currents which are headed for shallow water and the mangroves.

Two features of their life cycle have made Goliath groupers and other species vulnerable. Large-scale coastal development has wiped out large sections of coastal mangroves, obliterating the safe haven for juvenile groupers. And in the past, fishermen quickly understood that the spawning congregations were the easiest place and time to catch groupers en masse and on schedule. It led to a precipitous decline that is now being reversed through fishing bans and a better understanding of mangroves as nurseries and natural coastal barriers. But it will take time.

Another story about currents is well known but never ceases to amaze me. It’s the victory of the smallest of beings creating one of the most massive wonders of the world. It’s the story of the transformative power of collective action. It’s the journey of the tiny, fertilized coral egg, at the mercy of the currents, carried through vast stretches of open water to finally settle and build the largest natural structures on earth.

Expertly tuned to the cycle of tides and the moon, the massive collection of coral polyps that comprise the tropical reef engage in one of the most spectacular and effective events that can be observed in the sea. Experts in the Gulf of Mexico were able to give our team a range of days when the corals would spawn but not a precise schedule, so all we could do was to be prepared and watch. The experience of a lifetime began with the call from the ship’s deck: “It’s happening!” as a froth of gametes are spotted on the sea’s surface. Then it’s a race to get in the water and watch. Of course, it’s often the middle of the night.

Different species of corals simultaneously release eggs and sperm into the water column and, somehow, the right sperm from a variety of species finds the right egg among the millions of gametes clouding the sea. Fertilized eggs, tiny satellites of life, are carried away, not just to find new worlds, but to create them. Currents carry these packages of potential reefs hundreds of miles until the individual larva settles, becomes a coral polyp, and begins to build its astonishing architecture.

Clearly, the best science fiction is really just science. Mobile aliens in the water column settle on the bottom, shape shift into a completely different immobile form, and then create gigantic structures from nothing but what is already in the water.

The science of extending our own senses has taken an interesting turn, specifically when it comes to the Goliath grouper. The Ocean Research and Conservation Association (ORCA) and its collaborators are using an acoustic underwater camera to “see” through sound, much like the ultrasound on a pregnant woman or a dolphin’s sonar, into mangroves to track the presence of juvenile grouper that are obscured by murky waters. Since this grouper is critically endangered, it will give scientists a way of counting future generations that we would never be able to see naturally and possibly averting the loss of a spectacular species.

After a few years, the young groupers will leave the mangroves for deeper waters where they will eventually hear or feel the beat of the planetary clock governing moon and tides and be guided to the invisible highways that will carry the species into the future.

ABOVE: A Goliath grouper seeks shelter among the roots of mangrove trees in Florida Bay near the 7-mile Bridge, Florida Keys National Marine Sanctuary. Mangroves like these are important nurseries and habitats for many fish and invertebrates that eventually migrate to nearby coral reefs. This Goliath grouper may spend its first six years of life swimming among the roots of mangroves, seeking shade and staying clear of hungry mouths in the deeper reefs. BELOW: Corals reproduce in a synchronized spawning event, releasing thousands of eggs and sperm into the water where fertilization occurs. This spectacular event only takes place a few times a year, intricately timed with the full moon, tides and currents. Photo: © Carrie Vonderhaar, Ocean Futures Society/KQED

ABOVE: A close-up look shows the eggs of the coral emerging and ready to enter the water column, where they will be fertilized and then carried by the currents to settle and create a new generation of coral reefs. BELOW: The large outpouring of coral gametes may be a back-up mechanism to ensure that even in times of devastating events like hurricanes nature is able to maintain and restore itself. Here Fabien Cousteau experiences the reproductive abundance of what divers refer to as swimming through an upside-down snowstorm. Photo: © Carrie Vonderhaar, Ocean Futures Society/KQED

Goliath groupers gather on deepwater wrecks in the Florida Keys National Marine Sanctuary, one of many artificial reefs that provide a safe haven when it’s time to spawn.

The groupers gather annually around shipwrecks, deep patch reefs and rock ledges until the moon, the currents, and the tides are aligned for the spawning event. Then the groupers move to open water, swim towards the surface in a vertical dance and release their eggs and sperm, which are fertilized and carried to distant mangroves by the currents. Photo: © Carrie Vonderhaar, Ocean Futures Society/KQED

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