STRUGGLES

DEFINING THE DETAILS AS THE ‘BLOB’ ARRIVES IN THE KEYS

MASSIVE OFFSHORE WEEDLINES ARE THE STUFF OF KEYS ANGLERS’ DREAMS. BUT THE LATEST MASS AFFECTING THE ISLAND CHAIN IS ONE THAT SOME WISH WENT ELSEWHERE.

By now, most have heard about the massive “blob” of sargassum — composed of multiple brown algae species – approaching the Keys. Stretching nearly across the Atlantic Ocean, with an estimated mass of 13 million tons as of April, dense, odorous patches piling up on beaches throughout the island chain will continue causing problems in the coming months.

Earlier this year, Keys Weekly sat down with renowned Florida Atlantic University researcher Brian Lapointe and Florida Keys National Marine Sanctuary research coordinator Andy Bruckner to better understand what’s driving the algae, and what the Keys can expect from here.

WHAT IS “THE BLOB?”

First things first: This isn’t a one-time traveling mass that appeared out of nowhere. The Great Atlantic Sargassum Belt is the world’s largest recurring macroalgae bloom, often extending from the west coast of Africa to the Gulf of Mexico across the southern edge of the Sargasso Sea. The massive floating habitat is a hotspot for biodiversity, providing food and protection for fish, mammals, marine birds, turtles, crabs and more as well as a nursery for mahi mahi and jack species.

The belt’s annual bloom usually begins in the winter and spring months, typically peaking in early to mid summer. Its distribution throughout the Atlantic Ocean and Caribbean Sea is largely driven by currents and ocean circulation, and as Bruckner explained, much of the algae encountered in the Keys is carried by the Gulf Stream up from the Caribbean.

WHAT’S THE ISSUE?

While the floating version of sargassum provides critical offshore habitat, algae piles on beaches and in nearshore waters are problematic.

Heavy seaweed buildup covering alreadylimited sandy patches on Keys beaches can act as a physical barrier for females trying to nest, and can prevent hatchlings from emerging from nests and reaching the water. Sea turtle moms are known to avoid beaches smothered with sargassum, increasing competition for space at alternative nesting sites. In fact, studies from Florida Atlantic University conservatively estimated net hatchling production losses from sargassum to reach 22% on beaches in Boca Raton.

“Dead zones” can also replace vital nurseries as large quantities of sargassum create anoxic conditions that threaten marine life. In shallow water, degrading algae masses can kill plants and animals on the seafloor, while hydrogen sulfide gas released by the decomposing organism is a toxic eye and respiratory irritant – and potentially deadly for some marine life. As if that wasn’t enough, it smells like rotten eggs, pairing an unwelcome scent with an ugly sight for Florida’s tourist throngs.

HOW DID WE GET HERE?

Lapointe has studied sargassum since the 1980s, but he said that as he analyzed tissue from algae in the belt in more recent years, one nutrient in particular stood out.

“I was analyzing data from the 1980s that I collected. … In comparing those numbers with post-2010 data, that’s where we see nitrogen levels going up 35%, and the nitrogen:phospate ratio went up by 111%. That was my eureka moment,” he told the Weekly. “This sargassum looks like it’s being fed by the major rivers like the Amazon, the Orinoco, the Congo and the Mississippi.

“It just so happens that the nitrogen and phosphorus contents are highest in the winter and spring, just when the rivers are discharging the most. … By summertime, those river discharges are actually going down, and that’s when the growth slows down as tissues become depleted of nitrogen and phosphorus.”

Over the past 12 years, a formerly limiting nutrient to the growth and biomass of the belt ceased to be a handcuff, as human population growth fueled high reactive nitrogen levels with wastewater, fertilizers, deforestation and other contributors, Lapointe said. The belt is capable of doubling its size in anywhere from two to four weeks under ideal conditions, and with the algae continuing to exhaust the amount of available phosphorus, another critical nutrient, it turns to a chemical analog: arsenate, a salt of arsenic acid.

WHERE ARE WE NOW?

Researchers began actively tracking the size of the belt with multiple methods, including satellite imagery, during the first bloom in 2011. Since then, the 2018 bloom has been the record-setting standard, with 2022 as another severe event.

Thus far in 2023, the blob had an early start to its annual growth, and appears set to eclipse all previous years – but with the bloom set to peak around June or July, the final impact is yet to be seen. A sargassum