Sargassum is snowballing, scientists say
June 5, 2019
TAVERNIER — Dead fish and the remains of a green moray eel, turned chalk gray, floated amid a thick mat of sargassum seaweed in a Tavernier boat basin last week.
At least five eels perished in the deep and usually clear basin waters, along with untold numbers of parrotfish, snapper and other species that apparently fell victim to fatal oxygen depletion, residents said.
“I’ve never seen it this bad and I’ve lived here since 2000,” Ed Stoner said.
An unprecedented amount of sargassum looms as the likely culprit, pushed by easterly winds into Atlantic Ocean shorelines, basins and canals in the Florida Keys and along the state’s east coast.
Island nations in the Caribbean and Mexico have been dealing with expanding amounts of sargassum since a worrisome explosion of the thick, brown seaweed beginning in 2011. Normally, sargassum is an aquatic algae normally considered to be a critical ecosystem for oceanic species.
“Sargassum was something that was really unique and deserving of protection,” said Brian Lapointe, Ph.D., a research professor for Florida Atlantic University’s Harbor Branch Oceanographic Institute. “All of a sudden, global change is going on and sargassum is becoming harmful. Now it’s the largest harmful algal bloom on earth.”
Lapointe, a Big Pine Key resident of nearly four decades, said plumes of nutrient-laden fresh water from the Amazon River and Mississippi River have fueled the spread of sargassum off South America and in the Gulf of Mexico, where the Loop Current carries the thick algal mats through the Keys and onto the Florida east coast.
“There has been a lot of deforestation in the Amazon Basin and a major increase in fertilizer use,” Lapointe said. “Coupled with extremely heavy rain as a result of global climate change, that feeds the bloom.”
“As more and more seaweed material carries over from one year to the next, it’s like a snowball effect — getting bigger as it rolls downhill.” he said.
“To produce all that biomass, it has to have nutrients. Sargassum blooms in the tropical Atlantic ocean now come right across the Caribbean and go all the way to Africa,” said Lapointe, who served as a primary source for a sargassum article in the June 2019 edition of National Geographic magazine.
For decades, oceanic scientists were concerned about protecting the Sargasso Sea, an area bordered by currents between the U.S. and Europe since sargassum provides food and protection for marine species.
Now the seaweed threatens to deprive fish and coral of critical oxygen. Marine preserve managers in the Caribbean have reported fish kills. Nesting sea turtles struggle to reach the beach, and turtle hatchlings can die when snared amid the thick sargassum.
“There have been catastrophic effects on tourism in the Caribbean,” Lapointe said. “I’ve seen piles of sargassum 8 to 9 feet high on the beach in Barbados. When it rots, it releases toxic hydrogen-sulfide gas. People are having to evacuate from their homes to get away from this stuff.”
Chuanmin Hu, a University of South Florida professor specializing in optical oceanography, said residents of the Keys and Florida east coast should not expect relief from sargassum any time soon.
“Last year the bloom never ended. It lasted through the winter like a red tide sometimes does,” Hu said. “This time of year is when it’s at its worst and there is no sign of an improved situation. It does not look good.”
“Nobody can predict” which areas of the Keys or South Florida may be affected given the uncertainty of tides, currents and weather, Hu said.
Winds blowing in from the ocean have deposited large amounts of sargassum along some areas of the Keys recently.
“The most common wind direction here is out of the east and southeast during the spring months. It’s actually very normal,” said Andy Haner, a meteorologist at the National Weather Service Office in Key West. “Winds did pick up in speed which tends to happen when there are pressure differences, with high pressure to the north and low pressure to the south.”
Key Largo resident Thomas Frankovich, a Florida International University marine researcher, tested water in the Tavernier basin and found very low dissolved oxygen levels at the bottom, about 12 feet deep.
He also identified examples of potentially harmful phytoplankton, similar to red tide, that may have contributed to the fish kill.
By Monday, much of the sargassum was carried out of the Tavernier basin but FIU scientists installed a buoy that transmits water-quality information to researchers.