The potent smell of sargassum and the environmental problems the seaweed creates for the Cayman Islands are unlikely to diminish in the coming years, according to a study that appeared in Science magazine on Friday.
The study used NASA satellite photos and other data to show that the 2018 sargassum bloom, stretching from West Africa to the Gulf of Mexico, was the largest on record, and postulated that it represented a new norm for the region.
“There’s a high chance this phenomenon will continue [and] bloom at a similar magnitude,” said Mengqiu Wang, a postdoctoral researcher at University of South Florida, who was the lead author of the study.
Wang, who has been studying sargassum since 2015, worked with Chuanmin Hu, who has been doing satellite studies on the seaweed since 2006.
Wang and the rest of the team estimated the biomass of last year’s sargassum at more than 20 million tons. The ribbon of dense brown seaweed thrives on nutrients produced by a winter upwelling off the West African coast, as well as spring and summer runoff from the Amazon River in South America. In recent years, the researchers found, increased deforestation and the use of fertilisers has increased the nutrient level in the river runoff.
The circulation of ocean currents is also a factor in supporting sargassum growth, the study reports. That circulation has been impacted by climate change. On the other hand, the study says increased surface temperatures do not help the seaweed, which grows better in moderate to cool water.
While the mention of sargassum may make many in Cayman think of holding their noses, Wang said the seaweed does more than foul the shoreline.
“In the open ocean, mostly it’s a good thing,” she said. “Sargassum has great ecological value to a lot of marine life.”
An increase in the size of the floating brown mats of macro-algae, first described by Christopher Columbus, “is likely to affect the fish, the crabs, the turtles”, Wang said. “All marine life will likely be impacted.”
Even life in the deep sea is affected as the sargassum dies and sinks to the depths.
Along the coast, the material is less beneficial.
“Too much sargassum near the coast could be bad for the coral and the sea grass,” Wang said.
In addition to the unsightly rotting piles that wash up on Cayman’s beaches, and the pungent stink that results from that, sargassum can decrease the amount of sunlight getting to reef areas, stressing corals and sea grass and making it easier for coral-damaging algae to grow.
Recent surveys by the Central Caribbean Marine Institute have shown that algae growth on Cayman’s coral reefs is already at near critical levels. Wang said there is little likelihood the problem will go away.
“Right now,” she said, “we’re proposing [the increased sargassum] will have a big impact.”