His name is reminiscent of a pirate scouring the Caribbean in search of big booty. Sargassum is more of a brown seaweed that floats on the surface of the ocean. It looks like a small branch topped with berries. Sargassum accumulates in particular over thousands of kilometers in the Atlantic Ocean, thus forming a kind of sea meadow on the surface of the water.
It is said of the Sargasso Sea that it is the only one without coasts, since it is located in the heart of the Atlantic. It obviously owes its name to the accumulation of algae of the Sargassaceae family found there. The Sargasso Sea covers an area of 3 million square kilometres, about twice the size of Quebec. It is located east of the Bahamas and northeast of the Antilles. Navigators seeking the New World in the 15th and 16th centuries were particularly concerned about becoming entangled there.
A large mass of sargassum, 8000 km long, is expected to wash up by summer on beaches in the Caribbean, southern Florida and the Yucatán Peninsula, Mexico. Satellite images taken in February showed that deep-sea sargassum accumulation began earlier this year. However, the arrival of such a quantity of algae on the coasts is not without consequence.
This is not the first time this has happened, but the mass of sargassum moving towards the coasts this year is one of the largest that has been observed for several years. According to scientists, more than 10 million metric tons of Sargassum is advancing towards coastal areas. According to Rick Lumpkin, director of the Physical Oceanography Division at the National Oceanic and Atmospheric Administration (NOAA), this is “one of the strongest years” since 2011. The researcher told The Associated Press that the mass of sargassum on the move was however greater in 2018.
First there is the number. To paraphrase the Club Med tagline: a few seaweed is nasty, imagine thousands! They thus accumulate on the beaches and decompose, giving off an odor resembling that of rotten eggs due to the hydrogen sulphide released by the sargassum drying on the beach. These algae also release ammonia and methane. “Sargassum is not really a threat to human health,” Professor Michael Parsons told La Presse. “Hydrogen sulfide can be harmful and may be responsible for anecdotal reports of headaches, nausea, and fatigue,” adds the director of the Marine and Environmental Science Research Station at Florida Gulf Coast University. People who spend several hours removing Sargassum from beaches are most likely to be affected by this phenomenon.
Sargassum washing up on beaches can also be damaging to different ecosystems. Decaying algae attracts insects, smothers turtle nesting sites, and kills sea turtles and fish. If not picked up, these algae can promote the growth of fecal bacteria. The phenomenon also has economic consequences. A survey conducted in Guadeloupe estimated economic losses related to tourism at 5.5 million US dollars for the first half of 2015.
If these algae become a nuisance once washed up on the beaches, they nevertheless play an essential role as a marine ecosystem. “Sargassum creates habitat for many organisms: shrimp, crabs, fish, other algae, to name a few,” recalls Michael Parsons. The Sargasso Sea is particularly a prime location for humpback whales during their migration. A sign of their importance, oceanographer Silvia Earle also wants this area to become the first marine protected area on the high seas.
“Yes, to a certain extent,” says Michael Parsons. Many organisms will increase their metabolic rates at higher temperatures, including Sargassum. If there is enough light and nutrients, this can lead to higher growth rates and more biomass. The researcher specifies, however, that it will be necessary to further document the productivity of Sargassum since we only have satellite data since 2011.