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Specimens from at least 78 marine animal species , mainly fish and crustaceans, died in 2018 due to the decomposition of sargassum in the Caribbean , according to a report published in the Marine Pollution Bulletin on June 15.
The deluge of this floating algae in Mexico’s southeastern Caribbean region seems to repeat itself year after year, though higher levels of sargassum have been reported this year.
The report, which was part of a study conducted by scientists from Mexico’s National Autonomous University (UNAM), the Southern Border College (ECOSUR), and the Puerto Morelos National Reefs Park , indicates that 59% of dead species were fish; 28% were crustaceans; 5%, echinoderms; 4%, molluscs, and another 4% were bristle worms.
In an interview with EL UNIVERSAL , Dr. Rosa Rodríguez , who coordinated the reporting, highlighted the importance of its publication in a scientific magazine since it implies that its content has been checked, double-checked, and approved by other scientists. It is also the first report of its kind, since it describes the environmental impact of the massive arrival or sargassum on the Mexican Caribbean.
Different types of fish, sea cucumbers, sea urchins, and crabs were included in the list of species that have died as a result of this extreme sargassum influx, mainly in Puerto Morelos, Mahahual, and Xcalak .
However, the report only accounts for the total number of species affected and does not specify the exact number of deaths within each species.
The report indicates that these marine organisms died of hypoxia —asphyxiation—due to a lack of oxygen, combined with high concentrations of ammonia and hydrogen sulfide , which resulted from the decomposition of large amounts of sargassum accumulated on beaches.
The deterioration of water quality spread at least 480 meters from shore , and the continuing influx of sargassum “could have a negative impact on coral reefs,” the report states.
The die-off of marine organisms was documented along the coast line between Cancun and Puerto Aventuras , in the northern part of Quintana Roo, as well as in Sian Ka’an, Mahahual, and Xcalak.
Scientists have associated the massive death of fish to an overflow of sargassum in the region, as well as its decomposition and what is known as the sargassum brown tide.
Coral reefs in danger
As part of its introduction, he study shows that in 2018, the Mexican Caribbean received a mass influx of sargassum, which tends to accumulate and decompose, generating a negative impact on beaches and causing the water to turn brown.
“Between May and September of the same year, several reports on the mass mortality of sea life were issued. Based on these reports, we estimate that numerous specimens from 78 fauna species have died as a result of this event,” the report reads.
Scientists have also warned that placing barriers to protect coral reefs from the macroalgae before it reaches the shore could be counterproductive, since it can also affect marine fauna once it starts to decompose.
The “dark figure”
Historically, the Mexican Caribbean had seen relatively small amounts of sargassum in the past, mostly from the Atlantic Ocean .
In 2014, an unusually large amount of the so-called pelagic sargassum (Sargassum Fluitans and S. Natans) started arriving on the shores of Quintana Roo, peaking in 2015.
In 2016 and 2017, the sargassum influx showed a slight decrease. However, the seaweed plague returned in 2018 with full force.
Through satellite imaging, scientists were able to determine that the 2018 sargassum plague came from the coast of Brazil .
The reports came from tourist areas, which gained the most attention at the time. “This is why it is likely that the amount of dead specimens is actually higher than we imagine,” the report stated.
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