Sargassum: a transatlantic issue

Brown algae, (class Phaeophyceae), of Sargassum genus form dense populations constituting free floating rafts on the ocean surface. These Sargassum rafts have been observed for a long time in the northern Caribbean Basin and the Atlantic ocean, and their presence has notably given its name to the Sargasso Sea, located in the North Atlantic Ocean. However, since 2011, proliferations of Sargassum populations have been observed around the Caribbean region, including in locations where they were so far absent or extremely rare.

There are two species of Sargassum involved in this influx: Sargassum natans and Sargassum fluitans.

Both are holopelagic, meaning that they spend their entire life cycle in high seas without any benthic fixing stage. While the algae can be regarded as a nuisance when massive quantities are drafted on the beaches, it’s important to note that the Sargassum mats are home to many endemic species and provide ’nurseries’ and cover habitat for a range of species, including invertebrates, fish and turtles. There is emerging recognition of the crucial role it plays in the wider ecosystem ranging from the Atlantic to the Caribbean and the Gulf of Mexico : http://www.sargassoseacommission.org/storage/documents/Sargasso.Report.9.12.pdf.

As of today, the whole Caribbean region and West Africa have been affected by the massive landings of Sargassum. The latter do not affect the same locations in the Caribbean all year. As Sargassum are transported on currents, the influx progressively touched different locations across the region.

The West Indies and ten countries of West Africa (Senegal, Gambia, Guinea-Bissau, Togo, Benin, Sierra Leone, Liberia, Côte d’Ivoire, Ghana, and Guinea) have been particularly affected by this phenomenon since the first episode of 2011. Other similar events of lesser magnitude have been observed over the following years.

However, between 2014 and 2015, the region has experienced more intense episodes that have been almost continuous. Identified and potential impacts include economical (tourism, fishery, navigation), environmental (perturbation of marine species, beach erosion) and health aspects (decomposition of algae and release of H₂S).

Owing to both transatlantic and regional scales, the development of a coordination strategy is needed to cope with the landings.