In Senegal, questions and concerns are emerging after the sudden appearance of brown-orange slicks on the surface of the sea, on the Petite Côte, south of Dakar. Scientists from the Dakar-Thiaroye Oceanographic Research Center (CRODT) and the Research Institute for Development (IRD) conducted the investigation, with the participation of local residents: the culprit is a micro-algae, harmless to the environment. humans, but potentially toxic to marine organisms.
With our correspondent in Dakar, Charlotte Idrac
The effect was spectacular on the beaches of Saly, Somone and Popenguine, with suddenly very colorful water near the coast. A phenomenon due to what is called a bloom “: the explosion of the concentration of a micro-algae explains Patrice Brehmer, researcher at the IRD.
Noctiluca scintillans
“ In the present case, the Noctiluca scintillansit is a dinoflagellate which is toxic to the environment indirectlyexplains the researcher. When there are explosions like this of populations, it can produce high concentrations of ammonia and drop the level of dissolved oxygen in the sea. »
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The phenomenon would be linked to climatic factors, with a sudden rise in sea temperatures, and the end of the trade winds, therefore northeast winds. It will quickly fade, according to the researcher, but could become recurrent, and disrupt the food chain. The Noctiluca scintillans indeed consume diatoms, at the base of the food chain for small pelagics and yaboy.
Consequences over time
” There is no problem for the consumption of fish, reassures Patrice Brehmer. It is not directly dangerous for the fish either, but in the medium term, it is annoying because these Noctiluca scintillans enter into competition with the diatoms which are the favorite prey of the small pelagics of the yaboy in Senegal. »
the yaboy, in other words the sardinella. This could have long-term economic and social consequences. For the scientist, there is no direct link with the so-called disease from fishermen » appeared since 2020. But the phenomenon would require in-depth research.