bathers on the French coast, witnessing the presence of microalgae, must report it

If you are lucky enough to be on the coast on this Monday, May 1, or in the weeks to come, and you notice that the water has changed color in certain places, that it has become abnormally green, brown, red or yellow, it may mean that there has been an exceptional proliferation of microalgae. This is called an “efflorescence” or a “bloom”. This phenomenon can indeed occur in the spring when the water warms up and the sunshine increases.

This is not necessarily a worrying phenomenon but indeed, a small minority of these microalgae are toxic. Of the 5,000 species known to date, about twenty produce toxins and this may lead to a ban on the consumption of shellfish in the area concerned. Hence the importance of spotting them quickly. Moreover, by decomposing, these proliferations of microalgae can also asphyxiate other marine species. This is why the French Research Institute for the Exploitation of the Sea (Ifremer) invites citizens who spot unusually colored water to take a small quantity of it from a bottle or gourd and bring it quickly to the nearest Ifremer station, for analyses. Thanks to this participatory science program called Phenomer, more than 500 reports of microalgae have already been made by individuals in the space of ten years.

To help science

Public participation is important “because these phenomena are often very short-lived… they can occur in areas far from Ifremer’s observation stations” explains Anne Donner, coordinator of this participatory science program. Hence the importance of these contributions from individuals. Because beyond health monitoring, it is also for scientists to better understand these sudden proliferations of microalgae. We know that they can appear with the heat and with the increase in the quantity of nutrients in the water, in particular when there are urban, agricultural or industrial discharges of phosphate and nitrate. But this does not explain everything. And these algal blooms are likely to multiply with global warming, says Ifremer. This year, this phenomenon also occurred earlier than usual, from February in the bay of Audierne in Finistère. This is the first time that this phenomenon has been spotted so early.