We are starting to know a little more about the algae that proliferates on the Basque coast, and which is responsible for various symptoms in swimmers and surfers.
This Tuesday, the ARS of Nouvelle-Aquitaine specifies that the first report was made on July 31 by a group of surfers, indicating the presence of “algae giving off a strong nauseating odor in the area of the Erromardie spot of Saint- Jean-de-Luz. “Since then,” five reports have been sent: young people having frequented a beach in Saint-Jean-de-Luz, a resident of Errardie, lifeguards and surfers from Guéthary and Biarritz “, who all presented ENT symptoms. After water and algae samples were taken on August 3 by Ifremer (French research institute for the exploitation of the sea), “the analyzes revealed a high abundance of the Ostreopsis microalgae. “
Sunday, the municipalities whose beaches have counted a high abundance of microalgae wished, as a preventive measure, to close their beaches, which they reopened on Monday. “In view of the low number of reports and the fact that no serious case has been detected, the ARS, at this stage, does not recommend the closure of the beaches. However, a monitoring system is in place. 20 minutes asked Elvire Antajan, manager of the Ifremer Arcachon station, about the presence of this algae.
What do we know about the algae that has been found on the Basque coast?
It is an algae of the ostreopsis group. It is not aboutOstreopsis ovata that we have already observed in the Mediterranean, butOstreopsis siamensis. It is an algae that is present in the water, but it is also found in sea spray, which is why it also bothers people on the beach, who can breathe it. The symptoms described are respiratory discomfort, headaches, dry coughs… Some people also find that the water has a metallic taste.
Had it already been observed in the Basque country?
It had been identified in the Basque country, during an Ifremer study on ostreopsis on the Atlantic coast in 2018. And we had a first alert last year, towards the end of August-beginning of September , with people complaining of the same symptoms. During our samples, it turned out that there was a fairly strong presence of ostreopsis… There was therefore a concomitance of two events, but the health episode had been fairly short, and we had not been able to establish the causal link. But the fact that the phenomenon recurs two years in succession, really questions us.
So it’s not totally a surprise to find her there, and at this time of year?
It is not a surprise to find it there, on the other hand the abundances surprise us enormously. Our samples on August 3 north of Saint-Jean-de-Luz revealed very high concentrations of ostreopsis. And this Monday we relaunched other samples, which include the collection of macroalgae, because ostreopsis are microalgae that grow on macroalgae. This will give us the extent of the phenomenon, because there were other reports last weekend of people inconvenienced with respiratory problems.
What do we know about toxins fromOstreopsis siamensis ?
They are absolutely not the same asovata, which is very toxic, and so far we have never had a case showing that the toxins of siamensis could cause reactions in humans. If it does, it would be a novelty. It may be a question of quantity, and if this year we have an absolutely incredible proliferation of this alga, there may be a greater sensitivity. It is also necessary to study the meteorological conditions which can favor its release from macroalgae, and then carry it by the spray. In all cases, the precautionary principle must apply.
How do we explain the appearance of this algae on the Basque coast in recent years?
This is difficult to say because it has not been closely followed up, and the ostreopsis group is quite difficult to identify. Siamensis was first described in the Gulf of Siam (Thailand) at the beginning of the last century. But it has already been reported in the Spanish Basque country in 2016, and on the coast of Morocco in the 2000s. During the Ifremer study in 2018, DNA traces were even found in the Landes and on the Arcachon bay. But for the moment, the sector concerned goes from the Spanish border to Biarritz. It is clear that we will have to take an interest in it, because with the warming of the waters this species can settle and proliferate more easily. Although, we are surprised to see this phenomenon so early in the year, even though the temperatures are not extraordinary. We therefore still need hindsight to understand the environmental factors that promote the proliferation of this algae.