Fear over Arcachon Bay

A threatening seaweed

Maria and Jean-Michel Douet are standing on hot coals. In their cabin of the Cap-Ferret, the two young oyster famers are waiting for a fateful text message. « Tests performed in Arguin and in the Bassin came out positive for oyster and mussels. Everything is shut down. Courage and see you soon. » In oyster farming language this means disaster. Especially since the same scenario has been happening over and over again for the past five years and threatens 380 farms working on the 780 hectares of oyster beds yielding between 8,000 and 10,000 tons of oysters a year.

Jean-Michel and Maria Douet, young oyster farmers, are under pressure of the sanitary authorities © Philippe Henry / OCEAN71 Magazine

Dinophysis, a natural but toxic micro-alga seems to be the culprit. It releases a toxin which causes diarrhea in oyster eaters who ingest it. Oysters are water filters. They absorb and reject liters of sea water on a daily basis. They are thus the first to be contaminated. Even if this unwelcomed alga has never caused a single fatality, the European Union imposes the famous mouse biological test (see in chapter 2) in the name of the holly precaution principle, making oyster farmers hostages of the death, or survival of the little white mice…

The micro-seaweed dinophysis. If ingested the result in most cases is diarrhea. But this is enough for the French health authorities to forbid the sell of oysters © Philippe Henry / OCEAN71 Magazine

After years of research, the teams of the Institut français de recherche pour l’exploitation de la mer (Ifremer – French Institute for Exploitation of the Sea) have established a list of elements coinciding with the apparition of the dinophysis. « Spring unfortunately combines a number of events which seem to perfectly suit the alga, explains Roger Kantin, head of the Arcachon Ifremer station. Increasing daylight period, rise in water temperature (from 17°C) combined with fresh water influx carrying nitrates and phosphates from rivers which flow into the Bassin d’Arcachon. » As for the last two elements, they seem to be clearly resulting from human activity.

Other files

  • Soft and hard coral cuttings © Philippe Henry / OCEAN71 Magazine

    The miracle of coral

    Ecology, Economy3 chapters

    A little known and unusual type of farm has popped up in the port of Camaret in Finstere, Brittany. Johan Kergoat and Remi Plouhinec are cultivating coral…






  • Pearls of the Gulf © Francis Le Guen / OCEAN71 Magazine

    The pearl treasure of the Gulf

    Culture, Economy4 chapters

    Before the black gold made some families of the Arabian peninsula immensely wealthy, nomades settled down along the southern side of the Persian Gulf and risked their lives by fishing the earliest source of wealth in the region : pearls. Today, the practice has disappeared, but the Emirates still possess one of the most fabulous pearl’s treasure in the world. Here is an investigation on a well kept secret.






  • Video

    ORIKUM’S MYSTERIES

    Culture4 chapters

    Following a crew of Swiss and Albanian archaeologists, OCEAN71 Magazine went back to the antique village of Orikum, in Albania. This long-abandoned small port was a key location in Julius Caesar’s rise to absolute power. It’s not surprising that the scientists are amazed by the local discoveries. In this second season, the archaeologists will attempt to unravel the mysteries of this unique excavation site.