OCEAN71
Menu

Ecology, Economy

Fear over Arcachon Bay

Show on Google Maps

OCEAN71 Magazine tries to understand why oysters are particularly at risk into the Arcachon bay, in France. The scientists are studying the case, while all sorts of pollutions, mostly caused by human activities, seem to be responsible.

File summary

  1. A threatening seaweed
  2. The infamous mouse test
  3. And what if man was responsible ?
  4. Oyster eradication is possible

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

  • Gallery

    The seahorse’s secret

    Ecology, Economy – 1 chapter

    Oysters, the Arguin sandbank, the tides, many tourists visit the Arcachon bay ignoring that this unique biological maritime space hosts one of the most mysterious creatures of the sea : the seahorse. Almost extinct a decade ago, the bay is pride to have today the highest concentration of seahorses in France.

  • Video

    ORIKUM’S MYSTERIES

    Culture – 4 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.

  • The secret side of piracy

    Economy, Geopolitics – 2 chapters

    In the last 10 years, piracy has made a come back. From Somalia and Nigeria to the Caribbean and far-flung Asian archipelagos men are capitalising on weak leadership of the State to seize commercial ships and private yachts for ransom. We decided to investigate the reasons for this resurgence and discovered a world and practices that are witnessed by the ocean alone.