Site details

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5 stars - Fully protected as a national park or Natura 2000 site by national legislation
LTBR Focal Site

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Arcachon Bay, SW opening in the ocean. Photo: J Thomas

Synoptic description of site:

A 156-km2 mesotidal lagoon or semi-enclosed bay, 2/3 of which is intertidal with extended Zostera beds and oyster parks; maximum water depth is 20 m at low tide, but most channels are 5-10 m deep.

Extensive description of site:

The Bay of Arcachon is a 156-km² triangular-shaped mesotidal lagoon or semi-enclosed bay, 2/3 of which is intertidal with extended Zostera beds and oyster parks. Most channels are 5-10 m deep (max. 20 m). Moderate freshwater inputs come from a river in the SE. All habitats within the Bay of Biscay are present, although hard substrata are artificial.

Habitats present:
Seagrass bedsX

Description of fauna and flora:

Of special interest are the largest European Zostera (marina and noltii) beds and the long exposed sandy beaches at the entrance of the bay.

Pristiness: High


There is no extensive agricultural practice close to the bay. Since the early 70s, sewage and industrial (paper mill) wastewaters have been processed in treatment plants and discharged in the open sea. Some signs of eutrophication occurred in the 80s and the early 90s, but they are now clearly decreasing.

Human impact:

There is no sewage or industrial pollution. Nitrogen flux from agricultural practice is now stabilized at a moderate level. The bay is a major centre of natural hatching and rearing of the Pacific oyster, as well as a recreational area.


All facilities for marine biodiversity research are available at the Arcachon Marine Station (boat, fully equipped laboratories, library, accommodation).

Available database and website:

Species inventories of all components of the ecosystem have been regularly updated since 1865 and are available as electronic files and will be made accessible through the website of the Marine Station.

Commitment and ongoing research:

Biodiversity-related research in the area is supported by several local projects and national (CNRS, Ministry of Environment) programmes: spatial distribution patterns of macrozoobenthos (SIBA), invasive species (INVABIO), high time-resolution of phyto- and zooplankton spring development (PRIMEVERE), effects of macroparasites on the population dynamics of molluscs (PNEC-ART2), long-term monitoring of water parameters (SOMLIT).