Bassin d'Arcachon

The Parc naturel marin du Bassin d'Arcachon (Arcachon Bay Marine Natural Park) is a French marine protected area created by decree on 5 June 2014, making it the country's sixth marine natural park (parc naturel marin). ^[1] Managed by the Office français de la biodiversité (OFB), it covers roughly 435 km² of coastal waters in the Gironde department of Nouvelle-Aquitaine, spanning the entire tidal lagoon of Arcachon Bay together with a strip of Atlantic Ocean extending three nautical miles offshore between Le Porge and Biscarrosse. The park protects one of the Atlantic coast's most distinctive semi-enclosed bays, a mosaic of tidal channels, mudflats, salt marshes, oyster beds and Europe's most extensive dwarf-eelgrass meadows. It reconciles a rich living heritage, oyster farming, fishing, tourism and boating with the conservation of habitats and species, guided by a fifteen-year management plan approved in 2017 and steered by a management council seated at Le Teich. ^[2]

Arcachon Bay is an exceptional nursery and feeding ground where the shallow, food-rich tidal waters support hundreds of marine species. The seagrass meadows shelter both of France's native seahorses, the long-snouted (Hippocampus guttulatus) and short-snouted (Hippocampus hippocampus) seahorses, alongside common cuttlefish, gobies, pipefish, crabs and shrimp. The bay is a key stage in the life cycle of the European eel, which migrates through its channels, as well as sole, sea bass and mullet that spawn or grow in its sheltered flats. Above all, the bay is a birdwatching landmark on the East Atlantic Flyway: the 110-hectare Réserve ornithologique du Teich, at the mouth of the Leyre delta, has recorded more than 320 bird species since 1972, and the sandbanks host large colonies of sandwich terns and huge wintering flocks of shelduck, brent geese, dunlin, curlew and other waders and waterfowl. ^[1]

The bay's flora is defined by its intertidal seagrass meadows, the largest in Europe. Dwarf eelgrass (Zostera noltei) carpets the exposed tidal flats and, together with common eelgrass (Zostera marina) in the deeper channels, forms a habitat that Arcachon holds in greater abundance than anywhere else in France. These underwater prairies are biodiversity hotspots that stabilise sediment, oxygenate the water and feed the bay's shellfish and overwintering geese. Fringing the shore, extensive salt marshes support glasswort (Salicornia), sea purslane, sea lavender and cordgrass, grading landward into reedbeds along the Leyre estuary. On the surrounding dunes and sandbanks grow marram grass, sea holly and other pioneer species, while the bay is bordered by the vast maritime-pine forest of the Landes de Gascogne, one of the largest planted forests in Western Europe.

Arcachon Bay is a large, triangular tidal lagoon of about 150 km² set into the sandy Atlantic coast of the Aquitaine basin, formed as Holocene marine sediments and shifting dunes dammed the mouth of the Leyre river to create a shallow inlet linked to the ocean by a narrow, ever-changing entrance channel. ^[1] The bay's floor is a dynamic patchwork of sandbanks, mudflats and tidal creeks laid bare at low water, reworked constantly by strong tidal currents that migrate the sandbars at its mouth. Guarding the entrance is the Banc d'Arguin, a mobile spit of sand and shell. Immediately south rises the Dune du Pilat, the tallest coastal sand dune in Europe, which measured about 107 metres above sea level as of 2018; built of some 55 million cubic metres of sand, it advances slowly inland and lies just outside the marine park's boundary. ^[2] These sands overlie the wider geology of the Landes, a flat plain of Quaternary aeolian and fluvial deposits.

The bay has a mild oceanic climate strongly moderated by the Atlantic, with warm summers, gentle winters and abundant sunshine that make Arcachon a long-established seaside resort. Summers are typically warm and dry, with sea breezes tempering the heat and water temperatures pleasant for bathing; winters are cool and wet but rarely freezing, thanks to the maritime influence. Rainfall is spread across the year with autumn and winter maxima, and westerly winds off the ocean dominate, occasionally bringing Atlantic storms that drive the shifting of the sandbanks and dunes. The great tidal range, among the largest on the French Atlantic coast, is the defining rhythm of the bay, alternately flooding and exposing vast expanses of flats twice each day and governing the movements of birds, boats and oyster farmers alike.

People have exploited Arcachon Bay for millennia, gathering shellfish and fishing its sheltered waters since prehistory. For centuries the bay was a working coast of fishermen and salt marshes, its shores dotted with the emblematic cabanes tchanquées, stilt cabins raised over the water, and pinasses, the traditional flat-bottomed local boats. Oyster farming became the bay's signature activity in the nineteenth century, and Arcachon oysters remain internationally renowned; today the bay's growers supply the majority of the young oyster spat used across French production, working thousands of tidal parcels. ^[1] The town of Arcachon itself flourished after the arrival of the railway in the 1850s, when its Ville d'Hiver of ornate villas drew health-seekers and holidaymakers. Fishing, oyster culture, boatbuilding and seaside tourism have shaped a strong maritime culture that the marine park now works to sustain alongside conservation.

The idea of a marine protected area for Arcachon Bay grew from decades of concern over declining seagrass, water quality and the pressures of tourism, shellfish farming and boating on a fragile, semi-enclosed bay. After extensive public consultation, the Parc naturel marin du Bassin d'Arcachon was established by decree on 5 June 2014 as the sixth of France's marine natural parks. ^[1] It was originally administered by the Agence des aires marines protégées, which merged in 2020 into the Office français de la biodiversité, now the park's managing body. Governance rests with a broad-based management council of some fifty-six members, uniting local elected officials, the state, oyster farmers, fishers, recreational users and environmental groups. ^[2] The council adopted a fifteen-year management plan in 2017 setting long-term goals for the bay's ecology, activities and heritage, and the park marked its tenth anniversary in 2024. ^[3]

The bay's landmarks range from wild sandbanks to iconic silhouettes. At its mouth, the Réserve naturelle nationale du Banc d'Arguin, classified in 1972 and managed by SEPANSO, protects a shifting sandbank that is a major nesting site for sandwich terns and a resting ground for migratory birds. ^[1] Just south rises the Dune du Pilat, Europe's tallest coastal dune at around 107 metres, offering sweeping views over the bay, the ocean and the pine forest. ^[2] Within the lagoon lies the Île aux Oiseaux with its two famous cabanes tchanquées, stilt cabins that have become the emblem of Arcachon, reached by traditional pinasse and pleasure-boat excursions. The Réserve ornithologique du Teich, at the Leyre delta, offers birdwatching trails and hides among reedbeds and lagoons, while the resort town of Arcachon, its Ville d'Hiver villas, oyster villages such as L'Herbe and Le Cap Ferret complete the bay's attractions.

Arcachon Bay is one of the most accessible protected areas in France, lying about 60 km southwest of Bordeaux and served by frequent trains to Arcachon and by motorway. The bay is best explored by water: boat operators and the Union des Bateliers Arcachonnais run cruises to the Île aux Oiseaux, the cabanes tchanquées, the Banc d'Arguin and across to Cap Ferret, while traditional pinasses, kayaks and sailing offer closer contact with the tidal flats. Resort towns around the shore, Arcachon, Le Teich, Andernos-les-Bains, Arès and Lège-Cap-Ferret, provide beaches, cycle paths, oyster tastings, hotels and campsites. Land-based highlights include climbing the Dune du Pilat and walking the trails and observation hides of the Réserve ornithologique du Teich. Access to sensitive zones such as the Banc d'Arguin is regulated to protect nesting birds, and visitors are encouraged to follow the marine park's guidance on responsible boating, fishing and wildlife watching.

Conservation in Arcachon Bay centres on reversing the long decline of its seagrass meadows, which shrank markedly in the decades before the park's creation and are vital to the bay's fish nurseries, oyster farming and overwintering birds. The Office français de la biodiversité and the marine park run monitoring, water-quality and eelgrass-restoration programmes, and coordinate research on species such as seahorses through participatory science. ^[1] The park works to balance oyster culture, fishing, tourism and boating with the protection of habitats, tackling pressures from pollution, invasive species, coastal development and climate-driven changes such as rising temperatures and shifting sediment. It also safeguards the Banc d'Arguin's tern colonies and the migratory birds of the Teich, while supporting sustainable shellfish farming and low-impact recreation. Through its management plan and broad governance council, the park aims to keep Arcachon Bay a living, productive and ecologically rich lagoon for future generations.