The epibiotic community associated to the European flat oyster: a function of the state of development of the reefBiogenic Reefs

Abel Zempléni¹, Stéphane Pouvreau¹, Nicolas Desroy²

¹LEMAR, Ifremer, France - ²Ifremer, France

Biogenic habitats constituted by the native flat oyster Ostrea edulis were historically dominant in most European coastal ecosystems, probably constituting at that time the most important marine temperate reefs. Despite the global collapse of their populations over the last three centuries, flat oysters are still present on French coasts and are still able to create biogenic reef structures and provide a remarkable habitat for marine biodiversity. At present, the biotic assemblages associated with flat oysters remain poorly defined. This study aims to analyze biodiversity associated with the reef’s development stage by focusing on epibiotic community. The studied population is an old remnant bed located in the Bay of Brest, that has been undergoing restoration for five years. The epibiotic communities collected on scattered individual living and dead oysters, and on aggregates (4-5 ind.) from the ground and from a restored reef were compared. A total of 137 species were found; 22 were specific to individual oysters and 55 to aggregates. Shannon’s diversity indices remained constant for each reef development stage, displaying higher values than recorded on Lanice conchilega banks and Mytilus edulis beds on the French side of the English Channel, but lower than reported on Sabellaria alveolata reefs from the bay of Mont Saint-Michel and Zostera marina beds from the English Channel. Mean abundance and species richness per sample were higher for aggregated structures, but, when standardized to abundance per cm2 of shell surface, both parameters were significantly higher for individual oysters. Despite the degraded state of their remnant populations, flat oysters are still hosting important macrofaunal biodiversity, suggesting that restoring their populations / reefs could create main biodiversity hotspots in coastal environments. A comparison with the epibiotic community of other flat oyster beds from Brittany (France) is intended, as well as the inventory of all the species (infaunal species, cryptic and transient fish, crustaceans) associated to Ostrea edulis reefs on our study site, currently serving as a reference in France.