Modifications of the specific diversity and feeding guilds in intertidal sediment colonized by an eelgrass meadow (Zostera marina) (Brittany, France)

A sandy beach located in a bay of north Brittany (France) is partly colonized by an eelgrass meadow. The overall macrobenthic fauna, i.e. epifauna, endofauna and fish, living in this seagrass and in non-vegetated sands was compared in terms of species, abundance and biomass in the different feeding guilds. Seagrass makes this habitat more complex by increasing both its surface by 5.45–fold and volume by 4.79–fold. Eighteen species among the 23 living in the non-vegetated sands were observed in the seagrass assemblage. Their abundance and biomass were increased by 7.33–fold and 3.54–fold, respectively. The occurrence of Zostera was associated with the presence of 124 new species and 34 new feeding guilds. In the Zostera meadow, a spatial segregation exists among the taxa from the different microhabitats explored for food-quest. The balanced distribution of biomass within the various microhabitats may suggest that an optimization in the exploitation of feeding resources goes hand in hand with a higher complexity of the trophic web. It looks as if the architecturally increasing complexity of the habitat resulting from the development of a seagrass meadow on sediment both stimulates the abundance and biomass of the indigenous macrobenthic assemblage, increases the specific and functional biodiversity and favours the specialization of feeding guilds.