Changes in infaunal assemblage structure influence nutrient fluxes in sediment enriched by mussel biodeposition

Although many studies have described the influence of bivalve aquaculture on the benthic environment, effects on benthic functional diversity are poorly known, as are links with ecosystem processes. We investigated the response of a benthic ecosystem in terms of taxonomic and functional diversity (infauna >500 μm), biogeochemical indicators (organic matter content, redox potential, sulfides level, bacteria) and metabolism (nutrient fluxes), subjected to various levels of mussel biodeposition as a general model of organic enrichment. Results show that local benthic conditions may recover fairly quickly depending on environmental conditions whereas modifications of the benthic community structure persist over a longer time scale with an impact on benthic ecosystem functioning. Fauna-mediated oxidation of the sediment likely increased nitrogen recycling through nitrification whereas binding and release of phosphorus to the water column seems to be driven by more complex processes. Results highlight the importance of species identity (ecological traits) on biogeochemical cycling and solute exchange across the sediment-water interface, with implications for the ecological functioning of exploited areas.