Influence of oyster culture on water column characteristics in a coastal lagoon (Thau, France)

The development of shellfish farming activities causes great changes in ecosystems functioning. In the Thau lagoon, oysters are reared on long constantly submerged lines, and these become fouled by several epifaunal species. The assemblage (oysters and epifauna) is defined as Oyster Culture Unit (OCU). The aim of our study was to estimate (i) how much the composition and the abundance of the epifaunal species can influence the nutrient and oxygen fluxes recorded at the shellfish-water interface and (ii) how these fluxes modify water column characteristics. We used Principal Component Analysis with Instrumental Variables (PCAIV). Two analyses were carried out, using sets of data on fluxes, the specific composition of the cultivated communities, and on oxygen, nutrient and chlorophyll a concentrations in the water column. The highest fluxes at the OCU-water interface were measured when epifaunal species richness was maximum. However, at our measurement scale (i.e. the oyster frame) no influence of this filter-feeders assemblage was observed on the chlorophyll a level. Conversely, we found a significant influence of oyster culture on the oxygen and dissolved nitrogen concentrations in the water column. The use of this recent factorial analysis was helpful to estimate the influence of the biofouling species composition on the fluxes at the OCU-water interface, and to estimate the potential impact of oyster cultures on the conditions prevailing in the water column.[PUBLICATION ABSTRACT]