INFLUENCE OF OYSTER CULTURE ON WATER COLUMN CHARACTERISTICS IN A COASTAL LAGOON (THAU, FRANCE)

The development of shellfish farming activities causes great changes i n ecosystems functioning. In the Thau lagoon, oysters are reared on lo ng constantly submerged lines, and these become fouled by several epif aunal species. The assemblage (oysters and epifauna) is defined as Oys ter Culture Unit (OCU). The aim of our study was to estimate (i) how m uch the composition and the abundance of the epifaunal species can inf luence the nutrient and oxygen fluxes recorded at the shellfish-water interface and (ii) how these fluxes modify water column characteristic s. We used Principal Component Analysis with Instrumental Variables (P CAIV). Two analyses were carried out, using sets of data on fluxes, th e specific composition of the cultivated communities, and on oxygen, n utrient and chlorophyll a concentrations in the water column. The high est fluxes at the OCU-water interface were measured when epifaunal spe cies richness was maximum. However, at our measurement scale (i.e. the oyster frame) no influence of this filter-feeders assemblage was obse rved on the chlorophyll a level. Conversely, we found a significant in fluence of oyster culture on the oxygen and dissolved nitrogen concent rations in the water column. The use of this recent factorial analysis was helpful to estimate the influence of the biofouling species compo sition on the fluxes at the OCU-water interface, and to estimate the p otential impact of oyster cultures on the conditions prevailing in the water column.