RÔLE DES FACTEURS ABIOTIQUES SUR LE TAUX DE CROISSANCE D’ ULVA RIGIDA DANS DEUX SITES MÉRIDIONAUX

Environmental factors: water salinity, temperature, incident light, dissolved inorganic nitrogen (DIN), dissolved reactive phosphorus (DRP), and biotic factors: Ulva rigida biomass in field and relative growth rates (RGR) in cages of the two Mediterranean stations (Chanel of the Thau lagoon, France and Venice Lido, Italy) were compared. Principal Componant Analysis of environmental variables shows the linkage " salinity-temperature " in the eutrophicated Thau lagoon, and the linkage " salinity-incident light " in Venice Lido. Due to the water temperature the annual Ulva rigida RGR curve is bimodal (spring and autumn peaks) in contrast to the unimodal classical sheme. The PCA of biological and environmental variables underlines the DRP as the most limiting factor in spring at Venice Lido station and the incident light as a strigent limiting factor for autumn growth in the Thau lagoon