Role of abiotic factors on the growth rate in Ulva rigida from two southern sites

Environmental factors: water salinity, temperature, incident light, dissolv ed inorganic nitrogen (DIN), dissolved reactive phosphorus (DRP), and bioti c 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 envi ronmental variables shows the linkage " salinity-temperature " in the eutro phicated Thau lagoon, and the linkage " salinity-incident light " in Venice Lido. Due to the water temperature the annual Ulva rigida RGR curve is bim odal (spring and autumn peaks) in contrast to the unimodal classical sheme. The PCA of biological and environmental variables underlines the DRP as th e most limiting factor in spring at Venice Lido station and the incident li ght as a strigent limiting factor for autumn growth in the Thau lagoon.