The main photosynthesis and respiration parameters (dark respiration rate, light saturated production rate, saturation irradiance, photosynthetic efficiency) were measured on a total of 23 macrophytes of the Than lagoon (2 Phanerogams, 5 Chlorophyceae, 10 Rhodophyceae and 6 Phaeophyceae). Those measurements were performed in vitro under controlled conditions, close to the natural ones, and at several seasons. Concomitantly, measurements of pigment concentrations, carbon, phosphorous and nitrogen contents in tissues were performed. Seasonal intra-specific variability of photosynthetic parameters was found very high, enlightening an important acclimatation capacity. The highest photosynthetic capacities were found for Chlorophyceae (e.g. Monostroma obscurum thalli at 17 degrees C, 982 mu mol O-2 g(-1) dw h(-1) and 9.1 mu mol O-2 g(-1) dw h(-1)/ mu mol photons m(-2) s(-1), respectively for light saturated net production rate and photosynthetic efficiency) and Phanerogams (e.g. Nanozostera noltii leaves at 25 degrees C, 583 mu mol O-2 g(-1) dw h(-1) and 2.6 mu mol O-2 g(-1) dw h(-1)/mu mol photons m(-2) s(-1) respectively for light saturated net production rate and photosynthetic efficiency). As expected, species with a high surface/volume ratio were found to be more productive than coarsely branched thalli and thick blades shaped species. Contrary to R-d (ranging 6.7-794 mu mol g(-1) dw h(-1), respectively for Rytiphlaea tinctoria at 7 degrees C and for Dasya sessilis at 25 degrees C) for which a positive relationship with water temperature was found whatever the species studied, the evolution of PII curves with temperature exhibited different responses amongst the species. The results allowed to show summer nitrogen limitation for some species (Gracilaria bursa-pastoris and Ulva spp.) and to propose temperature preferences based on the photosynthetic parameters for some others (N. noltii, Zostera marina, Chaetomorpha linum).