Seasonal variations of pollution biomarkers in two populations of Corbicula fluminea (Müller).

Seasonal variations of pollution biomarkers have been studied in two populations of Corbicula fluminea (Müller) for 2 years. Clams were collected from the Sanguinet lake and the Dronne river (Southwest France), sites characterised by water of excellent and passable quality, respectively. Biological parameters studied were enzymatic activity (catalase, propionylcholinesterase, glutathione S-transferase, NADPH-cytochrome c reductase and NADH-cytochrome c reductase activities) and indicators of physiological (protein, carbohydrate, lipid and ash contents, fresh and dry tissue weights, condition factor) and reproductive (amount of oocytes present in gonads and clams incubating larvae in gills) status. Environmental parameters (e.g. water temperature, chlorophyll a concentration) were also monitored. Effects of site, sampling date and season (from spring to winter) were studied, as well as relationships between abiotic and biotic factors. Finally, an index of variability was calculated for each biomarker. Catalase, propionylcholinesterase, NADH-cytochrome c reductase and lipids experienced the most pronounced seasonal fluctuations, whereas glutathione S-transferase, NADPH-cytochrome c reductase and proteins suffered less pronounced ones. For some parameters, results differed depending on the site. Most seasonal changes were related to the reproductive cycle and/or water temperature. Implications of such variations in the use of pollution biomarkers in environmental surveys are discussed.