COMPARISON OF ANAEROBIC AND AEROBIC BIODEGRADATION OF MINERALIZED SKELETAL STRUCTURES IN MARINE AND ESTUARINE CONDITIONS

The knowledge of the biodegradation rates is essential to studies of t he biogeochemistry and ecology of aquatic systems. It helps us to quan tify the production and uptake rates of chemical components and their recycling, and to understand the mechanisms and rates of organic matte r accumulation in sediments. Experimental studies of biodegradation pr ocesses in six types of mineralized skeletons were performed in shallo w-marine waters of Calvi Bay, Corsica and in estuarine waters of Rosco ff, Brittany. Three types of mollusk shells, sea urchin skeletal plate s, crab cuticle and fish vertebrae were exposed to oxic and anoxic con ditions over periods of 15 days to 30 months. After recovery of the su bstrates, protein assays, bacterial counts and organic carbon analyses were performed. Quantitative protein assays and bacterial counts indi cate that biodegradation of mineralized skeletal structures occurs at a slower rate in anoxic conditions than in oxic conditions. Bacterial analysis showed that in anoxic environment, less than 0.5% of the cons umed organic matter is converted into bacterial biomass. The aerobic b iodegradation rate was positively correlated with the organic content of the skeletons. Anoxic biodegradation of skeletons occurred at much slower rates in estuarine sediments than in shallow marine sediments. Preservation of skeletal structures in estuarine conditions appears to be correlated with the abundance of dissolved organic matter rather t han with high sedimentation rates.