Relationship between sedimentary organic matter and benthic fauna within the Gulf of Lion: synthesis on the identification of new biochemical descriptors of sedimentary organic nutritional value

The abilities of several biochemical characteristics of sedimentary organic matter to describe quantitative changes in benthic fauna were assessed based on several surveys carried out within the Gulf of Lion during the last decade. Two sets of high frequency samplings were carried out both inshore and offshore, together with an assessment of seasonal variability along a depth gradient, and a synoptic assessment of mesoscale spatial variability. The considered biochemical parameters were: total organic matter, organic carbon, nitrogen, total proteins, available proteins, carbohydrates, lipids, total and available amino acids. The considered faunal parameters were the abundance and the biomass of both meio- and macrofauna. Our results contribute to unravel the relative importance of food digestibility and composition in controlling particulate organic matter nutritional value. Spectra of both total and available amino acids were almost constant irrespective of the seasons and/or the environments, which were studied during these surveys. This underlines the role of particulate organic matter digestibility relative to its ability to meet specific nutritional requirements in controlling benthic fauna. Multivariate analysis used to relate biochemical and faunal parameters suggest that available amino acids and lipids are the best descriptors of food nutritional value. In contrast with carbohydrates, these two parameters are both associated with the most labile fraction of particulate organic matter. This result suggests that the use of the sum of proteins, carbohydrates and lipids as a proxy for labile organic matter is precluded at least in areas similar to the Gulf of Lion.