Sediment organic matter and its nutritional quality: a short-term experiment with two exotic bivalve species

This study was aimed to investigate the role of two exotic bivalves (Ruditapes philippinarum and Musculista senhousia) on the trophic enrichment and the nutritional quality of sediments from the Sacca di Goro (northern Adriatic Sea) through manipulative experiments. The concentrations of sedimentary total organic matter, biopolymeric carbon, carbohydrates, proteins, lipids, and chlorophyll-a were determined through a 64 days-long period. The experimental setup consisted in three replicated treatments (R. philippinarum, M. senhousia and simply sand), with treatments and time as fixed factors. All the biochemical classes showed wide fluctuation, and significant differences among treatments were detected during the experimental period. Both bivalve species played a role in sediment enrichment process. At the end of the experimental period, proteins represented the main biochemical class of organic compounds in the treatments with bivalves (48.5 and 44.5% of the biopolymeric fraction in the M. senhousia and R. philippinarum treatments, respectively), while in the control treatment they were only 32.7%. The accumulation of proteic nitrogen increased the nutritional quality of the sedimentary organic matter. Moreover, the presence of M. senhousia also enhanced the accumulation of microphytobenthic carbon