Assessing shellfish farming-mediated benthic impacts based on organic carbon flux simulation and composition of...

Marine benthic environments serve as the ultimate sink for sediment organic matter (SOM), but shellfish farming can potentially disturb the natural sink of seston, altering ecosystem functioning. Understanding the potential disturbance of a shellfish farm and its ecological effects is therefore important for a responsible management of shellfish-mediated marine ecosystem. In this study, the variations in benthic organic carbon flux of a bottom-based Manila clam (Ruditapes philippinarum) farm in Laizhou Bay, China were estimated by using a carbon flux model coupled with hydrodynamic and individual growth models. SOM and macrofaunal community were monitored for 3 years to investigate their changes to the carbon fluxes. Model simulations illustrated that the carbon flux in an area of 247 km² was altered due to seston depletion and biodeposition, which caused decrease and increase in SOM in different areas, respectively. Cluster analysis based on taxonomic composition of macrofaunal community divided the sites into four groups, which corresponded with predicted changes of carbon flux. Increased carbon flux caused higher disturbance level (indicated by AMBI) to the macrofaunal community but increased species richness, abundance, and Shannon-Wiener index, suggesting the community was both disturbed and benefited from clam farming. This study confirmed that the benthic organic carbon flux is a key factor causing differences in SOM and macrofaunal community outside the farm, and thus can be used as an efficient method for estimating the benthic impacts of shellfish farming both in and outside the farming area.