Dynamics of organic carbon under bioturbation by mud crabs (Macrophthalmus japonicus) and clamworms (Perinereis aibuhitensis) in an estuary ecosystem

Understanding of the dynamic characteristics of organic carbon in estuary ecosystem is of great significance for the carbon cycle in terrestrial and marine ecosystems. In order to quantify effects of the clamworm (Perinereis aibuhitensis) and mud crab (Macrophthalmus japonicus) on the migration of organic carbon, an indoor experiment was carried out by using a microcosm system with in-situ substrate, water and living specimen from Dagu estuary, China. The results showed that macrobenthos accelerated the release of organic carbon from sediment into water body, which increased the concentration of dissolved organic carbon (DOC) in pore water and the DOC fluxes across the sediment-water interface. Crab promoted more DOC efflux in the early experiment while the contribution of the clamworm was greater in the later experiment. In addition, macrobenthos stimulated the release of colored dissolved organic matter (CDOM) into overlying water, especially humic-like substance. The content of CDOM of the clamworm and crab groups was always higher than that of the control group, and the humic-like peak A fluorescence intensity continued to increase and red shift occurred. In conclusion, the clamworm and crab accelerated the mineralization of organic matter in sediment and promoted the release of organic carbon, which may affect the carbon cycle in the estuary and change the income and expenditure characteristics of the organic carbon.