Sediment-focused environmental impact of long-term large- scale marine bivalve and seaweed farming in Sungo Bay, China

The sediment condition of Sungo Bay, China was assessed using macro-fauna investigations and sediment parameters (pH, Eh, visual observations) by MOM system (Modelling-Ongrowing fish farms-Monitoring). Based on the current status and comparison with previous results, the sediment environmental impact of large-scale bivalve and seaweed culture was analyzed. The main cultured species (oyster Crassostrea gigas, scallop Chlamys farreri, seaweed Saccharina japonica) and the culture methods have remained the same, but the culture areas have expanded to the outside of the bay. 10 sampling stations were set and a total of 76 sediment samples were collected during 2017–2018. The results showed: 1) Benthic macro-fauna was found in all samples that suggested sediment condition was “acceptable”. There was not significantly seasonal change in macro-fauna abundance, species number and diversity index, but the abundance in summer was significantly higher in 2017 than that of in 2006. 2) For all the sample stations, the redox potential stayed above +53 mV and sediment conditions belonged to condition 1 concerning chemical parameters. Most sample stations belonged to condition 1 with sporadic stations in condition 2 according to sensory parameters; 3) The sediment status of Sungo Bay was in “best condition” based on biological, chemical and sensory parameters, which hadn't changed compared to 10 years ago. The results suggest the effects of large-scaled bivalve and seaweed farming activities on the benthic environment of Sungo Bay is low. The reasons that the sediment environments maintain good conditions were analyzed.