Relationship between mild seasonal oxygen deficiency and seasonal variations of macrozoobenthic community: A case study in the Yangtze River estuary and its adjacent area, China

In the present study, environmental parameters and macrozoobenthos in the Yangtze River estuary and its adjacent area, China, were investigated in summer and winter of 2015, and significant seasonal differences were found. Biodiversity was found to be lower in summer, which may result from the higher deposition rate. The relationship between the macrozoobenthic community and environmental parameters (especially dissolved oxygen) was revealed. Linear models describing the response of macrozoobenthic biodiversity indexes to mild oxygen deficiency were constructed. Mild seasonal oxygen deficiency was revealed significantly related to seasonal variations of the macrozoobenthic community, but this deficiency could not damage the community. In contrast, when mild oxygen deficiency occurred, natural predators of macrozoobenthos decreased, which may relieve the survival pressure of macrozoobenthos to some extent. Dissolved oxygen alone could not explain many variations of macrozoobenthos, and other environmental parameters, especially water depth, phosphate concentration and turbidity, also greatly contributed to those variations.