Impacts of pen culture on alpha and beta diversity of fish communities in a large floodplain lake along the Yangtze River

Abstract

Pen culture is a cumulative factor leading to water quality degradation, competition intensification, habitat alteration and fragmentation. Despite the unprecedented expansion of pen culture areas in Chinese lakes due to the increasing demands on fishery products, little is known about the potential impacts of pen culture on fish communities. Here, we addressed this issue by quantifying changes in alpha and beta diversity with its turnover and nestedness-resultant components between pen culture areas (PA) and non-pen culture areas (NPA) in a large floodplain lake lying on the northern shore of the Yangtze River. Fish communities were sampled seasonally from January 2016 to December 2016 in 16 representative sites (PA, 8; NPA, 8) of Lake Huayanghe using fyke nets. In comparing with fish communities in NPA, we demonstrated an overall loss of fish species and a significant reduction in alpha diversity (richness) in PA, which were probably due to habitat alteration and fragmentation triggered by pen culture. We reported a significantly lower overall beta diversity with its turnover component and a significantly higher nestedness-resultant component in PA. The homogenized and nested trend for fish communities in PA was triggered by the synthesized effects of abiotic and biotic factors. Net pens caused habitat fragmentation and blocked the offset effects by supplementary fish species in nearby habitats, thus resulting in a significantly lower turnover and higher nestedness-resultant component in PA. The introduction of the same cultured fish species and the decrease of the wild native fish species made the fish communities in PA become more homogenized and nested. Pen culture had resulted in a significant decline in alpha diversity and a designed homogenization for fish communities in the lake. Our study highlighted the urgent need for systematic assessment of cultured fish and effective control of pen culture areas to avoid the future fish homogenization and species loss in Chinese lakes.