Succession of macrozoobenthic communities and its drivers in Meiliang Bay of Lake Taihu during the past 40 years

Abstract

Meiliang Bay is the largest bay in the northern Lake Taihu which has the most serious ecological and environmental problems. In recent years, while the governance of Lake Taihu has been strengthened, the understanding of the succession of its ecological status remains unclear. Based on the long-term monitoring data and historical literature, this study analyzed the temporal and spatial variation of macrozoobenlhos composition, the dominant species and density in Meiliang Bay since 1980s. Community succession and its relationship with environmental factors are examined by non-metric multidimensional scale analysis ( NMDS) and random forest (RF). The results showed that 44 laxa were recorded in Meiliang Bay from 1980 to 2019, mainly composed of chi-ronomid larvae and molluscs, with substantial inlerannual changes in total density. The benthic community structure has changed significantly in the past 40 years, with the dominant species have changed from sensitive species dominated by molluscs to pollution tolerant species characterized by oligochaetes and chironomids. Based on the results of NMDS and random forest analyses, the benthic community succession in Meiliang Bay can be roughly divided into four stages. Stage 1 (before 1980s) had Corbieula fluminea and oilier large molluscs dominated the community characterized by high species diversity. In stage 2 ( 1990s-2007), the benthic community degenerated rapidly, dominated by pollution-tolerant species. From 2008 to 2016 (stage 3), the ecological condition showed a recovery trend, with the sensitive species increased slightly. Stage 4 from 2017 to 2019, the dominance and density of pollution tolerant species rebounded. The changes of benthic communities in Meiliang Bay in recent 40 years are mainly regulated by sediment nitrogen and phosphorus, organic matter and water column nutrients, followed by aquatic macrophytes degradation.