Stochastic Assembly Process Indicates High Risks of Water Transfer on Fish Communities in Waters Along the East Route of the South-to-North Water Transfer Project, China

Abstract

Inter-basin water transfer projects (IBWTs) are closely associated with ecological impacts such as biological invasion, community homogenization, and ecosystem instability. However, the assembly mechanisms governing the response of fish communities to water transfer in IBWTs remain relatively unexplored. In this study, the species composition, assemblage structure, and community assembly of fish in three waters along the East Route of the South-to-North Water Transfer Project of China (ESNT) were determined using environmental DNA metabarcoding. In our system, the community in a terminal reservoir (Shuangwangcheng Reservoir, SWC) originated with diverted fish via the water transfer of the ESNT, provides a valuable reference against community variations in two natural lakes, i.e., Hongze Lake (HZL) and Nansi Lake(NSL). Our results showed that almost all species along the route were diverted into the SWC, and the assemblage compositions and structures in the three waters were similar with notable variations in communities before and after the transfer and dominated by omnivorous, demersal, and eurytopic fishes. These results suggested that facilitated dispersal may be the predominant way by which IBWTs impact fish communities. Our study also found that fish communities in the HZL and NSL underwent a conspicuous decline in diversity and homogenization of compositions and were stochastically assembled, whereas the environmental filtering hypothesis dominated the community assembly of fish in the three waters. The stochastic process in this study suggests that repeated disturbances of annual water transfers have a more profound influence and indicates that the combined effects of assembly mechanisms and repeated disturbances govern the responses of fish communities to water transfer. Our study highlights the importance of repeated water transfer disturbances in evaluating the ecological impacts of IBWTs and provides a theoretical basis for designing and optimizing future water transfer megaprojects.

Keywords: Assembly mechanism, eDNA, ecological impacts, inter-basin water transfer, repeated disturbances