禁捕初期黄湓河下游张溪段鱼类群落结构及其对环境扰动的响应OA

The Huangpen River Ctenogobius giurinus and Freshwater Shrimp National Aquatic Germplasm Resources Conservation Zone is located at the Zhangxi section of the lower Huangpen River.To date,the dynamic shifts and vulnerability of its fish community under multiple pressures during the fishing moratorium have not been systematically invesigated.To characterize the recovery dynamics and response mechanisms to environmental disturbances of the fish community during the early moratorium stage,six cruises of fish resources and environmental surveys were conducted during the fish spawning(June-July)and foraging(September-October)seasons from 2022 to 2024.A total of 70 fish species,representing 6 orders,11 families,and 48 genera,were collected,with Cypriniformes exhibiting absolute dominance(75.71%).The community was primarily characterized by freshwater sedentary species(82.86%),benthic species(40%),omnivores(50%),and drifting egg spawners(40%).Pseudobrama simoni,Xenocypris microlepis,and Coilia brachygnathus were the dominant species,collectively accounting for 64.94%of the total abundance and 45.93%of the total biomass.The overall Shannon-Wiener diversity index(H′)and Margalef richness index(R)were 2.04 and 6.53,respectively,indicating a moderate level of fish diversity.The community exhibited a distinct"disturbance-collapse-recovery"interannual dynamic.In 2023,extreme hydrological events triggered a structural collapse,characterized by a sharp decline in H′ to 0.89 and a surge in P.simoni abundance to 84.17%,resulting in single-species dominance and a negative W value in the ABC curve.In 2024,as environmental conditions stabilized,H′ rebounded to 2.62,the W value turned positive,and the community entered a recovery phase.Spatially,the relative abundances of river-lake migratory species were higher in the downstream area.Redundancy analysis identified total nitrogen,water depth,and ammonia nitrogen as the primary environmental drivers of community structure,while niche analysis revealed that dominant species possessed moderately narrow niche width(Bi=0.44-0.71).Although the fishing ban has facilitated initial resource recovery,the long-term operation of the Huangpen Sluice Gate has severely obstructed river-lake connectivity.This hydrological barrier is the fundamental cause of the community's fragile structure and low resistance to external disturbances.To ensure long-term ecological resilience,it is recommended to complement strict moratorium enforcement with targeted interventions,including the restoration of river-lake hydrological connectivity,ecological flow regulation,critical habitat restoration,and the establishment of a long-term monitoring and adaptive management system centered on functional groups and keystone species.