Initial response of fish trophic niche to hydrological alteration in the upstream of Three Gorges Dam

Introduction:Damming is one of the dramatic impacts to river food webs due to habitat fragmentation and changes in the hydrological regimes.The world’s largest dam,the Three Gorges Dam(TGD),has been constructed in the middle of Yangtze River since 2003.The objective of this study was to understand the effects of altered hydrological regime on the trophic structure of fish food web along the hydrological gradient in the TGD.Methods:Fish samples were collected from an upstream,a midstream and a downstream site of the Yangtze River upstream of the TGD in May and September of 2004.Muscle tissue of each fish species was determined for stable isotopic compositions(δ^(13)C and δ^(15)N)which were used to calculate isotope-based Bayesian community-wide trophic metrics.Results:Stable isotope trophic niche analysis reveals reduced utilization of basal resource and trophic niche space at the midstream and downstream sites.By contrast,community trophic diversity and species redundancy were higher at the downstream than the upstream and midstream,likely as the result of reduced the spectrum of basal resources.These findings suggested that the negative impacts on the overall trophic niche space from reduced flow,increased water depth and stagnancy occurred only one year after the completion of the TGD.Conclusions:Altered hydrological regimes posed multiple impacts to the aquatic food web.Reduced flow and increased water depth within TGD has posed initial effects to the fish community trophic structure.Further collections ana analysis of ecological data to compare the fish trophic structure revealed in this study are needed to assess the long-term impacts of TGD on fish community structure and resources utilization.