Response of estuary ecosystem to El Niño event: A case study in the Yangtze River Estuary

The knowledge of how the Yangtze River Estuary (YRE) ecosystem responds to and adapts to the El Niño events is limited but cannot be ignored. Based on the fishery survey data in the YRE in 2013, 2015, and 2017, we constructed and compared three Ecopath models representing three different periods: before, during, and after El Niño event. Results showed that the YRE ecosystem underwent significant change after the occurrence of El Niño. Biomass of phytoplankton and zooplankton increased substantially during the El Niño period, while the biomass of most fish groups and shrimp decreased. During the El Niño period, the YRE ecosystem exhibited low mean trophic levels and low energy transfer efficiency; some ecological network measurements (TPP/TR, TPP/TB, FCI) indicated a more fragile and highly disturbed ecosystem. After the EI Niño event, most of these changes recovered to varying degrees, with species in grazing food chain recovering faster than in detrital based food chain. The variations from 2013 to 2017 reflected the complex impact mechanism of EI Niño on the ecosystem, as well as its resilience after climate disturbance. This study enhances our understanding of how estuarine ecosystems respond to climate events, and may serve as a reference for the development of adaptive management strategies under climate change.