Zooplankton assemblages and indicator species in the Changjiang river estuary and its adjacent waters

Abstract

Zooplankton is a vital biological indicator in estuarine ecosystems. In this study, the Changjiang River Estuary (CRE) was investigated in the dry (March) and wet seasons (July) of 2019 for spatial and temporal fluctuations of zooplankton based on the indicator value (IndVal) index method. A total of 172 zooplankton taxa (146 adult taxa and 26 larvae) were identified. Zooplankton composition, abundance, biodiversity, grouping, and indicator species all showed substantial seasonal changes. The hydrological environment of the CRE was affected by diluted water and current intrusions. Compared to the dry season, the wet season had a higher abundance and biodiversity of zooplankton. Zooplankton communities from the inside-mouth fresh-brackish, intermediate transition, and offshore neritic regions were distributed in a three-segment pattern (fresh-brackish, transitional and neritic) and were significantly impacted by Changjiang River discharge. In general, freshwater and brackish species shifted toward the ocean during the wet season, whereas during the dry season, when river flow decreased, marine species shifted toward the estuary. Sinocalanus sinensis and Mesocyclops spp. were indicators of the Changjiang Diluted Water. Temora turbinata and Flaccisagitta enflata were good indicators of Taiwan Warm Current invasion, while Calanus sinicus may represent the effect of the Yellow Sea Coastal Current in the northern CRE. This research contributes to a thorough understanding of pelagic ecosystem dynamics and seasonal succession patterns in the CRE, which has a complicated hydrological environment.