Zooplankton spatial and diurnal variations in the Changjiang River estuary before operation of the Three Gorges Dam |
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| Authors: | Xuelu Gao Jinming Song Xuegang Li |
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| Institution: | (1) Key Laboratory of Marine Ecology and Environmental Sciences, Institute of Oceanology, Chinese Academy of Sciences, 7 Nanhai Road, Qingdao, 266071, People’s Republic of China;(2) Research Center for Remote Sensing and Marine Ecology/Environment (RSMEE), LED, South China Sea Institute of Oceanology, Chinese Academy of Sciences, 164 West Xingang Road, Guangzhou, 510301, People’s Republic of China;(3) Laboratory of Marine Ecosystem and Biogeochemistry, Second Institute of Oceanography, SOA. No. 36 Baochubei Road, Hangzhou, 310012, People’s Republic of China |
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| Abstract: | Estuarine plankton communities can serve as indicators of ecosystem modification in response to anthropogenic influences.
The main objectives of this study were to describe the spatial distribution and diurnal variability in zooplankton abundance
and biomass over almost entire salinity gradient of the Changjiang (Yangtze) River estuary and to provide a background reference
for future studies. To accomplish this, data were collected from 29 stations in the estuary from May 19 to 26, 2003, including
two anchor stations. The spatial and diurnal variations in zooplankton characteristics, i.e. abundance, biomass, and gross
taxonomic composition, were examined. Generally, both the abundance and biomass gradually increased seaward and presented
distinct spatial variations. In addition, the spatial data revealed a significant correlation between abundance and biomass;
however, there was no significant correlation between abundance and biomass for the diurnal data. Although the zooplankton
composition indicated distinct spatial differences in terms of dominant groups, copepods accounted for >50% of the total zooplankton
abundance in most regions and times. Three zooplankton assemblages were recognized through hierarchical cluster analysis.
These assemblages existed along the salinity gradient from fresh water to seawater, and their positions coincided with those
of the three principal water masses in the estuary. The assemblages were classified as: (1) true estuarine, (2) estuarine
and marine, and (3) euryhaline marine, which were characterized by the copepods Sinocalanus dorrii, Labidocera euchaeta, and Calanus sinicus, respectively. Both spatial and diurnal data indicated that there was no significant correlation between zooplankton abundance/biomass
and depth-integrated phytoplankton abundance. |
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