Ecological Indicators (Jun 2022)
Spatial distributions of zooplankton stable isotopes and their trophic positions in a bay under serious anthropogenic influences: Daya Bay, China
Abstract
Trophic structure of zooplankton community can effectively reflect the ecosystem health and the influence of anthropogenic disturbances. The Daya Bay is a semi-closed coastal bay under intensive anthropogenic impacts in northern South China Sea. Spatial variations of stable isotope values (δ13C and δ15N) and trophic positions of dominant zooplankton groups were investigated in Daya Bay during winter. The δ13C values of zooplankton ranged from −22‰ to −15.59‰, and the δ15N ranged from 4.19‰ to 12.65‰, respectively. Generally, the δ13C values of zooplankton were higher in the inner bay. This distribution pattern was determined by the less terrestrial organic matter input and high nutrient loading in Daya Bay. An abnormally lower δ15N value of zooplankton occurred near the Dan’ao River estuary. It suggested that the 15N-depleted signature of food source can be transferred to the zooplankton along the food chain. The isotopic Bayesian ellipses of dominant zooplankton groups were generally larger in the inshore region, suggesting a wider food source. In the offshore region, the isotopic ellipses of these dominant zooplankton groups were relatively separate. Our results suggested that eutrophication can increase the trophic overlap between zooplankton groups. The δ15N value indicated large Sagitta was the top predator in zooplankton community. Excluding the abnormal estuarine station, the relative trophic level of large Sagitta was generally lower in the inner bay, suggesting a shorter food chain in eutrophic waters. In addition, our results showed that the stable isotopic signatures of mysids were significantly different from other zooplankton groups. It can be speculated that the mysids might migrate from the open sea in a short time. This study provided detail information on the δ13C and δ15N values of different zooplankton groups in Daya bay, which will be useful for understanding the anthropogenic influence on the ecosystem structure and function.
