Zooplankton community and its environmental driving factors in Ulungur Lake, China

This study investigated the zooplankton community structure in Ulungur Lake, located in the arid region of Northwest China, which has been slightly polluted by exogeneous sources. A total of 44 zooplankton species were identified in Ulungur Lake, which were sorted into seven functional groups: protozoan filter feeders (PF), rotifer filter feeders (RF), rotifer carnivores (RC), small copepod and cladoceran filter feeders (SCF), mid-sized copepod and cladoceran filter feeders (MCF), mid-sized copepod and cladoceran carnivores (MCC), and large copepod and cladoceran filter feeders (LCF). The dominant zooplankton functional group varied according to seasonal change. The RF group was dominant in the spring, comprising 87.77% of the total biomass. In the summer, the dominant group was SCF, comprising 90.72% of the total biomass, while the RF group accounted for only 7.24%. In the autumn, the biomass was mainly distributed between the RC (36.38%), SCF (30.62%), and RF (30.06%) groups. This seasonal difference in zooplankton community structure is related to fish production in Ulungur Lake, as well as to the competition and predation relationship among zooplankton species. This study showed a significant positive correlation between the PF and LCF groups, and between the RC, MCC, and MCF groups. This positive correlation was found to be related to the competition and predatory relationships between these functional groups. The predation pressure within the zooplankton functional groups in Ulungur Lake was not as significant as the pressure of food competition. The zooplankton biomass showed no significant difference between spring (0.0615 mg/L) and summer (0.0621 mg/L), but the biomass in autumn (0.3051 mg/L) was significantly increased. Nitrite-nitrogen (NO2-N) and Secchi Depth (SD) had significant correlations between species and functional groups, and were the major driving factors affecting the community structure of Ulungur Lake. In this study, the seasonal variations in the biomass of zooplankton were strongly influenced by environmental factors, which played an important driving role in structuring the ecological communities of zooplankton.