The Co-Occurrence of Zooplankton and Phytoplankton in Shengjin Lake, a Typical Yangtze-Connected Lake in China

Species co-occurrence is closely linked to complex environmental changes and biological interactions in ecosystems. Freshwater ecosystems are among the most endangered ecosystems in the world, highly sensitive to environmental change, and rich in biodiversity. Clarifying the mechanisms of co-occurrence of zooplankton and phytoplankton, which are the basis of freshwater ecosystems, can provide important insights into ecosystem stability. We employed the Hierarchical Modeling of Species Communities (HMSC) within Joint Species Distribution Models (JSDMs) to fit the abundance data of zooplankton and phytoplankton dominant species sampled in April (spring) and July (summer) 2023 in Shengjin Lake to understand their co-occurrence pattern in typical Yangtze-connected lakes. Due to biotic interactions, rotifers primarily exhibit a positive co-occurrence pattern with one diatom and one cyanobacterium, while copepods mainly show a negative co-occurrence pattern with one diatom and one cyanobacterium. Only one rotifer and one chlorophyta mainly display a positive co-occurrence pattern, mainly driven by shared environmental preferences in that they are more likely to co-occur in areas with lower transparency, lower total phosphorus (TP) levels, and relatively higher pH levels. These findings show that the co-occurrence mechanisms of zooplankton and phytoplankton differ under the influence of biotic interactions and environmental factors, neither of which can be overlooked. These findings may provide important implications for the management of zooplankton and phytoplankton, the fundamental components of wetland ecosystems.