Functional groups and seasonal diversity of crustacean zooplankton in adjacent waters of Haizhou Bay, South Yellow Sea

Zooplankton are important linkages in the food web and can respond nonlinearly to environmental changes. Marine organisms thrive from spring to summer. Thus, it is crucial to understand how ecological functions of zooplankton communities may shift under seasonal environmental changes during this period. Samples were collected from May to August (May, June-I, June-II, July-I, July-II, and August) in 2018 in Haizhou Bay, Jiangsu, East China for zooplankton and environmental variables. Crustaceans accounted for 75 out of 134 zooplankton taxa and 91.8% of total zooplankton abundance. The average abundance of crustacean varied between 2 824.6±635.4 inds./m 3 in July-II and 6 502.7±1 008.8 inds./m 3 in June-II. Multivariate analyses results showed that the dissimilarity of community increased gradually in the time series. Body length, feeding type, trophic group, and reproduction mode were used to investigate crustacean community functions. Trait-based functional groups contained species with similar ecological roles. Functional diversity fused the differences of species and trait. The proportion of large-sized species (2–5 mm) decreased with the increasing proportion of medium-sized species (1–2 mm). The proportion of current feeders increased with the drop in the proportion of mixed feeders. Parthenogenesis species increased with decreasing free spawners, and omnivores-carnivores increased with decreasing omnivoresherbivores. Generalized additive models suggested that temperature was the main driver of variations in crustacean zooplankton function. Seven identified functional groups varied with increasing temperature. Omnivorous-herbivorous copepods declined (90.0%–68.0%), whereas the parthenogenetic cladocerans increased (0–24.1%). The small egg-brooding ambush copepods fluctuated (6.5%–9.3%) with increasing water temperature. The other functional groups changed slightly. Functional diversity also varied according to temperature changes. The community structure and ecological function of crustacean zooplankton community showed gradual changes with increasing temperature from spring to summer.