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 2824.6±635.4 inds./m3 in July-Ⅱand 6502.7±1008.8 inds./m3 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.

Trait-based approach revealed the seasonal variation of mesozooplankton functional groups in the South Yellow Sea

Functional traits determine the fitness of organisms and mirror their ecological functions.Although trait-based approaches provide ecological insights,it is underexploited for marine zooplankton,particularly with respect to seasonal variation.Here,based on four major functional traits,including body length,feeding type,trophic group,and reproduction mode,we quantified the seasonal variations of mesozooplankton functional groups in the South Yellow Sea(SYS)in the spring,summer,and autumn of 2018.Strong seasonal dynamics were identified for all traits but patterns varied among traits.Small zooplankton(47.7–88.6%),omnivores–herbivores(81.3–97.6%),and free spawners(54.8–92.5%)dominated in three seasons,while ambush feeders and current feeders dominated in spring(45.7%),and autumn(73.4%),respectively.Cluster analysis of the functional traits showed that the mesozooplankton in the SYS can be classified into eight functional groups.The biogeographic and seasonal variations of functional groups can be partially explained by environmental drivers.Group 1,represented by omnivores–herbivores,was the most dominant functional group,the abundance of which peaked in spring and was positively correlated with chlorophyll a concentration,indicating its close association with phytoplankton dynamics.The contribution of giant,active ambush carnivores,passive ambush carnivore jellyfish,current omnivores–detritivores,and parthenogenetic cladocerans increased with sea surface temperature.The proportion of giant,active ambush carnivores and active ambush omnivore–carnivore copepods decreased with salinity in autumn.This study presents a new perspective for understanding the dynamics of zooplankton and paves the way for further research on the functional diversity of zooplankton in the SYS.