Functional diversity and groups of crustacean zooplankton in the southern Yellow Sea

Functional trait and functional diversity indices reflect the variations of community structure and indicate their responses to environmental stress. In this study, based on four functional traits, including body length, feeding type, trophic group, and reproductive mode, the functional diversity and functional groups of crustacean zooplankton from the southern Yellow Sea (SYS) were explored over four seasons of 2019. A total of 53 species were identified and categorized into six functional groups. Copepods with ambush-feeding and omnivore–carnivore diet (Group Ⅱ) were dominant in spring (55.6%), while omnivore–herbivore copepods (Group Ⅰ) were the most abundant group in the other three seasons (>54.7%). The comparable distributions of functional diversity indices in different seasons were most likely due to hydrological variations. The Changjiang River Diluted Water promoted the coexistence of multiple traits carried by different functional groups (high functional richness (FRic) and functional dispersion (FDis)), but the stability of ecosystem function in this water mass was vulnerable to the loss of individual species (low functional evenness (FEve)) in summer. In winter, as a result of the Yellow Sea Warm Current, warm-water taxa increased FRic and FEve, suggesting that the community could buffer environmental fluctuations more effectively. Moreover, distribution of FRic values indicates the possible range and influence intensity of the Yellow Sea Cold Water Mass.