Characteristics of zooplankton community in North Yellow Sea unveiled an indicator species for the Yellow Sea Warm Current in winter: Euchaeta plana

Zooplankton distributions are largely influenced by both biotic and abiotic factors in the surrounding environment. Some zooplankton species can be used as bio-indicators for particular currents and water masses to help discover the dynamics of water current in the ocean. In this study, we investigated the distribution of zooplankton in North Yellow Sea (NYS) during winter when the Yellow Sea Warm Current (YSWC) influenced that area. Zooplankton communities in the NYS were dominated by temperate and warm-temperate species, such as Calanus sinicus, Paracalanus parvus, Acartia bifilosa, and Sagitta crassa. Two warm-water species, Eucheata plana and Sagitta enflata were also present. Cluster analysis grouped NYS zooplankton into three communities, the Shandong Coastal Community (SCC) in the Shandong neritic area, the Yellow Sea Central Community (YSCC) in the central waters of the NYS, and the Liaoning Coastal Community (LCC) in the Liaoning neritic area. Abundances varied significantly among these communities, with an average of 102.2 ind./m3 in SCC, 179.8 ind./m3 in YSCC, and 1 244.2 ind./m3 in LCC. Depth and the bottom (3 m from the sea floor) temperature were likely the primary abiotic factors influencing zooplankton distributions. The appearance of E. plana, an indicator species for the YSWC path, indicated a significant northwestward trend for the YSWC in 2007.