Distribution pattern of zooplankton assemblages in the eutrophic Hangzhou Bay, China

To reveal the distribution pattern of the zooplankton community in the typical eutrophic Hangzhou Bay in the northern East China Sea, we investigated the zooplankton community. The study was conducted in 2019 during the summer. A total of 57 species of zooplankton belonging to 6 phyla and 52 genera were identified. During the sampling period, the abundance of zooplankton in Hangzhou Bay was 26.7–497.2 ind/m3, with an average of 179.58 ind/m3. The abundance of zooplankton increased from west to east, and the abundance of zooplankton in most waters of the offshore area was higher than that in the coastal waters of Hangzhou Bay. The top dominant species, Tortanus vermiculus, was distributed in Hangzhou Bay, whereas Paracalanus aculeatus was mainly distributed in the mouth of Hangzhou Bay, and Acartia (Odontacartia) spinicauda and Centropages dorsispinatus were distributed between Zhoushan Island and Hangzhou Bay. The spatial distribution of the ShannonWiener index and evenness index of the zooplankton in Hangzhou Bay and its adjacent waters showed that the community structure of zooplankton was stable in the estuary of Hangzhou Bay and eastern part of the Zhoushan Islands. In addition to salinity and water temperature, eutrophication-related water quality parameters were also crucial to zooplankton species number, Margalef species richness and the abundance of the dominant species Tortanus vermiculus. The zooplankton dominant species and community composition were affected or restructured by eutrophication-related factors, especially for phosphate (PO4), nitrate nitrogen (NO3), dissolved inorganic nitrogen (DIN) and the eutrophic index (EI).