Abstract:Studies on the species, abundance and distribution of zooplankton have been extensive and mainly focused on either the entire or certain small parts of the Bohai Sea. In this study, we analyzed the composition, abundance, dominant species, and biodiversity of zooplankton based on samples collected in the central Bohai Sea in 2013. The distribution and its influencing factors were explored with multivariate analysis according to the sampling date and environmental parameters. A total of 74 zooplankton species/taxa (including 21 pelagic larvae) were identified in four surveys. Copepods were the most abundant species. The numbers of pelagic copepod and medusa species accounted for 25.7% and 24.3% of the total species respectively. The composition of the dominant species was consistent with previous reports. The Calanus sinicus and Sagitta crassa were the dominant species. The abundance of C. sinicus and S. crassa explained 19.5%–50.3% and 7.3%–39.6% of the total zooplankton abundance respectively. In spring, the average abundance, the average biomass, the Shannon-Wiener index (H′), and the Margalef′s index (D) were 782.0 ind/m3, 157.1 mg/m3, 2.36, and 1.02 respectively. In summer, the values of parameters above were 199.6 ind/m3, 135.8 mg/m3, 1.75, and 1.78. In autumn, they were 42.1 ind/m3, 122.5 mg/m3, 1.83, and 2.08 respectively. In winter, they were 72.1 ind/m3, 151.1 mg/m3, 1.63, and 1.53 respectively. The abundance and biomass fluctuated and showed distinct heterogeneity in the central part of the Bohai Sea. There was a seasonal variation in the primary environmental factors that affected the distribution of zooplankton. In spring, they were surface salinity, bottom DO, and water depth. In summer, they were bottom temperature, bottom salinity, and chlorophyll. In autumn, they were surface temperature, surface pH, and bottom pH. In winter, they were bottom pH and chlorophyll. Our research provided the fundamental information on the long-term observation of zooplankton ecology in the central part of the Bohai Sea. Compared to the data collected in 1959, 1998, and 2006, the number of species, abundance and biomass of zooplankton have decreased.
