Seasonal and bay morphology factors strongly influence temperate coastal zooplankton community structure

Zooplankton play a vital role in coastal bay food web, yet the impact of bay morphology on these communities remains unclear. We conducted synchronous seasonal sampling in Laoshan Bay and Dingzi Bay using two nets with different mesh sizes (0.505 mm and 0.160 mm, respectively) to analyse the effects of season and bay morphology on zooplankton of different sizes. A total of 75 zooplankton species were identified. Not only were there more same species in both nets (85 %), but the seasonal trends in richness were also similar. Mean zooplankton abundance and biomass were significantly higher in Dingzi Bay (0.505 mm: 1676.2 ind/m³, 647.9 mg/m³; 0.160 mm: 7381.2 ind/m³, 1231.0 mg/m³) than in Laoshan Bay (0.505 mm: 313.8 ind/m³, 438.8 mg/m³; 0.160 mm: 2698.6 ind/m³, 770.9 mg/m³), and the seasonal trends of larger zooplankton were bay-specific. The two bays had different biomarkers, suggesting that bay morphology influenced zooplankton composition, which may be related to substrate particle size and current velocity. Biomarkers at the phylum level existed between seasons, and the zooplankton community structure changed significantly between spring and summer, gradually returning to the spring state during autumn and winter, with the most significant seasonal changes being in Macrura larva. Zooplankton of different body sizes responded differently to environmental factors, mainly influenced by temperature and mean photosynthetically active radiation. The results of the study were important for understanding the distribution dynamics and sustainable development of zooplankton.