Study on the Construction Mechanism and Survival Strategy of Important Estuarine Zooplankton Communities in Qinhuangdao Sea, Bohai Sea, China

The objectives of this study were to investigate the zooplankton community in the important estuarine areas of Qinhuangdao Sea in the Bohai Sea, analyze the variation characteristics of the zooplankton community, and explore the construction and evolutionary mechanisms of its community structure and function. We conducted zooplankton monitoring in the four seasons of 2024 at Daihe Estuary (DHK), Yanghe Estuary (YHK), Shihe Estuary (SHK), Tanghe Estuary (THK), and Luanhe Estuary (LHK). The results showed that the diversity index and richness index in summer were significantly higher than those in winter (<i>p</i> < 0.05). Based on the body size, feeding habits, reproduction types, life cycles, and escape abilities of zooplankton, the zooplankton in the ecosystem were divided into 17 zooplankton functional groups. The zooplankton examined in this study were divided into 11 functional groups. Except for THK, the dominant functional groups in other estuaries in all seasons were SCF (Small copepods and claocera filter feeders) and LCF (Large copepods and claocera filter feeders); PP (Protozoan photosynthetic autotrophs) and PB (Protozoan bacterivores) functional groups dominated THK. Pearson correlation analysis and RDA multivariate statistical analysis revealed that interspecific competition, PO₄^3--P, NO₂^--N, and SAL were the primary driving factors influencing community construction. The spatial-temporal variations in T, PO₄^3--P, NO₂^--N, and SAL in the five estuaries were evident, and the pH and DO in the water environment exhibited a high degree of overlap in seasonal changes. The density of zooplankton functional groups was significantly positively correlated with PO₄^3--P, NO₃^--N, NO₂^--N, NH₄⁺-N and SAL (<i>p</i> < 0.05). Furthermore, the SCF and LCF functional groups played a dominant role. According to the analysis of niche overlap and AC interspecific association, it was shown that zooplankton populations in small-scale areas mostly exhibited negative correlations dominated by competition and predation. In contrast, the functional groups of zooplankton in large-scale areas mostly demonstrated mutually synergistic facilitative relationships. The results of this study showed that interspecific relationships are more important for the community structure of zooplankton. This study contributes to understanding the responses of primary producers and primary consumers to water environmental changes in estuarine ecosystems, laying a foundation for further analyzing the mechanisms of zooplankton community construction and survival strategy selection in special estuarine habitats. It also provides references for the scientific management of estuarine areas and the avoidance of pollution risks.