Fishery Communities in the Coastal Waters of Qingdao in Summer and Winter

The warm-temperate coastal waters of Qingdao, including Aoshan Bay, Jiaozhou Bay and Lingshan Bay, serve as crucial spawning and feeding grounds for diverse fishery organisms and as important fishing grounds. These areas have experienced significant ecological shifts due to escalated human activities, marine pollution, and increased fishing pressure, leading to changes in fishery resources towards miniaturization and domination by low economic value species. To understand the characteristics of the structural changes of the fishery resources in the coastal waters of Qingdao, the present study analyzed the composition, community structure, ecosystem stability, and biodiversity of fishery resources within the coastal waters of Qingdao, based on the data from the fishery surveys conducted in the summer (July-August) and winter (November-December) of 2022. The keystone species were identified using a food web topology, which is crucial for regulating marine ecosystems. A total of 92 and 86 fishery species were collected in the summer and winter with a notable replacement rate of 42.5% respectively. Specifically, Metapenaeopsis dalei is the predominant species in both seasons. The study also highlighted the seasonal dominance of Enedrias fangi and Hexagrammos otakii in summer and Loligo spp., Trachypenaeus curvirostris, Charybdis bimaculate and Syngnathus acus in winter. A discernible shift was observed in the structure of fishery resources, with the increasing dominance of invertebrates and a trend toward miniaturization and devaluation across fish, crustaceans, and cephalopods. In terms of biodiversity indices, the Shannon-Weaver (H') and Pielou evenness (J') indices were significantly higher in summer, whereas the Margalef richness index (D) was higher in winter, indicating normal ecosystem diversity and demonstrating stable seasonal horizontal structures and consistent community compositions. Notable ecological improvement was observed over the past decade, benefiting from the implementation of measures to restore fishery resources. The food web topology for the ecosystem, developed based on the feeding relationships of the local feeding relationships, incorporated 26–29 major species (S) and 116–165 feeding relationships, indicating substantial seasonal variations. The node density (Dd) in summer was greater (0.22 > 0.18), whereas other indices i.e., average path length (1.17 < 1.27), interspecific connectance (C) (0.17 < 0.20) and clustering coefficient (Cl) (0.18 < 0.25) were lower than those in winter. Based on a comprehensive analysis of the topological index ranking (D, Dout, Din, BC, CC, IC, TI1, TI3, TI5, K, Kb, Kt, F, and DF), Lophius litulon and Metapenaeopsis dalei were identified as key species, with the former being a primary predator and the latter an important prey species. Overall, the food web of the coastal waters of Qingdao exhibited relatively high connectivity and complexity, presenting strong stability and resilience against disturbances and thereby ensuring the provision of vital ecosystem services. Furthermore the role of keystone species must be fully considered in the subsequent conservation of fishery resources and adaptive management to achieve precise management. The findings of this study provide scientific data and knowledge for understanding the structure of the marine food web and biodiversity conservation in this area.