Fish community structure and functional diversity in the Southern offshore waters of the Shandong Peninsula

The fish community is a critical component of aquatic ecosystems, playing an irreplaceable role in maintaining ecological balance and biodiversity. Functional diversity, which reflects the variation in species' traits and ecological niches, provides a valuable perspective for assessing ecosystem functioning and stability. To understand the current state of the fish community structure and the spatiotemporal patterns of functional diversity in the offshore waters of southern Shandong Peninsula. This study conducted four seasonal bottom trawl surveys in the southern offshore waters of the Shandong Peninsula during spring (May), summer (August), autumn (October), and winter (December) of 2024. Using the dominance index and abundance-biomass comparison (ABC) curves, we analyzed the species composition, dominant species, and the level of community disturbance of fish in this area. Twelve functional traits from three categories (feeding, locomotion, and habitat adaptation) were selected. Using methods such as the community-weighted mean (CWM) and functional diversity indices, the spatiotemporal variations of fish functional diversity in the study area were investigated. A total of 51 fish species were collected, belonging to 49 genera, 33 families, and 10 orders across 2 classes. The fish biomass was highest in summer and lowest in winter, whereas the abundance peaked in summer and reached its minimum in autumn. Although the dominant species fluctuated across seasons, they were consistently dominated by small-sized fishes. The fish community was subjected to varying degrees of disturbance across the four seasons, with a moderate level of disturbance observed in autumn, while severe disturbance was recorded in the remaining seasons. CWM index analysis showed that, across all four seasons, the dominant functional traits were typical of fishes with moderate-to-high resilience, small adult body size, numerous but small offspring, rapid development, and low trophic levels. Functional diversity indices showed no significant differences among seasons but exhibited substantial spatial variation. In the Southern offshore waters of the Shandong Peninsula, the fish community was dominated by r-selected opportunistic species, making the assemblage susceptible to disturbance and the ecosystem relatively fragile. The functional space occupied by fishes remained relatively stable across seasons, with no significant edge expansion or contraction. This study can provide a scientific basis for the assessment of fish resources and the sustainable utilization of fishery resources in the Southern offshore waters of the Shandong Peninsula.