Which aspect of functional diversity shapes ecosystem functioning in exploited marine demersal fish community?

The biodiversity-ecosystem functioning (BEF) relationship is a critical topic in ecological research, as it guides the maintenance of ecosystem functioning in the face of climate change and human disturbance. However, the BEF relationship is complicated by the fact that biodiversity has multiple dimensions, and in particular functional diversity may be strongly correlated with community productivity. But the understanding is still lacking about how different functional traits determine community productivity. The present study tested the relationship between biodiversity and community productivity empirically in a demersal fish community, based on continuous bottom trawl surveys in Haizhou Bay, China from 2013 to 2022. Structural equation modeling (SEM) with composite variables was used to evaluate the relationships among environmental factors, species diversity (SD), functional diversity (FD), community weighted mean traits (CWM), and community productivity (CP), and the roles of different aspects of functional traits were further compared. The results showed that there were considerable heterogeneities in the temporal and spatial distributions of CP, and PCA revealed that the CP was weakly correlated with both species and functional diversity. SEM showed that CWM had the greatest influences on CP (r = 0.63), followed by SD (r = 0.52), and FD had the least impact (r = -0.42). This finding supported the mass ratio hypothesis, indicating that functional traits of dominant species determined community productivity. Environmental factors showed no direct impacts on CP but had indirect effects through biodiversity. Regarding the role of different functional traits, the trait of locomotion was the most important driver of CP in terms of CWM, while the food acquisition was more important than other components in terms of FD. Our study can contribute to an improved comprehension of the BEF linkages in marine fish communities, and serve as a guideline for fisheries management and biodiversity protection in the face of climate changes.