Seasonal differences in the relationship between biodiversity and ecosystem functioning in an overexploited shelf sea ecosystem

Aim Biodiversity loss results in reduced ecosystem functioning. However, the relationship between biodiversity and ecosystem functioning (the BEF relationship) in overexploited ecosystems remains controversial largely because of the lack of validation in nature. Therefore, in this study, through four seasonal trawl surveys of demersal fish assemblages off the shelf sea of Shandong Province, China, we explored BEF relationships and their seasonal variability. Furthermore, we assessed the relative importance of the environment and biodiversity on biomass variations. Location Shelf sea of Shandong Province, China. Methods At each station, we calculated taxonomic and functional diversity indices, and examined their association with ecosystem functioning based on the biomass index. Moreover, we examined the biomass index's association with two environmental variables, sea bottom temperature and sea surface chlorophyll-a concentration, to investigate the relative importance of the environmental conditions in explaining changes in ecosystem functioning. Results Two taxonomic diversity indices (species richness and variance) and two functional diversity indices (functional richness and functional evenness) were significantly associated with biomass in at least one season. However, the BEF relationships were not consistent among the seasons, highlighting the need to consider season-specific biodiversity indices (e.g., functional evenness). Specifically, despite consistently significant BEF relationships in the four seasons for species richness, variance, and functional richness, we noted temporally variable BEF relationships for functional evenness. Both the environment and biodiversity produced a strong synergistic effect on biomass, although their relative importance varied among seasons. Main conclusions Biodiversity greatly contributes to ecosystem functioning, underscoring the need to assess the consequences of biodiversity loss on ecosystems using integrated taxonomic and trait-based approaches. Our findings on season-dependent BEF relationships provide evidence for considering seasonal factors before applying BEF relationships to ecosystem-based management, at least in overexploited shelf sea ecosystems.