The influence of seasonality of the aquatic environment on food web has been notoriously understudied in empirical ecology. In this study, we focus on seasonal changes in one key attribute of a food web, the trophic level. We determine whether seasonal variations of fish trophic levels could be indicated by the change in food resources. Silver carp (Hypophthalmichthys molitrix) and bighead carp (H. nobilis) were used to explore the responses of trophic levels of the filter-feeding fish to seasonal variations of food resources. Combined stable isotopic analysis and dietary analysis revealed that filter-feeding fish tended to have a higher trophic level in spring (May) and autumn (September and October). This may result from the abundant density of food resources (zooplankton and phytoplankton) and fish flexible foraging strategy, as we predicted that the trophic level follows the seasonality of food availability. Pearson’ correlation analysis and a structural equation model showed that seasonal variation of total phosphorus and water temperature could indirectly affect trophic levels of silver carp and bighead carp by mediating the abundance of phytoplankton and zooplankton directly and indirectly along the food chain. According to these findings, the seasonal variation of food resources could be an important indicator of the temporal dynamics of the food web trophic pattern in freshwater ecosystems.

Understanding trophic interactions in food webs is crucial to revealing the transfer of substances and energy from primary food sources to consumers in aquatic ecosystems. We hypothesize that the trophic structure of consumers can be significantly affected by primary food sources (pelagic, benthic, and littoral sources) through complex trophic interactions. This study used stable isotope analysis and Bayesian mixing models to estimate the trophic levels of fish consumers and the contributions of primary food sources in the three sub-lakes (Eastern, Southern, and Western Dongting) of Lake Dongting, which have different physical and chemical parameters of water, fish species diversity, and plankton (phytoplankton and zooplankton) density. Results showed the differences in community structures of fish among sub-lakes. Fish trophic levels were significantly higher in Eastern Dongting than those in the two other areas. The contributions of primary food sources to fishes were as follows: the pelagic source was the main basal food source in Eastern Dongting, and littoral and pelagic sources played equally essential roles in Southern Dongting; fishes in Western Dongting relied on more benthic source to growth than those in the two other regions. This study can fill gaps in our knowledge of the influence of the underlying food available on trophic structure of consumers by exploring the role of primary food sources and making the trophic structure of consumers in the aquatic food web highly complicated and diverse through control of the distribution of primary food sources.

Microplastics, as globally emerging pollutants, threaten aquatic ecosystems through dual mechanisms: (1) exerting direct physicochemical stress on organisms, and (2) interacting synergistically with co-existing pollutants, ultimately disrupting food web integrity and jeopardizing both ecological security and human health. However, research on the ecological risks of microplastics faces important gaps: first, experimental conditions differ significantly from real environmental conditions, making it difficult to accurately simulate chronic low-dose exposure scenarios; second, cross-scale risk assessments from the molecular to the ecosystem level are lacking. This severely hinders the accurate understanding and effective management of microplastic risks in aquaculture systems. Based on this, this study systematically integrates the cross-scale mechanisms of microplastic impacts on aquatic organisms, focusing on their environmental distribution, biological exposure pathways, and bioaccumulation characteristics to elucidate their toxic effects and ecological risks. The study reveals the “individual-community-system” cascade effect of microplastics on aquatic ecosystems, and then proposes standardized suggestions for risk assessment of microplastics in aquaculture, providing a theoretical basis and practical guidance for risk control of microplastics in both natural and aquaculture systems.