In an unprecedented global analysis spearheaded by leading biodiversity researchers from the German Centre for Integrative Biodiversity Research (iDiv), Martin Luther University Halle-Wittenberg, and Friedrich Schiller University Jena, a transformative perspective has emerged on the fate of aquatic ecosystems. Drawing upon nearly 15,000 time series datasets of marine and freshwater fish communities spanning up to seven decades, the study reveals tectonic shifts within aquatic food webs that transcend traditional metrics such as species richness. Published in the prestigious journal Science Advances, this comprehensive investigation underscores that mere species counts inadequately reflect ecosystem dynamics in an era increasingly influenced by anthropogenic pressures.
A central revelation from this monumental synthesis is the profound restructuring of fish community composition, despite largely stable species richness over time. Researchers observed a systematic decline in the average body size of fish populating these ecosystems worldwide. This pervasive shift towards smaller-bodied species holds profound implications for ecosystem function, given the stepwise nature of aquatic trophic hierarchies where predator-prey dynamics are strongly size-dependent. Larger fish often occupy apex positions, preying upon smaller species; thus, reductions in body size can destabilize longstanding food-web architectures.
The study delved deeply into the interplay between organismal traits and trophic interactions by integrating species-level body size data with detailed dietary and trophic position information. This approach revealed that fish food webs have become increasingly densely connected, marked by a rise in dietary generalism. Species tend now to exploit a broader range of prey items compared to historical baselines, indicating a shift from specialized feeding relationships toward more overlapping and flexible diets. This structural change has disrupted the traditional hierarchical arrangement of predators and prey, undermining the distinct delineation of trophic levels.
Notably, the abundance of large top predators such as sharks, goliath groupers, muskellunge, and marble trout has markedly declined across numerous aquatic systems. Conversely, mid-level predators and primary consumers—species generally smaller in size—have experienced population increases. This redistribution modifies the flow of energy and nutrients through ecosystems and suggests a bottom-up shift influencing food-web stability and resilience. It is increasingly clear that the loss of apex predators reverberates widely across aquatic communities, altering ecosystem services and potentially diminishing ecological robustness against environmental stressors.
Professor Ulrich Brose, a leading figure at iDiv and Friedrich Schiller University Jena, highlighted the ecological ramifications of these findings. The increasing connectance within fish food webs may facilitate accelerated propagation of disturbances, such as those induced by climate warming, eutrophication, and overfishing, across species networks. Paradoxically, this same heightened interconnectivity could foster greater buffering capacity, allowing aquatic ecosystems to absorb shocks and maintain functionality in the face of escalating anthropogenic impacts. Such dual effects underscore the profound uncertainty surrounding the future trajectories of aquatic food webs under continuing global change.
The ripple effects of altered food-web structures extend beyond ecological communities to affect ecosystem services that humans rely on, from fisheries productivity to water quality regulation. The displacement of large predators by generalist feeders with overlapping diets may intensify the cascading impacts of human activities on aquatic ecosystems, heightening vulnerability to invasions, disease spread, and resource depletion. Understanding these complex processes is increasingly critical as societies grapple with sustainable management of marine and freshwater biodiversity in a rapidly changing planet.
Equally striking is the consistency of these trends across disparate aquatic environments globally. Whether examining coastal marine habitats or inland freshwater lakes and rivers, the patterns of downsizing body size, increasing generalism, and food-web reorganization appear nearly universal. This widespread similarity suggests that these shifts are not localized anomalies but rather manifestations of broad-scale, human-driven ecosystem degradation. It is only through integrating vast datasets and applying food-web theory that such global-scale patterns become discernible.
The study’s pioneering use of food-web perspectives to analyze long-term biodiversity data emphasizes the limitations of conventional monitoring approaches that focus predominantly on species numbers. While species richness remains an important biodiversity metric, overlooking variations in species traits, interactions, and ecological roles risks masking fundamental ecosystem changes. This work advocates for an enhanced multidimensional approach to biodiversity assessment, incorporating functional diversity and interaction networks alongside taxonomic inventories.
Moreover, these insights hold substantial promise for conservation science and policy development. By revealing how species interactions and food-web structure evolve alongside compositional changes, managers can identify critical ecosystem functions at risk and tailor interventions accordingly. For instance, restoring or protecting large-bodied top predators may help re-establish ecological balance and bolster resilience against future disturbances. Similarly, recognizing the rise of generalist feeders can inform adaptive strategies for fisheries management and habitat restoration.
Dr. Juan Carvajal-Quintero, who led much of the analytical work during his postdoctoral tenure at iDiv’s synthesis center, underscored the ecological principle that “big fish eat small fish” and how alterations in body size reverberate through food-web dynamics. As an assistant professor now at Dalhousie University, he emphasizes that shifts in predator-prey sizes not only reflect biodiversity loss but also drive fundamental changes in ecosystem functioning that species counts alone cannot capture.
Professor Jonathan Chase, senior author from iDiv and Martin Luther University, reiterated the unprecedented scope of this research. He noted that “no single study could reveal this level of global consistency,” highlighting the transformative potential of synthesizing diverse datasets with robust food-web frameworks. This approach illuminates the intricacies of ecosystem reorganization in the Anthropocene and challenges the scientific community to rethink biodiversity monitoring in the face of mounting environmental change.
In conclusion, this landmark study compellingly demonstrates that the degradation of fish food webs is a multifaceted phenomenon manifesting through altered species composition, reduced body size, and evolving trophic interactions. These changes are pervasive across aquatic ecosystems worldwide and signify profound ecological ramifications beyond what species richness metrics alone convey. Integrating trait-based and food-web perspectives into biodiversity research promises to deepen our understanding of ecosystem resilience and inform more effective conservation strategies poised to safeguard aquatic life in a rapidly transforming world.
Subject of Research:
Long-term restructuring and degradation of aquatic fish food webs globally, focusing on species composition, body size, and trophic interactions.
Article Title:
Degradation of fish food webs in the Anthropocene
News Publication Date:
18-Feb-2026
Web References:
http://dx.doi.org/10.1126/sciadv.adu6540
Keywords:
Fish food webs, species composition, body size, trophic interactions, aquatic ecosystems, species richness, biodiversity change, ecosystem function, generalist feeders, apex predators, global change, Anthropocene
