# Degradation of fish food webs in the Anthropocene

## TL;DR

Fish food webs are changing due to body size reductions, leading to more connected and less stable ecosystems.

## Contribution

The study reveals how selective species turnover and body size reductions reshape food web structure and function.

## Key findings

- Selective species turnover and body size reductions increase food web connectance and generalism.
- Changes in food web structure lead to higher predation pressure and increased prey vulnerability.
- Food webs become less modular and show cascading shifts in trophic level proportions.

## Abstract

Global change reshapes biodiversity through shifts in species composition, richness, and body size. How these shifts combine to alter higher-level ecological processes within food webs can have important implications for entire ecosystems. However, the strength and direction of these shifts will depend on combinations of ways that species and trait compositions change through time. We combine long-term data from ~15,000 freshwater and marine fish communities (1949–2019) with information about their size, diets, and trophic status to evaluate how food webs change through time at local spatial scale. We found that selective species turnover driven by body size reductions is associated with widespread alteration to fish food web topology and function, including increased connectance and generalism, leading to higher predation pressure and increased prey vulnerability. Food webs were also less modular. These changes extend across food web trophic structures, causing a cascading shift in the proportion of species across trophic levels. Our study highlights complex biodiversity responses to confluent changes across multiple facets.

The decrease in body size driven by the selective species turnover is widely altering fish food web topology and function.