A functional assessment of fish as bioturbators and their vulnerability to local extinction

The seabed is one of the key ecological interfaces on the planet, exerting a major influence on global biogeochemical cycles. Biological processes such as bioturbation - the reworking of sediment by activities of benthic fauna - are key in mediating fluxes of nutrients, carbon, and oxygen from the water column into the sediment. To date, most research on bioturbation has focused on the role of sediment-dwelling invertebrates with the contribution of other and often larger organisms such as fish largely overlooked. Here, we highlight the significant and underappreciated role of fish as bioturbators in benthic ecosystems and present the first systematic approach to assess fish bioturbation impact on the seabed based on ecological traits known to influence sediment reworking. We show that 185 fish species across 62 families are bioturbators on the UK continental shelf, exhibiting a range of bioturbation modes, for example through burrowing, feeding, and nesting activities. Our analysis demonstrates that many important bioturbators are highly vulnerable to loss and extinction. Out of the 185 fish species bioturbating on the UK shelf, 120 are commercially exploited, with some of the most significant bioturbators among the most highly commercially fished. Our findings highlight the risk of alteration of benthic ecosystem processes resulting from the potential removal of these key bioturbators. This novel framework provides a simple yet powerful tool for assessing fish contributions to benthic ecosystem functioning and represents a first step towards incorporating fish bioturbation into future seabed management decisions.