Estimating the contribution of the Irish Sea fish community to carbon sink potential

The marine biological carbon cycle plays a crucial role in the sinking and sequestration of atmospheric carbon and in regulating the global climate. Most existing research on biological carbon sequestration has focused on the role of oceanic (off-shelf) species and processes. We know little about how species living on continental shelves contribute to and influence carbon sinks due to the complex dynamics of biological and physical transport processes. However, continental shelves often have high levels of carbon productivity and a high potential for disturbance from human activities such as fishing, which strongly impact fish communities. Fish are important components of ecosystems that interact with the biological carbon cycle. Here, we used an Ecopath with Ecosim food web model of the Irish Sea coupled with biogeochemical equations to provide a novel quantitative assessment of the contribution of the fish community to the annual carbon reaching the continental-shelf seafloor over a four-decade simulation (1973–2016). Similar to the open ocean, faecal pellets dominated estimates of fish-mediated carbon flux in the Irish Sea. Our simulations imply that pelagic fish contribute more than half of the fish-mediated carbon, equivalent to approximately 2% of the plankton-mediated carbon deposited on the seafloor. Our results provide the first quantitative assessment and early insights into the relationship between fish species and the biological carbon sink in a shelf ecosystem.