Active Transport of Carbon to Demersal Fish Communities in Shelf‐Slope‐Abyssal Systems of the North Atlantic Ocean

Abstract The biological carbon pump sequesters carbon through passive fluxes of biologically derived carbon, and by active vertical movement of marine organisms. Trophic coupling between pelagic and benthic communities increases the efficiency of the biological carbon pump as less carbon is lost to remineralization. Such fish‐mediated benthic‐pelagic coupling, which can be described as the sum of carbon fluxes that is “passed on” when predators eat prey that occupy different vertical habitats in the water column, remains highly uncertain. Here, we applied a size‐ and trait‐based food web model to estimate the amount of carbon that fish actively transport through benthic‐pelagic coupling to the seafloor across the shelf‐slope‐abyssal continuum in different systems of the North Atlantic. The model estimates that benthic‐pelagic coupling transports on average 813 kg C km −2 yr −1 to the demersal fish communities in North Atlantic shelf‐slope‐abyssal systems, which is equivalent to 5% of the modeled detritus flux reaching the sea floor. In some slopes, midwater fishes mediate up to 50% of the carbon transported downwards via benthic‐pelagic fish coupling. We validated model‐estimated biomasses of demersal fishes with biomass estimates of bottom trawl‐surveys in the same area. Both modeling and survey approaches show that demersal fish biomass estimates are at the same order of magnitude and decrease with bottom depth following a similar trend. Our study shows that benthic‐pelagic coupling is an important mechanism transporting carbon to demersal communities, supplying energy to sustain abundant seafloor fish fauna and fueling commercially valuable fisheries.