Stable isotope analysis of benthic-pelagic coupling in North East Atlantic fishes

Abstract

In continental-shelf ecosystems, consumers may be sustained by benthic and/or pelagic pathways, the linkages between them contributing to benthic-pelagic coupling. The relative flux from each pathway can influence the productivity and stability of the food web, yet few studies have investigated this form of benthicpelagic coupling and its influence on resilience of species at ecosystem scale. This PhD investigated the extent to which shelf-sea fish species are affiliated with benthic and pelagic pathways across four UK seas (North, Celtic, Irish Sea and English Channel), what influences this and how this relates to fluctuations in fish abundance. Studied drivers of benthic-pelagic coupling included consumer body mass and trophic level, and water depth, temperature and salinity. Factors influencing variability in species’ abundances including benthic-pelagic coupling, life history characteristics and variability in fishing pressure, were also examined. Stable isotope analysis was used to reveal time-integrated species affiliations to the pathways. Isoscapes were created using queen scallops (sedentary bivalve) and predictor variables to correct for baseline spatial variation in sampled fish species’ isotopic values. δ13C and δ34S were used to assess the relative contribution of the pathways to fish consumer production. Use of both δ13C and δ34S isotopes as opposed to just δ13C reduced uncertainty in modal use estimates. Across UK seas most species relied to some extent on both pathways, suggesting strong benthic-pelagic coupling, potentially improving community resilience to perturbations. Trophic level most influenced species’ affiliations, with an increase in trophic level causing a marked increase in benthic affiliation and a decrease in pelagic affiliation. A positive but weaker relationship between benthic affiliation and mass was also present, whilst the environmental variables had small and inconsistent effects. A significant positive relationship between variability in species’ abundance and benthic-pelagic coupling was found, whilst weaker non-significant relationships existed with the other factors. These results may aid understanding of ecosystem resilience to climatic and anthropogenic perturbations.