Biological Traits of the North Sea Benthos: Does Fishing Affect Benthic Ecosystem Function?
Julie Bremner, Chris L. J. Frid, and Stuart I. Rogers
Abstract. The impact of fishing on benthic species and habitats has been well documented, but effects on the way the ecosystem functions are less well understood. The roles performed by benthic species contribute to ecological functioning, and changes in the types of species present may have implications for the whole ecosystem. Biological traits analysis, which uses a wide range of biological characteristics, is employed to investigate the effects of fishing on the variety of roles performed by benthic taxa. Eighteen biological traits were chosen to represent aspects of the morphology, life history, feeding, and habitat use of benthic infauna from the western North Sea. Differences in relative frequency of the traits were assessed in relation to changes in fishing pressure over a 30-year period. The communities were dominated by organisms exhibiting opportunistic traits. These traits responded positively to an initial increase in fishing effort and then remained relatively stable for the remainder of the study. Traits predicted to be associated with vulnerability to fishing impacts, such as long life spans, large oocytes, and shelled body designs, decreased in proportion in response to elevated fishing effort. Those organisms with high regeneration potential and asexual reproduction also responded negatively. Traits related to feeding modes of various taxa and their interactions with the benthic habitat remained relatively stable throughout the study. We conclude that fishing has altered the biological trait composition of this benthic community in both predictable and unexpected ways over the last 3 decades. Some aspects of functioning may have been affected, while others, including those related to trophic relationships and habitat usage, have been preserved in spite of changes in taxon composition. It is not yet clear what the larger-scale implications of these trait changes may be to ecosystem functioning, fisheries management, or, indeed, the management of anthropogenic activities in the sea. What is clear is that studies of the biological trait compositions of other marine ecosystem components are now required.