Demersal seas contribute from 30 to 40% of European fisheries production. They contain diverse fish communities, including fish living close to the seabed (like flatfish and gadoid species). These ecosystems have been fished for more than a century, thereby changing their biodiversity. In our new paper, we investigate demersal fish communities, shaped by fishing activities in the North Western European seas, and their relationship to the total fish biomass, informing on the functioning of the ecosystem.
We used a collection of bottom-trawl surveys and fish traits to investigate the relationships between biodiversity, environmental conditions, and biomass of the fish community with a structural equation modeling framework. Such a statistical tool allows us to test hypotheses about causation between multiple drivers and response variables.
While relationships between the number of species and biomass have been evidenced in multiple terrestrial, aquatic and marine systems, we found that biomass is unrelated to the number of species across the North Western European seas; demonstrating that a high number of fish species in one site does not necessarily lead to higher functioning of the food web. However, high fish biomass is related to the dominance of gadoid species. Typically, gadoids have a generalist diet and a high trophic level, thus they can feed on both pelagic and benthic food chains.
We show that biodiversity-ecosystem functioning relationships are not universal, but metric and context-dependent, especially across large spatial-scales. Our study further demonstrates the importance of biodiversity for one measure of ecosystem functioning in exploited ecosystems, and aids our understanding of the effect of changes in biodiversity on marine ecosystem functioning.
You can see the paper here.
About the photo: European flounder in Køge Bay, Denmark
Photo credit: Maxime Lescan du Plessix