The North Sea fish community has a long history of intense fishing and environmental change. Scientific bottom trawl surveys, which have been ongoing in the North Sea since the 1980s, provide excellent data on the abundance and spatial distribution of fish species over time. But what if instead of species, we look at how traits have changed over time and space in this community?
In our new paper, we looked at how the North Sea fish community has changed during the last 30 years in space and time, by exploring a set of ecological traits related to size, diet, life history, growth and reproduction. We calculated community-mean-trait values by weighting species trait values with species biomass. We found that the North Sea fish community has shifted from large, slow-growing and late-maturing species to smaller, fast-growing and early-maturing species. This shift in the fish community is caused by a combination of fishing pressure and bottom-up processes related to increasing water temperatures and shifts in the plankton community. Interestingly, temporal trends in fish community-mean-trait values differed markedly in space, with some areas having no trend or even opposite trends compared to the main trend over time. Also, when looking strictly at the spatial patterns of fish community-mean-trait values, we see large differences between areas. The spatial differences in fish communities can largely be explained by the different environmental conditions within the North Sea, particularly the strong gradients in depth, water temperature and seasonal variation in temperature.
Our paper shows how a trait-based approach to observational data of fish abundances can reveal community-wide responses to changes in the environment and fishing pressure. Especially taking into account multiple drivers and changes in both space and time are deemed important and a way forward to an ecosystem-based approach of managing marine ecosystems.
The paper can be read here
Beukhof E, Dencker TS, Pecuchet L, Lindegren M (2019) Spatio-temporal variation in marine fish traits reveals community-wide responses to environmental change. Marine Ecology Progress Series 610:205-222.