Chronic bottom trawling impacts on different size fractions of benthic communities and sediment properties: A case study from the Kattegat (North Sea)

Bottom trawling is one of the most destructive fishing methods currently in use, with acute impacts on benthic ecosystems and chronic impacts on macrofauna communities. However, the long-term effects of chronic bottom trawling on smaller components of benthic communities and on sediment biogeochemistry are less well understood. To address this knowledge gap, we examined the effects of bottom trawling and environmental variables (bottom water and sediment properties) on alpha diversity and community structure of prokaryotes, meiofauna (including metazoans and foraminifera), and macrofauna over a spatial gradient of commercial bottom trawling, including a marine protected area which has been unfished for 12 years after >100 years of chronic trawling. Our results showed that chronic trawling affected the four organism groups in different ways. Prokaryote and foraminifera diversities were slightly higher at sites with higher trawling intensities, due to a greater number of rare species. Community composition was affected by trawling in all groups except meiofaunal metazoans. Sedimentary carbon played a significant role in shaping all four communities, as well as carbon degradation rates, but was not itself affected by trawling. Our results highlight that the complex interactions between environmental variables and disturbances from bottom trawling affect different components of the benthic fauna in different ways. Differences in organism size, population turnover rates, metabolic and ecological plasticity, feeding traits, and sensitivity to physical disturbance probably explain these differences.