Long-term common trends in epifauna communities and associated demersal fish assemblages mediated by environmental and human stressors in the south-eastern North Sea

The North Sea provides valuable habitats for characteristic species and communities on different trophic levels, which have changed rapidly over the last decades, due to environmental and human impacts such as global warming, fisheries and de-eutrophication. In this study, we analyzed common trends in four characteristic epifauna communities and associated demersal fish assemblages in the south-eastern North Sea along an offshore to coastal transect (‘Tail End’, ‘Oyster Ground’, ‘Coast North Frisia’, ‘Coast East Frisia’), for which spatio-temporally overlapping epifauna and demersal fish data were available from 1998 to 2022. We applied a Dynamic Factor Analysis to identify common trends in epifauna communities and demersal fish assemblages in relation to trends of six environmental parameters and human activities. Common trends of all four epifauna communities and demersal fish assemblages indicated turning points between 2004-2006 and 2013-2017, which were related to cold winters and known regime shifts. These common trends furthermore significantly correlated with changes in winter and summer water temperature and de-eutrophication. They were also linked to lower sedimentation rates combined with stronger sea water velocities, which both led to lower mud contents. A decreasing trend in demersal trawling effort was visible in all four offshore to coastal communities and was particularly strong in the region ‘Coast East Frisia’. • 25-year time series (1998-2022) of spatio-temporally overlapping biotic and abiotic data • Covering an offshore-coastal transect in the south-eastern North Sea • Common trends in epifauna communities and fish assemblages showed regime shifts or turning points • De-eutrophication and changes in water temperature were key drivers of common trends • Changes in sediments, sea water velocity and trawling effort also influenced common trends