Stomach content analysis indicates multi decadal trophic stability in a temperate coastal fish food web, western Dutch Wadden Sea

Information about stomach content composition of fish species of a temperate coastal fish community (western Dutch Wadden Sea) over the period 1930–2019 was analysed to reconstruct long-term trends in trophic position of individual species. Stomach data were not evenly distributed but clustered both with respect to years as well as fish species. For 18 fish species, all being omnivorous and belonging to different functional groups (pelagic, benthopelagic, demersal) and guilds [(near)-resident, juvenile marine migrants, marine seasonal visitiors], prey consumption and trophic position over time could be analysed. Prey occurrence in the stomachs of different fish species showed variability over time, most likely due to fluctuations in prey abundance, but without a trend. For all species, individual fish showed variablity in trophic position in the order of 1 unit or even more both within and between years. However, in all 18 species, no significant trend in mean trophic position over time could be found, despite the serious anthropogenic stress (pollution, eutrophication events, climate change) and the decrease in fish abundance in the area during the last 50 years. The present study does not indicate any changes in trophic position of individual species in the western Dutch Wadden Sea over the last 80 years. At the community level, trophic structure varies due to interannual fluctuations in species composition and year-to year fluctuations in the relative abundance of the various fish species. At the ecosystem level the trophic role of the fish community has been degraded due to the decrease in total fish biomass in the area.