Only a few key prey species fuel a temperate coastal fish food web Version 9

The food web structure of a coastal fish community (western Dutch Wadden Sea) was studied based on stomach content data from samples collected from 2010 to 2018. In total 54 fish species were caught and 72 different prey items were identified. Fish species had consumed from a few up to more than 30 different prey species, suggesting the presence of both opportunistic and more specialized feeders. No significant differences between years nor switches in food source with fish size were found. The trophic positions of the Wadden Sea fish community ranged between 2.0 and 4.7, with most trophic positions above 3.0. In the past, (near)-resident species were the most abundant functional group in spring and juvenile marine migrants in autumn. Nowadays, all functional groups are present in almost similar but low abundances. The (near)-resident community consisted of about 20 species which especially were feeding on amphipod crustaceans, brown shrimps and juvenile herring. There was only a slight overlap in diet with the group of marine juvenile migrants (5 species of juvenile flatfishes and clupeids), whose preferred preys were copepods, polychaetes and brown shrimps. About 15 species of marine seasonal visitors showed an overlap in diet with both the (near)-resident and the marine juvenile migrant especially for brown shrimps and to a lesser extent herring and gobies. Our results illustrate (1) the pivotal position of a few key prey species for the coastal Wadden Sea fishes: amphipod crustaceans, brown shrimps, juvenile herring and gobies, and that (2) the substantial prey overlap in the diet of some predators cannot exclude some intra- and inter-specific competition for some predators.