Spatial variability in the Wadden Sea fish food-web structure was studied by comparing
stomach content and bulk stable isotopes of fish species caught simultaneously in the Ems
and Marsdiep basins during 2012−2014. Almost all 31 fish species caught were generalist feeders.
In both basins, similar predator−prey relationships were found in which a few key prey species
fuelled the fish food web. Copepods and brown shrimp were the most important prey species in
both basins, mysid shrimp were more important as prey in the Ems basin, while shore crab and
herring were more important prey species in the Marsdiep basin. The observed spatial variability
in prey preferences was most likely the result of local differences in predator and prey abundances.
Published absolute trophic positions based on compound-specific stable isotopes were
available for some fish species and indicated low variability between the basins. Estimated
absolute trophic positions based on stomach content and on bulk stable isotopes could not be used
for the analysis of spatial variability due to sensitivity to sampling procedure (stomach content)
and sampling size and baseline (bulk stable isotopes). Although estimates based on bulk stable
isotopes underestimated absolute trophic levels in both basins, they can be used for the analysis
of relative trophic positions of fish species. Relative trophic positions showed a significant correlation
for most fish between the Ems and Marsdiep basins, also indicating a large spatial similarity
in trophic structure.
