Species and functional group assignment.

Each species was assigned to a functional group (FG) based on Greenfield et al.[47]. Densities of FGs in bold (1–6) were included as explanatory variables in statistical analyses. Only adult specimens of S. cylindrifer, M. liliana and A. stuchburyi were included in the FG, as juveniles were expected to confound possible density effects. For Naineris sp. only juveniles were found. Species in bold were selected for isotope analyses and used as response variables in separate statistical tests. Underlined species were screened for isotope enrichment (per capita uptake) but not included in statistical analyses because of insufficient enrichment (e.g. A. stutchburyi) or low abundance.