Description: A sound knowledge on trophic interactions is essential to understand ecosystems and their resilience to anthropogenic perturbations. Stable isotope analysis (carbon and nitrogen) and literature information on taxon-specific prey spectra were combined to explore the food web structure of two major benthic assemblages in the German Bight (southern North Sea): the Amphiura filiformis-association of silty sands, and the Tellina fabula-association of fine sands. Carbon isotopic signatures of suspended particulate and sediment organic matter were consistent with ranges reported for temperate marine phytoplankton, suggesting that both food webs are mainly fueled by pelagic primary production. More negative δ13C values at the Amphiura filiformis-station furthermore indicated a small contribution of continental organic matter at this station, which is located off the Weser and Elbe estuaries. Primary consumer feeding guild composition varied between assemblages, reflecting differences in physical properties of sediments and food availability: deposit- and interface feeders were the most important primary consumer guilds in the Amphiura filiformis-association, whereas filter- and interface feeders played a major role in the Tellina fabula-association. Both communities had four trophic levels, with fishes and predatory polychaetes occupying the highest trophic positions. While primary consumer guilds occupied the same trophic level in the Amphiura filiformis-association, deposit feeders of the Tellina fabula-association had a trophic level intermediate of other primary and higher order consumer guilds, likely due to differences in species composition and selective feeding. Both food webs were characterized by their high directed connectance, trophic generalism of consumers, and a large proportion of cannibalistic taxa. These features are characteristic of marine food webs in general, but also reflect a selection for opportunistic taxa in the southern North Sea, a region characterized by high levels of environmental and anthropogenic disturbances.

Description: We examined whether taxonomically distinct benthic communities from contrasting sediments in the German Bight (southern North Sea) also differ in their trophic structure. As a case study, we compared the Amphiura filiformis community (AFC) of silty sands and the Bathyporeia-Tellina community (BTC) of fine sands using a combination of stable isotope analysis and data on trophic interactions. Differences between the food webs were evident in the feeding guild composition of important primary consumers: deposit and interface feeders are the most diverse primary consumer guilds in the AFC, whereas suspension and interface feeders play a major role in the BTC, reflecting differences in physical properties and food availability at the sediment-water interface. While all primary consumer guilds had the same trophic level (TL) in the AFC, deposit feeders of the BTC occupied a trophic position intermediate between other primary and higher-order consumer guilds, likely explained by partially incomplete knowledge of their trophic ecology and selective feeding, including the ingestion of meiofauna. Most food web properties, however, were similar between the AFC and BTC: they mainly depend on pelagic primary production, reach TL 4 and are characterized by a prevalence of generalist higher-order consumers. Furthermore, both trophic networks had similar linkage densities and high directed connectance, the latter feature suggesting considerable food web robustness. Our findings suggest that although communities in the German Bight differ in some aspects of their trophic structure, they share a similar food web topology, indicating a comparable degree of resilience towards natural and anthropogenic disturbances.