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Benthic trophic networks of the southern North Sea: contrasting soft-sediment communities share high food web similarity

Jan Steger*, Hendrik Pehlke, Benoit Lebreton, Thomas Brey, Jennifer Dannheim

*Corresponding author:

ABSTRACT: 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 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, reached trophic level 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 indicate 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.