Description: The snow crab Chionoecetes opilio and Arctic lyre crab Hyas coarctatus are prominent members of the Chukchi Sea epifaunal community. A better understanding of their life history will aid in determining their role in this ecosystem in light of the changing climate and resource development. In this study, the size frequency distribution, growth, and mortality of these two crab species was examined in 2009, 2010, 2012, and 2013 to determine temporal and spatial patterns within the eastern Chukchi Sea, and to identify potential environmental drivers of the observed patterns. Temporally, the mean size of both sexes of C. opilio and H. coarctatus decreased significantly from 2009 to 2013, with the number of rare maximum sized organisms decreasing significantly to near absence in the latter two study years. Spatially, the mean size of male and female crabs of both species showed a latitudinal trend, decreasing from south to north in the investigation area. Growth of both sexes of C. opilio and H. coarctatus was linear over the sampled size range, and mortality was highest in the latter two study years. Life history features of both species related to different environmental parameters in different years, ranging from temperature, the sediment carbon to nitrogen ratio of the organic content, and sediment grain size distribution. Likely explanations for the observed temporal and spatial variability are ontogenetic migrations of mature crabs to warmer areas possibly due to cooler water temperatures in the latter two study years, or interannual fluctuations, which have been reported for C. opilio populations in other areas where successful waves of recruitment were estimated to occur in eight year intervals. Further research is suggested to determine if the spatial and temporal patterns found in this study are part of the natural variability in this system or if they are an indication of long-term trends.

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.