Fjordic Lagoons of the Barents Sea as Models for Study of the Dynamics of Coastal Communities with Alien Red King Crab ( Paralithodes camtschaticus , Decapoda, Lithodidae)

Benthic communities of the semi-isolated deep fjordic Linjalampi and Sisajarvi lagoons in the apex part of Ambarnaya Bay, Varanger fjord, Barents Sea, are affected by the limited water exchange and wave action in combination with other abiotic and biotic factors. Among the biotic factors, the presence of a numerous group of red king crab ( Paralithodes camtschaticus ) that naturalized in the southern part of the Barents Sea in the second half of the 20th century may play a particularly important role. The median density of juvenile and adult crabs in the lagoons (42.5–52 specimens/1000 m 2 in most years of observation) is comparable to their density in the neighboring open parts of the Varanger fjord. A narrow and shallow strait connecting the lagoons with the sea may restrict crab migrations between these habitats. Thus, adult crabs are present in the lagoons in the seasons when they migrate from the coast to greater depths in their usual habitats. The food chains starting from phytoplankton and macrophytes to benthic predators, red king crabs, spider crabs ( Hyas araneus ), and hermit crabs ( Pagurus pubescens ) have been studied using stable isotope analysis. The trophic level of adult king crabs in the lagoons (2.88) is lower than that of both spider crabs (3.16–3.42) and those king crabs that occur in the open part of the coastal area (3.44). This indicates differences in the feeding habits of crabs in the lagoons and in the open coastal waters. The food chain kelp–sea urchins–red king crabs typical for the coastal zone in the Barents Sea is not expressed in the food web of the lagoons. The low abundance and distribution patterns of sea urchins may be due to their consumption by red king crabs over a long period. Although fjordic Linjalampi and Sisajarvi lagoons are full marine water bodies, they are similar to continental lakes in some characteristics. In particular, the conditions in the lagoons make them convenient models for the study of the long-term dynamics of communities and ecosystems.