Studies on impact of the alien Red King Crab (Paralithodes camtschaticus) on the shallow water benthic communities of the Barents Sea

The red king crab Paralithodes camtschaticus (Tilesius, 1815) was introduced in the Barents Sea from the North Pacific in 1961-1969 to establish a fishery. Currently the crab inhabits an area from Kolguyev Island in the east to Soroya in the west, and the total number of adults exceeds 40 million. The crab is a large generalist predator, so its potential impact on native bottom communities is expected to be high. The goal of this study was to review our publications related to the possible impact of the red king crab on the shallow water benthic communities of the Kola Peninsula inlets. First, we reviewed field and experimental data on feeding ecology of different size groups of the crab. Secondly, we examined the data on the benthic communities' structure in the bays. Finally, assess possible changes in the community structure caused by the red king crab predation. The crab diet includes about 100 species of invertebrates, algae, and fish remnants. Diet of juveniles varied in three studied areas, but bivalve and gastropod mollusks dominated. Experiments on the juvenile feeding showed their positive selection for ophiuroids. Caught prey was usually not completely consumed. Food losses decreased from 50 to 60% in crabs with 35-40 mm carapace width (CW) to 25% in crabs with 70-80 mm CW. Within and between bays trends in the benthic community structure related to the crab density were revealed. Generally, proportion of the stations with disturbed community structure decreased eastward from 80% in the Kola Bay to 18% in the Dolgaja Bay and it was negligible in the Dal'nezelenzkaja Bay. This pattern coincides with the juvenile crab density decreasing eastward. On a smaller scale in the Kola Bay we observed a negative correlation between biomass of macrozoobenthos and juvenile crab density, which was likely related to the crab predation. Comparison of the new data obtained in 2006 with the detailed survey of soft bottom macrobenthos conducted in 1990 in Dolgaja Bay showed a decrease of the diversity of soft bottom communities as well as in species richness, density and biomass of bivalves. Our data demonstrate that the proposed impact of the crab on the bottom communities of the Barents Sea is not as dramatic as have been expected from its high feeding activity and wide diet. We hypothesize that the crab omnivory distributes its predation pressure among various groups of organisms and prevents elimination of particular species or taxa.