Red king crab (Paralithodes camtschaticus)

Source: The Barents Sea Report, UNEP, 2004. Matishov, G., Golubeva, N., Titova, G., Sydnes, A. and B. Voegele. Barents Sea, GIWA Regional assessment 11. University of Kalmar, Kalmar, Sweden. [17.4 MB pdf]

The greatest intended large-scale change in the Barents Sea coastal ecosystem was the introduction of another Far East species, the Red king crab (Paralithodes camtschatichus) by Soviet scientists during the 1960s.

Photo: Thomas Nilsen / www.barentsinfo.orgThe crabs were transported by aeroplane to the Barents Sea. The majority were caught in the Peter the Great Bay, only one batch in 1965 (31 specimens) was from the Ozernovsky Fish Enterprise (West Kamchatka). The crabs were released into small inlets adjacent to the Kola Bay. During the period 1961-1969, 1.5 million larvae, 10 000 juveniles and more than 3 000 adult crabs were released into the Barents Sea (Orlov 1965, 1977).

The first specimen (a female with eggs) was caught in 1974 (Orlov 1978). From this time the number of crabs caught, both adult and juvenile individuals, increased steadily, indicating that a reproductive population had established in the Barents Sea. After a significant increase in abundance, an analysis of the possibilities of commercial exploitation of Red king crab was carried out. Results of investigations carried out in the Barents Sea show that the acclimatisation of the Red king crab follows the classic steps for the introduction of new species (intended or unintended introduction). From the 1970s to the mid-1990s the acclimatisation process underwent the two first stages: survival of the resettled specimens (phase one), and reproduction and growth of the population (phase two). In the second half of the 1990s, the population growth and the growth of commercial crab fisheries were exponential. Now, the population is in its third stage of the acclimatisation process; the abundance burst. In the fourth stage, an increased conflict between the introduced species and the surrounding biota can be expected. A decrease in individual fecundity might be evidence that the crab abundance in the Murmansk area already has reached its limit, and natural mechanisms restricting population growth have started acting.

In Finnmark, however, a reduction in fecundity has not been observed yet, and further growth of the population and expansion to the west is expected.

The introduction of the Red king crab, which is a large mobile predator and polyphage, influences the existing community. Through rapid population growth, food access was limited for the king crab as well as for other benthic organisms including fish fry. Furthermore the king crab is an intermediate host for a parasite on cod fry and an increased infection rate is expected in the coming years, including a potential decrease in cod abundance.

 A number of investigations during recent years show changes in the benthic community structure along the Finnmark and Murmansk coast, including Kola and Motovsky bays. In Zelenetskaya Bay (Dal’niye Zelentsy settlement area), for example, a decrease in sea-urchin biomass by a factor of 5 compared to the period before the Red king crab introduction has been recorded. These might be natural changes in abundances, but similar changes in a number of areas might be evidence for the impact of the crab on benthic communities. Distribution of the Red king crab along the warm Atlantic water masses and expansion into new warm water habitats have been observed. In the east it has likely already reached its distribution limits. In the north, it has been recorded by fishermen at the west coast of Spitsbergen (these records have not been proved by scientists yet) (Kirkeng-Andersen 2003). In the west, it will continue its expansion along the Norwegian coast. The central area of distribution is the coastal zone of the Kola Peninsula from Cape Teriberka to Varanger Bay. The Red king crab has not changed its typical behavioural characteristics in the Barents Sea, despite the change in abiotic conditions. As in its original area, it migrates depending on age and season. Hatching, spawning and mating takes place during spring in shallow waters (10-30 m) and both sexes appear together. A female crab may spawn from 25 000-400 000 eggs, depending on body size. The larvae live in the pelagic for 1-2 months before they metamorphose in shallow waters. During their first years, they stay in shallow waters and move to deeper waters at a size of 50-70 mm carapace length.

The crabs have a social behaviour, and usually appear in aggregated groups of the same sex and size. Reproduction and availability of food are considered the most important factors governing the migration patterns of the crab throughout the year. The successful reproduction and high abundance of the crab in the Barents Sea show its ability to adjust to the environmental conditions of the region, such as polar day and night and the seasonal characteristics of biological processes typical for high latitudes.

As the algal genus that serves as a habitat in the Pacific (Ahnfeltia) does not have any significant abundance in the Barents Sea, the Red king crab have changed the habitat for the early larval stages, and uses the genera Laminaria and Desmarestia instead. Most of the year, the crab is found in soft bottom habitats. Investigations of its diet performed by Fiskeriforskning (now Norwegian Institute of Marine Research) show that it eats whatever is available of bottom living organisms. Small mussels, bristle worms (particularly Pectinaria spp.) and echinoderms are the main prey items, but also dead fish and algae are eaten by the crab. The latest analyses have documented that the crab also eats fish eggs. An ongoing research programme is now being carried out to investigate the intensity of foraging on capelin eggs and the potential effect on the capelin population. The adult crab has no natural predators, but bottom-dwelling fish, such as catfish, cod and several flatfishes, eat juvenile crabs.

New commensal relations are formed with species of the local fauna, as for example with the fish leech Johanssonia arctica. The leech is connected with the crab in the Pacific, but has not yet been recorded in the Barents Sea. However, it is expected that the Barents Sea species will migrate westwards together with the Red king crab and expand its previous range (Sundet 2003).

More information on the King crab