Kamchatka crab, Alaskan king crab
The red king crab (Paralithodes camtschaticus), also called Kamchatka crab or Alaskan king crab, is a species of king crab native to cold waters in the North Pacific Ocean and adjacent seas, but also introduced to the Barents Sea. It grows to a leg span of 1.8 m (5.9 ft), and is heavily targeted by fisheries.
The red king crab is the largest species of king crab. Red king crabs can reach a carapace width up to 28 cm (11 in), a leg span of 1.8 m (5.9 ft), and a weight of 12.7 kg (28 lb). Males grow larger than females. Today, red king crabs infrequently surpass 17 cm (7 in) in carapace width and the average male landed in the Bering Sea weighs 2.9 kg (6.4 lb). It was named after the color it turns when it is cooked rather than the color of a living animal, which tends to be more burgundy.
Mature female red king crabs must stay in warmer water (near 4 °C) to ensure the eggs will be ready for hatching, while the male red king crabs stay in relatively cold water (near 1.5 °C) to conserve energy. In spring (May), female red king crabs move to shallow coastal areas to molt and spawn, and males join the females in the shallow water before molting. In the summer (mid-June through mid-November), these crabs spend their time in fairly deep water, below the established summer thermocline. When the thermocline breaks down, the red king crabs migrate back to intermediate depths, where they stay until the female red king crabs release the eggs fertilized in the previous spawning.
The red king crab has a wide range of tolerance to temperature, but it affects their growth. The organism's growth and molting is slow when outside temperature falls below 8 °C; around 12 °C, they molt rather quickly.
Overall, red king crabs have a high adaptation capacity in changes of salinity level because the crabs retain their vital functions and their feeding activities. A difference is seen, though, in the salinity tolerance between juvenile and adult red king crabs. Juveniles are slightly more tolerant to low salinity because their volume regulation is significantly better. Juveniles are consistently hyposmotic to the seawater because they have lower sodium concentration in their hemolymph. As the juveniles are smaller, their exoskeleton is more rigid. The adult red king crabs are hyperosmotic in high salinity and becomes hyposmotic in lower salinity. The hyperosmoticity is due to the higher sodium and potassium concentrations in the hemolymph compared to the surrounding water they live in.
A slight fluctuation on the pH level of the water (i.e. making the water more acidic) would have great effect on the red king crab. They grow slower in acidified water (pH 7.8 instead of 8.0) and eventually die after longer exposure times because of the imbalance of the organisms' acid-base equilibrium.
The red king crab is native to cold waters in the North Pacific Ocean and adjacent seas, ranging from the Bering Sea south to the Gulf of Alaska, off the Kamchatka Peninsula, and in the Sea of Okhotsk and Sea of Japan. It was introduced artificially by the Soviet Union into the Murmansk Fjord, Barents Sea, during the 1960s to provide a new, and valuable, catch in Europe.
Red king crabs have been seen in water temperatures that range from −1.8 to 12.8 °C (28.8–55.0 °F), with typical being 3.2 to 5.5 °C (37.8–41.9 °F). Immatures prefer temperatures below 6 °C (43 °F). The depth at which it can live has much to do with what stage of its lifecycle it is in; newly hatched crab (zoea larvae) stay in the shallower waters where food and protection are plentiful. Usually, after the age of two, the crabs move down to depths of 20–50 m (66–164 ft) and take part in what is known as podding; hundreds of crabs come together in tight, highly concentrated groups. Adult crabs are found usually more than 200 metres (656 ft) down on the sand and muddy areas in the substrate. They migrate in the winter or early spring to shallower depths for mating, but most of their lives are spent in the deep waters where they feed.
P. camtschaticus faces many predators in its native range including Pacific cod, walleye pollock, rock sole, flathead sole, rex sole, Dover sole (Microstomus pacificus), arrowtooth flounder, Elasmobranchs, halibut, sculpin, Greenland turbot, Pacific salmon, Pacific herring, otters (Enhydra lutris) and seals.
