Red king crab
|Red king crab|
The red king crab, Paralithodes camtschaticus, also called Kamchatka crab or Alaskan king crab, is a species of king crab native to the Bering 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 of 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.
The red king crab is native to the Bering Sea, North Pacific Ocean, around the Kamchatka Peninsula and neighboring Alaskan waters. It was introduced artificially by the Soviet Union into the Murmansk Fjord, Barents Sea, during the 1960s to provide a new, and valuable catch. Red king crabs have been seen in water temperatures that range from −1.8 to 12.8 °C (28.8–55.0 °F), with average 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 (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 metres (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 m 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.
It is the most coveted of the commercially sold king crab species, and is the most expensive per unit weight. It is most commonly caught in the Bering Sea and Norton Sound, Alaska, and is particularly difficult to catch, but is nonetheless one of the most preferred crabs for consumption.
Red king crabs are experiencing a steady decline in numbers in their native far east coastal waters for unclear reasons, though several theories for the precipitous drop in the crab population have been proposed, including overfishing, warmer waters, and increased fish predation. Fishing controls set by the United States in the 1980s and 2000s have failed to stem the decline.
In the Barents Sea, however, it is an invasive species and its population is increasing tremendously. This is causing great concern to local environmentalists and local fishermen, as the crab eats everything it comes across and is spreading very rapidly. Since its introduction, it has spread westwards along the Norwegian coast and also northwards, having reached the island group of Svalbard. The species keeps on advancing southwards along the coast of Norway and some scientists think they are advancing around 50 km (31 mi) a year.
Despite these concerns, the species is protected by diplomatic accords between Norway and Russia, and a bilateral fishing commission decides how to manage the stocks and imposes fishing quotas. West of the North Cape on Norway's northern tip, Norway is allowed to manage its crab population itself. Only 259 Norwegian fishermen are allowed to catch it, and they see the king crab as a blessing , as it is an expensive delicacy.
Mature female red king crabs must remain 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 output. In spring (May), female red king crabs move to shallow coastal areas to moult and spawn, and males join the females in the shallow water prior to moulting. In the summer (mid-June through mid-November), these crabs spend their time in fairly deep water, below established summer thermocline. When the thermocline breaks down, the red king crabs migrate back to intermediate depths where they remain until the female red king crab release the eggs fertilized in the previous spawning.
Although the red king crab has a wide range of tolerance to temperature, it has an effect on their growth. The organism's growth, called moulting, is slow at temperatures below 8 °C and at high temperatures around 12 °C they moult quickly.
Overall, the red king crabs have a high adaptation capacity in changes of salinity level because the crabs retain their vital functions and also their feeding locomotor activities. However, there is a difference in the salinity tolerance between juvenile red king crabs and adult red king crabs. Juvenile red king crabs are slightly more tolerant to low concentrations of salinity because the juvenile's volume regulation is significantly better. Juveniles are consistently hyposmotic to the seawater because they have lower sodium concentration in their hemolymph. Due to the smaller size of the juveniles their exoskeleton is structurally 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 (8.0->7.8 pH level) and eventually die after longer exposure times because of the imbalance of the organisms' acid base equilibrium.
The red king crab has five sets of gills that are used for respiration which are located in the branchial chamber within the carapace. The carapace is a covering that consists of sheets of exoskeleton that overhang the thorax vertically to fit over the base of the thoracic legs. The carapace encloses two branchial chambers which in turn enclose the gills. The gill surfaces are covered in chitinous cuticle, which is permeable to gases; therefore, allowing gas exchange. Internal gills, like other specialized gills, require metabolic energy to pull water over the respiratory surface.:622 To induce a current into the branchial chamber the crab uses back and forth movements of an appendage called the scaphognathite. The water is drawn in from behind the walking legs then expelled from the branchial chambers through the tubes called prebronchial apertures which are located beside the mouth. To filter the water before entering the branchial chamber crabs have branchiostegal hairs which can collect debris. Due to the environment it is exposed to, the posterior gills of the crab can also be cleared of parasites and sediment by increasing the movement of its fifth set of primitive legs.
Each gill has a main axis with a large number of lateral filaments or lamellae that are vascularized. The afferent channel transports blood from the gill axis into each filament through a fine afferent canal to the gill top. Blood returns by way of a minute efferent canal to the gill tip to the efferent channel and passes to the pericardial chamber, which contains the heart. Gases are exchanged in the numerous filaments, and oxygen absorption is especially facilitated by hemocyanin. Red King crab exhibit unidirectional ventilation. This can be described as the flow of water in a U-shaped course; water passes posteriorly from the incurrent opening, an opening in the carapace near the base of the chelipeds, dorsally over the gills, and anteriorly to exit beside the head.
Due to the respiratory system's limited ability of diffusional delivery, there is a need for transporting respiratory gases around the body.:303–306Paralithodes camtschaticus have an open circulatory system with a dorsal, ostiate heart. An open circulatory system has circulating fluid which somewhat passes freely among the tissues before being collected and recirculated. The heart lies in a pericardial chamber, and blood passes through this chamber into the lumen of the heart through two pairs of osti Seven arteries conduct blood from the heart to various somatic regions. Each region branches extensively, and smaller arteries ultimately end in the hemocoel. Venous blood drain into the sternal sinus, where it is conveyed by channels to the gills for aeration and returned again to the pericardial sinus.
They have a neurogenic heart, which have rhythmic depolarization that is responsible for initiating heartbeats.:653 Heartbeats originate in nervous tissue; innervated muscle cells cause the heart to contract when stimulated by nerve impulses. The cardiac ganglion, which consists of nine neurons, attaches to the dorsal wall of the heart. The anterior neurons innervate the heart, whereas the other posterior neurons make synaptic contact with those anterior neurons. The posterior neuron acts as the pacemaker but also functions as the cellular oscillator and the central pattern generator. This posterior neuron produces a train of impulses, which excites the other posterior neurons. The heart contracts when the posterior neurons activate the five anterior neurons, which send impulses to the muscle cells. This is how the Frank–Starling mechanism works within crustaceans. The Frank-Starling mechanism refers to the vitally important intrinsic control of the heart; mainly the stretching of the cardiac muscle tends to increase the force of its contraction by an effect at the cellular level.:654 This mechanism is important as it allows the organism to match its output of blood with its input of blood. Because of the stretching between beats, the Frank-Starling mechanism allows the heart to then naturally contract more forcefully, allowing greater flow of blood, which results in the matched heart output to the increased blood received.:654 The Frank-Starling mechanism is a little different in crustaceans, as it involves the cardiac ganglion as described previously. The stretching of the heart induces the ganglion to fire more regularly and powerfully.
The red king crab blood contains leukocytes and the second most common respiratory pigment called hemocyanin.:488 Arthropod hemocyanin is a distinct variation specific to arthropods and is a metalloprotein that uses copper atoms that are bound to its structure. Two copper atoms are needed to bind one O2 molecule. Because it is a large protein molecule it is found in the blood plasma but is not found in body tissues or muscles. Hemocyanins are named appropriately because when oxygenated their color changes from colorless to blue.:622
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