Alaska snow crabs are found primarily in the northern Pacific Ocean, in the Bering, Beaufort, Chukchi, and Japan Seas, as well as the Sea of Okhotsk and off the Aleutian Islands. They may also be found along the eastern coast of Russia, along the coast of northern Siberia, on the shelf of North Primorsky Krai, and in Peter the Great Bay. They are also found on the Scotian Shelf,in the northwestern Atlantic Ocean, from northern Labrador, Newfoundland, and Greenland to the Gulf of Maine, including the southern Gulf of St. Lawrence. ("Species Fact Sheet: Chionoecetes opilio (O. Frabricius, 1788)", 2013; Chuchukalo, et al., 2011; "Alaska Snow Crab (Chionoecetes opilio)", 2012; Tremblay, 1997)
Alaska snow crabs are benthic animals that are found at a wide range of depths, from 13 to 2187 m, with the majority of individuals found no deeper than 110 m. Temperature and substrate surfaced seem to be the most important factors in habitat determination; these crabs prefer to live on muddy bottoms, although smaller individuals prefer gravely substrate. They generally live at temperatures ranging from -1 to 5°C, but may be found at temperatures as high as 10°C. (Chuchukalo, et al., 2011; Comeau, et al., 1998; Tremblay, 1997; Wicksten, 2010)
Alaska snow crabs have a relatively round carapace with a short rostrum; when fully grown, the carapace width ranges from 40-160 mm. Males are typically much larger than females. Females have a maximum carapace width of only about 80-95 mm, and leg spans averaging 38 cm, while males may have a carapace width of up to 165 mm and leg spans of approximately 90 cm. On average, commercially caught males weigh 0.5-1.35 kg, while females weigh only 0.5 kg. Sexes can also be distinguished by claw size (males with larger claws) and abdominal flap shape: females have more rounded flaps while male flaps are more triangular. The carapace and legs are typically reddish in color and covered with small bumps or spikes; however, the carapace of crabs that are about to molt are dark greenish in color. The legs are whitish in color along the sides and bottoms, and these crabs are yellowish-white underneath. Alaska snow crabs are bilaterally symmetrical, with 5 pairs of limbs. The back 4 pairs of limbs are used for crawling along the sea floor, while the front pair are chelae (claws), used for catching and manipulating food. The first 3 pairs of walking legs are much longer than the chelipeds (claw-bearing appendages). The eyes are green or blueish-green. ("Species Fact Sheet: Chionoecetes opilio (O. Frabricius, 1788)", 2013; Comeau, et al., 1998; Fisheries and Oceans Canada, 2009; Hoenig, et al., 1994; "Alaska Snow Crab (Chionoecetes opilio)", 2012; Wicksten, 2010)
Fertilized eggs are carried on a female's pleopods until they hatch (dependent largely on water temperature, typically from April through late May), as much as 1-3 years after fertilization. Larvae are shrimp-like and free-swimming. After three molts (typically taking 3-5 months to complete), larvae become become known as megalops. During this stage, intermediate between larvae and adult, megalops settle to the sea floor and feed on detritus for about 30 days. After this, they molt again, becoming juveniles. Males and females go through three slightly different stages of development after the megalops phase. Males begin as juveniles, mature to adolescents (at which time their reproductive organs become functional), and finally reach adulthood, in which their larger claws are apparent. Females begin development immature, then progress to a prepubescent stage in which ovaries begin to develop, and finally become reproductively mature adults. Both sexes molt 1-3 times per year until sexual maturity and completing a terminal molt. (Fisheries and Oceans Canada, 2009; Hooper, 1986; Kogane, et al., 2007; "Alaska Snow Crab (Chionoecetes opilio)", 2012)
Alaska snow crabs are polygynandrous. In the presence of excess females, males mate with multiple partners. Females are multiparous (capable of laying eggs multiple times). In the absence of additional males, a female may store sperm in her spermatheca and use it to fertilize her eggs at a later time. As early as three weeks before mating, a male will hold a female, preparing to aid her through her terminal molt, also feeding and caring for her during this time. He will defend his position fiercely from other males. Females are very selective when choosing mates, fighting off unwanted suitors. After the female has molted, the male will transfer sperm to her spermatheca, where fertilization occurs. When the eggs begin to hatch (up to 1-3 years later, dependending on water temperatures), a male will assist in larval release by holding and waving the female around. Larvae are generally released in the spring, when there are high levels of phytoplankton in the water. Once released, the larvae are completely independent. (Elner and Beninger, 1992; Fisheries and Oceans Canada, 2009; Hooper, 1986)
Male Alaska snow crabs reach reproductive maturity at 4-11 years (8-13 molts) while females take only 4-6 years (8-10 molts) to reach sexual maturity. These crabs mate in the spring after migrating to shallower water; there is evidence that, at least in a lab setting, males are fertile year-round. Females carrying their first clutch of eggs during a given breeding season are known as primiparous. Multiparous females are those carrying a second or third egg clutch, either fertilized by a different male or by sperm stored from a previous copulation. After fertilization, females carry a clutch of 12,000-160,000 eggs for 1-2 years, until they are ready to hatch and water conditions are appropriate. 100% of females carry eggs each year. ("Species Fact Sheet: Chionoecetes opilio (O. Frabricius, 1788)", 2013; Elner and Beninger, 1995; Fisheries and Oceans Canada, 2009; Hooper, 1986)
Parental investment occurs pre-fertilization (males) and pre-hatching (females). Prior to fertilization, a male holds on to a female for up to three weeks, during which he protects her from predators, feeds her, and then helps her to molt before releasing his sperm; after this, there is no further male investment. After fertilization, a female carries fertilized eggs for 1-3 years before releasing larvae, during which time she provides protection to the eggs but does not provide any nutrients. After larvae are released, they are completely independent from both parents. (Elner and Beninger, 1992; Fisheries and Oceans Canada, 2009; Hooper, 1986)
The estimated maximum age for females is 12-13 years (approximately 5 years after the terminal molt), while the maximum age for males is estimated to be 13-19 years (4-5 years after the terminal molt). (Comeau, et al., 1998)
Alaska snow crabs are motile, using different types of locomotion at different stages in their life cycle. In the zoeal (early) larval stage, they use their appendages to swim. However, once zoeal larvae morph into megalops larvae, they settle on the sea floor. Juveniles and adults use their legs to crawl along the sea floor. These crabs migrate to shallower waters to breed and also are known to migrate to deeper waters as they age, in order to accommodate their changing preferences for prey, water temperature, and substrate types. Outside of breeding, males and females are solitary and segregated, with males found on muddy bottoms in deeper waters and females found on gravelly or rocky bottoms in shallower waters. ("Species Fact Sheet: Chionoecetes opilio (O. Frabricius, 1788)", 2013; "Alaska Snow Crab (Chionoecetes opilio)", 2012)
These crabs are not known to occupy a particular home range or defend territories, outside of males defending the immediate proximity of a female when preparing to mate. (Elner and Beninger, 1992)
It is thought that pheromones may play a role in mate attraction for this species. In general, crabs perceive their environments visually using compound eyes on stalks which can be retracted into sockets on the carapace for protection. Setae on their walking legs are used to perceive tactile cues, such as differences in substrate. (Hooper, 1986; Museum Victoria, 2002)
Adult Alaska snow crabs feed on sessile or slow moving benthic invertebrates including shrimps, brittle stars, polychaete worms, gammarid amphipods, bivalves, hydroids, sea stars, squids, and gastropods. They may also feed on algae, sponges, and bryozoans. In addition to feeding on live organisms, Alaskan snow crabs are scavengers, feeding on detritus and dead organisms such as fish and other crabs. Larval stages consume plankton. (Chuchukalo, et al., 2011; Lovrich and Sainte-Marie, 1997; Wieczorek and Hooper, 1995)
Alaska snow crabs may burrow into soft substrate to avoid predation. Their reddish brown coloration also helps to camouflage them against the ocean floor, and their sharp claws can deter potential predators. Larval stages are prey to fishes and, as they grow, juveniles and adults become prey to marine mammals and invertebrates as well. (Halflinger and McRoy, 1984; "Alaska Snow Crab (Chionoecetes opilio)", 2012)
Alaska snow crabs are scavengers to some extent, cleaning organic material from the ocean floor. They also serve as prey for larger organisms. They are known hosts to two species of amphipods: Gammaropsis inaequistyli and Ischyrocerus commensalis. These amphipods live on a crab's carapace, with no negative effect to their host. Alaska snow crabs may also host other polychaete, bryozoan, and hydrozoan epizoites, as well as endoparasites, particularly a dinoflagellate that causes Bitter Crab Disease. ("Alaska Snow Crab (Chionoecetes opilio)", 2012; Steele, et al., 1986; Wheeler, et al., 2007)
Alaska snow crabs are primarily important to humans as a source of food due to their flesh's sweet taste and high protein but low fat content. This species became more important to fisherman in the early 1980s when the king crab market crashed and fisherman needed another source of income. Alaska snow crabs were fished heavily until 1999, when they were declared overfished and more regulations were imposed. Since then, populations have been managed effectively, with fishing quotas reaching 89.9 million pounds in 2011/2012. This species has become better known and increasingly economically important with the popularity of the television series "Deadliest Catch" on the Discovery Channel, which documents the struggles of crab fishing on the Bering Sea. The series began airing in April 2005. ("Alaska Snow Crab (Chionoecetes opilio)", 2012; Toothman, 2012)
There are no known adverse effects of this species on humans.
Alaska snow crabs are abundant and populations are not currently threatened. Regulations put in place in the late 1990s and early 2000s are still in place, keeping fishing sustainable. Only adult males can be caught during the winter season, when mating and molting does not occur. A cap, set annually and based on the previous year's population, is also placed on the total number of crabs that can be harvested each season. ("Alaska Snow Crab (Chionoecetes opilio)", 2012; Toothman, 2012)
Justin Siegel (author), University of Michigan-Ann Arbor, Alison Gould (editor), University of Michigan-Ann Arbor, Jeremy Wright (editor), University of Michigan-Ann Arbor.
living in the Nearctic biogeographic province, the northern part of the New World. This includes Greenland, the Canadian Arctic islands, and all of the North American as far south as the highlands of central Mexico.
living in the northern part of the Old World. In otherwords, Europe and Asia and northern Africa.
Referring to an animal that lives on or near the bottom of a body of water. Also an aquatic biome consisting of the ocean bottom below the pelagic and coastal zones. Bottom habitats in the very deepest oceans (below 9000 m) are sometimes referred to as the abyssal zone. see also oceanic vent.
having body symmetry such that the animal can be divided in one plane into two mirror-image halves. Animals with bilateral symmetry have dorsal and ventral sides, as well as anterior and posterior ends. Synapomorphy of the Bilateria.
helps break down and decompose dead plants and/or animals
an animal that mainly eats meat
flesh of dead animals.
uses smells or other chemicals to communicate
having markings, coloration, shapes, or other features that cause an animal to be camouflaged in its natural environment; being difficult to see or otherwise detect.
a substantial delay (longer than the minimum time required for sperm to travel to the egg) takes place between copulation and fertilization, used to describe female sperm storage.
an animal that mainly eats decomposed plants and/or animals
particles of organic material from dead and decomposing organisms. Detritus is the result of the activity of decomposers (organisms that decompose organic material).
animals which must use heat acquired from the environment and behavioral adaptations to regulate body temperature
fertilization takes place outside the female's body
union of egg and spermatozoan
A substance that provides both nutrients and energy to a living thing.
a distribution that more or less circles the Arctic, so occurring in both the Nearctic and Palearctic biogeographic regions.
Found in northern North America and northern Europe or Asia.
offspring are produced in more than one group (litters, clutches, etc.) and across multiple seasons (or other periods hospitable to reproduction). Iteroparous animals must, by definition, survive over multiple seasons (or periodic condition changes).
A large change in the shape or structure of an animal that happens as the animal grows. In insects, "incomplete metamorphosis" is when young animals are similar to adults and change gradually into the adult form, and "complete metamorphosis" is when there is a profound change between larval and adult forms. Butterflies have complete metamorphosis, grasshoppers have incomplete metamorphosis.
makes seasonal movements between breeding and wintering grounds
eats mollusks, members of Phylum Mollusca
having the capacity to move from one place to another.
the area in which the animal is naturally found, the region in which it is endemic.
active during the night
an animal that mainly eats all kinds of things, including plants and animals
reproduction in which eggs are released by the female; development of offspring occurs outside the mother's body.
chemicals released into air or water that are detected by and responded to by other animals of the same species
photosynthetic or plant constituent of plankton; mainly unicellular algae. (Compare to zooplankton.)
an animal that mainly eats plankton
the regions of the earth that surround the north and south poles, from the north pole to 60 degrees north and from the south pole to 60 degrees south.
the kind of polygamy in which a female pairs with several males, each of which also pairs with several different females.
mainly lives in oceans, seas, or other bodies of salt water.
an animal that mainly eats dead animals
breeding is confined to a particular season
reproduction that includes combining the genetic contribution of two individuals, a male and a female
mature spermatozoa are stored by females following copulation. Male sperm storage also occurs, as sperm are retained in the male epididymes (in mammals) for a period that can, in some cases, extend over several weeks or more, but here we use the term to refer only to sperm storage by females.
uses touch to communicate
uses sight to communicate
animal constituent of plankton; mainly small crustaceans and fish larvae. (Compare to phytoplankton.)
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