Geographic Range
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.
- Biogeographic Regions
- nearctic
- palearctic
- Other Geographic Terms
- holarctic
Habitat
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.
- Habitat Regions
- polar
- saltwater or marine
- Aquatic Biomes
- benthic
Physical Description
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.
- Other Physical Features
- ectothermic
- bilateral symmetry
- Sexual Dimorphism
- male larger
- sexes shaped differently
Development
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.
- Development - Life Cycle
- metamorphosis
Reproduction
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.
- Mating System
- polygynandrous (promiscuous)
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.
- Key Reproductive Features
- iteroparous
- seasonal breeding
- gonochoric/gonochoristic/dioecious (sexes separate)
- sexual
- fertilization
- oviparous
- sperm-storing
- delayed fertilization
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.
- Parental Investment
-
pre-fertilization
- provisioning
-
protecting
- male
-
pre-hatching/birth
-
protecting
- female
-
protecting
Lifespan/Longevity
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).
Behavior
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.
Home Range
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.
Communication and Perception
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.
- Other Communication Modes
- pheromones
Food Habits
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.
- Primary Diet
-
carnivore
- eats non-insect arthropods
- molluscivore
- vermivore
- eats other marine invertebrates
- scavenger
- omnivore
- planktivore
- detritivore
- Animal Foods
- carrion
- mollusks
- aquatic or marine worms
- aquatic crustaceans
- echinoderms
- other marine invertebrates
- zooplankton
- Plant Foods
- algae
- phytoplankton
- Other Foods
- detritus
Predation
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.
- Anti-predator Adaptations
- cryptic
Ecosystem Roles
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.
- Ecosystem Impact
- biodegradation
- Gammaropsis inaequistyli (Class Malacostraca , Phylum Arthropoda )
- Ischyrocerus commensalis (Class Malacostraca , Phylum Arthropoda )
- Alcyonidium gelatinosum (Class Gymnolaemata , Phylum Bryozoa )
- Hydractinia (Class Hydrozoa , Phylum Cnidaria )
- Hematodinium sp. (Class Syndiniophyceae , Phylum Dinoflagellata )
- Polychaete worms (Class Polychaeta , Phylum Annedlida )
Economic Importance for Humans: Positive
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.
- Positive Impacts
- food
Economic Importance for Humans: Negative
There are no known adverse effects of this species on humans.
Conservation Status
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.
Additional Links
Contributors
Justin Siegel (author), University of Michigan-Ann Arbor, Alison Gould (editor), University of Michigan-Ann Arbor, Jeremy Wright (editor), University of Michigan-Ann Arbor.
- Nearctic
-
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.
- native range
-
the area in which the animal is naturally found, the region in which it is endemic.
- Palearctic
-
living in the northern part of the Old World. In otherwords, Europe and Asia and northern Africa.
- native range
-
the area in which the animal is naturally found, the region in which it is endemic.
- holarctic
-
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.
- polar
-
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.
- saltwater or marine
-
mainly lives in oceans, seas, or other bodies of salt water.
- benthic
-
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.
- ectothermic
-
animals which must use heat acquired from the environment and behavioral adaptations to regulate body temperature
- bilateral symmetry
-
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.
- metamorphosis
-
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.
- polygynandrous
-
the kind of polygamy in which a female pairs with several males, each of which also pairs with several different females.
- iteroparous
-
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).
- seasonal breeding
-
breeding is confined to a particular season
- sexual
-
reproduction that includes combining the genetic contribution of two individuals, a male and a female
- fertilization
-
union of egg and spermatozoan
- external fertilization
-
fertilization takes place outside the female's body
- oviparous
-
reproduction in which eggs are released by the female; development of offspring occurs outside the mother's body.
- sperm-storing
-
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.
- delayed fertilization
-
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.
- diurnal
-
- active during the day, 2. lasting for one day.
- nocturnal
-
active during the night
- motile
-
having the capacity to move from one place to another.
- migratory
-
makes seasonal movements between breeding and wintering grounds
- solitary
-
lives alone
- visual
-
uses sight to communicate
- tactile
-
uses touch to communicate
- chemical
-
uses smells or other chemicals to communicate
- pheromones
-
chemicals released into air or water that are detected by and responded to by other animals of the same species
- visual
-
uses sight to communicate
- tactile
-
uses touch to communicate
- chemical
-
uses smells or other chemicals to communicate
- carrion
-
flesh of dead animals.
- zooplankton
-
animal constituent of plankton; mainly small crustaceans and fish larvae. (Compare to phytoplankton.)
- phytoplankton
-
photosynthetic or plant constituent of plankton; mainly unicellular algae. (Compare to zooplankton.)
- detritus
-
particles of organic material from dead and decomposing organisms. Detritus is the result of the activity of decomposers (organisms that decompose organic material).
- cryptic
-
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.
- biodegradation
-
helps break down and decompose dead plants and/or animals
- food
-
A substance that provides both nutrients and energy to a living thing.
- carnivore
-
an animal that mainly eats meat
- molluscivore
-
eats mollusks, members of Phylum Mollusca
- scavenger
-
an animal that mainly eats dead animals
- omnivore
-
an animal that mainly eats all kinds of things, including plants and animals
- planktivore
-
an animal that mainly eats plankton
- detritivore
-
an animal that mainly eats decomposed plants and/or animals
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