A Dive Into the Wondrous World of King Crabs

King Crabs
King crabs are hunted worldwide for their delicious meat. Read on to find out more about these unique and valued decapods.
Did You Know?
Despite their name, king crabs don't belong in the same group as true crabs. Other nominal 'crabs' that don't belong to the biological group are hermit crabs, horseshoe crabs, and porcelain crabs.

King crabs are part of a group of crab-like decapod (ten-legged) invertebrates known as Anomura or Anomala. The Anomura and the Brachyura (true crabs) together form the clade Meiura.

King crabs, also called stone crabs, are among the largest arthropods in the world, reaching leg spans of up to 1.8 m (6 ft) and weighing up to 20 lb. They are found in cold waters, and along with shrimps are one of the most commercially important arthropods: The red king crab is a universally desired seafood, due to its pleasant taste.

King crabs have five pairs of legs -- like crabs -- but unlike crabs, their fifth pair of legs is hidden beneath their carapace (the armor-like central part of their body) and is used for non-locomotive purposes. The two legs are used to clean the underside of their body and their embryos, or as a tool to transfer sperm during copulation.

Classification

Kingdom: Animalia
Phylum: Arthropoda
Subphylum: Crustacea
Class: Malacostraca
Order: Decapoda
Suborder: Anomura
Family: Lithodidae

King crabs share the suborder Anomura with other 'false crabs', such as hermit crabs and horseshoe crabs.

There are more than 120 species of king crabs, divided into 10 genera: Lithodes, Cryptolithodes, Glyptolithodes, Lopholithodes, Neolithodes, Paralithodes, Phyllolithodes, Rhinolithodes, Sculptolithodes, and Paralomis.

Among the three commercially important species of king crabs, the red and the blue king crab belong to the Paralithodes genus (P. camtschaticus and P. platypus, respectively), and the golden king crab belongs to the Lithodes genre (L. aequispinus).

Physical Description


Red King Crab

Although king crabs are capable of reaching truly massive (for decapods) proportions, most species do not exceed 1 foot in width and weigh less than 10-15 lb. The largest king crabs -- the red king crab and the blue king crab -- can reach widths of up to 1.8 meters.

Habitat

Like true crabs, king crabs are found in temperate and cold waters. They are plentiful in the North Pacific, found in sizable numbers around Canada, Japan, Russia and Alaska.

King crabs carry out annual migrations: some, like the red king crab, migrate inland and far into the sea, while some, like the golden king crab, only migrate between deep and shallow waters (vertically) while not changing their location relative to the coast.

Diet

King crabs primarily feed on detritus from the upper layers (organic matter from dead and decaying organism), other smaller crustaceans (sometimes including other king crabs), and molluscs. The diet of king crabs depends largely on the particular species and its habitat -- the diet of a red king crab at a depth of 100 meters may differ drastically from that of a golden king crab at a depth of 300 meters.

Life Cycle


King Crabs in Early Developmental Stage

Embryos are sheltered in the mother's tail flaps until they hatch. They hatch in the form of swimming larvae, although they are highly dependent on the prevalent direction of the current and tide for locomotion. After molting several times, the larvae transform into crabs, albeit much smaller than adults (smaller than a dime!). During this transformation, they start to frequent the depth they would populate further in their lives; juvenile red and blue king crabs are generally found around 100-200 feet in, while the deeper-dwelling golden king crabs are found about twice as much deep.

Initial cycles of molting also build up the all-important exoskeletons -- the 'shells' -- of young crabs. Due to their rapid development, molting in crab larvae is much more frequent than in adults. They reach sexual maturity around 4-5 years in, after which molting becomes an annual, or even -- in case of males of nearly all species -- a biennial event.

Molting is required before a female can mate, but males can mate without having undergone a molt. The molting-mating cycle is intertwined with their migratory patterns. Crabs migrate towards the shore at the end of winter, and the emergence of new hatchlings coincides with spring.

King Crabs As Food


King crabs are much valued as seafood, and red king crabs in particular are highly prized. In the US, Alaska accounts for an overwhelming majority of king crab fishing, while Russia and Norway contribute significantly in the global trade.

The prime target, the red king crabs, are found in the Bering Sea and on the nearby islands. The heavy equipment required to catch these giants, combined with the notoriously unpredictable and dangerous weather in this area, makes this a risky trade. Still, the lure of the highly profitable deal means that this is a bustling business.

Invasive Species?

Recently, king crabs were found to have acclimatized to harsh Antarctic waters by taking advantage of the increasingly warm currents flowing under the ice. This could prove to be catastrophic for the endemic wildlife, and for the precariously balanced web of predation. The Antarctic marine ecosystem doesn't have a predator capable of cracking the tough shells of these crabs, giving them an unopposed run for the post of the unassailable apex predator.

Ironically, there is concern over the dwindling number of these crabs in the northern hemisphere due to overfishing, while on the other hand, their unprecedented presence in the southern hemisphere is ringing alarm bells!