Tag Archives: Red King Crab

Biology and Life Cycle of the King Crab

Researchers do not fully understand the biology and life cycles of any of the king crab species, but red king crabs have been the most extensively researched. Scarlet king crabs live very deep where they are challenging to study, so biologists know little about their life history. The following describes the life cycle of the red king crab, except where noted.

Before mating, a female king crab must molt by shedding her shell. A few weeks before molting, the female begins releasing pheromones into the water, signaling to males in the area she will soon be ready to mate. When the male finds the female, he grasps her first pair of legs in his claws and holds her facing him for several days. Meanwhile, the female begins to molt. Her old shell separates, and it takes her only 15 minutes to climb out of the shell. A new, soft carapace now covers her, and she absorbs water and swells, making her appear larger.

After the female has molted, the male turns her upside down and places her beneath him. He inserts his ventral surface under her abdominal flap, where he releases strings of sperm. The female releases her ova from paired openings on the underside of her second walking legs. As soon as each ovum is exposed to seawater, a sac forms around it, and the sperm fertilizes the ovum. This process can be repeated several times over the next few hours. Once he finishes, the male releases the female and shows no further interest in her.

The female incubates the eggs under her tail flap for eleven to twelve months. A female king crab, depending on her species and her age, will carry between 45,000 and 500,000 eggs. Blue king crabs have bigger eggs and a lower fecundity than red king crabs. The female releases her larvae between February and April over a period of approximately 29 days. When they first hatch, the larvae resemble tiny shrimp. The larvae pass through four zoeal instar stages, each lasting between ten days to two weeks, and they finally transition into the stage which resembles a small crab. The larvae eat both phytoplankton and zooplankton and become more carnivorous as they age. When the young crabs finally settle to the bottom, they are about the size of a dime and are very susceptible to predation. The larvae settle from July through early September.

Red King Crab Pod –NOAA

Young king crabs migrate to depths of 150 ft. or deeper. Red king crabs are known to form giant pods, and biologists believe they assemble in these pods to protect against predators. Other king crab species have not been observed forming pods. Around age four or five, king crabs move to shallower water during the spring migration to join the adults.

Red king crabs spawn every year, but blue king crabs reproduce every two years. After spawning, adult red king crabs settle at depths between 90 and 200 ft. for the remainder of the year.  Red king crabs seem to prefer soft sand. Red and blue king crabs are known as shallow-water species, while golden king crabs settle at least 300-feet deep, and scarlet king crabs seek out even deeper habitats.

King crabs are opportunistic feeders, and they eat sponges, barnacles, sand dollars, brittle stars, sea stars, worms, clams, mussels, snails, crabs, and other crustaceans. What they eat depends on their size and available prey species.

King crabs have several predators, including fishes such as Pacific cod, halibut, sculpins, and yellowfin sole. A king crab will prey upon a smaller king crab, and octopuses and sea otters also eat king crabs. Nemertean worms consume king crab embryos.

King crabs are also susceptible to parasites and many diseases. The Rhizocehpalan barnacle invades a king crab’s internal tissues, producing an immunosuppressive agent to cloak its presence. The barnacle eventually castrates the crab and stunts its growth. Liparid fish parasitize king crabs by depositing their eggs in the gill chambers of the crabs. The egg mass interferes with respiration and can lead to death.

Biologists estimate king crabs can live twenty to thirty years.


Robin Barefield is the author of three Alaska wilderness mystery novels, Big Game, Murder Over Kodiak, and The Fisherman’s Daughter. To download a free copy of one of her novels, watch her webinar about how she became an author and why she writes Alaska wilderness mysteries. Also, sign up below to subscribe to her free, monthly newsletter on true murder and mystery in Alaska.

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Alaska King Crab

The family Lithodidae, known as the stone or king crabs, has 16 genera and 95 known species. Four species are commercially fished in Alaskan waters. These are the red king crabs (Paralithodes camtschaticus), the blue king crabs (Paralithodes platypus), the golden king crabs (Lithodes aequispinus), and the scarlet king crabs (Lithodes couesi). Of these, red king crabs are the most abundant and extensively studied species. Scarlet king crabs are much smaller than the other three species, and because they live in very deep water, researchers know little about their life cycle. Since scarlet crabs are smaller than red, blue and golden king crabs, they are not commercially significant.

Red King Crab

 All four species have different but overlapping distributions throughout the Gulf of Alaska, Bering Sea, and the Aleutian Islands. Red king crabs range from British Columbia to Japan and north to the Bering Sea. They are most abundant in Bristol Bay and the Kodiak Archipelago. Red king crabs exist from the intertidal zone to 600 ft. (183 m) or deeper.

King crabs receive their common names from the color of their carapaces. All king crabs are decapods, meaning they have ten legs. Unlike brachyuran crabs, which are considered “true” crabs, king crabs are not symmetrical but have an asymmetrical abdomen, asymmetrical first pair of walking legs, and modified fifth pair of walking legs. Biologists think king crabs are more closely related to hermit crabs than they are to brachyuran crabs such as Dungeness crabs.

Blue King Crab

King crabs have tails or abdomens which are fan-shaped and are tucked underneath the rear of the shell. Of their five pairs of legs, the first is their claws or pincers. The right claw is usually the largest. The next three pairs are their walking legs, and the fifth pair of legs are small and usually tucked underneath the rear of their carapace. Adult females use these specialized legs to clean their embryos, and males use them to transfer sperm to females during mating.

A crab’s skeleton is its external shell made of calcium. In order to grow, a crab must periodically shed and grow a new, larger carapace, during a process called molting. Juveniles molt frequently during their first few years but less often when they reach sexual maturity at the age of four or five years. Adult females must molt in order to mate, but a male does not need to shed his shell to mate. Adult female red king crabs molt and mate once a year, but males often keep the same shell for two years. King crabs shed their shells by absorbing water, causing the shell to crack.

Golden King Crab

Red king crabs are the largest of the king crab species. Blue crabs are the second largest, and golden king crabs are the third largest. Female red king crabs reach a maximum weight of 10.5 lbs. (4.8 kg), and males grow as large as 24 lbs. (10.9 kg). A large male has a leg span of nearly five ft. (1.52 m) and a carapace as long as 11 inches (27.9 cm). King crabs can live 20 to 30 years.

Scarlet King Crab

Red, blue, and golden king crabs migrate annually from nearshore to offshore. They migrate to shallow water in the late winter or early spring where the female’s embryos hatch. Adult females and some adult males then molt, and mating occurs before the crabs return to deep water. Once they have mated, adults segregate by sex. Biologists studying male red king crabs near Kodiak noted some males migrate up to 100 miles (161 km) round-trip annually, and at times, they move as fast as a mile (1.6 km) per day. While depth ranges and habitats overlap, red, blue, gold, and scarlet king crabs rarely co-exist.

In my next post, I will cover the lifecycle and feeding habits of king crabs as well as the status of king crab populations and the threats they face.


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Robin Barefield is the author of three Alaska wilderness mystery novels, Big Game, Murder Over Kodiak, and The Fisherman’s Daughter. To download a free copy of one of her novels, watch her webinar about how she became an author and why she writes Alaska wilderness mysteries. Also, sign up below to subscribe to her free, monthly newsletter on true murder and mystery in Alaska.

Mystery Newsletter

Sign Up for my free, monthly Mystery Newsletter about true crime in Alaska.