Crab 101
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Reproduction and Lifecycle


     The Paralithodes camtschatica are dioecious, meaning separate sexes, and have external fertilization.1  External fertilization is possible for this species because they are aquatic and able to transfer sperm outside the body, without risk of the sperm to dry out.  Also, the females are polygynous, only mating once a year.2

Grasping male and female pair.  -photo by Jan Haaga. The reproduction cycle of the red king crab begins with the females attracting the males by pheromones after their eggs are hatched.  Once the male finds the female, he then attaches to her, grasping her by the claws into a face-to-face position.  They stay connected until the female molts her carapace and creates new eggs.  Once the female is in her soft-shell state, mating can then occur.3  The male then spreads his spermatophores over the females pleopods by his fifth pair of legs, the eggs being released immediately after mating.  The female can also store the sperm if the eggs are not ready to be released yet. 


Red king crab egg clutch.    Once the eggs are released, they are fertilized when passing over the spermatophores, then held in a spongy mass between her abdominal flap and body, on her pleopods.4  An average clutch size for the female crab is between 150000-400000 eggs.5  Here they stay attached for about a year, the female keeping them healthy, by “waving” water over them, and protected, sheltered from predators.6  Then once the eggs are hatched, the cycle begins again.



The lifecycle of the Paralithodes camtschatica has three main stages of development: 1. Zoea, 2. Megalops, 3. the Adult decapod.

Crab zoea. -photo by Celeste Leroux    The life of a red king crab begins inside the egg, where 2 stages of larval development occur.1  Then, the eggs hatch into the newborn king crab, called zoea, and act as free swimming organisms, carried along by the ocean currents.  The zoea does not resemble the adult decapod, differing from the true crab form by having a tail, or telson, and also having feathered limbs instead of clawed limbs.2  This all changes as it undergoes metamorphosis, having 4 developmental stages during the first two to four months, molting up to five times, each time increasing its size, form, and functions.3  The zoea are adapted for swimming, yet do not have much power against the ocean currents, thus being swept away from the “parental grounds” to an unknown destination, in hopes they end up in a good habitat, full of food and away from much predation.4   

Juvenile red king crab.    The next stage of the red king crab is the megalops stage, where the feathered limbs are now clawed limbs and the juvenile crab now more closely resembles the adult.  Still the abdomen is prominent and the crab is about an eighth of an inch.  Megalops develop a benthic, or bottom dwelling lifecycle5 and also develop a special colonial characteristic called podding, when around the age of 2.  In podding, the juvenile crabPod of red king crab.  -photo by Braxton Dew form large groups of individuals at shallow depths, used for protection.  This is good system for protection because the megalops are still vulnerable.6  Because they are not highly armored like the adult, staying in these massive groups makes the predator have to find them and also saves many from predation because the predator can only eat so many.7 Also these big groups help during the molting season, the time the crab is most susceptible to predation.8 The megalops stage can last up to 4 years and then the crab passes onto adulthood.


Adult king crab.  -photo by Ed Cheung    Adult red king crabs now migrate to the depths of the ocean, to depths of about 200 meters or below.  The adult is heavily armored with a hard calcified carapace and have sharp spines extending from the shell. (9.3)  The adult decapod has few predators, it is free to roam the ocean floor.  Interesting fact of the adults is that they are segregated by sex when in their deep environment, and only do they then come together for the mating season in the spring.  (9.2)  The adult keeps growing and growing, molting every time, their main limit now on life being over-fishing.9