Mating and Life Cycle



Red rock crabs are dioecious and reproduce sexually. Mating occurs in summer when females are in the their soft shell state of molting. Females release a pheromone in their urine in order to attract males and stimulate their behavior. Males will often guard a female who is preparing to molt, by holding her under his abdomen sometimes for several weeks. He then guards her until her new exoskeleton grows in and is hardened.  Eggs are fertilized internally then extruded after 11 weeks. Females may carry from 172,000 to 597,000 eggs on the pleopods of the abdomen and looks like an orange spongy mass.


Growth through Molting

Larval development goes through 5 stages with one megalopal stage. Average larval development time for red rock crabs to the megalopal stage is about 100 days. The color of juveniles is often extremely variable ranging from pure white to a variety of color patterns including bands of brown and white or red and white stripes. Red rock

crabs grow to  carapace widths of 20cm in males and 16 cm in females. Life expectancy is about 8 years.


Growth of the red rock crab is achieved through a process called molting where the crab sheds its old shell for a new one. Young crabs may molt several times a year, but by the time they reach about four inches in width, the frequency is reduced to about once a year. Females usually molt in spring before the males so they can mate. Males usually molt during summer and early fall, but this can vary.


 All crustaceans have an exoskeleton containing the polysaccharide chitin. The exoskeleton surrounds the outside of the crab as well as some internal structures such as the gills. Parts of the exoskeleton are calcified and ridged providing the crab a suit of armor with hinged joints. The shell can not expand as the crab grows, so the crab must periodically molt. Secretion of hormones starts the molt cycle. A new cuticle forms, separates from the old cuticle, and some calcium is reclaimed from the old shell. The crab quits feeding before and relies on energy stored in the hepatopancreas. When the exoskeleton is shed, the crab backs out of its old cuticle through a fracture below the carapace called the molt line.


The crab at this time is extremely vulnerable to attack and predation. Males with a mate will often guard the female until their new exoskeleton is hardened. They hide buried in sand several days until the shell begins to harden. The new soft wrinkled cuticle fills with water and swells up to thirty percent. The crab then begins to feed to restore its energy reserves, fill out its muscles, and completely harden its shell, in a recovery process which may take up three months. It is during this recovery period that we find soft crabs with poor quality meat.


To learn about their interactions with other species click here!

To go back to the home page click here!