Spawning peaks in Callinectes sapidus are closely associated with the region they inhabit. Unlike males, female C. sapidus mate only once in their lifetime, after the pubertal or terminal molt. When approaching this final molt, females attract males by releasing a pheromone in their urine. Male crabs compete for females and until molting occurs they will protect them. At this time mating occurs, and may last as long as 5-12 hours.

Mating System: polygynous

Callinectes sapidus is highly fertile, with females producing from 2 - 8 million eggs per spawn. When females are in their soft-shell stage immediately after molting, the males transfer their sperm to them for storage. The male then protects the female until her new shell hardens. The females will spawn two to nine months after mating, laying up to eight million eggs. Spawning season is from December to October, with a peak both in spring and summer. When females are ready to spawn, they fertilize the eggs with the stored sperm and place them on the tiny hairs of the appendages on their abdomen. The female is called a "sponge" or "berry" crab while she carries eggs like this. The blue crab's incubation time is 14-17 days, which is when the eggs are brooded. During this time females migrate to the mouths of estuaries so that larvae may be released into high salinity waters. Blue crab larvae have a salinity requirement of at least 20 ppt, and show poor survival below this threshold. The megalops (or larvae) pass through eight stages in about two months before they begin to resemble adult crabs. Usually only one or two crabs survive to become adults, and they have a lifespan up to three years.

Breeding interval: Males mate more than once, during each mating season, where females only mate once in their lifetime.

Breeding season: All year, but spawning occurs mostly during the months of December until October.

Range number of offspring: 2 million to 8 million.

Average number of offspring: 1.

Range gestation period: 14 to 17 days.

Average time to independence: 2 months.

Range age at sexual or reproductive maturity (female): 12 to 18 months.

Range age at sexual or reproductive maturity (male): 12 to 18 months.

Key Reproductive Features: year-round breeding ; gonochoric/gonochoristic/dioecious (sexes separate); sexual ; fertilization (Internal ); broadcast (group) spawning; ovoviviparous

Males tend to stay and protect the female until she has grown her hard shell after molting, but males have no interaction with the young. The female will protect the young while they hatch, but do not have a significant role in parenting. This is because there are so many eggs, and the maturing time is much too long for her to watch over them. They have to be independent from the time they hatch, which is why most of them will die before they reach the adult age.

Parental Investment: pre-fertilization (Protecting: Male); pre-hatching/birth (Provisioning: Female)