The Life Cycle of Blue Crabs

The blue crab, or Callinectes sapidus, is a species of crab native to the western Atlantic Ocean. It is named for the bright blue markings on its frontal region. The majority of its body is a dark brown color. The blue crab is especially abundant in the Chesapeake Bay area and is the official state crustacean of Maryland. The blue crab's life span is approximately three years. During this three-year period, the blue crab goes through a series of life stages beginning in the larva stage, then moving to the "first crab" stage, then to adulthood.

  1. Reproduction

    • Before mating, the female blue crab molts, shedding her hard outer shell.

      The female blue crab mates only one time during her life. Before mating, a pheromone is released in the female blue crab's urine that attracts male crabs. When the female crab selects a mate, the male crab carries her in order to protect her. The female is extremely vulnerable to predators during and before reproduction because she undergoes a process called molting. During molting, the female crab releases hormones that slowly detach her outer shell from her body. Then, she backs out of her shell, leaving her body soft and unprotected against predators. When the female's body is without the hard, outer shell, the male mates with her, releasing his sperm into receptacles on the female's body. The female continues to carry the sperm in these receptacles until she fertilizes her eggs some time later.

    Spawning

    • The female blue crab lays a cluster of eggs that appears sponge-like.

      Several months after mating, the female blue crab travels to waters with high salt levels and burrows in the mud. The female blue crab lays her eggs in a large cluster that is orange-yellow and sponge-like in appearance. This egg laying process lasts approximately two hours. A blue crab egg sac can contain as many as 2 million eggs. This egg sac stays attached to the female blue crab until the blue crab larvae emerge from it.

    Larvae

    • A blue crab larva measures only about 1/4 mm in length.

      When the blue crab larva emerges from its mother's egg sac, it measures about 1/4 mm. Because they are so small and light, they usually drift out to sea from the spawning area where they eat by filtering plankton and algae from the water, and grow. The young blue crabs must molt several times in order to have enough room to grow. Like the females during mating, the young blue crabs remove their hard outer shell during molting. After about one month, the young blue crab measures close to 1 mm in length, having quadrupled in size since it emerged from the egg sac.

    Young Blue Crabs

    • The young blue crab feeds on dead fish, underwater plant material and macroinvertebrates in the water.

      When the blue crab larva measures approximately 2.5 mm in length and appears more like an adult crab, it is referred to as in its "first crab" stage. The first crabs generally move to less salty waters. Young blue crabs feed on dead fish, underwater plant material, and benthic macroinvertebrates. Like the larvae, the first crabs go through a series of several molts in order to grow in size. This growth can continue for over a year before the blue crab reaches sexual maturity. The blue crab can molt up to twenty times from hatching to maturity.

    Adult Blue Crabs

    • Adult blue crabs are caught and eaten in places along the western Atlantic Ocean, including Maryland.

      Adult female blue crabs generally stay in waters of high salinity while adult male blue crabs prefer lower salinity levels. Male blue crabs continue to molt and grow throughout their lifetime while females stop growing after reproduction. Adult blue crabs can live one to three years after reaching sexual maturity. Adult blue crabs feed on clams, oysters, shrimp, underwater plants, fish and even other crabs.