How do the crab reproduce?

When male and female crabs reproduce, they assume the doubler position, which is when the male carries the female. Mating lasts about five-and-a-half hours, but the crabs may stay in this position for up to three days afterward. The female stores the male's sperm on the underside of her abdomen, where it will be used for two more spawnings that occur within her three-year lifespan. The females migrate to slightly saltier waters after mating and attach between 100,000 to two million eggs to the sperm stored under the abdomen. The incubation period lasts about two weeks, until the crab larvae hatch and are released into the ocean to fend for themselves. For the next 40 days, the crab larvae continue to grow until they reach the adult crab stage.

Source: http://www.ehow.com/how-does_4781305_crabs-reproduce.html