By February in the lower Chesapeake Bay, mature female blue crabs are buried in the sediment, waiting for the arrival of summer to hatch their eggs and continue a life cycle that takes about two years to complete. A winter dredge survey helps determine blue crab populations. FALL — Migration After mating, a fertilized female feeds in a tributary until fall, when she migrates to saltier waters in the lower bay. She holds the male’s sperm in a special organ, using it to fertilize her eggs after she relocates to the mouth of the bay. Males do not migrate. Male abdomen shaped like the Washington Monument Female abdomen shaped like the Capitol dome Young egg Underside of female with eggs Mature egg SUMMER — Lower bay, ocean Eggs hatch into larvae called zoea, which float in and out of the mouth of the bay for more than a month, eating zooplankton and molting seven times as they grow. SUMMER The zoea develops into a megalopa, a more advanced larval stage that lasts for about a week. It uses flood tides to drift into the bay and then settles into struc-tured habitats, such as sea grasses. Atlantic Ocean DEL. N.J. PENN. MARYLAND D.C. Chesapeake Bay PotomacRiver Lower bay Upper bay DelawareBay SUMMER to FALLThe megalopa molts into a tiny juvenile crab, which can either swim or walk on the bay bottom, using sea grasses or shoreline shallows as refuge. Once it grows to about ¾ inch, it rides flood tides into the shallow nursery habitat of a tributary. It molts 16 to 20 times before maturing and mating the following summer. SUMMER — Lower bay, ocean Females carry a spongy mass underneath them with an average of 3 million eggs, which they release in the lower bay. Females can produce several such sponges each year for a few years. Of the tens of millions of eggs that a female produces during her lifetime, only about two eggs will lead to mature crabs. WINTER Adult and juvenile crabs bury themselves in sediment to wait out the cold weather. Scientists conduct a winter dredge survey to assess the crab population. 1 SUMMER — Bay tributaries When an immature female is about to become an adult, she releases chemi-cals to attract males. A male will cradle her for a couple of days until she sheds her exoskeleton, or molts. After her molt, they mate. She will mate only once, during this brief period in her lifetime. VIRGINIA N.C. Flood tides carry larvae into the lower bay, where they settle to become tiny crabs. After about two months, juveniles ride flood tides into the upper bay. Females swim along the bottom to the lower bay in the fall. ’90 ’95 ’00 ’05 ’10 ’14 POPULATION IN MILLIONS Female spawning-age crabs in the bay 0 50 100 150 200 215 70 Target population Population depleted 2 3 4 5 6 7 Life cycle of the blue crab VA. MD. VA.

SOURCE: Smithsonian Environmental Research Center, Chesapeake Bay Stock Assessment Committee, Maryland Department of Natural Resources .