The favorite food of blue crabs appears to be thin-shelled bivalves. When bivalves become depleted, however, cannibalism on juvenile crabs increases. Habitat Immediately after molting, crabs are vulnerable to predators because they are soft, so they often hide in Bay grass beds for protection. Young crabs use Bay grass beds for nursery areas, and crabs of all sizes forage for food there. Bay scientists have found that 30 times more young crabs were found in Bay grasses than in areas without grass.
Male crabs prefer lower salinity areas in the upper Bay and tributaries.
Females prefer the higher salinity of the lower Bay and the mid to lower tributaries, and many overwinter in southern Bay waters. Blue crabs, like other Bay creatures, are susceptible to summer's low oxygen conditions. Fueled by nutrient pollution from farms, sewage treatment plants, homes, and cars, algal blooms remove oxygen from the water, and crabs may be driven from low-oxygen areas. They may even die from low oxygen levels when trapped in crab pots under these conditions. The zoea are transported to the continental shelf, where they develop for a period of 30 to 45 days, through seven or eight distinct stages.