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Blue Crab

Fast Facts:

If the apron of a blue crab looks like the Washington Monument then it’s a mature male. If the apron of a blue crab looks like the dome of the Capitol Building then it’s a mature female.

Size Adults can grow up to 9 inches.
Habitat Blue crabs are distributed throughout the U.S. Atlantic and Gulf coasts. Blue crabs can be found in freshwater areas where salinity is 0 to the ocean where the salinity is full strength (32+ ppt). Males are often found in the upper reaches of the Bay while females are typically found further downstream and down-Bay where salinities are higher. Submerged aquatic vegetation (SAV) areas are important nursery habitats for juvenile blue crabs for two reasons: 1) SAV provides refuge from predators. Crabs that are molting are less likely to be spotted and eaten in SAV than in shallow marsh areas with no SAV.  2) SAV provides a large abundance of prey.
Reproduction Mating occurs from June to October in the mid-Bay regions. Females still soft from molting, mate with males. Males stay behind to spend the winter in the muddy bottoms of the Bay. Females migrate towards the mouth of the Bay to release the fertilized eggs (750,000 to 8 million eggs) that are developing in her apron. Newly developed eggs are usually a golden orange but later turn black as the eggs near hatching. Females can be found near the mouth of the Bay from May to October when small zoeae larvae begin to hatch from the eggs. After a series of molts, the second larval form, the megalopa, is produced. Because of the megalopa’s appearance, it is often mistaken for a tiny crayfish or lobster. The megalopa begins to move along the bottom while making its migration further up the Bay. During this migration, several more molts occur. With each molt, the megalopa slowly transforms into the identifiable shape of a blue crab. When the crab reaches 12 to 16 months, it is approximately 5 inches and is ready to mate. Blue crabs generally only live for 3 years.
Feeding Adult blue crabs generally feed on clams, soft-shelled crabs, SAV, fishes, oysters and anything else they can successfully capture or scavenge. They will even eat other blue crabs that are still soft from a recent molt!  Blue crab larvae and post-larvae probably feed on rotifers, worm larvae, copepod nauplii and adult copepods.
Predators Small fishes and jellyfishes feed on the larvae. Larvae are often consumed by grass shrimp (Palaemonetes pugio), sand shrimp (Crangon septemspinosa), juvenile blue crabs and juvenile fishes. Adults are consumed by American eels (Anguilla rostrata), striped bass (Morone saxatilis), Atlantic croakers (Micropogonias undulatus), cobia (Rachycentron canadum), red drum (Sciaenops ocellatus), black drum (Pogonias cromis), oyster toadfish (Opsanus tau), sandbar sharks (Carcharhinus plumbeus), bull sharks (Carcharhinus leucas), cownose rays (Rhinoptera bonasus), speckled/spotted trout (Cynnoscion nebulosus), weakfish (Cynoscion regalis), catfish (Ictalurus spp.), gars (Lepisosteus spp.), largemouth bass (Micropterus salmoides), loggerhead turtles (Caretta caretta), Atlantic Ridley turtles (Lepidochelys kempi), herons and egrets (family: Ardeidae), various diving ducks and raccoons (Procyon lotor).
Description Blue crabs have a brilliant blue color on their front claws (tips are red on females) with an olive or bluish-green carapace. They have a pair of paddle shaped legs that are excellent for swimming. Crabs can also be identified by the nine marginal teeth behind each eye, with the last pair of teeth ending in a sharp spine.
Additional Information Saving the Blue Crab

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