Blue Crabs

     Blue crabs are good eating, but they are far more than that.  Though they usually are difficult to see in the larger bodies of water they inhabit, these crustaceans, which are related to shrimp and lobsters, are an attractive, interesting form of life that lives in brackish to salt water along the Atlantic and Gulf Coasts from Nova Scotia to the Gulf of Mexico, the Caribbean Islands and down the South American Atlantic Coast to northern Argentina.  They are also in most of the Chesapeake and Delaware Bays, and back waters behind barrier islands along the Atlantic Coast.  They are named for the blue legs of adult blue crabs, although mature females have red tips on their blue pincers, making them even more attractive. 
     The top shells of blue crabs reach nine inches across upon maturity and are mottled brown for camouflage on the bottoms of large waters.  Those shells have several sharp points on their edges to defend their owners from predation to some extent.  The bottom shells of blue crabs are much lighter than the top ones because their was no habitat pressure on the bottom ones to blend in to their surroundings since they aren't visible anyway. 
     Crab shells usually are hard, but crabs, like many invertebrates, have exoskeletons, meaning their hard parts are on the outside for defense.  To be able to grow, crabs, and other crustaceans, have to shed their hard shells.  But there is another, soft, shell underneath that grows and allows the growth of the crabs' bodies.  Those crabs are called soft-shelled and they hide and don't eat until their new shells are hard enough to defend their owners.  Each crab sheds its shell several times in its lifetime.   
     Each crab has ten legs, of which the back pair are paddle-like for swimming and the front pair are pincers for picking up food and defense.  Crabs use their other legs for walking sideways on the bottoms of waters. 
     Blue crabs are omnivores that live on the bottoms of larger, brackish bodies of water.  They ingest mollusks, including oysters, plant material and carrion, all items they can easily get a hold of.  They even bury themselves in the mud of those bottoms during winter to protect themselves from cold and predation. 
     Unfortunately, blue crabs have declined in numbers because of over-harvesting and habitat loss.  But they are making a comeback in many parts of their natural range, and they have been introduced to other parts of the world, including in the Mediterranean and around Japan, for example.
     Blue crabs have a rather complex reproductive system.  Males live in fresher water while females live in saltier water, which means there is less competition for food between the genders, meaning more of them could survive with a greater amount of food for each gender.  Blue crabs spawn in the high-salt  areas of their habitats.  Each female spawns once in her lifetime, spawning up to two million tiny eggs in a mass that is attached to her abdomen for the eggs' protection. 
     Baby blue crabs grow in several stages after hatching and leaving their mothers' abdomens.  The first is zoeae, which are tiny, float on the surface of the ocean and feed by filtering tiny edibles from the water.  Megalops is the next stage, which swims freely near the bottom.  Finally, each individual is crab-like in shape as it gets older and bigger.  And these crabs seek brackish water rather than salt water as they mature. 
     But blue crabs are preyed on by many kinds of predators in each stage of their lives, which means very few mature and reproduce.  Adult crabs, the ones we are most likely to experience, are eaten by large fish, sea turtles, certain kinds of diving ducks, raccoons, a variety of herons and many other kinds of predators. 
     Blue crabs are beautiful, intriguing critters that deserve protection from overharvesting and habitat loss.  They can be taken for human food, but only in a way that they won't be in danger of extinction.
When along the seacoast or an estuary, look for these lovely crabs.