The Blue Crab and Maryland Crabcakes

The blue crab has made the state of Maryland famous. Who would come to Maryland without eating a famous Maryland crabcake? The crab is both a formal and informal symbol of the State of Maryland. The blue crab, Callinectes sapidus, lives in estuaries along the eastern coasts of North and South America. Crabs are found in sheltered coves and bays in the brackish water of estuaries and mouths of rivers, especially muddy shores and bottoms. The crab prefers brackish water, a mixture of fresh and salt water, containing some areas of sea grasses or weeds. Like most large crustaceans, the blue crab has a hard shell, or carapace. The carapace ranges in color from olive, brown, or reddish, to varying shades of blue and is made of chitin that is hardened with calcium. The eyes, which rest on short stalks, are compound eyes, like those of insects. Stalked compound eyes permit the crab to see even the smallest of movements in almost all directions.

As a true crab, the blue crab has five pairs of legs. In the male, these legs have a bluish-grey color and are the source of the common name "blue crab". In the female, however, the tips of the legs are reddish-orange. (http://www.aqua.org/animals/species/bluecrab.html) The first pair of legs ends in sharp claws. The claws are used to capture and hold food. They are also used for protection and may hold onto a predator with a painful grip. If threatened or trying to escape from a predator, the crab can allow the claw to drop or break off and then grow another. The crab will regrow this claw through a growth process called molting. During molting, all of the hard outer shell is lost. A new softer shell just under this swells and hardens in the seawater to a larger size. Molting starts as a break in the shell at a line just below the crab's eyes and on either side of its mouth and extends all the way to the points of the shell. This break opens the shell so that the crab may back out. Each time that the crab molts, any missing limb grows a little larger until it is fully formed again. (http://www.chesapeakebay.net/blue_crab.htm)

Mating takes place from June through October. During courtship, the male, or "jimmy" puts on a dance and show with much waving of his pair of swimming paddles. The female, also called a "sook," is usually one and a half years old at this time, but the age of the male varies. The female must be in the "soft-shell" stage to mate. To reach this stage, she must molt. A few days before she sheds her shell, the male moves over the female and holds her beneath him. A male carrying a female in this manner is called a doubler. The female is then released so that she may molt. At this time the crab is extremely vulnerable and weak. Most try to hide in protected areas such as marshes, grass beds, and old car tires. It is during this critical period, before the new shell hardens, that mating occurs. The male protects the molted female.(Adeleik, 277.)

After a couple of days, the female's shell hardens and she separates from the male. He leaves to try to mate again. The female does not mate again. She moves closer to the ocean and burrows in the mud for the winter. The following summer the sook deposits up to two million fertilized eggs to the underside of her apron. She is now called a "sponge crab" because the bright orange eggs look like a sponge. Over a two week period, during which the eggs are brooded, they develop into larvae and change to yellow and finally brown before they hatch. Of the many eggs that hatch, as few as two may live to reproduce. The larvae are only 2 millimeters (0.1 inches) in size. They spend the first stages of their lives as part of a vast community of drifting plants and animals called plankton. The small crabs do not look like their parents and go through a rapid series of molts, every three to five days, to accommodate their growing bodies. The first larval stage is called a zoea.

After many molts the crab's body changes shape and the second larval form, the megalops, is achieved. The megalopa stage looks very similar to a tiny lobster or crayfish. As the young approach 1.3 centimeters (0.5 inches) wide, molting takes place every ten to fifteen days, and crabs 10 centimeters (4 inches) wide or larger shed their shells every twenty to thirty days. The male crab continues to molt throughout its lifetime at a slower rate as it gets larger. The female stops molting upon maturity, after twenty-one molts. The rigid carapace and formidable claws of the crab make for a hardy animal that is well adapted to its life in the water. The blue crab is a fascinating animal. It is no wonder that scientists named it Callinectes sapidus, which translates to beautiful swimmer. (http://www.acnatsci.org/research/anserc/bluecrab.html)

Blue crabs serve as both predator and prey in the benthic and planktonic food webs of the Chesapeake Bay. They serve as food in their postlarval and juvenile stages for eel, drum, spot, Atlantic croaker, striped bass, sea trout and catfish. Some sharks and cownose rays feed on juveniles and larger crabs. The Atlantic Ridley sea turtle, an endangered species, migrates to the Bay every summer to find its preferred food, the blue crab. Cannibalism of young blue crabs by larger crabs is common and may regulate population abundance. Adult blue crabs are omnivorous: they feed on bivalves, crustaceans, fish, annelids (such as marine worms), plants, detritus, and nearly any food item they can find (including dead fish and plants). The favorite food of blue crabs appears to be thin-shelled bivalves. When bivalves become depleted, however, cannibalism on juvenile crabs increases. The blue crab is a scavenger and eats edible wastes in the water. Crabs are also predators. They feed on clams, oyster and mussel beds, as well as some types of marsh grasses and seaweeds. (http://www.mdsg.umd.edu/crabs/about.html)

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. (http://www.bayjournal.com/97-06/crab1.htm)

The blue crab supports one of the Chesapeake Bay's largest and most valuable fisheries. They also support a way of life. Those who live in Bay country have come to depend on the blue crab for food, for income, for fun. For decades blue crab harvests have risen and fallen, most likely in concert with climate and other factors we still do not fully understand. Since the 1990s, however, concern has grown that pressure on the blue crab - both commercial and recreational - may be too high. State agencies such as the Maryland Department of Natural Resources and the Virginia Marine Resources Commission, along with bi-state groups such as the Bi-State Blue Crab Advisory Committee and the Chesapeake Bay Stock Assessment Committee, have focused their efforts on trying to understand the current status of (Hovel, 151). Analysis of fishing surveys conducted in Chesapeake Bay indicate that blue crab abundance is approaching the record low and has been declining in recent years. The current status of the stock was compared to numbers in January, 2001. All indications are that the low abundance combined with a high exploitation rate indicates low levels of crab that raise serious concerns. (http://skipjack.net/le_shore/crab/crabbing.html)

To Marylanders, the blue crab is more than just a state symbol. The blue crab is a part of the economy and a part of our culture. We need to support efforts to ensure that the Maryland blue crab is with us for years to come!