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When Crabs Attract …

Love is in the water

Blue crabs do a beautiful dance to attract a mate, says Dr. J. Sook Chung, an expert on crab reproduction at the Institute of Marine and Environmental Technology in Baltimore.
       It’s not just people who engage in an elaborate courtship with gifts of roses and chocolates, explains scientist Dr. J. Sook Chung. Maryland’s blue crabs also have their tricks in choosing a mate.
      “They do a beautiful dance to attract a mate,” says Chung, an expert on crab reproduction at the Institute of Marine and Environmental Technology in Baltimore’s Inner Harbor.
       A female crab mates only one time in her life (usually in the late spring to early summer or early fall), so she only has one chance to pick the right partner. When she is about to molt for the last time, she sends pheromone signals out into the water. Then it begins.
       “The male smells it and comes along. She has to attract as many as possible, and she has to find the best one. The male has to dance for her to show her he has good genes,” she says. “He shows her ‘I am big and tall!’ He stands on his tiptoes and spreads out his claws 180 degrees, waving his swimming legs up and down like a fan, and he’s moving his mouth parts like a mad dog. 
       “Occasionally she rejects a male. He tries really hard. Sometimes, if he’s not successful, he may eat her,” she adds. “Usually, within five seconds she cooperates. He holds and protects her until she is ready to molt. She molts in front of him, and then they mate while her shell is still soft.”
       This part can last four to five hours until the male crab releases her and swims off. The female crab can then store sperm in her body for up to two years. She uses it to fertilize a couple of million eggs at a time, which she holds outside of her shell in a sponge-like mass until they hatch and swim off into Chesapeake Bay. Choosing to mate with the larger males is key: it ensures she will have more sperm on hand to fertilize more eggs, since only one out of two million baby crabs she produces will survive to adulthood.
       Located in Baltimore’s Inner Harbor, the Institute of Marine and Environmental Technology is a strategic alliance involving scientists at the University of Maryland Center for Environmental Science, the University of Maryland Baltimore and the University of Maryland Baltimore County. Scientists are engaged in cutting-edge research in microbiology, molecular genetic analysis and biotechnology, using marine life to develop new drug therapies, alternative energy and other innovations to improve public health and economic opportunities. IMET also contributes to sustainable marine aquaculture and fisheries in the Chesapeake Bay and marine ecosystems.