In this video, a blue crab breaks open the shell of a Macoma clam and scoops out the inside. This blue crab lives in a tank at the Smithsonian Environmental Research Center and is wearing a telemetric "beeper" to let researchers know when it's feeding. The Macoma clam has a thin shell that's incredibly easy to crack and is commonly found in shallow brackish waters, making it one of the preferred food items for the blue crab.
Blue crabs are an important link in the food web of the Chesapeake Bay. They are predators as well as prey for other animals, including humans. Because crabs mainly stay on the bottom when looking for food, their preferred diet is clams, which they even dig up in the muddy or sandy bottom of the Bay.
Under healthy environmental conditions, blue crabs also eat range of other animals, such as fish, worms, and crustaceans like shrimp, barnacles, mud crabs, and other blue crabs. Some think blue crabs are also scavengers and when food is scarce blue crabs are found to be willing and able to eat anything: plants and animals, alive or dead.
Blue crabs don't usually eat oysters because the shell of the oyster is too hard to open. They do like to crawl around an oyster reef and look for other fish and invertebrates.
Blue crabs are also prey for many other animals, such as fish, birds, and even other blue crabs. When blue crabs molt, their shell is soft, which makes them vulnerable to other predators. A small hard shell blue crab can easily capture and eat a larger soft shelled crab.
The blue crab also spends its first month or so in the plankton community, during which time it is a very easy prey for many of the filter feeders in the Bay, such clams, oysters, menhaden, bay anchovies, and barnacles.
The abundance of predators, including other blue crabs, makes searching for food an ongoing adventure for the crab.
Click on the image above to see a short QuickTime movie of an eating blue crab. This is a soft-shell clam called a Macoma. The blue crab has no problem breaking the shell and eating the clam inside.