Hard Clam
Mercenaria mercenaria
Hard clams are found in the lower Chesapeake Bay from the shoreline to depths of about 60 feet. (Matt Pettengill/Flickr)
Hard clams have thick, rounded shells with concentric ridges. (NOAA Photo Library)
The inside of a hard clam is usually white with dark purple patches. (Vilseskogen/Flickr)
The hard clam is a bivalve with thick, ridged, rounded shells. It lives in the salty waters of the lower Chesapeake Bay.
Appearance
The hard clam's thick, rounded shells vary in color from brownish to gray or whitish and can grow to 4 inches or longer. Concentric ridges appear on the shells, which are joined at the hinge by a thick, brown ligament. The shell's interior is usually white with dark purple patches. A hatchet-shaped foot and two short siphons periodically extend from inside the clam.
Feeding
Like many bivalves, hard clams are filter feeders. While buried in the sand, the clam’s two siphons stick up above the surface. The clam draws in water through one siphon, filters out plankton from the water, and eject unused water and particles through the other siphon.
Predators
Adult clams have many natural predators, including gulls, tautogs, waterfowl, cownose rays, blue crabs and oyster drills. Humans harvest hard clams for recreational and commercial purposes.
Reproduction and Life Cycle
Spawning occurs between May through October, once clams produce ripe gametes and water temperatures rise above 68 to 73 degrees. Females can release between 16 and 24 million eggs per spawn. Eggs are fertilized in the water column. Free-swimming larvae develop over 1 to 2 weeks. During this time they grow a foot, which is used to crawl over and “explore” a surface before settling. When larvae find a suitable place to settle, they anchor themselves using thin threads secreted from a gland on their foot. Larvae slowly metamorphose into juveniles, developing gills, siphons and digestive viscera. Hard clams may live as long as 40 years.
Did You Know?
- Also known as quahogs, little necks, cherrystones and chowder clams. The various commercial names are based on clam size.
- Native Americans used hard clam shells as wampum, white shell beads used in traditional ceremonies or often traded as currency.
Sources and Additional Information
- Life in the Chesapeake Bay by Alice Jane Lippson and Robert L. Lippson
- Chesapeake Bay: Nature of the Estuary, A Field Guide by Christopher P. White
- Maryland Fish Facts: Hard-shell Clam – Maryland Department of Natural Resources
- Animal Diversity Web: Mercenaria mercenaria – University of Michigan Museum of Zoology
- Mercenaria mercenaria – Smithsonian Marine Station at Fort Pierce
Quick Facts
Species
Native
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Habitat
Found from the shoreline to a depth of about 60 feet. Uses its foot to bury itself just below the surface of the sand or mud.
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Range
Lives in the salty waters of the lower Chesapeake Bay. Mostly found in Virginia waters; in the Maryland portion of the Bay, hard clams are restricted to Tangier and Pocomoke sounds.
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Diet
Filter feeders
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Lifespan
Up to 40 years
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Status
Stable
