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Hard Clam

Mercenaria mercenaria

Hard clam shells are often found washed up on lower Bay beaches. (dsbrennan/Flickr)
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Hard clam shells are often found washed up on lower Bay beaches. (dsbrennan/Flickr)

The hard clam is a bivalve with thick, ridged, rounded shells. It lives in the salty waters of the lower Chesapeake Bay.

Appearance:

  • Thick, rounded shells that vary in color from brownish to gray or whitish
  • Concentric ridges on the shells
  • Shells are joined at the hinge by a thick, brown ligament
  • Interior is usually white with dark purple patches
  • Hatchet-shaped foot and two short siphons periodically extend from inside the clam
  • Can grow to 4 inches or longer

Habitat:

  • Uses its foot to bury itself just below the surface of the sand or mud
  • Found from the shoreline to a depth of about 60 feet

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.

Feeding:

  • Filter feeder
  • While buried in the sand, the clam’s two siphons stick up above the surface. The clam draws in water through one siphon, then filters out plankton from the water. Unused water and particles are ejected 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:

  • Spawns between May-October, once clams produce ripe gametes and water temperatures rise above 68-73 degrees
  • Females can release 16-24 million eggs per spawn. Eggs are fertilized in the water column.
  • Free-swimming larvae develop over 1-2 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 the foot
  • Larvae slowly metamorphose into juveniles, developing gills, siphons and digestive viscera
  • May live as long as 40 years

Other Facts:

  • 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 are wampum

Sources and Additional Information:




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