| Size |
Up to 2.5 inches. |
| Habitat |
Brackish water clams are commonly found in the sandy and muddy
substrates of subtidal and intertidal areas. They thrive in tidal freshwater and low salinity river systems such as the
Potomac River (below Washington D.C.), the Rappahannock River (below Fredricksburg) and
the James River (below Richmond). When they were first introduced to the Chesapeake
Bay they were only found in low salinity waters. Today they have invaded the tidal
freshwater areas as well as areas of higher salinities (£ 18 ppt). Winter kills in the shallow waters of the
Chesapeake Bay suggest that this clam cannot survive in temperatures at or below freezing
(32° F/0° C). |
| Reproduction |
The reproductive cycle and environmental conditions necessary for spawning are not well known. Spawning is initiated by a rapid
increase or decrease in salinity. Fertilization occurs in the water column and larvae become
shelled within 24 hours after fertilization. Most larvae settle on the bottom between
September and March and a second settling can occur in midsummer. How the juveniles
disperse is uncertain. Adult brackish water clams rarely move. |
| Feeding |
Brackish water clams are filter feeders feeding primarily on phytoplankton, detritus and some vascular plant material. They
filter the water for food particles by pumping water in through one siphon, passing it
over the gills where the food particles collect, and pumping it out with the other siphon.
|
| Predators |
Brackish water clams are included in the diets of catfish, freshwater drum (Aplodinotus
grunniens), spot (Leiostomus xanthurus),
black drum (Pogonias cromis),
river shrimp, blue crabs (Callinectes sapidus) and waterfowl. Moon shell snails
(Family: Naticidae) may also be predators because of the typical drill holes left in the
shells. Ctenophores can eat large numbers of larvae if they are
abundant during the clam's spawning period. |
| Description |
Brackish water clams are an introduced species to the Chesapeake Bay.
Introduction has been linked to ballast water collected in ports spanning over the
mid-Atlantic bays south to the Gulf of Mexico. Brackish water clams began to appear in the
Chesapeake Bay in the early 1960’s. They have a rough exterior with a thick white
shell and a grayish brown paper thin covering, called the periostracum. The shell is oval shaped and is thick and heavy.
The inside of the shell is glossy white with a blue or gray tinge. Brackish water clams
are often mistaken for Asian clams (Corbicula fluminea) and careful examination
should be used in identification. The life span of the brackish water clam has not been
confirmed. The average life span is thought to be between 4 and 5 years with a maximum of
15 years. |
| Other |
The brackish water clam is known by several other names including
Atlantic rangia clam and common rangia. |
