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Chapter 2 - Coastal Ecosystemsfrom the Gulf of St. Lawrence (Canada) to the Gulf ofMexico. In the region, most remaining oysters are locatedfrom Delaware Bay south. Oysters form reefs in subtidalareas to depths of 10 m and intertidal areas (primarilysouth of Long Island), tolerating a wide range of temperaturesand salinity levels. Spawning is temperaturedependent, and larvae are planktonic. Larvae require hardsubstrate and prefer biogenic surfaces (e.g. shell bottom)for successful recruitment.Hard Clam (Mercenaria mercenaria)Hard clams, also known as quahogs or littlenecks, arewidely-distributed in subtidal areas of the NorthwestAtlantic. A commercially valued species, dense beds ofhard clams create benthic habitat and contribute to improvedwater quality. The hard clam is found from theGulf of St. Lawrence (Canada) to Texas, although theyare most abundant from Massachusetts to Virginia. Hardclams aggregate in intertidal and subtidal areas to depthsof 15 m, and typically occur in locations with salinity levels>19 ppt. Spawning is temperature dependent. Larvae areplanktonic and settle in a variety of substrate types, includingsand, sandy mud, and gravel.Softshell Clam (Mya arenaria)Softshell clams, also known as steamers, are a dominantfilter-feeder in intertidal areas and mudflats of coastalembayments, from the Bay of Fundy to the mid-Atlanticcoast, but are most abundant from New England to theChesapeake Bay. An important commercial species, especiallyin New England, this species also stabilizes softsediments and is capable of considerable water filtration.Softshell clams populate intertidal and subtidal areas todepths of 200 m, with preferred salinity levels > 20 ppt innorthern areas and 4-15 ppt in southern areas. Spawning istemperature dependent. Larvae are planktonic and settlein a range of substrate types, including sand, sandy mud,mud, clay, and gravel, but not in cobble or rocky ledges.Bay Scallops (Argopecten irradians)Bay scallops, unlike deeper-water sea scallops, areprimarily estuarine bivalves that congregate in subtidallow energy areas such as seagrass meadows. Bay scallopsare historically an important commercial species, andexisting populations help maintain water quality byfiltering algae and phytoplankton. Distributed fromNew England to Texas, they are most abundant fromCape Cod (Massachusetts) to Virginia. The speciesoccurs in low-energy, shallow subtidal areas to depths of18 m. Bay scallops do not tolerate low annual salinitylevels (< 10 ppt). Spawning is temperature dependent,and the planktonic larvae may attach to eelgrass shootsbefore settling to the bottom.Blue Mussel (Mytilus edulis)Blue mussels are found extensively in subtidal and intertidalareas throughout the Northwest Atlantic region,Europe, and other temperate waters. Beds are commonfrom Labrador (Canada) to South Carolina, and typicallyfound in littoral zones to depths of 100 m (maximumdepth 500 m). Considered of lesser commercial value thanother shellfish, mussels have become dominant shellfishspecies in northern regions, forming large reefs and filteringextensive reaches of coastal water bodies. Blue musselsare preyed upon by many aquatic species, especiallywaterfowl and macro-invertebrates. This species toleratesa wide range of salinity levels and temperatures. Spawningis temperature and food-dependent and may occur morethan once a year. The planktonic larvae settle first onalgae and seaweed before attaching to hard shell or rocksubstrates.Ribbed Mussel (Geukensia demissa)Ribbed mussels inhabit salt marshes throughout theregion and oyster reefs in southern parts of the region.Where present, these mussels can form colonies as denseas 100 m -2 that provide sediment stabilization, water qualitycontrols, and food sources for many crustacean andavian species. Ribbed mussels occur from the Gulf of St.Lawrence (Canada) to Texas. The species prefers intertidalareas of salt marsh and oyster reef habitat, and toleratesa wide range of salinity levels and temperatures. Spawningis temperature and food dependent. Larvae are planktonicand must attach to filamentous or reef-type structures.Northwest Atlantic Marine Ecoregional Assessment • Phase 1 Report 2-17