The Virginia Marine Resources Commission has designated hard-clam broodstock sanctuaries in order to increase the probability of fertilization thus increasing the population (Cool 1998). The Hard Clam Broodstock Program piloted a site at Lower Brown Shoals in April 1995 for hard-clam sanctuaries (Cool 1998). The Back River Reef BroodStock Sanctuary, created February1997, has kept the commercial fishing and natural predators from preying on the hard-clams in that area (Cool 1998). And, the Middle Ground Light Broodstock Sanctuary, created March 28, provides good disbursement for larvae (Cool 1998). These are all attempts to increase the amount of commercial supplies while maintaining the clam population.
US Federal List: no special status
CITES: no special status
In Britain, a cold spell during 1947, 1962, and 1963 killed off the entire soft-shelled clam, Mya arenaria, population (Mitchell 2001). With the introduction of Mercenaria mercenaria the niche was filled and, and the Mya arenaria population has never recovered (Mitchell 2001).
Mercenaria mercenaria is an edible species, and is the most important commercially harvested species in the Virginia Bay, raking in approximately $4 million to $6 million annually (Cool 1998). In addition, they also filter and recycle organic material in the Chesapeake Bay, removing toxic materials and clarifying the water (Cool 1998). With the introduction into Great Britain in 1960 they have become a large economic market in France and Italy where introduction attempts have already failed (Stewart 1996). Also, it is thought that the liver may contain chemicals that have selectivity for cancerous cells (Mercenaria mercenaria 2000).
Mercenaria mercenaria are suspension feeders which means that they feed on small plants and animals called plankton which are drawn in with water (Britannica 2000, Plourde 2001). When the clam buries itself under a layer of silt and mud it sticks its siphons straight up through the surrounding muck. The inhalant siphon draws in water, which is passed over the gills. Millions of tiny cilia, hair-like structures, move the water across the gills and any food particles are caught in a mucous sheet that coats the gills (Plourde 2001, Stewart 1996). This food-mucous mixture is passed along a groove above the foot to a pair of muscles called the palps, which force the material into the mouth (Plourde 2001). It then follows the digestive tract consisting of a stomach, intestine, and anus to be excreted through the exhalent or excurrent siphons, as pseudofeces (Britannica 2000, Plourde 2001).
Mercenaria mercenaria live in intertidal zones at depths of up to 10 m (Britannica 2000). This species' native distribution is along the east coast of North America, from the Gulf of St. Lawrence into the Gulf of Mexico (Mercenaria mercenaria 2000, Plourde 2001). However, it has been introduced to other areas including the coasts of California, England, Humboldt Bay, and Southern Brittany (Mercenaria mercenaria 2000, Mitchell 2001). Attempts were also made to introduce the clam to the Etang de Thau on the south coast of France and around Sicily, but no populations have successfully established in the Mediterranean Sea (Mercenaria mercenaria 2000). There have been other attempts to introduce the clams but most don't result in a self-sustaining population (Mitchell 2001).
Biogeographic Regions: atlantic ocean (Native ); pacific ocean (Introduced )
Mercenaria mercenaria are found in the intertidal zone from the Gulf of St. Lawrence to the Gulf of Mexico (Britannica 2000). They are found most abundantly on mud flats, mud/sand flats, and sand flats which reach depths of 10 m (Plourde 2001, Stewart 1996). However, soft muddy bottoms cannot support the weight of the clam due to its heavy shell. This causes sediments to be stirred up, and silt may block the siphon of the clam from filtering out the water (Stewart 1996). Also, it is important that they have tides in order to receive food and oxygen and to carry away waste, but turbulent waters, found in the surf zone, may wash them away (Stewart 1996). The perfect salinity range for Mercenaria mercenaria larvae are 20 to 35 parts per thousand, however adults can be more tolerant (Stewart 1996). The Chesapeake bay is an excellent habitat because it provides the needed salinity and temperatures that are optimal for the hard-clam's survival.
Aquatic Biomes: coastal
Mercenaria mercenaria has a fairly large and thick shell with uneven, elevated hinges on the anterior (Mercenaria mercenaria 2000). Both shell halves are approximately even in size and sub ovate, or triangular in shape (Stewart 1996). The shell is increased by a daily layering of aragonite secreted by the outermost fold of the organism, giving it numerous concentric lines that are closely space near the margins of the shell and widely spaced at the umboes (deMenocal 2000, Mercenaria mercenaria 2000). Its shell is a composition of proteins and calcium carbonate (Plourde 2001, Brown 1995). The shell is joined at a hinge called the umbo and is held closed by two pairs of adductor muscles located on each side of the shell (Plourde 2001). The clam opens its shell by relaxing the adductor muscles and contracting a pair of ligaments located on each side of the umbo (Plourde 2001). Mercenaria mercenaria contain three well-developed teeth located on the edge of the shell, which serve to enhance its tightness when closed (Stewart 1996). The external color is dirty white or gray, while the interior is usually white with distinct violet areas near the umbo. The clam contains a foot, which allows it to burrow into the sand (Plourde 2001). The clam also contains a set of long siphons, which stretch from the clam's mantle, the membranous sac that contains the internal organs and constitutes the body of the clam, to the surrounding medium outside of the shell (Plourde 2001). It uses these siphons for respiration and gathering food. Mercenaria mercenaria are sub classified by length. Chowders are the biggest measuring up to 3 inches in width, Cherrystones are 2 to 3 inches, Top Necks are 2 inches in width, and Little Necks are the smallest measuring 1 to 2 1/3 inches (International Seafood).
Other Physical Features: ectothermic ; bilateral symmetry
The clam's history with introduction into England has shown that deliberate introduction of a species has the capability of working commercially (Mercenaria mercenaria 2000). The Algonquin tribes would grind up the shells and make beaded necklaces that would be used as wampumpeag or wampum, which means money (Grzimek's 1974). It is thought that quahog is the corruption of "Poquahock" which is the Narragansett Indian name for Mercenaria mercenaria (Plourde 2001). When European settlers came to America they used the word "clamps" because of the locking system the animals had, which was eventually shortened to "clams" (Plourde 2001).
When the water temperatures approach 23°C (73°F), and other environmental cues such as pH change, spawning commences(Britannica 2000, Stewart 1996). Some species have adapted to spawn at temperatures ranging from 4°C and lower (Mitchell 2001). The male clam discharges sperm into the water, which stimulates the female to release eggs (Stewart 1996). Because fertilization is random, high densities of spawning clams increase the probability of success (Cool 1998). Due to favorable conditions, spawning is most likely to occur during neap tides (Stewart 1996). During the first 12 to 14 hours, the fertilized eggs turn into trochophore larvae (Stewart 1996). In this form, they are cylindrical with tiny cilia, which allow them to swim about (Stewart 1996). During this period they feed on diatoms, microscopic algae that are encased in silica shells (Stewart 1996). By the end of the first day, the trochophore larvae transform into veliger larvae, which contain tiny lobes that may be used as paddles (Stewart 1996). During the next six to ten days, the body organs, shell and foot begin to form (Stewart 1996). They then shed their lobes and the newly developed foot secretes byssal threads that anchor the larvae to rocks, seaweed, or other sediment deposits (Plourde 2001, Stewart 1996). They will then secrete their shell, which begins to calcify between 8- 29°C, and detach the byssal threads, thus becoming adult clams (deMenocal 2000). During their free floating period they are dispersed by currents and preyed upon by other animals such as crabs. Approximately 10% of all veliger larvae reach the adult stage (Stewart 1996). Temperatures that vary below 80°C may reduce the growth stages dramatically (Mercenaria mercenaria 2000).
The hard clam (Mercenaria mercenaria), also known as the round clam, hard-shell (or hard-shelled) clam, or the quahog,[a] is an edible marine bivalve mollusk that is native to the eastern shores of North America and Central America from Prince Edward Island to the Yucatán Peninsula. It is one of many unrelated edible bivalves that in the United States are frequently referred to simply as clams. Older literature sources may use the systematic name Venus mercenaria; this species is in the family Veneridae, the venus clams.
Confusingly, the "ocean quahog" is a different species, Arctica islandica, which, although superficially similar in shape, is in a different family of bivalves: it is rounder than the hard clam, usually has black periostracum, and there is no pallial sinus in the interior of the shell.
The hard clam has many alternative common names. It is also known as the Northern quahog, round clam, or chowder clam.[1]
In fish markets, there are specialist names for different sizes of this species of clam. The smallest legally harvestable clams are called countnecks or peanuts, next size up are littlenecks, then topnecks. Above that are the cherrystones, and the largest are called quahogs or chowder clams.[2]
The most distinctive of these names is quahog (/ˈkoʊhɒɡ/ KOH-hog, /ˈkwɔːhɒɡ/ KWAW-hog, or /kwəˈhɒɡ/ kwə-HOG, also spelt quahaug, quohog or cohog).[3][4] The word comes from the Narragansett word "poquauhock", which is similar in Wampanoag and some other Algonquian languages; it is first attested in North American English in 1794.[5][6] Native polities on the eastern Atlantic seaboard made valuable beads called wampum from the shells, especially those colored purple; the species name mercenaria is related to the Latin word for commerce. Today people living in coastal New England still use Algonquian words for the clam, as they have done for thousands of years.
In many areas where aquaculture is important, clam farmers have bred specialized versions of these clams with distinctions needed for them to be distinguished in the marketplace. These are quite similar to common "wild type" Mercenaria clams, except that their shells bear distinctive markings. These are known as the notata strain of quahogs, which occur naturally in low numbers wherever quahogs are found.[7]
Hard clams are quite common throughout New England, north into Canada, and all down the Eastern seaboard of the United States to Florida; but they are particularly abundant between Cape Cod and New Jersey, where seeding and harvesting them is an important commercial form of aquaculture. For example, the species is an important member of the suspension-feeding, benthic fauna of the lower Chesapeake Bay.
Rhode Island is situated right in the middle of "quahog country" and has supplied a quarter of the U.S.'s total annual commercial quahog catch. The quahog is the official shellfish of the U.S. state of Rhode Island. The species has also been introduced and is farmed on the Pacific coast of North America and in Great Britain and continental Europe. It reproduces sexually by females and males shedding gametes into the water.[2]
Quahog parasite unknown (QPX)[8] is a parasite that affects the hard shell clam Mercenaria mercenaria. While little is known about the disease, research is currently under way in several laboratories.[9] This research is fueled by the need to inform aquaculturists, who suffer financially because of the mortality rates in clams that QPX inflicts and the ensuing years in which runs must be left fallow to clear the disease. It was discovered along the coast of Cape Cod, Massachusetts in 1995.
Quahog parasite X (or quahog parasite unknown [QPX]) disease of the hard clam Mercenaria mercenaria is caused by a poorly known protistan parasite. Its DNA sequence analysis places the QPX parasite among the thraustochytrid stramenopiles. Thraustochytrids are common protists in marine sediments and the water column, but only a few thraustochytrids are known as parasites of marine animals. Although QPX disease was first recorded on the Atlantic coast of Canada in the early 1960s, it did not become a major economic problem until its appearance in cultured clams at Prince Edward Island, Massachusetts in 1992, and Virginia in 1997. Infected clams are characterized by the presence of blisters or pustules in the mantle and later by gaping and death.[10]
In coastal areas of the New England states, Long Island, and New Jersey, restaurants known as raw bars or clam bars specialize in serving littlenecks and topnecks raw on an opened half-shell, usually with a cocktail sauce with horseradish, and often with lemon. Sometimes littlenecks are steamed and dipped in butter, though not as commonly as their soft-shelled clam cousin the "steamer". Littlenecks are often found in-the-shell in sauces, soups, stews, and clams casino, or substituted for European varieties such as the cockle in southern European seafood dishes. The largest clams are quahogs or chowders and cherrystones; they have the toughest meat and are used in such dishes as clam chowder, clam cakes, and stuffed clams, or are minced and mixed into dishes that use the smaller, more tender clams.
Historically, Native Americans used the quahog as a component in wampum, the shell beads exchanged in the North American fur trade.[11] The Narragansetts used the hard clam for food and ornaments.[12]
A population of hard clams exists in Southampton Water in Hampshire, England. Originally bred in the warm water outflows at Southampton Power Station for use as eel bait, the population became self-sustaining and can now be found in Southampton Water and has also spread to Portsmouth Harbour and Langstone Harbour.
The term "red tide" refers to an accumulation of a toxin, such as saxitoxin, produced by marine algae.[13][14] Filter-feeding shellfish are affected, such as clams, oysters, and mussels.[13][14] The toxin affects the human central nervous system.[13] Eating contaminated shellfish, raw or cooked, can be fatal.[13] Some other kinds of algal blooms make the seawater appear red, but red tide blooms do not always discolor the water, nor are they related to tides.[13]
The hard clam (Mercenaria mercenaria), also known as the round clam, hard-shell (or hard-shelled) clam, or the quahog, is an edible marine bivalve mollusk that is native to the eastern shores of North America and Central America from Prince Edward Island to the Yucatán Peninsula. It is one of many unrelated edible bivalves that in the United States are frequently referred to simply as clams. Older literature sources may use the systematic name Venus mercenaria; this species is in the family Veneridae, the venus clams.
Confusingly, the "ocean quahog" is a different species, Arctica islandica, which, although superficially similar in shape, is in a different family of bivalves: it is rounder than the hard clam, usually has black periostracum, and there is no pallial sinus in the interior of the shell.
