Quahog clams can "walk" on a muscular "foot"!
Quahog Clam Scientific Classification
- Scientific Name
- Mercenaria mercenaria
Quahog Clam Conservation Status
Quahog Clam Facts
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The quahog clam is an edible marine saltwater invertebrate found primarily along the Atlantic coast of North America. They prefer the shallow inland waters of bays and estuaries. A strong muscle controls their hinged shells, which open and close at will. The flesh of these clams is mild, sweet, and briny with a firm texture.
5 Quahog Clam Facts
- Hinged shell: As bivalves, these clams have hinged shells that can open and close. Additionally, they can stick their bodies out between the halves, like a tongue.
- Able to “walk”: This remarkable clam is able to use its muscular “foot” to “walk” across sand or bury itself. It most often walks during spawning season when it seeks out mates. However, its pace is extremely slow, only 1-2 inches every 15 minutes.
- Popular food source: People around the world value this species for food, to the point that fisheries harvest it commercially.
- Filter-feeders: These clams are omnivores, eating whatever they can strain or filter out of the water around them. They rely on filter-feeding to survive, as they cannot effectively pursue prey.
- Shells made of calcium carbonate: Clam shells are primarily composed of calcium carbonate, a substance also found in rocks, eggshells, and pearls.
Quahog Clam Scientific Name
The scientific name for the quahog clam is Mercenaria mercenaria. Alternate names for this species include the hard clam, northern quahog, hard-shell clam, round clam, and chowder clam. It should not be confused with the ocean quahog (Arctica islandica), which is a type of clam belonging to the family Arcticidae. By contrast, Mercenaria mercenaria belongs to the family Veneridae, the Venus clams. Within this family, it belongs to the genus Mercenaria, which also contains the southern quahog (Mercenaria campechiensis).
In a broader taxonomic sense, the quahog clam belongs to the phylum Mollusca, which contains molluscs or mollusks (soft-bodied invertebrates contained within a hard shell). It further belongs to the class Bivalvia, which comprises mollusks enclosed by a two-part hinged shell (bivalves). This subdivides into the order Venerida, a group of primarily saltwater clams, many of which humans use for food.
Quahog Clam Appearance
Quahog clams are soft-bodied invertebrates that protect themselves by means of a hard, rounded shell. Calcium carbonate is the primary material found in the shell, accompanied by a small percentage of other tissues. This thick shell is grey or white in color with concentric growth rings; the inside of the shell is white and violet. Some hatchery clams feature “notata,” dark zigzag stripes across the shell’s exterior.
Inside the shell is the clam’s soft, fleshy body. This body is vulnerable to predation. Two protruding siphons allow these clams to draw water in for filtration and expel the filtered water back into the ocean. Clams of this species possess a fairly large shell, ranging from just under 3 inches to 5 inches in size.
Quahog Clam Evolution and History
The earliest bivalve fossils come from the Early Cambrian Period (541 to 485.4 million years ago), which is the first geologic period of the Paleozoic Era. These tiny organisms belong to the order Fordillida, which has no extant species. To date, scientists have not discovered bivalve fossils from the Middle Cambrian to the Early Ordovician. This was a time of explosive diversity when many organisms were growing in size and expanding into new habitats. Notably, the development of byssal threads in mollusks occurred during the Early Ordovician.
Bivalves became more dominant as a group of marine bottom-dwelling invertebrates after largely surviving the devastating Permian-Triassic extinction event 251.9 million years ago. This event wiped out over 90% of Earth’s species, including many of the rival brachiopods. Throughout the Mesozoic Era, beginning with the Early Triassic, bivalves greatly diversified.
The Cretaceous-Paleogene extinction event, which took place approximately 66 million years ago, destroyed around 65% of bivalve genera. Those that survived are the ancestors of modern bivalves, including quahog clams.
Quahog Clam Behavior
The quahog clam spends most of its time buried in the sand, which protects it from predation and the punishing surf. It accomplishes this by expanding and contracting a powerful muscle. It can also use this muscle to “walk” across sediment, typically during spawning season when it seeks out a mate.
This clam is a bivalve, which means it has a two-part hinged shell that can open and close at will. A muscle controls the movement of the shell. When feeding, the clam opens its shell and extends its soft body as it filters organisms out of the water.
Quahog Clam Habitat
Quahog clams are marine animals that require adequate salinity to survive. They inhabit both intertidal and subtidal regions in bays and estuaries, living most of their lives buried in sediment. They typically do not exceed water depths of 118 feet, preferring to remain at 50 feet or above.
These clams occur along the Atlantic coast from Canada’s Gulf of St. Lawrence all the way to Florida. They also inhabit the Gulf Coast down to Mexico’s Yucatán Peninsula. Fisheries have introduced them to countries like the United Kingdom, France, Belgium, Holland, Puerto Rico, and Taiwan, as well as western U.S. states, like California and Washington.
Eastern states in the U.S. with a quahog clam population include Maine, New Hampshire, Massachusetts, Rhode Island, Connecticut, New York, New Jersey, Delaware, Maryland, Virginia, North Carolina, South Carolina, Georgia, Florida, Alabama, Mississippi, Louisiana, and Texas.
Quahog Clam Diet, Predators, and Threats
Although quahog clams are mostly sessile, they have adapted to find a way to eat without having to move. Being almost completely immobile, they are also fairly easy targets for predators.
What Eats Quahog Clams?
These clams have a variety of predators like fish, crabs, infauna, and birds. Fish predators include angelfish, wrasses, and triggerfish. Crab predators include the blue crab, the green crab, and the mud crab. Lobsters also pose a threat to adult clams. Infauna like worms and snails inhabit soft sediment and may be able to infiltrate a clam’s shell. Additionally, bird species like the American oystercatcher are capable of opening clams and feeding on their insides. Some gulls drop clams from great heights to crack them open.
What Do Quahog Clams Eat?
This species’ diet is limited due to its inability to effectively pursue prey. As a filter-feeder, it mostly consumes phytoplankton, though it consumes tiny animal organisms like plankton as well. It does this by pumping water through its body and straining out the desired organisms.
Quahog Clam Reproduction and Life Cycle
Quahog clams are protandrous hermaphrodites, beginning life as males but often transitioning to females within their first year. They reproduce sexually during the spring, early summer, and fall. The males release sperm into the water, which stimulates the females to release eggs. Female clams release anywhere between one and five million eggs while spawning. This may happen several times a year.
Once fertilization of the eggs occurs, embryo development is swift. The eggs hatch after about 12 to 14 hours into trochophores. These microscopic larvae swim by means of cilia, tiny hairlike growths. After almost 24 hours of development, trochophores enter the veliger stage, during which they acquire wing-like lobes for swimming, a shell, and a muscular foot. This stage lasts six to 10 days, ending in the juvenile stage. Here, the clam loses its lobes and settles to the ocean floor where it will live out the rest of its life.
Sexual maturity for this species depends more upon shell size than age. Some clams mature by the time they reach 1.4 inches in length, though this may not hold true for all individuals. This can take between one to two years. A typical lifespan for the species is 12 to 20 years, though remarkable specimens have lived as long as 40 years!
Quahog Clam Population
Though there is no exact data on the quahog clam population worldwide, conservationists do not consider the species to be endangered. Fisheries in the United States currently farm and harvest these animals under sustainable conditions.
The IUCN does not have a listing for this species as of 2022.View all 8 animals that start with Q
Quahog Clam FAQs (Frequently Asked Questions)
Are quahog clams carnivores, herbivores, or omnivores?
These clams are omnivores. They strain both animal and plant matter from the water around them for consumption.
Where are quahog clams found?
These clams are native to the Atlantic Ocean along the Atlantic coast of North America, from the Gulf of St. Lawrence to the Yucatán Peninsula.
Are quahog clams good to eat?
These clams are generally good to eat and form an important part of the seafood industry. However, consumers should be aware that clams can be a source of shellfish toxins and bacteria.
Are quahog clams healthy?
They are a healthy seafood option. In particular, they are an excellent source of omega-3 fatty acids.
Is the quahog clam an endangered species?
This species is not currently endangered. The IUCN does not have a listing for it as of 2022.
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- Britannica (1970) britannica.com/animal/clam#ref218421
- fisheries.noaa.gov, Available here: https://www.fisheries.noaa.gov/species/hard-clam-northern-quahog#overview
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