Scallop Facts: Habitat, Behavior, Diet

Found in saltwater environments like the Atlantic Ocean, scallops are bivalved mollusks that can be found around the world. Unlike their relative the oyster, scallops are free-swimming mollusks that live inside a hinged shell. What most people recognize as a "scallop" is actually the creature's adductor muscle, which it uses to open and close its shell in order to propel itself through the water. There are more than 400 species of scallops; all are members of the Pectinidae family.

Description

Scallops are in the phylum Mollusca, a group of animals that also includes snails, sea slugs, octopuses, squid, clams, mussels, and oysters. Scallops are one of a group of mollusks known as bivalves. These animals have two hinged shells that are formed of calcium carbonate.

Scallops have anywhere up to 200 eyes that line their mantle. These eyes may be a brilliant blue color, and they allow the scallop to detect light, dark, and motion. They use their retinas to focus light, a job the cornea does in human eyes.

Atlantic sea scallops can have very large shells, up to 9 inches in length. Bay scallops are smaller, growing to about 4 inches. The gender of Atlantic sea scallops can be distinguished. The females' reproductive organs are red while the males' are white.

Habitat and Range

Scallops are found in saltwater environments worldwide, ranging from the intertidal zone to the deep sea. Most prefer beds of seagrass amid shallow sandy bottoms, although some attach themselves to rocks or other substrates.

In the United States, several kinds of scallops are sold as food, but two are prevalent. Atlantic sea scallops, the larger kind, are harvested wild from the Canadian border to the mid-Atlantic and are found in shallow open waters. Smaller bay scallops are found in estuaries and bays from New Jersey to Florida.

There are large scallop populations in the Sea of Japan, off the Pacific coast from Peru to Chile, and near Ireland and New Zealand. The majority of farmed scallops are from China.

Diet

Scallops eat by filtering small organisms such as krill, algae, and larvae from the water they inhabit. As water enters the scallop, mucus traps plankton in the water, and then cilia move the food into the scallop's mouth. 

Behavior

Unlike other bivalves such as mussels and clams, most scallops are free-swimming. They swim by clapping their shells quickly using their highly developed adductor muscle, forcing a jet of water past the shell hinge, propelling the scallop forward. They're surprisingly speedy.

Scallops swim by opening and closing their shells using their powerful adductor muscle. This muscle is the round, fleshy "scallop" that anyone who eats seafood will instantly recognize. The adductor muscle varies in color from white to beige. The Atlantic sea scallop's adductor muscle may be as big as 2 inches in diameter.

Reproduction

Many scallops are hermaphrodites, which means that they have both male and female sex organs. Others are only male or female. Scallops reproduce by spawning, which is when organisms release eggs and sperm into the water. Once an egg is fertilized, the young scallop is planktonic before settling to the sea floor, attaching to an object with byssal threads. Most scallop species lose this byssus as they grow and become free-swimming.​

Conservation Status

There are hundreds of species of scallops; in general, they are not endangered. In fact, according to NOAA: "U.S. wild-caught Atlantic sea scallop is a smart seafood choice because it is sustainably managed and responsibly harvested under U.S. regulations." Bivalves such as scallops, however, are threatened by ocean acidification, which affects the ability of these organisms to build strong shells.

Species

Scallops are marine bivalve mollusks of the family Pectinidae; the best-known are species of the genus Pecten. Scallop species vary in their habitats; while some prefer coastal areas and intertidal zones, others live deep under the ocean.

All scallops are bivalves, and in most species, the two valves of the shell are fan-shaped. The two valves may be ribbed or smooth or even knobbed. Scallop shells vary radically in color; some are white while others are purple, orange, red, or yellow.

Scallops and Humans

Scallop shells are easily recognized and have been a symbol since ancient times. The fan-shaped shells have deep ridges, and two angular protrusions called auricles, one on either side of the shell's hinge. Scallop shells range in color from drab and gray to vivid and multihued.

Scallop shells are an emblem of St. James, who was a fisherman in Galilea before becoming an apostle. James is said to be buried at Santiago de Compostela in Spain, which became a shrine and pilgrimage site. Scallop shells mark the road to Santiago, and pilgrims often wear or carry scallop shells. The scallop shell is also the corporate symbol for the petrochemical giant Royal Dutch Shell.

Scallops are also a major commercially harvested seafood; certain species (Placopecten magellanicus, Aequipecten irradians, and A. opercularis) are highly prized. The large adductor muscle is the part of the scallop that is typically cooked and eaten. Scallops are harvested around the world; the most productive scallop grounds are off the coast of Massachusetts and in the Bay of Fundy off the coast of Canada.

Additional References

• Foster, Kelli. "What's the Difference Between Bay Scallops and Sea Scallops?" TheKitchn.com. 13 May 2016. 
• Goff, Stanley. "What Do Sea Scallops Eat & Where Do They Live?​" ​Sciencing.com. ​25 April 2017.
• Madrigal, Alexis C. "Did You Know Scallops Have *Eyes*? Me Neither, but Look." TheAtlantic.com. 28 March 2013.
• Ramos, Juan. "What Exactly Are Scallops?" ScienceTrends.com. 17 Jan. 2018.