Scallops are marine bivalve mollusks, belonging to the family Pectinidae, found across the world’s oceans. These invertebrates possess two hinged, typically fan-shaped and often ribbed, shells that protect their soft bodies. Scallops inhabit diverse saltwater environments, from shallow coastal areas to deep ocean floors, frequently residing on sandy or gravelly substrates. As filter feeders, they consume microscopic organisms like phytoplankton from the water column, playing a role in marine ecosystems. Their position as prey for various marine animals and as a significant food source for humans places them within the marine food web.
Marine Predators
Scallops face a range of natural predators throughout their lives, each employing distinct strategies to access the mollusk’s soft tissues. Sea stars are prominent predators. Species like the Forbes sea star slowly crawl onto a scallop, using their tube feet to pull on the shell. This persistent effort eventually tires the scallop’s adductor muscle, creating a small gap for the sea star to digest the scallop’s body externally. Marine snails also pose a threat, with some species drilling holes into the scallop’s shell or entering through existing openings to consume the flesh.
Crustaceans, such as various crab species, are also common predators of scallops. With their strong claws, crabs can crush the scallop’s shell or pry it open to reach the soft internal parts. This method is particularly effective against smaller or juvenile scallops. Fish represent another category of predators, including species like cod, wolffish, eel pout, and flounder, which feed on both juvenile and adult scallops.
Rays, including eagle and cownose rays, are specialized predators known for their ability to crush protective bivalve shells. These “durophagous” rays possess strong jaws, allowing them to consume scallops and other mollusks. Sea turtles also include scallops in their diet, particularly in shallow coastal areas. Various birds can prey on scallops in shallower waters, while certain jellyfish species may consume scallop larvae or juveniles, impacting their survival rates early in life.
Human Harvesting
Humans harvest scallops using methods that vary in scale and technique. The most common commercial method is dredging, which involves towing a heavy metal frame, known as a dredge, along the ocean floor. This dredge is equipped with a toothed bar that digs into the seabed, flipping scallops into a collecting bag. Vessels can tow multiple dredges simultaneously, collecting large quantities. Once onboard, the scallops are typically shucked, and the adductor muscle is removed and stored on ice.
Another harvesting method is hand diving, often called “diver scallops” or “dive-caught.” This technique involves skilled divers manually collecting scallops from the ocean floor. While less common for large-scale commercial operations than dredging, hand diving is used in certain areas and has a lower environmental impact. Scallops are a globally valued seafood with significant economic importance. The United States, for instance, has one of the largest sea scallop fisheries in the world.
Scallop Defenses
Scallops employ various defense mechanisms against predators. Their primary escape mode is rapid swimming, a unique ability among most bivalves. When threatened, a scallop quickly claps its shells together, expelling jets of water near the hinge. This jet propulsion allows them to move swiftly, though often erratically, through the water, helping them evade slower predators like sea stars. This “clapping” motion is powered by their strong adductor muscle, the same part consumed by humans.
The scallop’s shell provides physical protection, acting as a hard barrier against attack. The two valves, made of calcium carbonate, are hinged and can be tightly closed to deter predators.
Beyond physical barriers and movement, scallops possess a ring of numerous simple eyes located along the edge of their mantle. These eyes enable scallops to detect changes in light, shadows, and movement, providing an early warning system for approaching threats. Some scallop species also burrow into sandy substrates or attach themselves to objects with byssal threads, offering concealment or stability against predators.