Calico Scallops – General Information
Calico scallops (Argopecten gibbus) are found in coastal waters of the eastern U.S. states from Maryland to Florida, throughout the Gulf of Mexico and the Caribbean Sea, and down to Brazil. Calico scallops generally live in depths from 10 to 400 meters (30 to 1,200 feet) on sandy or shelled bottoms
Calico and bay scallops are bivalve (two-shells) molluscs in the Pectinidae family and are similar in both anatomy and life history. While bay scallop shells are solid in color, the upper shell of a calico scallop is a patchwork of red and pink. The typical life span of a calico scallop, 18 months, is longer than that of a bay scallop and some may live as long as 24 months. Calico scallops are generally smaller than bay scallops with maximum shell heights between 40 and 60 millimeters (1.6 to 2.4 inches).
Anatomically, calico scallops are almost identical to bay scallops. They pump water across gills to filter out food particles and use their large adductor muscle to open or close their shells. When done quickly, this rapid reflex propels the scallops up off the bottom and to a new location on the seafloor. Calico scallops have several blue eyes located in the mantle cavity along the edge of each shell, which they use to detect shadows and movement.
During its lifetime, a calico scallop will usually reproduce three to four times. Calico scallops as small as 19 millimeters (less than 1 inch) or as young as 4 months can become reproductively active. Adults generally spawn year-round, with peak spawning periods in the spring and late fall when sudden or significant changes in water temperature occurs. Like bay scallops, calico scallops are hermaphrodites (possessing male and female organs) and broadcast spawners, meaning fertilization occurs outside the animal in the water column. After a two-week pelagic (open water) larval phase the juvenile scallops, commonly called spat, settle out of the water and attach to hard surfaces, usually older calico scallop shells. Calico scallops that settle in the spring generally reach a size of 30 to 35 millimeters in shell height by the following fall and are fully able to reproduce. As a result of this rapid growth and early maturation, groups of scallops, or cohorts, may overlap and scallops of many different sizes may occupy a bed at any given time.
Infection by a parasite of the genus Marteilia may have been responsible for a calico scallop population crash recorded off Cape Canaveral along Florida’s east coast in 1991. The parasite appears to infest the calico scallop’s digestive gland to such an extent that they starve to death.