Bay Scallops in Florida Seagrass Beds

Bay scallops, Argopecten irradians--found in shallow seagrass beds in the coastal areas of Florida, including many areas throughout our region (e.g., St. Joe Bay, Lanark, and St. Marks)--are bivalved mollusks, meaning that they possess two valves or shells.

Although the scallop shell is a ubiquitous symbol of the seashore, many know it only as a culinary favorite from seafood restaurants or as an empty shell washed ashore on beaches throughout the Gulf States. Yet the scallop is far more interesting alive and in the wild, so it is worth mentioning some of its natural history

The bay scallop is a colorful, active inhabitant of seagrass meadows from Massachusetts to Mexico. Unlike many bivalves the scallop is a free-living animal that will quickly take evasive swimming action when startled. Detecting a potential predator is easy for the scallop as it has about 20 pairs of baby blue eyes located around the edge of its shell. One shadow cast over an eye is generally enough to launch the scallop into a wild swimming escape as it claps its valves together like a pair of castanets and zig-zags through the water. Direction of the swimming is not as important as speed to a bay scallop as any experienced scalloper will attest. Swimming is accomplished using the large adductor muscle located between the shells; rapid contraction causes water to be jetted out the rear of the shell and the scallop is off! A careless scalloper will learn just how strong the scallop muscle is if a finger is placed between the shells.

Scallops use sensory organs to perceive the environment around them. When scallops are faced with predators such as the horse conch in this video, they use adductor muscles to rapidly open and close their shells, expelling water for propulsion in order to escape

Scallops are filter, or suspension, feeders. They lie on the bottom or on seagrass blades and filter water across their large gills, which remove food particles such as algae and oxygen for respiration from the water. Scallops need clean high salinity water to thrive; the water must be low in sediment content as the scallop is not efficient at removing sediment. For this reason we usually see scallops in areas where water clarity is excellent such as in coastal lagoons like the one behind Lanark Reef near the FSUCML. Other areas known for scallops are St. Joe bay and the area near Steinhatchee, FL. Unfortunately this extremely clear water can make harvesting of scallops very easy, so it is a summertime tradition for many families in the northern Gulf of Mexico. Although we should limit our harvest of this fascinating animal, there is nothing that can compare to the flavor of a fresh scallop right out of the shell.

The bay scallop has a short life span in the Gulf, living for about one year, and their life ends after spawning. Scientists have demonstrated that some scallops live for more than a year and probably spawn at least twice, and it is possible that this phenomenon is more common in the northern Gulf. The bay scallop is both a male and a female. Reproduction occurs primarily in the fall as water temperature begins to drop and scallops release eggs and sperm into the water. Although most of the gametes do not survive, in a healthy population enough will survive to produce the next generation of scallops. Fertilized eggs develop into a swimming larval stage known as a veliger. The veliger develops into a juvenile scallop in about two weeks, when it then settles from the water and attaches to seagrass blades. In the spring the juvenile scallops grow rapidly and detach from the seagrass to take up their free-living lifestyle.

Scallops in the Gulf of Mexico are generally colored gray or gray-brown with radiating rays on the upper shell. The famous French scientist Lamark called the scallop the "peigne rayonnant" or radiant comb. The lower shell is typically white, but in about 4% of the population can be bright orange and about 1-2% of the scallops are lemon yellow. Many shell collectors seek the "colored" scallop shells.

Scallops are dependent upon clean water and healthy seagrass. Unfortunately, coastal development in Florida has resulted in progressive declines in water quality and seagrass beds. Many high salinity estuaries and coastal lagoons such as Tampa Bay and Charlotte Harbor/Pine Island Sound have lost much of their seagrass and seen drastic declines in both water quality and scallop populations. In combination with over harvest of scallops in remaining healthy populations, the bay scallop is in serious danger of becoming a memory in Floridan coastal waters. Scientists with the state of Florida Fish and Wildlife Conservation Commission have been attempting to restore or enhance some scallop populations, but populations can only remain viable where the seagrass habitat remains healthy. Because of serious concerns the harvest of bay scallops is now only allowed in from the Pasco-Hernando county line to Mexico Beach in north Florida and then only by recreational fishers taking scallops by hand or using a dip net.

To learn more about scallops, visit the FWC website on bay scallops. Other sources of information include the popular mollusk guide A Field Guide to Shells of the Atlantic and Gulf Coasts and the West Indies by R, Tucker Abbot, Percy Morris, and Roger Tory Peterson, Houghton Mifflin (1995), ISBN 0618164391.