Bay Scallops

Argopecten irradians

ScallopBay Scallops are bivalve mollusks that range in size from 10 mm to 65 mm. Bay scallops were abundant in Pine Island Sound until the late 1980s; many long-time residents of Sanibel remember collecting buckets of them legally. Today, recreational harvest of scallops in Pine Island Sound is prohibited and illegal. This is because of the low abundances recorded in annual surveys by the Florida Wildlife Research Institute (Dr. Steve Geiger's lab). 

The local scallop populations in bays and estuaries on Florida's west coast are connected through the transportation of larvae (Arnold et al. 1998). Adult scallops spawn when there are rapid temperature changes, such as the spring or fall. The eggs and sperm are mixed in the water column and a fertilized egg will develop into a veliger larvae. The larvae settle on seagrass leaves and develop into juveniles, then adults.

Bay Scallops are sensitive to changing environmental conditions. Loss of seagrass, too much freshwater runoff, and destabilization of consolidated sediments can result in the collapse of a local population (Blake 2005, Marelli et al. 1999). From annual volunteer scallop searches, we have determined that year-after-year, there are favorable habitats for Bay Scallops, yet their abundances remain low. We feel that there is a critical abundance, above which, the Bay Scallop will be self-sustaining and begin to increase. Efforts by SCCF near Demere Key in collaboration with FWC and in the semi-enclosed Tarpon Bay have yielded encouraging results. Scallops that are protected from predation are allowed to reproduce in cages in Tarpon Bay. Evidence of scallop spat settlement within Tarpon Bay increased during caging periods. 

Bay Scallops, are very sensitive to Florida Red Tide and the brevetoxin it produces (Summerson and Peterson 1990). Repeated Red Tide blooms near Sanibel Island threaten efforts to restore Bay Scallops in Tarpon Bay. 

The minimum salinity determining overall distributions of the Bay Scallop is 14 (Belding 1910), however, laboratory experiments demonstrated that scallops become inactive at 16 with reduced activity at 22 (Duggan 1973). Scallop larvae have optimal development at 25 (Tettlebech and Rhodes 1981) and are not found below 22.