The coquina clam (Donax variabilis) is a common inhabitant of Florida's sandy beaches. Known for their highly variable color patterns, coquinas can be found buried just under the surface of the sand in the wave-swept area of the beach known as the swash zone. These algae filter-feeders are a critical food source for fish, crabs and shorebirds. Along with other animals such as the mole crab (Emerita talpoida) and ghost crab (Ocypode quandrata), coquina clams are considered indicator species for beach habitat. Because of their sensitivity to environmental changes, indicator species can act as an early warning system for biologists.
Coastal erosion is a major issue along Florida’s coastline, especially in the wake of tropical storms and hurricanes. Beach nourishment, a process in which sand from an outside source is used to replace eroded beach sand, is a method used to mitigate the effects of erosion. Managers regulate the timing and location of sand placement based on biological considerations, including how indicator species such as coquina clams are affected by beach nourishment.
From 2005 to 2008, scientists with the FWC’s Fish and Wildlife Research Institute and Florida Institute of Technology (FIT) looked into the effects of beach nourishment on indicator species populations in Florida. They conducted field sampling programs in Pinellas County on Florida’s west coast and Indian River County on the east coast to record patterns in the abundance of coquina clams and mole crabs in the swash zone and ghost crabs along the upper beach on nourished and un-nourished beaches. Each month, they monitored the physical attributes (beach width, slope, grain sizes) and the invertebrate populations of multiple beaches. Researchers scooped sand samples to collect coquina clams and mole crabs from the swash zone and counted the number and diameter of ghost crab burrows. Specific objectives were to record changes in the number and size of key beach-habitat species across space and time and to note the effects of beach nourishment on these target species. The results of this study will help managers develop beach nourishment strategies that minimize the effects on these species.
Coquina clams are edible, but consumers should follow the Florida Department of Health seafood safety guidelines and only consume shellfish collected from areas open to harvesting, which can be found on Florida Department of Agriculture and Consumer Services website.