Monitoring the Effects of Beach Nourishment

The coquina clam Donax spp. is a common inhabitant of the intertidal zone of Florida’s sandy beaches. Known for their highly variable color patterns (right), 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 represent a critical food source for fish, crabs, and shore birds. Because their naturally high abundance and ecological importance, coquina can be used as an indicator species for beach communities.

 

Although they are not mollusks, other fauna commonly found on the beach includes the mole crab Emerita talpoida (left) and the ghost crab Ocypode quadrata (below left). Like coquina, mole crabs are filter feeders that burrow in the fluid sand of the swash zone. Ghost crabs are found on the upper portion of the beach, above high tide. These animals normally reside in burrows (below right) during the day and forage at night. Very little is known about the effects of beach nourishment on the natural populations of these fauna.

Molluscan Fisheries at the Fish and Wildlife Research Institute began monitoring the physical attributes and invertebrate populations of six Pinellas County beaches in September 2005. Belleair Shores, Redington Beach, and Fort DeSoto Beach were chosen as control sites while two locations along Indian Rocks Beach and Indian Shores were within the construction area of the 2005 Sand Key Beach Renourishment Project.

All sites are monitored monthly and measurements taken to monitor changes in the height and width of the beach. Sediment cores on the upper and lower beach are collected to compare changes in grain size and organic matter content due to the addition of sand taken from offshore dredging. Surveys of Ocypode quadrata burrows are conducted on the upper beach to estimate changes in population abundance. Samples from the swash zone are carefully sorted to find Donax spp. and Emerita talpoida. These animals are quantified and the measured to monitor the natural population abundance and impacts of nourishment.