Donax variabilis

The coquina clam, Donax variabilis, ranges from the eastern coast of the United States, from New York to the Caribbean, and across the Gulf of Mexico and into Texas. (Ruppert and Fox, 1988)

Coquina clams are commonly found at sandy beach fronts in the intertidal zone, where the tides ebb and flow. Some can also be found in knee-deep waters. (Delancey, 1999)

Coquinas have small, long, triangular-shaped shells, ranging from 15 to 25 cm in length. These shells contain very colorful bands, with a range of colors anywhere from red to violet. (Miner, 1950)

Coquina clams undergo indirect development, first from a trochophore larva to a veliger larva. The veliger larva uses its ciliated velum for swimming and feeding on plankton. Eventually, the veliger will settle to the seafloor, where it undergoes metamorphosis to the adult stage. ("Bivalves", 2007)

Coquinas typically live in close proximity of each other, sometimes in colonies. They release their gametes when gravid and their close proximity with each other heightens the chances of fertilization. ("Coquina Clam", 2009)

Coquina clams are dioecious (male and female) broadcast spawners. Eggs and sperm are released synchronously into the water for external fertilization. ("Coquina Clam", 2011)

There is no form of parental care. Fertilization occurs externally and larvae are left to feed and swim independently. ("Bivalves", 2007)

Coquinas typically live between 1 to 2 years in the wild but can only live up to 3 days in the absence of moving water. Lack of water deprives the coquina of nutrients obtained through filter feeding. ("Coquina Clam", 2011)

Coquinas are active animals, found migrating up and down beaches with the assistance of waves. They use their muscular foot to burrow into the sand as waves recede down the beach to prevent being swept away. They are also known to use the waves in order to move up the beach and are capable of moving horizontally along the beach. (Delancey, 1999; Ellers, 1995; Turner, Jr. and Belding, 1957)

There is no known social communication between coquinas. However, they have a tendency to live within close proximity of each other, most likely due to favorable environmental factors for the clams. ("Coquina Clam", 2009)

Coquinas are filter feeders, feeding primarily on phytoplankton, algae, detritus, bacteria, and other small particles suspended in the surf as the waves ebb and flow. Feeding is performed through the use of short siphons. (Delancey, 1999)

Coquinas are consumed by various fish (such as Trachinotus carolinus and Menticirrhus spp.), shore birds, and humans (Homo sapiens). ("Coquina Clam", 2011; Delancey, 1999)

Coquinas serve as food sources for shorebirds, fish, and humans. In addition, the abundance of coquinas on beaches is an indicator of the beach habitat’s ability to sustain life. A beach with a large number of coquinas indicates a healthy beach habitat due to the presence of naturally-formed sand and the absence of external factors such as human construction. ("Coquina Clam", 2011)

Coquinas are eaten and used as decoration because of their colorful markings. The shells are also be used in ornamental landscaping. ("Coquina Clam", 2011)

Through their filter-feeding, coquinas can concentrate toxins and harmful organisms (bacteria, viruses, etc) that may cause harm to humans when eaten. ("Bivalves", 2007)

Coquinas are not listed in the IUCN, as they are very common along beaches in the eastern United States. However, coquinas face certain challenges, such as rising sea levels, global warming, and beach erosion. Laws and regulations that curtail erosion and maintain the natural flow of sand on beaches benefit populations of this clam. (Delancey, 1999)

Other common names for Donax variabilis include bean clam, butterfly clam, donax clam, and southern coquina. ("Coquina Clam", 2011)