Donax variabilis

Geographic Range

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)

Physical Description

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

  • Sexual Dimorphism
  • sexes alike
  • Range length
    15 to 25 mm
    0.59 to 0.98 in


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)

  • Breeding interval
    Gametes are released when gravid

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

  • Parental Investment
  • no parental involvement


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)

  • Typical lifespan
    Status: wild
    2 (high) years


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)

Communication and Perception

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)

Food Habits

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)

Ecosystem Roles

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)

Economic Importance for Humans: Positive

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

  • Positive Impacts
  • food
  • body parts are source of valuable material

Economic Importance for Humans: Negative

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

Conservation Status

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 Comments

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


Mike Luna (author), Rutgers University, Jonathan To (author), Rutgers University, David V. Howe (editor), Rutgers University, Renee Mulcrone (editor), Special Projects.


Atlantic Ocean


World Map



World Map

bilateral symmetry


causes disease in humans



uses smells or other chemicals to communicate


the nearshore aquatic habitats near a coast, or shoreline.


an animal that mainly eats decomposed plants and/or animals





external fertilization

fertilization takes place outside the female's body


union of egg and spermatozoan







intertidal or littoral





having the capacity to move from one place to another.

native range







an animal that mainly eats plankton


an animal which has a substance capable of killing, injuring, or impairing other animals through its chemical action (for example, the skin of poison dart frogs).

saltwater or marine



remains in the same area




uses touch to communicate


2007. Bivalves. Pp. 311-20 in Encyclopedia Britannica, Vol. 24, 1 Edition. Chicago: Encyclopedia Britannica, Inc.

2011. "Coquina Clam" (On-line). Encyclopedia Britannica. Accessed March 03, 2011 at

Scienceray. 2009. "Coquina Clam" (On-line). Scienceray. Accessed December 29, 2010 at

Delancey, L. 1999. "Coquina Clam" (On-line). Accessed February 26, 2011 at

Ellers, O. 1995. Behavioral control of swash-riding in the clam Donax variabilis. The Biological Bulletin, 189: 120-7.

Miner, R. 1950. Field Book of Seashore Life. New York: G.P. Putnam's Sons.

Ruppert, H., R. Fox. 1988. Seashore Animals of the Southeast. Columbia: University of South Carolina Press.

Turner, Jr., H., D. Belding. 1957. The tidal migrations of Donax variabilis Say. American Society of Limnology and Oceanography, 2: 120-4.