Variable Coquina
Donax variabilis Say, 1822
Family Donacidae (Wedge Clams and Coquinas)
Coquinas are found in great numbers in the surf zone of sandy beaches. Although these clams spend most of their time buried in the sand, they emerge several times per tidal cycle to migrate with the waves. This process is not merely the passive erosion of clams from the sand; rather the clams actively jump out of the sand, using sound to identify large waves. Activity is greatest during the rising tide, when the clams emerge to ride only the largest (loudest) 20% of waves, which move them furthest on the beach. Donax variabilis is renowned for its polychromism (many colors), believed to act as an anti-predator device, preventing shore birds from forming a single search image of the clam. The family Donacidae is known since the Cretaceous Period and is represented by ca. 5 living genera and ca. 60 species, distributed worldwide.
