The disco clam, Ctenoides ales, is a remarkable marine bivalve known for its captivating light display. Its distinctive, rapid “flashing” appearance immediately draws attention. This light show is not bioluminescence, where organisms chemically produce their own light, but rather a unique optical illusion created by the clam itself.
The Unique Light Display
The disco clam’s flashing light is generated by specialized mantle tissue. This tissue has two distinct layers. One layer is densely packed with highly reflective silica nanospheres that reflect blue light, the predominant light in their habitat. The other layer of tissue is opaque and absorbs light.
The clam creates the illusion of flashing by rapidly flipping these two layers of tissue back and forth, exposing and hiding the reflective silica-filled side. This rapid movement, occurring at about 2 flashes per second, causes the ambient light to reflect and then disappear, producing a strobe-like effect. This method of light production, relying on rapid reflection rather than chemical reactions, is a rare adaptation among marine organisms.
Where Disco Clams Live
Disco clams are found in the shallow tropical and subtropical waters of the Indo-Pacific region. Their geographical distribution spans areas from Indonesia to the Palau Islands and New Caledonia. These bivalves inhabit coral reefs and rocky crevices, attaching themselves to the underside of rocks or within small holes.
They position themselves in dark nooks and crannies, allowing only their vibrantly colored mantle to be exposed. This strategic placement within crevices helps them remain hidden from potential threats while still showcasing their unique visual signal. Disco clams are encountered at depths ranging from 10 to 160 feet below the surface.
Life in the Reef
Within their reef environment, disco clams are sessile filter feeders, meaning they remain attached to a surface and strain food particles from the water. They use their gills to filter out tiny plankton and other detritus.
The disco clam’s light display is believed to be a warning signal to predators. The flashing, combined with their bright reddish-orange mantle tissue, which may contain unpalatable compounds, deters potential threats like fish, cephalopods, and crustaceans. While they possess around 40 small eyes, these clams cannot see the flashes from other disco clams, indicating the display is not for mating or attracting prey.