The clam, a familiar sessile bivalve mollusk, is often perceived as a silent resident of the seafloor. Clams are filter feeders that spend most of their lives partially or completely buried in sediment, relying on their protective shell for survival. While clams do not possess the biological structures for purposeful acoustic communication, their movements can and do create incidental noises.
Do Clams Produce Intentional Sounds?
Clams do not intentionally produce sounds for communication, which sets them apart from many fish and marine mammals. They lack the specialized organs required for purposeful acoustic signaling, such as a larynx, vocal cords, or drumming muscles.
The consensus among marine biologists is that clam communication is primarily non-acoustic, relying instead on chemical or tactile signals. Their relatively low metabolic rate and generally passive existence do not favor the evolution of high-energy acoustic displays. Furthermore, producing a loud sound could unnecessarily attract predators, a risk a largely immobile organism cannot easily afford.
Incidental Sounds from Clam Movement
Despite their general acoustic reticence, clams are not completely silent, as their daily activities and defensive maneuvers create transient noises. The most distinct sound a clam makes is a sharp click or clack when it rapidly closes its two shells, known as valves. This action is a direct, reflexive response to a perceived threat, such as a shadow passing overhead or a predator’s touch. The sudden, forceful contraction of the adductor muscles brings the shell halves together, producing a short-duration, high-impact sound pulse.
Another source of incidental noise comes from the clam’s method of burrowing into the sediment. During the digging process, the clam extends its muscular foot to anchor itself deep in the sand or mud. It then contracts its adductor muscles, causing the shell valves to contract inward and eject a jet of water. This expelled water helps to liquefy the surrounding sediment, reducing friction and allowing the clam to pull itself deeper into the substrate. The repeated, rhythmic ejection of water and the grinding of the shell against the sediment generates low-frequency sounds that can be picked up by sensitive hydrophones.
Noisy Neighbors: Other Sound-Producing Bivalves
The clam’s relative silence is highlighted when compared to some of its bivalve relatives. Scallops, for example, are known to produce distinct sounds when they swim to evade predators. They rapidly clap their valves together to create jet propulsion, and this movement generates a sharp crack followed by a softer, prolonged puffing sound, with frequencies that can reach 27 kilohertz.
Other invertebrates are far louder and often dominate the soundscape of shallow coastal waters. The snapping shrimp is a well-known example, generating extremely loud, rapid popping sounds through the cavitation of a water jet from its specialized claw. While clams do not contribute to the ocean’s acoustic environment in a purposeful way, many bivalves, including oysters, are highly sensitive to sound and will react to noise pollution by closing their shells.