How do marine invertebrates produce sounds?

Sound production by marine invertebrates has not been investigated to the same extent as it has been for fishes and marine mammals. However, sound production in the European spiny lobster, semi-terrestrial crabs, and snapping shrimp has been well documented. Other marine invertebrates may also produce sound, but their sound production mechanisms have not been studied in great detail.

Most marine invertebrates known to produce sound do so by stridulation or rubbing two body parts together. Spiny lobsters produce a rasping sound using their antennae. The method a spiny lobster uses to produce sound has been compared to that of a violin. In a violin, the bow “sticks and slips” over the strings due to friction, generating acoustic vibrations. Spiny lobsters also produce sound using “stick and slip” friction. When the lobster moves its antennae in certain ways, a piece of soft tissue called the plectrum rubs against a smooth, stiff file located near the eye, resulting in the production of sound. Most marine invertebrates that use stridulation to produce sound rely on hard surfaces. However, spiny lobsters are unusual in that they produce stridulatory sounds using a soft-tissue plectrum. Because the “stick and slip” method does not require hard parts, spiny lobsters can still make sound when their exoskeleton softens during the molting process. This reduces their vulnerability to predators because they can still produce sound as a defense mechanism.

This diagram illustrates how spiny lobsters produce sound. They make a “rasp” sound by rubbing a plectrum (an extension off of the base of each antenna) over a file which is located on each side of a plate below the eyes. The plectrum is made of soft tissue and the file is smooth, which means that spiny lobsters make sound differently than other arthropods. Most arthropods rub a hard pick over a series of bumps to make sound (like a washboard). Instead, spiny lobsters use “stick-slip” friction between the soft plectrum and sticky-smooth file to make sound pulses (like a bow moving over the strings of a violin). Artwork © Sally J. Bensusen/Visual Science Studio (

Some species of semi-terrestrial crabs also use stridulation to produce sound. Sounds produced by the crabs are transmitted through the air and the substrate. Fiddler and mangrove crabs produce stridulatory sounds within their burrows. Multiple anatomical structures on the claws, walking legs, and carapace of fiddler crabs are used for stridulation. The crabs rub their enlarged claw against any of these other structures to produce sound. Mangrove crabs also produce stridulatory sounds. These crabs have hard ridges, or tubercle and rows of bristles, called setae, on the dorsal side of their enlarged claws. When one claw rubs against the other, a rasping sound is created. The crabs may also place one claw on the substrate and move the other claw up and down against the stationary claw, producing sound. With one claw in contact with the substrate, vibrations may be transmitted through the ground (see: How do marine invertebrates detect sound?).

Semi-terrestrial crabs also produce sound by vibrating their appendages (legs, claws, tail), dancing, drumming two body parts together, and/or drumming a body part against the substrate. Male ghost crabs have very elaborate visual and acoustic displays. Rapping sounds are produced as a result of the crabs hitting the ground with one of their claws. The crabs produce faster and longer rap trains by drumming with both claws. Rapid stepping during dance displays also produces a low level scurrying sound. Male fiddler crabs also use their claws to produce sound by striking various parts of their body or the substrate. A variety of sounds produced this way have been described as drumming, honking, rasping, hissing, and rapping. Some species can be identified by the frequency and time interval of their sounds. For example, the sand fiddler crab produces rapping sounds between 600 and 2400 Hz and the mudflat fiddler crab produces sounds between 300 and 600 Hz.

Ocypodej ousseaumei, a species of ghost crab that produces sound by stridulation and/or rapping its claws against the substrate. Image courtesy of David Clayton, Sultan Qaboos University (Oman).

Ghost crab, Ocypodej ousseaumei, producing rapping sounds. Sounds were recording by inserting a small microphone into the substrate near crab burrows.
Sound clip provided by David Clayton, Sultan Qaboos University (Oman).

The Long-spined sea urchin has been observed to produce crackling sounds through stridulation of its long, stiff spines during movement. Stridulatory sounds may also be produced by the test and a special feeding structure, the Aristotle’s lantern. The five teeth present in the lantern protrude from the ventral side of a sea urchin and are used to scrape kelp or invertebrates from the substrate. The calcified test of the sea urchin can also act as a resonator. In the Kina, a species of sea urchin found in New Zealand, the scraping of the Aristotle’s lantern against the rocks causes the fluid inside the urchin to resonate, which causes sound to be produced. There are other noises associated with Kina feeding activity, such as the spines and feeding apparatus of the urchin scraping against rock. However, scientists found these sounds to be secondary that which was produced by the exoskeletal resonance. Underwater sounds associated with grazing Kina urchins range in frequency from 800 Hz-28 kHz and contribute to the surrounding soundscape. Scientists found ambient sound intensity levels in New Zealand coastal waters to increase as much as 2-3 orders of magnitude (20-30 underwater dB) during the sunrise/sunset periods – an increase related to sea urchin feeding activity.

Most sea urchins possess – in addition to a calcified test and numerous spines – a complex feeding apparatus, the Aristotle’s lantern. This structure is composed of multiple calcified elements and numerous soft parts such as muscles and connective tissue. Each lantern contains five teeth that protrude from the ventral side of the sea urchin. These teeth are used to scrape the sediment in order to obtain food. This scraping action produces an almost constant underwater noise in areas inhabited by sea urchins. 3D and 2D visualizations based on a micro-computed tomography scan of the European edible sea urchin (Echinus esculentus). Images courtesy Alexander Ziegler, Harvard University.

The snapping shrimp, is a common, well-researched sound producer in the ocean. Snapping shrimp have two claws, one of which is greatly enlarged and can grow up to half the size of the entire body. It was once thought that sounds produced by snapping shrimp occurred as a result of the top and bottom parts of the claw striking each other when it was snapped shut. However, it was later discovered that the sound is actually caused by the popping of a bubble that is produced when the claw opens and closes rapidly. The enlarged claw is usually slightly opened but during muscle contraction, the claw closes at a very high speed. This causes the water to cavitate and form a bubble of vapor. The sound that is heard from the shrimp is produced upon collapse of this bubble.

Freeze-framed images from a high-speed video recording showing the bubble produced by the snapping shrimp. Photo series courtesy of Department of Applied Physics, University of Twente.

Some marine invertebrates use rapid muscle contractions to produce sound. Muscle contractions at the base of the American lobster’s antennae, for example, cause vibrations of the animal’s carapace. These vibrations create low frequency “buzzes” at approximately 180 Hz. Some benthic mantis shrimp also produce sound by vibrating their carapace. Low frequency “rumbles” by the California mantis shrimp have a dominant frequency of 167 Hz, on average, and last about 0.2 s. Scientists have recorded multiple individuals in an area producing rumble sounds simultaneously.

The California mantis shrimp, Hemisquilla californiensis, produces sounds by vibrating its carapace. The low frequency rumbles of the mantis shrimp are approximately 167 Hz and last approximately 0.2 s. Acoustic activity is high during dawn and dusk, a time when the animals are feeding or guarding their burrows. Image credit: Roy Caldwell, University of California, Berkeley.

Many New England mussel produces sound with its byssal threads, which the animals use to attach themselves to hard substrates. At temperatures above 10 degrees Centigrade, mussels can produce snapping sounds by stretching and breaking the byssal threads. Sound production attributed to the New England mussel provided the first understanding of background noise levels produced by marine organisms in areas other than the southern and tropical coasts. Scallops “cough”, rapidly contracting the two valves of their shell to expel water, feces, and other substances from inside their central cavity. This action produces a sharp “crack” followed by a long puffing noise as the two valves close. These distinct sounds ranging in frequency from 20-27 kHz.

“Coughing” sounds are produced by scallops as they rapidly contract the two valves of their shell to expel particle matter.
Sound courtesy of Lucia DI IORIO, CHORUS (released under Creative Commons Attribution, Non-Commercial)

Additional Links on DOSITS