The use of feeding noises to determine the algal foods being consumed by individual intertidal molluscs

Summary

To study the diets of individual animals in the context of intraspecific resource partitioning, it is desirable to detect what individuals are eating without disturbing them. Animals such as slow-moving molluscs on two-dimensional algal foods would be convenient to study, but the mouth is usually difficult to see, especially with limpets. However, one can often hear how an herbivorous mollusc is feeding. Even when the mouth region can be checked for feeding movement, feeding noises can indicate to what degree a mollusc is “licking” microscopic material off the surface of a plant versus biting into the plant, though licking microscopic material off the plants seems to be rare. Noises also indicate the food's texture, identifying the food species when several different algae are near the mollusc's mouth. Comparing various molluscan taxa, differences in radular structure and movement are associated with different feeding noises, even while different molluscs are eating the same alga. Sound thus aids in specifying which species are feeding where molluscs are close together.

Feeding is most common on wet surfaces at night. While the molluscs are above water or less than 5 cm deep in calm water, several listening methods are useful after some practice. Even the unaided ear can hear emerged molluscs rasping resonant kelps. One can detect rasping by molluscs greater than 1 cm in length by gently contacting the alga closest to the mouth with a stethoscope or with a gum rubber tube sealed against one's ear. A cassette tape recorder with a contact microphone and headphones is useful for both emerged and submerged animals. Representative feeding noises have been documented using oscillograms from tape recordings. Analogous sounds in both terrestrial and marine environments can be useful in numerous behavioral studies.