The underside of a sea urchin’s body is referred to as the “oral surface”, because it contains the mouth. The mouth of most urchins is comprised of a complex five-part, triangular, calcium-carbonate structure (called Aristotle's lantern) with large teeth and a fleshy tongue-like sucking part. The hard, triangular teeth are primarily used to scrape algae from the substrate. Although sea urchins are primarily herbivorous (eat plants), they can also feed on sea cucumbers, mussels, worms, sponges, and brittle stars. Sea urchins are important grazers, however, if their population becomes too large, they can completely strip marine environments of plant material.
Grazing sea urchins produce underwater sounds that contribute to the surrounding soundscape. The calcified test of the sea urchin acts as a resonator. In the Kina, the scraping of the rocks by the teeth causes the fluid inside the urchin to resonate. This resonance causes sounds to be produced that range in frequency from 800 Hz-28kHz. Scraping of the feeding apparatus and spines also produce sound, but scientists found the sounds associated with resonance to be dominant.Ambient sound levels in coastal waters tend to increase immediately before sunrise and after sunset during the “dawn” and “evening chorus”. The evening urchin chorus is distinctive and may be an important acoustic source of habitat information for other marine organisms listening to this sound (see How to marine animals use sound?). In New Zealand waters, feeding sounds associated with Kina sea urchins dominate the evening chorus in the 700-2000 Hz frequency range. Other sea urchin species could be responsible for evening choruses with a similar frequency bandwidth in other parts of the world.
- Stanford University, "Sea Urchin Embryology, Natural History (of sea urchins)" (Link)
- University of Michigan, "Animal Diversity Web, Echinoidea." (Link)
- Wikipedia, "Sea Urchin." (Link)
- Radford, C.A., J.A. Stanley, C.T. Tindle, J.C. Montgomery, and A.G. Jeffs. 2010, "Localized coastal habitats have distinct underwater sound signatures." Marine Ecology Progress Series. 401: 21-29.