A giant clam, Tridacna crocea, burrows into the solid carbonate rock made by tropical reef corals. The mechanism used by giant clams as a means of creating shelter had remained a mystery for decades, even to prominent coral reef scientists, but researchers led by Michigan State University's Richard Hill and UC Berkeley's Eric Armstrong, and including Martin Tresguerres' laboratory at Scripps Institution of Oceanography at UC San Diego, discovered it, describing the work in a paper appearing in the Royal Society journal Biology Letters June 13. The clam secretes acid that dissolves the calcium carbonate structures of coral reefs. Before, scientists had not been able to witness the secretion in the lab through traditional techniques. This team, however, allowed the clam to rest on a pH-sensitive foil undisturbed and were able to detect secretion of acid with pH in the 4 to 5 range. The secretions are made by the pedal mantle, a fleshy tissue mass that can be protruded from a clam, touching a reef surface. Intriguingly, the acid-secreting enzyme is the same "proton pump" that allows Osedax boneworms to dissolve and feed on whale carcasses, stingrays to regulate blood pH, and corals to promote photosynthesis by their symbiotic algae.
Besides Hill, Armstrong and the Tresguerres laboratory, researchers from San Francisco State University, and the University of Tsukuba and University of the Ryukyus in Japan contributed to the study. Photo: James Fatherree