New Publication: Acid secretion by the boring organ of the burrowing giant clam, Tridacna crocea

The giant clam (Tridacna crocea) in its natural habitat. Image from Figure 1a of Hill et al., 2018

The giant clam Tridacna crocea, native to Indo-Pacific coral reefs, is noted for its unique ability to bore fully into coral rock and is a major agent of reef bioerosion. However, T. crocea’s mechanism of boring has remained a mystery despite decades of research. By exploiting a new, two-dimensional pH-sensing technology and manipulating clams to press their presumptive boring tissue (the pedal mantle) against pH-sensing foils, we show that this tissue lowers the pH of surfaces it contacts by greater than or equal to 2 pH units below seawater pH day and night. Acid secretion is likely mediated by vacuolar-type Hþ-ATPase, which we demonstrate (by immunofluorescence) is abundant in the pedal mantle outer epi- thelium. Our discovery of acid secretion solves this decades-old mystery and reveals that, during bioerosion, T. crocea can liberate reef constituents directly to the soluble phase, rather than producing sediment alone as earlier assumed.

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