The sound of the world’s largest parrot fish swimming toward him, says Douglas McCauley, is not some watery swish, swish. It’s crunch, crunch. “You can hear a school of them before you see it,” he says.
Bumphead parrot fish (Bolbometopon muricatum) grow to “about the size of a junior high school kid” as McCauley puts it. And feeding is a noisy business because they eat -- and loudly digest -- what’s essentially rock.
The fish gouge out hunks of reef and snap thumb-sized coral branches. But what McCauley finds even more impressive are the noises of the parrot fish’s down-deep throat teeth, which can grow wider than half dollars, milling the coral chunks.
Crushing coral uncovers what the fish really want: fleshy polyps and other tiny organisms hiding inside. Bumpheads excrete the broken-up coral as gravel and a plume of white sand that “just hovers,” McCauley says, “as if you had opened a carton of milk underwater.”
So prodigious a grinder of coral is the bumphead that more than four tons of coral sediment land on the reef in a year from the excretions of a single parrot fish.
Calculating that number required 130 days underwater from McCauley, now at the University of California, Santa Barbara, and a series of helpers carrying syringes the size of turkey basters for collecting excreted coral.