Fish
Bumphead Parrotfish
Bolbometopon muricatum · also called green humphead parrotfish, buffalo parrotfish
The bumphead parrotfish is a fish the size of a large dog that eats the reef. It bites off living coral, crushes it in its throat, and the leftover skeleton comes out the other end as fine white sand. On some islands, a lot of the beach used to be inside a parrotfish.
Overview
Bolbometopon muricatum is the largest parrotfish, up to 1.3 m and 75 kg, with a steep forehead that grows a bony bump in adults. It lives on Indo-Pacific coral reefs in grazing herds and eats live coral and reef algae, grinding the coral skeleton with tooth plates in its throat.
Headbutting and sand
Large bumpheads ram coral outcrops with their heads to break off pieces, one of the few fish known to use the head as a tool. The indigestible coral comes out as sand — a single big fish can make hundreds of kilograms a year, and the species is a major source of tropical beach sand.
Easy to wipe out
It is big, slow, active by day, and sleeps at night in predictable groups in caves, so night spearfishing clears it from a reef quickly. It matures late and lives 30 to 40 years, so it recovers slowly.
Status
Vulnerable and declining across the Indo-Pacific, surviving best on remote reefs and in no-take marine reserves.
Bumphead Parrotfish: common questions
Does the bumphead parrotfish really make beach sand?
Yes, and on some reefs it is one of the biggest single producers. A bumphead parrotfish spends its day biting off and swallowing chunks of living coral and reef rock. Its gut digests the thin layer of living tissue and algae, and the hard calcium carbonate skeleton is ground up by tooth plates in the throat and passes out as a stream of fine pale sand. Researchers who have measured this put the output of a single large adult at somewhere between one hundred and one thousand kilograms of sand per year. Multiply that across a healthy population and parrotfish, with the bumphead prominent among them, are responsible for a large share of the white carbonate sand on tropical beaches and low islands.
Why does it headbutt coral?
To break the reef into bite-sized pieces. Adult bumpheads have been filmed swimming hard at a coral outcrop and striking it with the front of the head, sometimes repeatedly, to snap off branches or crack a surface before biting. Very few fish are known to use their heads as tools this way. The behaviour seems to develop with age and body size, roughly in step with the growth of the bony forehead bump, and biologists think the two are linked, with the bump both a product of the impacts and, possibly, a display feature used between rival males.
Is the bumphead parrotfish endangered?
It is listed as Vulnerable and is in decline across most of its range. The problem is a combination of an easy-to-catch fish and a slow life history. Bumpheads are huge, unafraid, active by day, and sleep at night in predictable groups in caves, so a diver with a light and a spear can take a whole aggregation in one night, and this has emptied reef after reef near populated coasts. Because the fish matures late, lives for decades, and spawns at particular sites, a stripped population recovers only very slowly. It now does best in remote reefs and in marine reserves where fishing is banned.
How is a bumphead parrotfish different from a humphead wrasse?
They are both very large reef fish with a bulging forehead, they share parts of their range, and their names are almost interchangeable, but they are unrelated. The bumphead parrotfish is a parrotfish, with a fused parrot-like beak, and it eats coral and reef algae, living in grazing herds. The humphead wrasse, also called the Napoleon wrasse, is a wrasse, with thick separate lips and peg-like teeth, and it is a predator of hard-shelled animals such as sea urchins, molluscs, and crustaceans, including crown-of-thorns starfish. The wrasse is generally the heavier of the two and is also threatened, mainly by the live reef food-fish trade.