Well, we have a fish that poops out tropical beaches!
Wait…beaches are made of poop?
What kind of fish could poop this much sand? Surely it must be huge? A whale shark perhaps?
Nope, it’s something far smaller – a parrotfish!
Parrotfish are small, beaked fish. Their beaks are actually 15 rows of over 1 000 teeth that grow continuously – like a rodent! In a feat of natural nano-technology, these teeth are woven together, forming lattices of razor-sharp mineral fibres just 2 millionths of a metre wide. These are the strongest teeth of any animal that has ever lived.
Despite their beak, and reputation for being voracious coral-eaters, most parrotfish actually eat algae. These algae grow in the skeleton of corals, so by biting off these bits of infected coral, parrotfish are actually improving the health of the reef!
The predatory parrotfish are even more significant, they eat coral polyps and use special teeth in their throats to grind up the coral skeletons. In fact, one average-sized adult parrotfish can grind up and poop out almost 100kg of coral sand a year!
This behaviour is actually good for the corals. The bits eaten by parrotfish are often infected with algae, diseased or have been stunted – the “damage” caused by the fish, actually helps the corals grow. The sand that the parrotfish poop out forms a substrate that the corals can grow onto, thus helping the reef to become more permanent.
Surely not all beaches can be made of parrotfish po-po!?
Sand is any mineral that is ground up finely, it is not always fish poop. The beaches around Cape Town, for example, are made of quartz – the ground-up remnants of millions of years of erosion of the Cape Peninsula. Most sand consists of eroded minerals like this – white quartz, yellow and pink feldspar and black volcanic glass.
White tropical sands are a different story, much of this is made of organic matter – ground-up corals eaten by parrotfish and the shells of dead shellfish and microscopic organisms.
Eighty-five percent of all the sand of Vakkaru Island of the Maldives is parrotfish poop.
In Hawaii, each parrotfish can eat 380kg of coral a year – converting 60% of the reefs' growth into white sand. They poop out so much sand, that they are called uhu in Hawaiian, meaning “loose bowels”.
But, the king of all parrotfish, the giant humphead of Mexico and the Caribbean, can poop out almost 5 tons of sand a year (video below)! It would take you more than 30 years to poop that much!
In South Africa we see bluebarred parrotfish (Scarus ghobban), ember parrotfish (S. rubroviolaceus) and blue humphead parrotfish (Chlorurus cyanescens) in the subtropical waters of KwaZulu-Natal. Like other herbivorous parrotfish, they chomp up corals for algae and make sand in the process.
No studies have been done on South African beaches, but next time you dig your toes into some lovely beach sand, there’s a good chance that it’s parrotfish poop (we’re looking at you Durban).
Thank you for the beaches parrotfish!