Lying on an idyllic island in the Maldives surrounded by crystal clear waters and palm trees might feel like you're in paradise. But whilst the waters lap the beach and you sip your piña colada, what you might not want to think about is the fact that you’re actually relaxing on a massive pile of feces.

Parrotfish feces to be precise. Researchers from Exeter University were able to calculate that the fish, which eat the coral, were producing roughly 85% of the sediment that goes into creating Vakkaru Island in the Maldives archipelago. In addition to this, they reckon that another 10% of the sand could be traced to the algae Halimeda. They’ve published their study in the journal Geology.      

Reef islands, of which Vakkaru is one, are by their nature composed only of sediment that is produced from the surrounding reefs. They occur wherever large coral reefs exist, from the Caribbean to Hawaii to the Pacific Ocean. How they are formed, however, hasn’t really been looked at. But it would seem that whilst the parrotfish are certainly beautiful to look at, they’re also playing a second role by topping the island up with their poo.   

The parrotfish are known to help control the algal growth on reefs and promote coral growth, explained Chris Perry who carried out the research. But the fish are particularly fond of coral polyps, and when the coral goes in one end, something has to come out of the other. No one, however, had really considered how much of a role they play in sediment production.  

The bony beak that gives the parrotfish their name is perfectly suited for chomping off lumps of coral. The fish then grind it with their teeth in order to extract the soft polyps that live in the rock. Once they’ve digested all the edible bits, they then excrete the sand. With all the fish swimming in the reefs, this sandy poo adds up. In fact, the researchers estimate that the fish produce 531,000 kilograms of new sand each year. That’s a lot of poop.

“Our study quantifies another fascinating aspect of the species – the major role they can play in producing the sediment necessary to build and sustain reef islands,” explained Perry.

The study highlights the vital links that exist between the life living on the reefs and the renewal of the islands you holiday on. “Coral reef islands are considered to be among the most vulnerable landforms to climate change and especially to future sea-level rise,” said Perry. “We provide evidence that protecting parrotfish populations, and the habitats on which they depend, is likely to be vital to ensuring a continued supply of the sediment from which these Maldivian reef islands are built.”

So just remember, next time you’ve decided to unwind on the beach, you’re actually just walking through one big pile of shit.