For the first time, drones have revealed the huge scale of sea cucumber poo at an Australian reef, and it has scientists worried about the ecological impact if their numbers decline.
Their high value on Asian markets has encouraged overfishing, and sea cucumbers are now under threat from commercial fisheries.
"Our research found that each year sea cucumbers can poop over 60,000 tonnes of sediment across a coral reef, approximately the mass of five Eiffel towers," study co-author Vincent Raoult said.
"It is likely that most of the sediment found on coral reefs has been through a sea cucumber many times, and therefore the disappearance of these creatures would have negative flow-on effects to reef ecosystems."
Sea cucumbers spend their lives eating sediment, digesting the microorganisms present, and pooping out 'clean' sediment, just like earthworms.
The process plays an important role by aerating the sea floor, providing 'fresh' sediment, and releasing calcium carbonate into the water as a by-product to help support coral growth.
"There is great concern among scientists that the important ecological function of sea cucumbers will be lost," lead researcher Jane Williamson said.
"Until now though we did not know just how large this effect could be on a reef, because counting sea cucumbers on such a vast scale is difficult."
On Heron Island off Queensland, researchers deployed drones to map nearly 30,000m2 of the reef lagoon at very high resolution,allowing sea cucumbers to be seen and counted.
"Using satellite data, we then extrapolated these patterns to the entire reef to have an approximate total number of sea cucumbers present," Associate Professor Williamson said.
"In parallel, we ran experiments in aquarium facilities to determine how much sediment was passed by individual sea cucumbers on a daily basis."
By combining this information, researchers were able to calculate the amount of poo produced by sea cucumbers every year across this 18km2 reef.
"Data on this scale would have been impossible using traditional methods, which requires swimming in approximately straight lines and manually recording every sea cucumber that is seen," Dr Raoult said.
The study was published by researchers from Macquarie University, the University of Newcastle and James Cook University.
They're hoping that the method of surveying can be expanded to ensure global populations are adequately measured, understood and managed.