Coral reefs face a large amount of threats, including damages from human use of the seas and areas around them, as well as a variety of pollutants. There are efforts all over the world to help save them, but one species is doing its part to help… with its poo.
Researchers from Macquarie University, the University of Newcastle and James Cook University in Australia recently studied how sea cucumbers’ poo is helping the Heron Island Reef in Queensland. They say what they found shows the importance of this animal.
Dr. Vincent Raoult, co-author and marine scientist at the University of Newcastle, explains, “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. 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 play an important role because they eat sediment, digest the micro-organisms within it, and poop out clean sediment. The process is similar to what earthworms do on land. Bioturbation, as it’s called, aerates the sea floor, provides fresh sediment, and releases calcium carbonate into the water as a by-product to help coral grow.
To determine just how much of an impact these creatures and this process have, the study used drones to map nearly 30,000 square meters of the Heron Island Reef lagoon. The images were high enough resolution to allow researchers to see and count sea cucumbers. Jane Williamson, lead researcher and Associate Professor from Macquarie University, says they used this information to estimate how many sea cucumbers were present along the whole reef. At the same time, they determined how much sediment was passed by an individual sea cucumber by conducting experiments in an aquarium setting. With both sets of information, they were able to estimate how much poo all of the sea cucumbers within the reef produced.
After learning that the annual figure added up to more than 60,000 tonnes, researchers say the study really underscores the importance of these animals and highlights the threats they are facing.
Williamson said, “There is great concern among scientists that the important ecological function of sea cucumbers will be lost. Until now, though, we did not know just how large this effect could be on a reef, because counting sea cucumbers on a such a vast scale is difficult.”
The researchers note that sea cucumbers are the victims of overfishing, especially due to their value in Asian markets. They are now threatened globally, with seven species endangered and nine in a vulnerable category. The problem is found globally. Dr. Raoult says even in Australia, the animals are often only valued for their importance to fisheries, not reefs.
He explains, “Perhaps because they’re seen as boring, they get ignored and the risk is that as a result they haven’t been considered an important factor in the ecosystem of coral reefs.
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“If we want to have healthier reefs, we can’t just ignore the fact that sea cucumbers are disappearing and focus solely on climate change, even though that is the major threat to coral reefs, we have to make sure that we address other issues such as overfishing as well. It’s very hard though for scientists to have a sense of what the loss of a species might be if we don’t know the scale of their role in the ecosystem.”
The researchers say the takeaway from their work should be that sea cucumbers likely play a bigger role in the health of reefs than was previously thought, and there needs to be more of a focus on their management and ecology, as well as the overharvesting of reefs.
Reefs could use all the help they can get to stay healthy. The U.S. Environmental Protection Agency says reefs are threatened due to ocean acidification, coastal development, dredging, quarrying, destructive fishing practices, boat anchors and groundings, and recreational misuse, as well as a variety of pollutants that enter the oceans from land. Those include sedimentation from coastal development and agriculture, nutrients from fertilizer use and sewage discharges, pathogens from poorly treated sewage and livestock runoff, trash, microplastics, and more.Whizzco