TRANSCRIPT
Crown-of-thorns starfish populations are again flourishing along the Great Barrier Reef.
Symon Dworjanyn is a professor of marine ecology at Southern Cross university.
"Crown-of-thorns starfish, they're actually natural to the Barrier Reef and all through the Indo-Pacific, but what they do (is), they eat coral, which is completely natural, but what happened in modern times is we believe there's been more common outbreaks of crown-of-thorns starfish. And what they do is, they can devastate coral reefs because they eat coral. And our concern, and the thing that we don't know, is why their numbers have increased in modern times."
As Professor Dworjanyn says, these starfish consume the corals that make up the Great Barrier Reef.
Christina Skinner, a marine biologist at Queensland University, explains the importance of coral.
"We obviously value live coral as something that's quite important to the reef, especially the Great Barrier Reef. The live coral provides structure and a kind of home to loads of animals and loads of fish and these starfish are very, very good at stripping away all that coral very, very quickly, which then stops it from being able to grow back in time."
But now something new is known about the crown-of-thorns starfish.
Matthew Clements has co-authored a new report by the University of Sydney.
The report says researchers found in their juvenile form, the crown-of-thorns starfish are incredibly resistant to heat, which allows them to survive even through the most intense sea temperature rises brought on by global warming.
"Generally for marine invertebrates, the juvenile stage is usually less tolerant of changes in temperature, it's called a thermal window. They have a lower thermal window compared to the adults."
He then goes on to specify how biologists believe crown-of-thorns starfish were able to replicate this trait.
He says it was born from a characteristic of a completely different type of starfish.
"So some predatory seastars - there's one in European waters, in the northern hemisphere, called marthasterias glacialis - and so these large predatory seastars, they have a juvenile stage which seems to be able to alter their physiology to be able to remain in the juvenile stage."
Dr Dworjanyn says even though the juvenile crown-of-thorns don't eat coral, their resistance to heat still poses a significant threat.
"That juvenile phase, when they're not eating coral, they're particularly resistant to heat. So, more resilient than, for example, coral are. So, coral, if you get (global) warming, if you get a heat wave of one to three degrees, something like that, they'll start bleaching and start dying, but these juvenile crown-of-thorns starfish seem very resilient to that level of heat - and that's a concern."
So those herbivorous juveniles survive the bleaching event, and mature into coral-eating adults.
The University of Sydney researchers noted a new population explosion along the Great Barrier Reef.
Marine biologists seem unsure about the reason behind this latest sudden surge and, as Queensland University's Dr Skinner explains, if they remain unchecked, this could lead to bigger problems.
"So, some of the work that we're doing at the moment is, we've got these kind of models that represent the Great Barrier Reef and we're able to look at the difference between actually controlling these starfish by manually removing them and not doing anything at all. And we've found that when they are left unchecked, they will increase in numbers and take away much more live coral than if we actually remove them and keep their numbers low."
Dr Skinner goes on to detail how they're reducing the crown-of-thorn starfish population.
"So, at the moment I think the best thing that we have managed to do is manually remove them. So there are teams of divers that go into the water and they'll inject these starfish with vinegar. Just household vinegar. And what that does is, it will actually kill the starfish and it will hopefully stop them from then replicating and eating all the live coral."
But, as Dr Skinner explains, crown-of-thorns starfish still remain a valuable member of the marine ecosystem.
"I would highlight that they are natural. I mean, they're not an invasive species, which I think a lot of people tend to misunderstand. So they are supposed to be there, they're supposed to be in the ecosystem and they do play quite an important role, just kind of keeping things in check, in equilibrium. So they tend to feed most on the fast-growing branching coral, which is the acropora, and it's actually quite good to remove that sometimes, just to allow slow-growing other corals to come through. But the problem at the moment is that they're becoming really high in number and having these outbreaks, which is obviously not what we would normally see."
