A crown-of-thorns starfish outbreak has been discovered on the little-known coral reefs of Western Australia's Pilbara region, which are already suffering from severe coral bleaching
Ben Collins ABC News 27 Nov 14;
Crown-of-thorns starfish are synonymous with threats to the world-famous Great Barrier Reef (GBR) which stretches along Queensland's populated coastline. The coral-eating invertebrate is considered to be a major cause of the loss of over half of the GBR's coral cover.
But a recent attempt to learn more about the poorly studied coral along the opposite coast, adjacent to the Pilbara's deserts and iron ore mines, has revealed the crown-of-thorns starfish has boomed as the remote reefs struggle with recent bleaching events.
Senior research scientist with the CSIRO Dr Russ Babcock told ABC North West WA radio's Hilary Smale the starfish outbreak was hitting the Pilbara reefs while they were down.
"With the bleaching that's happened in many parts of the region, areas that do still have reasonably good coral cover are a magnet for these starfish because they can smell the food, literally, and they'll just crawl right up to them," he said.
Coral eater
For millions of years the crown-of-thorns starfish has evolved to eat coral polyps, the tiny animals that build sometimes massive coral reefs. But increasingly, the balance of coral growth and destruction has been tipping.
"If you get too many starfish, the rate at which they eat the coral is going to be faster than the rate at which the coral can replace itself," Dr Babcock said.
When Dr Babcock and his colleagues started their research aimed at building up knowledge of North West Australian reefs, they quickly realised that there was a previously unknown problem with crown of thorns.
"We noticed significant numbers of starfish and thought, 'Well we had better go and do some proper measurements of this and see how extensive they are'," he said.
When scientists count more than 10 starfish per hectare, then the situation is described as an 'outbreak' of crown of thorns. In the subsequent counts of crown-of-thorns starfish along the Pilbara coast, scientists counted as many as 220 per hectare around Barrow Island and the Montebello Islands.
Bad timing
The outbreak comes at a time when scientists were already concerned about the impacts of 'marine heatwaves' and subsequent coral bleaching destroying reefs in the area. Some ancient coral heads that have survived for over four centuries have recently succumbed to rising ocean temperatures.
"We suspect this bleaching event was due to marine heatwaves that occurred in the region over the past few summers, and to see it up close was sobering," Dr Babcock said.
While the impact of coral bleaching is severe, crown-of-thorns starfish are an equally potent threat.
"They're one of the not only largest starfish on the planet, but they're also probably the fastest growing and most voracious," he said.
"It's equal to the impact of cyclones in terms of knocking back coral cover."
And actual cyclones are prevalent along the Pilbara coast, combining with the starfish and bleaching to create a situation that is deeply concerning Dr Babcock.
"The Pilbara is the most cyclone prone part of the coast of Australia, it's recently suffered from three out of four years where it's had bleaching, and now it's got crown of thorns. So that's going to have some impact on the ability of reefs to recover."
Deadly combination
The combined threat to the Pilbara's coral reefs could lead to the demise of the very ecosystems that Dr Babcock originally intended to document.
"The coral provides the home for all the fishes and everything else in the ecosystem that depends on the shelter and the structure that they build," he said.
Protecting coral reefs from this trifecta of threats is extremely difficult. There is some evidence that manual removal of crown-of-thorns starfish has helped on parts of the GBR. But this high-maintenance approach will be logistically difficult in the remote North West.
Coral bleaching and a growing intensity of cyclones have been linked to global warming, and scientists can do little more than observe the impacts. And observing the fate of the Pilbara's coral reefs is Dr Babcock's best available option.
"We're still searching for a more detailed understanding of the ways that outbreaks can ultimately start, and try to use the system itself to help it stay in balance," he said.
Watch researchers investigating a crown of thorns starfish on the Pilbara coast.
