Predators can't stop hungry starfish
Why are there so many crown-of-thorns starfish on the Great Barrier Reef?
Scientists say natural predators of the crown-of-thorns starfish can't control the species' population outbreaks believed to be triggered by flooding on the Great Barrier Reef.
Earlier this week the Australian Institute of Marine Science [AIMS] released a study saying the starfish is responsible for almost half of the coral cover lost on the reef in the last 27 years.
One of the co-authors of the study, Dr Hugh Sweatman says flooding is a likely factor in the population increase.
"In the historical record there's a link between big floods and then a few years later you begin to see [a lot of] the starfish," he says.
"Run off from floods brings nutrients into the water, increases the phytoplankton on which the larvae feed, that leads to a hugely different number of larvae and very different numbers of starfish."
"If you lay 50 million eggs each year, you don't need a big change in survivorship to make a very big difference in the numbers."
One of the crown-of-thorns few predators is the triton, a large sea snail which paralyses the starfish with its saliva.
But despite being 'enthusiastic predators' Dr Sweatman says the triton simply can't eat enough crown-of-thorns to make much of a difference.
"We know that they're fierce predators of crown of thorns starfish ... but our studies suggest that they only eat maybe one starfish a week and when you get to outbreak numbers and there are
hundreds of starfish per hectare then one starfish a week isn't enough," he says.
"They're nocturnal so they could be there and we wouldn't know but they're not likely to be controlling agents on the crown of thorns starfish."
Commercial fisherman, Marty Cunningham says the number of crown-of-thorns starfish have reached 'plague proportions' in some parts of the Great Barrier Reef.
"There's been a significant increase to the north-east of Cooktown on a group of reefs and a more significant burst just off Port Douglas on Tongue and Bat Reef," he said.
"Because of the history of movement of crown-of-thorns out of that area, it really indicates the commencement of another significant burst."
Mr Cunningham says the increase in the starfish has had no impact on his business so far but adds he's still concerned.
"Reduction in coral cover across the board on the Great Barrier Reef is a worry to anyone associated with the marine park," he says.
"Coral are the building blocks of the reef and without that it will create the demise of anyone's business that's associated with the Great Barrier Reef."
Triton are a protected species within the Great Barrier Reef Marine Park.