Great Barrier Reef: warmer waters helping coral-eating starfish thrive

The survival chances of crown-of-thorns starfish increase by as much as 240% if sea-surface temperatures rise 2C, say Australian researchers
Joshua Robertson The Guardian 12 Feb 15;

Warmer seas are creating an additional threat to the Great Barrier Reef, with new research suggesting rising temperatures are helping a key coral predator thrive.

Crown-of-thorns starfish that eat coral are more likely to survive with rising sea-surface heat levels, according to a study by the Australian Institute of Marine Science (Aims).

An Aims scientist, Sven Uthicke, said a study largely carried out at the institute’s marine laboratory in Townsville showed a 2C rise in sea temperature increased the starfish’s chances of survival by up to 240%.

“Warmer sea temperatures were found in this study to enhance COTS [Crown-of-thorns starfish] survival along with other, cumulative pressures on the reef,” he said.

“Given that the most moderate climate change scenarios predict a 1C-2C increase in average sea temperatures, the present study further demonstrates the value of taking a holistic, multi-variable approach to understand better how cumulative factors affect the survival of species such as COTS.”

Outbreaks of the starfish, also known as Acanthaster planci, have been instrumental in coral cover on the reef halving between 1985 and 2012, a range of previous studies indicated. Scientists attributed 40% of that overall decline to the starfish.

Warmer seas also kill coral through bleaching. Extensive bleaching can be triggered by as little as six weeks at temperatures of 1C-1.5C above the long-term summer maximum, according to the federal environment department.

Uthicke said scientists could better understand starfish outbreaks by recognising the synergies of sea-surface temperatures and increased nutrient flows that feed starfish larvae.

For the study, Uthicke and other scientists used the institute’s national sea simulator, which enables them to manipulate environmental factors to conduct large, long-term experiments on the impact of complex environmental changes.

The study was published on Thursday in the online peer-reviewed journal Scientific Reports.

Unesco’s world heritage committee is due to publish a draft report on the Great Barrier Reef in mid-May, and a decision on whether the site should be listed as “in danger” is to be made later this year.