Breakthrough on crown-of-thorns causes

by jcu.edu.au on 23 Oct 2015 James Cook University researchers have made a crucial discovery on what drives outbreaks of the coral-eating Crown of Thorns Starfish (CoTS).

The starfish is present on the Great Barrier Reef in epidemic numbers, and it’s one of the primary reasons for the decline in live coral.

Jon Brodie, Chief Research Officer at JCU’s Centre for Tropical Water and Aquatic Ecosystem Research (TropWATER) and Scott Wooldridge, formerly at AIMS and now Adjunct researcher at JCU, said they had now defined the weather conditions needed to ensure an outbreak.

Researchers already knew that nutrient run-off, most of which is from farm fertilisers and soil erosion, produced high numbers of nano and microplankton cells that CoTS larvae feed on.

But there had been a mysterious absence of CoTS in some years. “We knew CoTS thrived on nutrient run-off from farmland, but an outbreak did not always follow a big river discharge into the Great Barrier Reef area. We discovered there also has to be weaker currents, that allow them to cluster, for an outbreak to occur,” said Mr Brodie.

He said as the climate shifted between El Nino and La Nina weather systems, ocean currents decreased and allowed concentrations of both the CoTS larvae - and the plankton they fed on - to build.

Mr Brodie said the scientists had also figured out why a CoTS outbreak didn’t occur immediately after a heavy runoff event, with the optimum conditions needing two years to produce increased numbers of the starfish on the reef.

He said the La Nina and El Nino flows couldn’t be predicted, but outbreaks seemed to happen about every 16 years as coral abundance recovers from the previous outbreak. “1962, 1978, 1993 and 2009”. So we could expect another one in the 2023 – 2027 period,” he said.

Mr Brodie said while not much could be done to control the ocean currents, and killing the CoTS on an individual basis was ineffective in controlling the population generally, much more could be done to reduce runoff from farms.