A team of leading marine researchers has produced the first conclusive evidence to demonstrate the link between nutrient run-off and escalating crown-of-thorns starfish infestations in the Great Barrier Reef lagoon.

The collaborative effort of CRC Reef scientists from the Australian Institute of Marine Science (AIMS), Dr Glenn De’ath, Dr Katharina Fabricius and Dr Ken Okaji, and from James Cook University (JCU), Mr Jon Brodie may end 40 years of intense scientific and community debate.

Many have feared the crown-of-thorns starfish plagues spelled the end of the reef and blamed human activity, while others argued that it is a natural phenomenon.

Water quality expert Mr Jon Brodie said the study shows an increase in nutrient run-off has led to higher levels of phytoplankton, which is food for the starfish larvae.

Statistical modeller Dr Glenn De’ath said laboratory experiments reveal that twice as much phytoplankton results in a ten-fold increase in larval survival.

"This increase in larval survival could stimulate a population explosion causing severe outbreaks of adult starfish," he said.

Dr De’ath said field surveys indicate that phytoplankton levels on reefs off the developed central Great Barrier Reef are double those north of Cooktown, where there is little human influence.

A computer model developed by Dr De’ath predicts that such a doubling of phytoplankton will create more frequent outbreaks, from one every 50-100 years to one every 15 years; frequencies consistent with those observed in the northern and central Great Barrier Reef.

"The high frequency of outbreaks means the coral has less time to fully recover. In regions such as the far north, where conditions are relatively pristine, the models predict coral cover 2-4 times higher than in areas of the central region of the GBR where human influence is strong. These predictions agree with surveys of the two regions," Dr De’ath said.

The scientists believe the research demonstrates that improved water quality will create greater coral cover and a healthier reef by reducing the frequency of crown-of-thorns starfish outbreaks.

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