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Third wave of crown-of-thorns fading away

The latest report of AIMS Long Term Monitoring Program (LTMP) has both good news and bad news about the Great Barrier Reef.

The good news is that the third recorded crown-of-thorns starfish (COTS) outbreak is waning after more than 14 years. The outbreak has worked its way down the Reef since the early 1990s. Crown-of-thorns starfish outbreaks account for the largest proportion of coral mortality detected by the AIMS surveys.

Fewer starfish were seen in AIMS’ surveys of GBR reefs in 2007 than in any year for the past two decades and last year was the first since 1985 in which there were no outbreaks of the starfish in the Swain Reefs off Yeppoon.

But the LTMP team has also detected a rise in coral disease in some parts of the Reef, notably those areas where hard coral cover is high.

Head of the LTMP, Dr Hugh Sweatman, said that Status Report No.8 on the state of the Great Barrier Reef represented a synthesis of monitoring data collected up to the 2007 field season. The LTMP has been surveying the Great Barrier Reef since 1993 and findings from 2006 and 2007 have not been reported before.

"The percentage of reefs with outbreaks of COTS has fluctuated but has been declining as the third recorded wave of outbreak fades," Dr Sweatman said.

Crown-of-thorns starfish

Image: AIMS LTMP

"There were outbreaks on six per cent of the 104 reefs surveyed in 2006, and on just four per cent of the reefs we surveyed in 2007," he said. At the peak of this third recorded outbreak, up to 17 per cent of the GBR’s reefs were afflicted by COTS. This figure was recorded in 1999 and 2000. Reefs that were afflicted lost nearly all of their coral.

COTS remains a mysterious phenomenon and it is not known when the next wave will begin. The LTMP team is continuing to conduct intensive surveys in the area where the waves of outbreaks start, to detect them in the early stages.

AIMS staff have monitored COTS populations since 1986, when the second recorded COTS wave was underway, and have been at the forefront of scientific investigation of this phenomenon. The first recorded wave took place during the 1960s and 1970s and little is known about it.

The LTMP status report also found falls in coral cover on the outer Barrier Reef near Lizard Island because of outbreaks of coral diseases, including a suite of diseases known as white syndrome. White syndrome causes massive tissue loss among the large table corals and was first documented in Australia in 1999. Its causes remain unclear, and it is an active area of study at AIMS.

The trends in occurrence of coral diseases have been uneven. White syndrome declined in most sub-regions after a peak in 2003, but then returned to intermediate levels in 2006 and 2007. This occurred particularly in the Cooktown-Lizard Island sector in the north of the GBR and on outer shelf reefs in the Cairns, Townsville and Capricorn-Bunker sectors further south.

The disease is found particularly where hard coral cover is high. "What we see is that the healthy reefs with lots of coral cover are the ones at risk," Dr Sweatman said.

The full LTMP report can be downloaded from www.aims.gov.au/reef-monitoring or is available as a CD from AIMS. It is designed to provide information on population trends in key groups of organisms, particularly crown-of-thorns starfish, corals and reef fishes along the length of the GBR.

 

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Number 9 - June 2008    Hit Counter


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