Australian Scientists keeping a watch on Great Barrier Reef bleaching

Scientists from the Australian Institute of Marine Science have found significant bleaching of corals on inshore reefs off Townsville and Innisfail in the Central Great Barrier Reef (GBR). Surveys off Cairns to the north - have found more limited bleaching and work currently underway in the Whitsundays to the south - has found little to date. These surveys are part of an ongoing and long-term monitoring program of the GBR carried out in close collaboration with the Great Barrier Reef Marine Park Authority.

'Summer time bleaching of corals is a regular occurrence on the GBR but does not usually kill too many corals,' said AIMS' Principal Research Scientist, Dr Terry Done. 'The extent of the present bleaching looks like being the greatest since 1982 but it will probably be another month or two before we know whether the corals are mortally sick or just off-colour'.

A recent media report, by NOAA, attributed the bleaching to El Niño-induced drought but AIMS scientists believe it is more likely to be related to warm inshore waters and the major flooding in the Townsville region in the second weekend of January. This flooding poured large volumes of freshwater into the inshore waters of the GBR.

An extensive array of temperature loggers and monitoring sites across the length and breadth of the GBR will allow AIMS and GBRMPA to determine the long-term effects of the present bleaching, to clarify its causes and interpret its significance in the greater picture of the GBR.

'A week after the Townsville flood our long-term coral study site closest to the shore was okay, but after an additional four weeks of hot weather 80% of corals were bleached, but still living to a depth around 10 metres. The reef looked like it was covered in snow. We will be checking in about 10 days time, when we will estimate what portion has died,' said Dr Done.

An AIMS survey team is currently visiting reefs far offshore - off Lizard island and Townsville - to assess how wide-spread the bleaching is. So far they have only seen the nearshore reefs, that divers and tourists never visit, but which scientists find very interesting as they are closest to any possible influences of run offs from the land.

There is a real concern that a global climate change will increase the frequency of very hot and very wet years on the GBR. The climate change could lead to increased frequency of bleaching events and decreases in the rates that corals lay down their skeletons. These are potentially serious and long-term changes and our preference is to be very careful in reporting them - not to go public half way through an event which may amount to very little.

We can get a better idea of how serious the event is by looking at the ages of the corals killed. If they are many centuries old, it is a far more significant event in the reef history then if they are only a few years old. Our nearshore study reef was severely bleached in 1994 but recovered virtually without trace of the event by 1996.

Our long-term monitoring of over 60 reefs, 6 of them since 1980, gives us the best basis for finding out what is going on.

AIMS' Associate Director of Research, Dr David Williams, said 'The NOAA satellite maps of seasurface temperature reported last week are pretty impressive, but the interpretations first reported have to be taken with a grain of salt because they have not usually been subject to the rigorous peer review process involved in conventional scientific literature. NOAA's draft press release had a headline that our current heat wave was El Niño and drought related, and associated with nearly cloudless skies. It also reported the trend of coral bleaching from south to north in the GBR. These facts are not substantiated. Once we download the loggers and analyse the coral data, we will have a ground truth data set for the satellite. When we analyse patterns of death and recovery in the corals, we will be able to say something definitive about the significance of the event'.

For further information contact:
Dr David Williams, AIMS, Associate Director of Research
ph: +61 041 967 9753

Wendy Ellery, AIMS
ph: +61 (07) 47534409