36. What is the history of outbreaks on the Great Barrier Reef?

Two series of outbreaks of crown-of-thorns starfish have been recorded on the Great Barrier Reef (see Fig. 14) over the last 25 years; the first series occurred between 1962 and 1977 whilst the second, which is still underway, began towards the end of 1979.

Figure 14 Map of the Great Barrier Reef. This animal made structure comprises some 2,900 individual reefs and is about 2,300 km in length.

Outbreaks were first observed on Green Island in 1962. As very little was known about the starfish and its effects at that time surveys were undertaken to determine the extent of outbreaks initially in the region near Green island and subsequently in areas further afield.

From between 1962 and 1965 outbreaks were reported on many of the reefs near Green Island. By 1967 they were observed on reefs as far south as Innisfail and as far north as Cooktown. Reefs near Townsville began to experience outbreaks by the early 1970's. They persisted for several years in this region after which time they were again reported further south on reefs between Ayr and Bowen. By 1973 the southernmost extent of the outbreaks was on reefs near Mackay. Large populations of starfish were not reported on reefs further south except in the Swain complex during the mid-1970's. The last reports of outbreaks were received from this area in 1977.

After 1977 no outbreaks were reported until late 1979 when a second outbreak of crown-of-thorns starfish was reported on Green Island. At that time the starfish population was estimated to comprise about 3 million individuals. Within 2-3 years outbreaks were reported on reefs near Innisfail and by 1984 they had moved further south to reefs off Townsville. During that period large numbers of starfish also were observed on reefs around Lizard Island. Over the last few years the outbreaks off Townsville have diminished and newer ones are now being reported on reefs between Ayr and Bowen. A number of small populations of starfish have been recorded in the southern end of the Swain Reef complex since 1985.

Several general trends are now beginning to emerge from the data which have been collected over the last 15 years. These are:-

1. Outbreaks appear to originate in the region of reefs near or just to the north of Green Island, although this has yet to be confirmed.
2. They occur increasingly further south over the years. Recent analyses of the survey data and models of the water currents (hydrodynamics) in the central region of the Great Barrier Reef have provided a much better understanding of this process.
3. Outbreaks have not been reported north of Princess Charlotte Bay or in the Capricorn-Bunker Group of reefs in the far south.
4. Some reefs (eg, Green Island, John Brewer Reef) seem to be more susceptible to outbreaks than others as they have experienced very large populations of crown-of-thorns starfish on both occasions. This may be partly due to the influence of water currents.

AIMS home page

web@aims.gov.au
Last updated - 12 December 97

Copyright ©1997 Australian Institute of Marine Science

URL http://www.aims.gov.au