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Crown-of-thorns starfish eating corals on Keeper Reef.
Image : AIMS Long-term Monitoring Team.

Reefs where fishing is not allowed are much less prone to infestation by the devastating crown-of-thorns starfish (COTS), according to a new analysis of AIMS' long-term surveys of the Great Barrier Reef.

The starfish is a major management problem on coral reefs from Central America to Kenya and the Red Sea. They eat coral voraciously and wipe out nearly all coral on the reefs they infest. In the past 40 years they have caused much more damage to GBR reefs than have storms or coral bleaching.

Waves of outbreaks last about 15 years, beginning in the northern reaches of the GBR and then moving southward through the central areas.

AIMS scientist Dr Hugh Sweatman predicts that any future waves of COTS outbreaks will not be as destructive as the three waves that have affected the GBR since 1960, because the area of no-take zones on the GBR was increased from 4.5 per cent of the Reef to 33 per cent in 2004.

No-take zones, regulated by the Great Barrier Reef Marine Park Authority, are designated areas known as "green zones" where no fishing is allowed.

By comparing the frequency of starfish outbreaks on no-take reefs and on reefs where fishing was allowed, a clear pattern has emerged. The relative frequency of outbreaks on reefs that were open to fishing was 3.75 times higher than that on no-take reefs in the mid-shelf region of the GBR, where most of the outbreaks occur. However, the ecological link between exploited fishes and COTS remains uncertain. 

The reef fishes that fishermen target are unlikely to prey upon COTS, but there may be several links in the ecological chain: more large predatory fishes in no-take areas may reduce the numbers of smaller fishes, in turn reducing predation on invertebrate species such as worms and crustaceans that prey on very small juvenile starfish. This process remains to be fully researched.

This study provides an additional argument for establishing effective marine protected areas to increase the ecological resilience of coral reefs faced with the threat of climate change.