Australian Institute of Marine Science

Crown-of-Thorns Starfish on the Great Barrier Reef

The AIMS Long Term Monitoring Program Surveys:

Crown-of-thorns starfish (COTS) populations are surveyed by towing an observer with a manta board behind a small boat around the perimeter of a reef. After towing for two minutes, the boat stops and the observer writes down how many COTS were seen.

Crown-of-thorns starfish feeding

In principle, COTS populations are described as outbreaks when they reach densities such that the starfish are consuming coral tissue faster than the corals can grow.

There are various ways of estimating this level, but when populations on a reef average one per tow the coral cover will certainly be reduced; this is referred to as an active outbreak. Average densities as low as 0.22 COTS per tow can cause damage; this is referred to as incipient outbreak.

One way to get a historical view of the status of COTS on the Great Barrier Reef is to look at the proportion of reefs with outbreaks. Of the reefs surveyed in 2014, 14% have outbreaks. This compares with 10% in 1988 when COTS caused widespread destruction on reefs in the central Great Barrier Reef. The graph below shows the population of reefs with outbreaks in each year since 1986.



Another way to look at COTS populations is to consider the average COTS density across the entire Great Barrier Reef. This is expressed as COTS per 2-minute tow.

On the reefs surveyed in 2014, the average density was .13 cots per tow. This compares with 1.17 in 1988. The graph below shows the average COTS density since 1986.

The following reefs had outbreaks of crown-of-thorns starfish when last surveyed:
(click on reef name for detailed information)

Sector Reef ID Date Surveyed Outbreak
Cape Upstart Shell 19028SMar 2007Active
Cape Upstart Showers 19076SMar 2007Incipient
Pompey Creal 20297SSep 2012Incipient
Cooktown / Lizard Island Irene 15084SOct 2012Active
Cooktown / Lizard Island 15-077 15077SOct 2012Incipient
Cooktown / Lizard Island Linnet 14126SOct 2012Incipient
Torres Strait Aureed 00082SFeb 2013Incipient
Cooktown / Lizard Island Martin 14123SOct 2012Incipient
Cooktown / Lizard Island Eyrie 14118SOct 2012Incipient
Cooktown / Lizard Island Lizard Is 14116SOct 2012Incipient
Cooktown / Lizard Island Macgillivray 14114SOct 2012Incipient
Cooktown / Lizard Island North Direction Is 14143SOct 2012Incipient
Cooktown / Lizard Island South Direction Is (A) 14147AOct 2012Active
Cooktown / Lizard Island Helsdon 14135SOct 2012Incipient
Cooktown / Lizard Island Two Isles 15002SOct 2012Active
Cooktown / Lizard Island Three Isles 15005SOct 2012Incipient
Cooktown / Lizard Island Forrester 15009SOct 2012Active
Cooktown / Lizard Island Startle (East) 15028S2Oct 2012Active
Cooktown / Lizard Island Marx 15027SOct 2012Incipient
Cooktown / Lizard Island Boulder 15012SOct 2012Incipient
Princess Charlotte Bay Clack 14017SFeb 2013Active
Princess Charlotte Bay Corbett 14016SFeb 2013Incipient
Cairns 16-017 16017SJan 2013Incipient
Cape Grenville Quoin Is 12027BFeb 2013Active
Cape Grenville Kay 12010SFeb 2013Incipient
Cape Grenville Sir Charles Hardy (1) 11184C1Feb 2013Incipient
Cape Grenville Sir Charles Hardy (2) 11184C2Feb 2013Incipient
Cairns Green Is 16049SJan 2013Incipient
Torres Strait Waier And Dauar 00088SFeb 2014Incipient
Cairns Arlington 16064SMar 2014Incipient
Pompey 21-062 21062SDec 2013Active
Pompey 21-064 21064SDec 2013Active
Pompey 21-060 21060SDec 2013Active
Capricorn Bunker Lady Musgrave Is 23082SSep 2013Incipient
Capricorn Bunker Fairfax Is'S 23081SSep 2013Active