Monitoring Crown-of-Thorns Starfish on the Great Barrier Reef

AIMS monitors crown-of-thorns starfish populations on the Great Barrier Reef to determine the current state of outbreaks along the Reef, which factors influence the likelihood of a crown-of-thorns starfish outbreak, and how long it takes coral to recover after an outbreak.
Crown-of-thorns starfish feeding

We survey crown-of-thorns starfish by towing a snorkeler with a manta board behind a small boat around the perimeter of a reef. The boat stops every two minutes (which is approximately every 200 m) to allow the observer to write down what they have seen.

Crown-of-thorns starfish populations are considered to be '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 numbers of crown-of-thorns starfish on the Great Barrier Reef is to look at the proportion of reefs with outbreaks. Of the reefs surveyed in 2015, 18 per cent have outbreaks. This compares with 10 per cent in 1988 when crown-of-thorns starfish caused widespread destruction on reefs in the central Great Barrier Reef. The graph below shows the percentage of surveyed reefs with outbreaks in each year since 1986.

Another way to look at crown-of-thorns starfish populations is to consider their average density across the entire Great Barrier Reef. This is expressed as crown-of-thorns starfish per two-minute tow.

In 2015, the surveyed reefs had an average density of .18 crown-of-thorns starfish per two-minute tow. This compares with 1.17 in 1988. The graph below shows the average crown-of-thorns starfish (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 Grenville Sir Charles Hardy (2) 11184C2Feb 2013Incipient
Cape Grenville Kay 12010SFeb 2013Incipient
Cape Grenville Quoin Is 12027BFeb 2013Active
Cape Grenville Sir Charles Hardy (1) 11184C1Feb 2013Incipient
Cape Upstart Shell 19028SMar 2007Active
Cape Upstart Showers 19076SMar 2007Incipient
Princess Charlotte Bay Corbett 14016SFeb 2013Incipient
Princess Charlotte Bay Clack 14017SFeb 2013Active
Torres Strait Aureed 00082SFeb 2013Incipient
Cairns 16-017 16017SJan 2013Incipient
Cooktown / Lizard Island Linnet 14126SOct 2012Incipient
Cooktown / Lizard Island Martin 14123SOct 2012Incipient
Cooktown / Lizard Island Two Isles 15002SOct 2012Active
Cooktown / Lizard Island Three Isles 15005SOct 2012Incipient
Cooktown / Lizard Island Boulder 15012SOct 2012Incipient
Pompey Creal 20297SSep 2012Incipient
Cooktown / Lizard Island Eye 14134SDec 2014Active
Cooktown / Lizard Island Helsdon 14135SDec 2014Active
Cooktown / Lizard Island Forrester 15009SDec 2014Active
Cooktown / Lizard Island Marx 15027SDec 2014Active
Cooktown / Lizard Island Irene 15084SDec 2014Active
Pompey 21-062 21062SMar 2016Active
Cairns Pickersgill 15093SMar 2015Incipient
Cairns Evening 15095SMar 2015Incipient
Cooktown / Lizard Island 15-077 15077SNov 2014Active
Cooktown / Lizard Island Macgillivray 14114SDec 2014Incipient
Torres Strait Waier And Dauar 00088SFeb 2014Incipient
Princess Charlotte Bay 13-124 13124SDec 2014Incipient
Cooktown / Lizard Island Swinger 15030SDec 2014Active
Cooktown / Lizard Island Startle (East) 15028S2Dec 2014Active
Pompey 21-060 21060SDec 2013Active
Innisfail Mcculloch 17016SDec 2015Incipient
Innisfail Peart 17024SDec 2015Active

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