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 2013, 29% 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 tow.
On the reefs surveyed in 2013, the average density is .22 cots per tow. This compares with 1.17 in 1988. The graph below shows the average COTS density since 1986.
Record your observations - have you seen COTS on a recent visit to the GBR?The following reefs had outbreaks when last surveyed:
(click on reef name for detailed information)
|Cape Grenville||Sir Charles Hardy (1)||11184C1||Feb 2013||Incipient|
|Cape Grenville||Sir Charles Hardy (2)||11184C2||Feb 2013||Incipient|
|Cape Grenville||Quoin Is||12027B||Feb 2013||Active|
|Capricorn Bunker||Fairfax Is'S||23081S||Sep 2013||Active|
|Cape Upstart||Shell||19028S||Mar 2007||Active|
|Cape Upstart||Showers||19076S||Mar 2007||Incipient|
|Cooktown / Lizard Island||Irene||15084S||Oct 2012||Active|
|Cooktown / Lizard Island||15-077||15077S||Oct 2012||Incipient|
|Cooktown / Lizard Island||Linnet||14126S||Oct 2012||Incipient|
|Cooktown / Lizard Island||Martin||14123S||Oct 2012||Incipient|
|Cooktown / Lizard Island||Eyrie||14118S||Oct 2012||Incipient|
|Cooktown / Lizard Island||Lizard Is||14116S||Oct 2012||Incipient|
|Cooktown / Lizard Island||Macgillivray||14114S||Oct 2012||Incipient|
|Cooktown / Lizard Island||North Direction Is||14143S||Oct 2012||Incipient|
|Cooktown / Lizard Island||South Direction Is (A)||14147A||Oct 2012||Active|
|Cooktown / Lizard Island||Helsdon||14135S||Oct 2012||Incipient|
|Cooktown / Lizard Island||Two Isles||15002S||Oct 2012||Active|
|Cooktown / Lizard Island||Three Isles||15005S||Oct 2012||Incipient|
|Cooktown / Lizard Island||Forrester||15009S||Oct 2012||Active|
|Cooktown / Lizard Island||Startle (East)||15028S2||Oct 2012||Active|
|Cooktown / Lizard Island||Marx||15027S||Oct 2012||Incipient|
|Cooktown / Lizard Island||Boulder||15012S||Oct 2012||Incipient|
|Cairns||Green Is||16049S||Jan 2013||Incipient|
|Princess Charlotte Bay||Clack||14017S||Feb 2013||Active|
|Princess Charlotte Bay||Corbett||14016S||Feb 2013||Incipient|
|Cape Grenville||Kay||12010S||Feb 2013||Incipient|
|Torres Strait||Aureed||00082S||Feb 2013||Incipient|
|Torres Strait||Waier And Dauar||00088S||Feb 2013||Incipient|
|Capricorn Bunker||Lady Musgrave Is||23082S||Sep 2013||Incipient|