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COTS index
COTS Q&A

 
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 2004, 16% 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 2004, the average density is 0.24 cots per tow. This compares with 1.17 in 1988. The graph below shows the average COTS density since 1986.

Methods - description of methods
Data Summaries - more detailed summaries

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)

 

Sector	Reef	ID	Date Surveyed	Outbreak
Cape Grenville	11211	11211S	Sep 2003	Incipient
Cape Grenville	Forbes Is's	12016B	Sep 2004	Incipient
Princess Charlotte Bay	Davie	13130S	Sep 2003	Active
Cooktown/Lizard Is	Stapleton It	14054S	Sep 2003	Incipient
Innisfail	Gilbey	17057S	Aug 2001	Incipient
Townsville	18026	18026S	Feb 2002	Active
Townsville	Kelso	18030S	Nov 2002	Active
Townsville	Little Kelso	18031S	Mar 2003	Active
Townsville	Slashers No.2	18043S	Mar 2003	Active
Townsville	Hopkinson	18073S	Mar 2003	Active
Townsville	Lodestone	18078S	Mar 2003	Active
Townsville	Keeper	18079S	Mar 2003	Active
Townsville	Chicken	18086S	May 2004	Active
Townsville	18099	18099S	May 2004	Incipient
Townsville	Little Broadhurst	18106S	May 2004	Active
Cape Upstart	Faith	19044S	Nov 2003	Incipient
Cape Upstart	Charity	19047S	Dec 2002	Active
Pompey	Credlin	20287S	Oct 2003	Incipient
Pompey	Southampton (Briggs)	20299D	Oct 2003	Incipient
Swain	Turner Cay	21562S	Oct 2003	Active
Swain	Chinaman	22102S	Oct 2003	Active
Swain	Horseshoe	22104S	Oct 2003	Active

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Last updated - November 17, 2004

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