Crown of thorns starfish larval flow

Acanthaster planci, COTS, feeding front

In the past 50 years, four waves of crown-of-thorns starfish outbreaks have had a major impact on the many reefs that make up the Great Barrier Reef. These began in 1962, 1979, 1993 and 2009 with each wave lasting about 15 years (Babcock et al. 2016; Pratchett et al. 2017).

Crown-of-thorns starfish (also known as COTS) are marine invertebrates that feed on coral. They occur naturally on reefs throughout the Indo-Pacific region, and when conditions are right, they can reach plague proportions that devastate hard coral communities.

Crown of thorns starfish larval flow

Key concepts that relate to its connectivity

During summer months adult crown-of-thorns starfish spawn. Each female can release 10’s millions of eggs (Caballes et al. 2016), resulting in huge quantities of larvae that drift in the ocean current (Uthicke et al. 2015). The larvae are ready to settle after about 11 days of development (Pratchett et al. 2017) during which they rely on phytoplankton for food (Brodie et al. 2005)). If the larvae don’t find a reef they can continue to drift for several more weeks before they die (Pratchett et al. 2017)). This allows the larvae settle on reefs 100’s of kilometres from their parents.

Larval Cycle of Crown-Of-Thorns Starfish (COTS)

Once settled the juvenile crown-of-thorns starfish can reach adulthood in 2 years where if there are enough of them they will form a new outbreak.

Historically the initial outbreaks have been detected between Cairns and Lizard Island (Wooldridge and Brodie 2015). They then slow spread down the coast over a 15 year period where they finally dissipate off the coast from the Mackay.

The outbreaks also occur in the reefs in far north Queensland, the Swains Reefs, the Capricorn-Bunkers and Torres Strait, however far less is known about the patterns of outbreaks due to a lack of surveys in these regions. Outbreaks are not known to occur in the Coral Sea reefs, however no regular surveys have conducted.

The crown-of-thorns starfish larvae feed on phytoplankton in the water column (Okaji 1997) and so additional nutrients from rivers runoff are thought to contribute to an increase in the survival rate of larvae (Brodie et al. 2005; Fabricius et al. 2010) and the frequency of outbreaks (Fabricius et al. 2010). Overfishing of CoTS predators may also play a role in the frequency and severity of outbreaks (Cowan et al. 2017).

Crown-of-thorns starfish outbreaks map on GBR


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Brodie, J., Devlin, M., Lewis, S. 2017. Potential Enhanced Survivorship of Crown of Thorns Starfish Larvae due to Near-Annual Nutrient Enrichment during Secondary Outbreaks on the Central Mid-Shelf of the Great Barrier Reef, Australia. Diversity 9, 17. doi:10.3390/d9010017.

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Babcock, R.C.; Dambacher, J.M.; Morello, E.B.; Plagányi, É.E.; Hayes, K.R.; Sweatman, H.P.A.; Pratchett, M.S. Assessing different causes of crown-of-thorns starfish outbreaks and appropriate responses for management on the Great Barrier Reef. PLoS ONE 2016, 11, e0169048.

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