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By Amy Edwards 18 February 2019 4 min read

Starfish. You see them in children's books, sweetly smiling at mermaids. You might have taken photos of them, on a trip to the beach. But the crown-of-thorns starfish, well ... it's not so friendly.

Not the stuff of fairy tales

The crown-of-thorns starfish, or COTS, are a major threat to the World Heritage-listed Great Barrier Reef, along with climate change, poor water quality and coastal development. Although COTS are native to the Great Barrier Reef, it’s no fairy tale when an outbreak occurs. The hungry starfish eat massive amounts of coral on our favourite Aussie icon.

During an outbreak, COTS can eat 90 per cent of live coral tissue on a particular reef.  COTS feed by extruding their stomach out of their bodies and onto the coral reef, and then using enzymes to digest the coral polyps. This process can take several hours. After the coral polyps are digested, the starfish moves off, leaving only a white coral skeleton behind.  Within a few days algae begins to grow over the coral's scar, leaving an ugly brown patch. So yeah, not pleasant.

In 2014 James Cook University researchers in Australia developed an innovative way to cull COTS with a single injection of a bile salts.

More recently, researchers from Vanuatu and James Cook University in Australia have refined another handy and cheap kryptonite for this thorny coral-eating critter. And it’s something you’ve got in your kitchen – humble vinegar.

You catch more starfish with vinegar

Divers inject the starfish with either vinegar or bile salt solution, and leave them in place on the reef. These controls techniques kill quickly and effectively. Within 24 hours there’s basically nothing left of the starfish, who go into an autoimmune self-destructive process.

Because vinegar is affordable and readily available, it can be used both in small community efforts around the world, and in the large-scale, coordinated control programs, like the one currently operating on the Great Barrier Reef.

Injecting the starfish with vinegar or bile salts is an effective means of killing these coral killers. But it’s not the only thing we need to do to help keep this pest in check.

[Image appears of the CSIRO logo]

[Music plays and an animated image appears of the sea coast with vegetation and trees]

Narrator: The Great Barrier Reef is the largest coral reef in the world.

[Animation image changes to show divers swimming through the reef]

A global icon and uniquely diverse ecosystem.

[Animation image shows a reef with fish swimming past and then the camera zooms in on a Crown of Thorns starfish]

But the reef is under threat. Crown of Thorns starfish are one of the major causes of coral loss.

[Animation image changes to show a map of the reef with a growing purple mark showing the reefs affected areas and to the left of the screen a year count down appears counting from 1982 to 2017]

Any future outbreaks remain key threats to this important Australian ecosystem.

[Animation image changes to show a diver with a spear gun destroying a Crown of Thorns starfish, and then appearing above the water surface at a life buoy]

At the CSIRO, our current focus is on reducing immediate damage and preventing or reducing damage in the future.

[Animated images move through of a life buoy with the CSIRO logo in the centre, six life buoys with other organisational logos floating towards it, and then dotted lines connecting the buoys]

We do this through a collaborative research effort.

[Animation images move through to show a Tropical Water Quality Hub map with people standing in front of the map, and then a researcher wearing green gloves]

Our approach draws on the experience of crown of thorns starfish control operators, policy makers and researchers.

[Animation image shows a hand signing a document then animation image moves to the left to show a diver destroying the Crown of Thorns starfish]

We use this combined expertise to develop strategic and operational approaches to controlling Crown of Thorns starfish.

[Animation image changes to show a researcher walking through a laboratory and then the image changes show a map of the reef with a growing purple mark showing the reefs affected areas]

These strategies improve the rates of control and focus on achieving meaningful outcomes for the entire reef.

[Image changes to show the CSIRO logo and text appears: www.csiro.au]

At CSIRO, we imagine, we collaborate, we innovate.

Dethroning the crown

The current COTS outbreak, which has been occurring for more than five years, continues to move through the central section of the Great Barrier Reef, and will move further south over the coming years. Meanwhile, a separate outbreak is occurring in the Swains section in the southern region of the Reef. The loss of coral to COTS adds to the damage done by other threats – such as bleaching and cyclones – and reduces the resilience of coral reef ecosystems.

Since 2015, CSIRO has been instrumental in addressing the starfish problem through our efforts to assess COTS control and ways to improve it. The results of our analysis suggest that manual control at sites that have been revisited intensively has been very effective in reducing COTS densities and in enabling improvement in hard coral cover. Marine protected areas have also had a positive effect on reducing the impact of COTS on coral.

We're part of a stellar starfish team

A key part of CSIRO’s contribution has been to lead the development of the COTS Integrated Pest Management Program. Working closely with our research, policy and on-water control team partners, we have developed a control program and research strategy as part of the NESP Tropical Water Quality Hub research.  This strategy, and the research that it has produced, now underpins the implementation of the COTS Control Program being managed by Great Barrier Reef Marine Park Authority (GBRMPA) and funded by the Australian Government.

Since 2015 there has been an increase in the scale of the COTS program from one to six on-water vessels. This enables operators to cull more COTS and regularly target specific priority reefs. While some might think the reef is too big for effective manual control like this, outbreaks don’t occur at the scale of the entire reef, and not all sites have outbreaks at the same time. While we can’t yet stop an outbreak, by thinking carefully about where and when we invest in control we can minimise its impact and reduce the number of starfish ending up downstream.  This means minimising coral damage and improving the recovery of coral. This is vitally important to the long term resilience of the Great Barrier Reef.

[Music plays and image shows fish swimming through reef coral. Text appears: Not all starfish are the stuff of fairy tales]

[Image shows several crown of thorns starfish on bleached coral, and text appears: The Crown-of-Thorns Starfish eats coral,]

[Image shows an aerial view of the Great Barrier Reef and text appears: making it a major threat to the Great Barrier Reef.]

[Image shows a diver injecting a starfish, and text appears: But scientists have discovered the starfish’s kryptonite.]

[Image shows the diver pushing aside starfish, and text appears: And it’s something you have in your kitchen cupboard…]

[Image shows two divers]

[Image shows a starfish being injected and text appears: Divers are injecting the Crown-of-Thorns Starfish with vinegar.]

[Image shows starfish being turned over with a hook, and text appears: It’s one of the ways we’re helping control this menace of the Reef.]

[Image shows three divers injecting starfish, and text appears: And we’re working with a stellar team of starfish busters]

[Image shows a group of people standing on a dock around a dead starfish and text appears: including Indigenous trainees, tourism operators, researchers and policy makers.]

[Image shows brightly coloured coral and fish, and text appears: Together, we’re helping bring colour back to the Reef.]

[Image shows orange fish swimming through green coral]

 [Image fades to black]

[CSIRO logo appears and text appears: Australia’s innovation catalyst]

Quick facts about crown-of-thorns starfish

  1. The population of crown-of-thorns Starfish (COTS) undergoes natural cycles and, historically, there have been outbreaks roughly every 17 years. The outbreaks are thought to be becoming more frequent and lasting longer.
  2. Scientists typically link outbreaks of COTS to ocean 'stressors' including spikes in ocean nutrients caused by coastal and agricultural run-off into the ocean as well as a loss of predators due to overfishing.
  3. Removing large individuals through manual control is important because the larger starfish consume the most coral, they are most fertile and they contribute most to population reproductive success.

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