Dose of household vinegar found to kill off reef-eating starfish

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Vinegar could provide an economical and effective way to combat the crown-of-thorns starfish(Credit: James Cook University)

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The crown-of-thorns starfish poses a major threat to the wellbeing of Australia's Great Barrier Reef. Wild, uncontrollable outbreaks over the past few decades have seen the pests multiply to devour vast amounts of coral, and as it stands there's little that can be done. One method conservationists have used to some effect is injecting them with ox bile, but researchers have now discovered that a simple dose of vinegar can do much the same job, promising to significantly cut the cost of an expensive battle to rid a World Heritage Site of this damaging pest.

A 2012 study carried out by the Australian Institute of Marine Science showed that along with tropical cyclones, the crown-of-thorns starfish is one of the leading causes of coral loss in the Great Barrier Reef over the past 27 years. And to rub salt into an already salty wound, other research has shown rising sea temperatures improve the survival rate of the species.

In an effort to make a dent in the growing population, scientists have injected ox bile into the starfish one-by-one to kill them off. In addition to being hugely labor-intensive, ox bile is expensive and not all that easy to source. But now a team from James Cook University led by ecologist Lisa Boström-Einarssonfrom has discovered the same vinegar you might find in your kitchen can be just as deadly.

"It is a different process (to using ox bile)," Boström-Einarssonfrom explains to Gizmag. "There is acid in the vinegar and because the starfish is made mostly of water, it cannot regulate the pH and its tissue just melts away."

Vinegar had been experimented with in previous attempts to counter the crown-of-thorns starfish epidemic, but without success. Boström-Einarssonfrom says that it was through considerable trial and error that she happened across a technique that finally proved effective, which basically involved trying different concentrations, needle sizes and injection locations.

The resulting approach uses 20 ml of vinegar (0.67 fluid oz) and has a 100 percent strike rate, with all starfish in the trial meeting their demise within 48 hours of being injected. But what may prove the approach's biggest strength is the relative accessibility of vinegar and the fact that it costs around half the price of ox bile, making it a more viable option for developing countries.

Killing off the starfish one-by-one could make for a lengthy campaign as there are an estimated four to 12 million crown-of-thorns starfish on the Great Barrier Reef, with each female produces 65 million eggs every breeding season. With two full-time boat crews last year, divers managed to kill off around 350,000, which they say can go some ways to preserving individual reefs. Other researchers are working on more effective ways to control the population, such as aquatic robots (which could now potentially switch to a vinegar payload) that seek out and destroy the pests. However, currently the options remain limited.

"Ideally we could stop outbreaks from happening all together," says Boström-Einarssonfrom. "But we don't have the knowledge to do that yet. We don't know what causes the outbreaks, so this is all we have, to fight them one by one."

The research is to be published in the Journal of the International Society for Reef Studies and can be read online here.

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