The Great Barrier Reef. The only living organism that can be seen from space, and my favourite place on this blue planet of ours. Sadly, just like the rest of the ocean, the Great Barrier Reef is threatened by the pressures of issues such as climate change and marine debris. Unlike the rest of the ocean though, there is one issue more pertinent here than on any other reef, in the form of a nasty looking starfish that is responsible for 42% of the Great Barrier Reefs coral loss. Fortunately though, scientists have recently discovered the food item you probably have in your kitchen cupboard that can stop it.

During 2011, I was part of a program run by the Queensland Government that was designed to eradicate crown-of-thorns from the outer Great Barrier Reef. When I explained to people I was killing starfish for a living, the look I received in response was like I’d just told them I personally killed Bambi’s mother. These starfish are about as far as you can get from the cute and colourful sea stars you see diving on coral reefs. Besides cyclones, crown-of-thorn starfish are one of the leading causes of coral loss in the Great Barrier Reef.   About the same size as a dinner plate, crown-of-thorns feed on a diet of coral and look pretty much exactly like their name suggests. Their spikes can deliver a painful sting (just ask my old man) and if you reach two or three strikes then you’re out. The poison inside a crown-of-thorns builds up in our bodies if we get stung, and if you end up getting spiked more than twice your body can go in to anaphylactic shock.

These starfish aren’t actually pests. In fact,  they are an integral part of a healthy functioning reef ecosystem. They eat faster-growing coral, such as staghorn and plate corals, keeping it in check so slower growing corals have a chance to catch up. It’s when populations of crown-of-thorns (COTS) rise too high and too quickly that they present a big problem.

The Great Barrier Reef has faced outbreaks of COTS since the 1960s. Scientists are still trying to pin-point the reason why, but it’s thought to be linked to agricultural run-off resulting in more phytoplankton in the water (the diet of COTS larvae) and a decline in population of the few predators this starfish has. According to the Great Barrier Reef Marine Park Authority, crown-of-thorns starfish populations are under control if you only see a lone starfish on a 20 minute swim, or about 15 per hectare. On a single COTS eradication dive I undertook whilst I was working on a dive live aboard in the Great Barrier Reef, I killed a total of 45. On another trip organised specifically to cull crown-of-thorns in Bait Reef, one of the most pristine and untouched sections of the Great Barrier Reef, we killed 269. So, a few more than one on a 20 minute dive.

The thing about COTS though, is that they are hardy little predators. Until recently, divers thought they were lending the reef a hand by spotting one on a dive, whipping out their dive knife and cutting off each of their 20 arms so they could never feast on the reef’s precious coral again. How very misconceived they were.

Cam 1 (6)
Culling the invasive crown of thorns starfish in the Great Barrier Reef.

Starfish possess the ability to regrown their limbs. Like something out of a sci-fi movie, every one of their amputated limbs can grow into a whole new separate starfish. Until recently,  crown-of-thorns could be culled using multiple shots of sodium bisulphate solution or a single shot of bile salts. These methods worked, and didn’t harm any of the surrounding marine life. However, the latter method comes with a hefty price tag attached, and for an organisation to purchase half a kilo of the salts alone will set them back around one hundred and twenty dollars.

Researchers from the James Cook University have recently discovered a solution that will cost quite a bit less than this, is safe for all the other creatures that call the ocean home and readily available. Within 48 hours of a lab based crown-of-thorn starfish being injected with a 20ml dose of vinegar it was dead. Yep, the exact same vinegar you have with your hot chips. Lead scientist of the project,Lisa Boström-Einarsson, said that within 24 hours of administering the vinegar all that was left of the spiky echinoderm was a smear of slime. The researchers will soon be testing their new method out in the ocean.

Last year 2 full-time COTS control crews managed to cull 350 000 starfish. This sounds like a pretty big figure, but there are approximately 12 million crown-of-thorns starfish currently on the Great Barrier Reef, and females can lay up to 65 million eggs over a single spawning season. This research could potentially be the saviour of one of the world’s most iconic underwater landmarks. The cheap, easy access and safe nature of vinegar means potentially anyone can be a reef hero. Who knows, maybe by the time you head to Australia for a dive live aboard adventure you’ll be able to cull these pests yourself!

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