Is there anything vinegar can't do? It's an all-purpose cleaner, stain remover, deodorizer, fabric softener and salad dressing, among other household uses.
And according to new research, we can add yet another skill to its repertoire: helping protect Earth's largest coral-reef ecosystem from a plague of spiky marauders.
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The crown-of-thorns starfish has been decimating Australia's Great Barrier Reef for years, a natural predator run amok due to environmental changes like nutrient runoff from land and depletion of its own predators. Coral cover on surveyed reefs has declined by 50 percent in the past 30 years, according to Australian authorities, and nearly half of that damage is due to the crown-of-thorns starfish (CoTS), which is the only species of sea star known to prey directly on live coral.
The venomous invertebrates are breeding at "epidemic levels," warn researchers from James Cook University, despite a flurry of efforts to control outbreaks. Until recently, a common strategy involved divers poisoning them with sodium bisulphate, which required about eight injections per animal. That has since lost favor to a solution made from ox bile, which requires only a single injection to kill. And in a new study, JCU scientists report an even better method: one shot of vinegar.
"Currently divers use 10 or 12 [milliliters] of ox bile to kill each CoTS," lead author Lisa Boström-Einarsson says in a statement. "It's expensive, requires permits and has to be mixed to the right concentration. We used 20 ml of vinegar, which is half the price and can be bought off the shelf at any local supermarket."
Vinegar had been tried before with little success, Boström-Einarsson adds, but she and her colleagues refined the process to achieve a 100 percent kill rate. The CoTS in their trials were reportedly all dead within 48 hours of being injected.
Fish that then fed on the dead CoTS showed no signs of harm, but the researchers say this will need to be supported by larger-scale field trials before the treatment can be declared safe for other marine life. "There's no reason to think it won't work or it'll be dangerous, but we have to be sure," Boström-Einarsson says.
Killing the starfish one at a time won't save the Great Barrier Reef, the researchers note, since they number in the millions across a reef system that spans 344,000 square kilometers (132,000 square miles). But that's the only practical option so far, and while it may not solve the problem, it could prevent CoTS from wiping out some individual coral colonies. It might become more efficient, too, if vinegar-equipped human divers are joined by COTSbot, a new starfish-hunting robot.
"It has been estimated there are between 4 and 12 million of the starfish on the Great Barrier Reef alone, and each female produces around 65 million eggs in a single breeding season," Boström-Einarsson says. "They managed to kill around 350,000 last year with two full-time boat crews. While it would take an insane effort to cull them all that way, we know that sustained efforts can save individual reefs."
Under normal conditions, the crown-of-thorns starfish can be a productive member of coral ecosystems. It tends to feed on faster-growing species like staghorn and plate corals, giving slower varieties a better chance to establish colonies of their own. This helps boost the biodiversity of coral reefs — until CoTS get carried away.
Corals may recover from sparse starfish attacks, but it doesn't take much to outpace coral growth. Heavy rains often wash excess nutrients from farms into the reef, for example, which can trigger a CoTS outbreak if it happens in their spawning season. Fishing and shell collecting have also reduced populations of animals that prey on CoTS, including giant triton snails and humphead Maori wrasse.
On top of that, many corals are already hurt by human activities, from local water pollution and ship traffic to the global carbon emissions that spur ocean acidification and coral bleaching. These and other threats led UNESCO in 2014 to propose listing the Great Barrier Reef as "in danger," a precursor to losing its World Heritage status. Australia responded by pledging new protections for the reef, persuading UNESCO to give the country until 2016 to prove its rescue plan is working.
In the meantime, Queensland's government released a report card this week hinting at how difficult that will be. Despite some progress in reducing sediment, nutrient and pesticide runoff, it warned farmers have been too slow in adopting reef-friendly practices, while the ongoing loss of forests and wetlands is worsening erosion near the coast. Overall, it gave the Great Barrier Reef's health a grade of C-minus.
"If one of my kids came home with a report card like this," Queensland Environment Minister Steven Miles told reporters, "I'd be a bit disappointed."