The University of Newcastle, Australia

Humble salt fights mass frog extinction

Wednesday, 21 February 2018

It’s been touted as a natural health cure for centuries, now a new study reveals that humble salt may halt devastating chytrid disease (chytridiomycosis) in frogs.

Green and gold bell frog

University of Newcastle lead researcher Dr Simon Clulow said that with no cure or viable treatment in the wild until now, the highly infectious chytrid disease had proliferated, sending more than one third of the world’s frog species into decline and driving more than 100 species to extinction.

“Chytrid disease is incredibly prevalent worldwide. It has devastated frog populations in Australia, the Americas, Africa and Europe. In fact, it’s easier to say where chytrid isn’t found as the only major climatically suitable landmass left on earth where it hasn’t been detected is New Guinea,” said Dr Clulow.

“Chytrid is probably the main driver of current frog extinctions and until now we haven’t been able to develop effective controls, especially for wild populations.”

Dr Clulow said the research offered real hope for the survival of frogs worldwide.

“This treatment requires the use of simple pool salt, which is very affordable and easy to access. This overcomes many initial hurdles, particularly in majority world countries where resources are scarce and so many species are at risk.”

“People working in conservation or environmental science across the globe will be able to implement this technique quickly and easily for many species and hopefully change the worrying trajectory so many frog species are on,” said Dr Clulow.

The Chytrid effect

Dr Clulow said that chytrid is actually a type of fungus that transmits infection by releasing small bodies known as a ‘zoospores’.

“Zoospores shuttle around cool, wet environments, rapidly spreading from place to place in water or damp surfaces such as soil and can pass from the skin of infected amphibians,” said Dr Clulow.

Dr Clulow said chytrid attacked the keratin in the skin of frogs, ultimately disrupting the flow of electrolytes and eventually killing them.

“Chytrid gets into the skin of frogs resulting in an imbalance of electrolytes. This leads to a breakdown of the electrical regulation of the heart, effectively giving them a heart attack.”

Saving the Iconic Green and Golden Bell Frog

The iconic Australian Green and Golden bell frog, considered to be under high risk of extinction in NSW, was the species selected for the study.

Dr Clulow said conservation programs known as ‘translocations’, where frogs were bred in captivity and released back into the wild, typically failed as the new colonies eventually succumbed to chytrid which remained in the environment.

“Translocations are a popular way for conservationists to fight extinction around the globe, however so many of these programs fail because disease is still present or eventually establishes in the translocation site,” said Dr Clulow.

“In this study, the Green and Golden Bell frog had a 70 per cent increased survival rate when translocated into habitats where small amounts of salt were added to the water. This is an incredible outcome and gives us the first viable treatment option for chytrid in the wild.”

The healing power of salt

Dr Clulow’s team decided to test the effects of salinity after their prior discovery that several isolated populations of endangered Australian Green and Golden Bell frogs persisted with chytrid near the coast, despite nearby inland populations succumbing to the disease.

The study used simple, low-cost swimming pool salt to elevate pond salinity very slightly – still within the natural pond variation found in the field, to a level of 3-4 parts per thousand.

“This study established that by elevating salt levels very slightly - we’re still talking fresh water that you could drink, we can block the disease and lower the transmission rate of the disease from one frog to another.”

Global impact

Dr Clulow now plans to team up with scientists in Ecuador to further test the study.

“We are planning to visit a similar translocation program currently underway in Ecuador, where habitat is being constructed for a translocation program for the endangered Riobamba marsupial frog.”

“This offers an ideal system to further test our salt strategy. If we can show that this works just as well on the other side of the globe, it should provide further proof of concept that this strategy could help declining frogs everywhere.”

Access the full study.

Study Science and the Environment

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