Frog ID program to help solve mystery of South Australia’s mass frog kill event at Bool Lagoon

The cause of a mass frog kill on South Australia’s Limestone Coast last year continues to elude experts and is to be investigated alongside a number of other similar unsolved events across the country. 

More than 200 southern bell and striped marsh frogs died at Bool Lagoon near Naracoorte in January 2023. 

The cause was initially believed to be from chytrid fungus, but testing on the dead frogs ruled it out as the sole cause and has left authorities stumped. 

“We did detect it [chytrid fungus] in some samples but not all of them,” SA Department for Environment and Water evolutionary biologist Sophie Bass said. 

Bool Lagoon, near Naracoorte, is a freshwater lagoon rich with native wildlife.(Supplied: Brian Robbins)

“Due to the scale of the event, hundreds of frogs dying is such a huge deal, you’d expect there to be a really high consistent positive if they were all dying from chytrid [fungus].” 

Dr Bass added it was likely some frogs died while carrying chytrid fungus but not as a result of the disease. 

She said frogs were very sensitive to environmental changes, and multiple factors likely played a part in deaths at Bool Lagoon. 

“Frogs are very sensitive. They absorb pollutants very easily through their skin, are very sensitive to habitat disturbance and habitat destruction,” Dr Bass said.

The striped marsh frog has also been found at Bool Lagoon.(Supplied:Jodi Rowley)

“Most likely, it’s going to be a combination of all different things working together, so chytrid-affecting frogs that are already stressed by climate change may have been around pollutants and things like that.”

Unsolved deaths ‘concerning’

The Bool Lagoon event has been referred to the Frog ID project, led by the Australian Museum, Taronga Zoo and the University of Melbourne. 

It’s one of a number of deaths around Australia without a known cause since 2020 that have researchers worried about the future of native frogs. 

Steve Donnellan says the growth in citizen science had been a “game changer” for frog research.(Supplied: Steve Donnellan)

Steve Donnellan, former head of evolutionary biology research at the South Australian Museum, said getting to the bottom of the unexplained deaths was important. 

“Frogs are a really important indicator of the conditions in their aquatic habitats and around their aquatic habitats,” Dr Donnellan said. 

“If they start disappearing, then you’ve got to be concerned about the quality of the ecosystem around them in general. 

Dr Donnellan says frogs are a really important indicator of the conditions in their aquatic habitats.(Supplied: Department for Environment and Water)

“But when you have a specific disease that goes through and takes out frogs, then that’s a bigger worry because it’s targeting those organisms.” 

Citizen science boosts capacity

The Frog ID program has created a smartphone app allowing the public to record frog sounds and send them instantly to experts, who upload them to a nationwide database. 

Dr Donnellan said the growth in citizen science had been a “game changer” for frog research, allowing scientists to get real-time data on frog populations and respond quickly to mortality events. 

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