Eradicating feral cats on Australia's remote Macquarie Island has devastated the environment after rabbit numbers exploded, a new study shows.
The study says it will cost $24 million to fix the World Heritage-listed island located about halfway between Australia and Antarctica.
Scientists writing in the British Ecological Society's Journal of Applied Ecology, said conservation agencies could learn important lessons from what happened on Macquarie Island.
According to the article, rabbit numbers on the island were reduced from a high of 130,000 in the 1978 to less than 20,000 in the 1980s, after a program to spread the disease myxomatosis.
But as rabbit numbers fell, cats introduced in the early 1800s began to hunt the island's native burrowing birds, and in 1985 a cat eradication program began.
After the last cat was killed in 2000, myxomatosis failed to keep rabbit numbers in check and their numbers jumped.
In little over six years, rabbits substantially altered large areas of the island, the study found.
Dr Dana Bergstrom, who works for the Australian Antarctic Division and was lead author of the report, said the rabbit population had reverted to 1978 levels, with up to 130,000 on the island.
By 2007 the impact on protected valleys and slopes was acute, she said.
"We estimate that nearly 40 per cent of the whole island area had changed, with almost 20 per cent having moderate to severe change," Dr Bergstrom said.
About half of this vegetation change occurred on the island's coastal slopes, home to penguin colonies.
"Before, it was lush tussocks up to 1.5m high," Dr Bergstrom told AAP.
"In some of the most severe cases, the tussocks have been eaten down to the ground."
The disappearance of the tussocks has exposed penguin "roads" developed over hundreds of years by penguins making their way from colonies to the beach.
As a result, the penguins were exposed to large predatory birds, called skuas, Dr Bergstrom said.
The study said changes documented were a rare example of "trophic cascades", when changes in one species' abundance cause several other parts of the food web to be altered.
Macquarie Island, which is just 34km long and 5km wide, was declared a World Heritage Site in 1997.