© Australian Antarctic DivisionRabbits caused plant cover to decline starkly on this royal penguin "run" between 2001 (top) and 2007 (bottom).
The removal of cats in 2000 caused "catastrophic" damage to the ecology of a sub-Antarctic island, a study says.

Since cats were removed from Macquarie Island, rabbit numbers have soared, and the animals are now devastating plants.

Cats previously kept a check on rabbits but were eradicated because they were also eating seabirds, scientists relate in the Journal of Applied Ecology.

The Australian government plans to eradicate rabbits, rats and mice from the island, a World Heritage Site.

The rabbits have now caused so much damage to the island's flora that the changes can be seen from space.

The scientists behind the research say conservation agencies must "learn lessons" from the episode.

"Our study shows that between 2000 and 2007 there has been widespread ecosystem devastation and decades of conservation effort compromised," said Dana Bergstrom from the Australian Antarctic Division.

"The lessons for conservation agencies globally is that interventions should be comprehensive and include risk assessments to explicitly consider and plan for indirect effects, or face substantial subsequent costs."

In this case, one element of the cost is the 24m Australian dollars ($17m, £11m) that authorities will spend eradicating rabbits and the rats and mice that eat seabird chicks.

© BBC NewsAs with mainland Australia, rabbits were an introduced species.
Rabbits were introduced to Macquarie Island in 1878 by seal-hunters to provide food.

The first attempt to control them, in the 1960s, involved introducing myxomatosis.

That brought numbers down to about 10,000. But subsequently numbers have grown again.

Since the eradication of cats eight years ago there are now an estimated 100,000 rabbits munching the foliage of Macquarie Island, which lies about halfway between Australia and Antarctica.

It is the most important breeding site for the royal penguin, and several other species of penguin also breed there.

Removal of plant cover is thought to make penguins more vulnerable to predation.

Eradication of rabbits and rodents will involve dropping poisoned bait around the island. It is due to start next year.