Killing rats could save coral reefs

The much maligned rat is not a creature many would associate with coral reefs.

But scientists studying reefs on tropical islands say the animals directly threaten the survival of these ecosystems.

A team working on the Chagos Islands in the Indian Ocean found that invasive rats on the islands are a "big problem" for coral reefs, BBC News reports.

Rats decimate seabird populations, in turn decimating the volume of bird droppings - a natural reef fertiliser.

Scientists now advocate eradicating rats from all of the islands to protect these delicate marine habitats.

The Chagos Archipelago provided a large-scale natural laboratory to answer this question; although the islands are uninhabited by humans, some of them are now home to invasive rats, brought by ships and shipwrecks. Other islands have remained rat-free.

"The islands with and without rats are like chalk and cheese," said lead researcher Prof Nick Graham from Lancaster University.

"The islands with no rats are full of birds, they're noisy, the sky is full and they smell - because the guano the birds are depositing back on the island is very pungent.

"If you step onto an island with rats, there are next to no seabirds."

By killing seabirds, this study revealed, rats disrupt a healthy ecosystem that depends on the seabird droppings, which fertilise the reefs surrounding the island.

On rat-free islands, seabirds including boobies, frigatebirds, noddies, shearwaters and terns travel hundreds of kilometres to feed out in the ocean. When they return to the island, they deposit rich nutrients from the fish they feed on.

"These nutrients are leaching out onto the reef," explained Prof Graham.