London, 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.

Rats decimate seabird populations, in turn decimating the

volume of bird droppings – a natural coral fertiliser. The findings are

published in Nature.

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 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’s 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, frigate birds,

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.

He and his team were able to track the source of those

nutrients back to the fish that seabirds fed on by analysing algae and

sponges growing on the reef.

“We also found that fish on the reefs adjacent to islands with seabirds

were growing faster and were larger for their age than the fish on reefs

next to rat-infested islands,” Prof Graham explained.

There were also significantly more fish on rat-free reefs than on

those around “ratty islands”.

Coral reefs cover less than 0.1% of the ocean’s area, but house

about one third of ocean biodiversity.

“Coral reefs are also hugely threatened,” said Prof Graham. “So

anyone who cares about extinctions and biodiversity needs to care

about the future of coral reefs.”

The reefs and their abundance of marine life provide livelihoods

for millions of people around the world, so the decline in coral reefs is

poised to become a humanitarian crisis.

This team of researchers advocates rat eradication projects on

islands throughout the world.

“Coral reef systems are at crisis point because of climate change,” said

Prof Graham. “And we’re desperately trying to find ways to enhance

the resilience of coral reefs and allow them to cope with climate

change.

“This is one of the clearest examples so far, where eradicating rats will

lead to increased numbers of seabirds and this will bolster the coral

reef,” the BBC reported.

Source: Oman News Agency