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
A team working on the Chagos Islands in the Indian Ocean
found that invasive rats on the islands are a “big problem” for coral
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
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
“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