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Eradicate rats to bolster coral reefs

13 July 2018

With potential benefits for not only island ecosystems but also nearby coral reefs, eradicating island rat populations to restore seabird-sourced nutrients should be a priority, the authors conclude.

The rat-free islands were found to have more seabirds, whose waste supplies the soil with abundant nitrogen. The researchers tested for heavy nitrogen isotopes on 12 islands, half of which had no rats and the other half was rat infested, and in nearby coral reefs.

As the state of the world's coral reefs appear to be getting worse with every passing year, an global team of scientists studying the reefs of tropical islands have come up with an unusual idea for how to help them: Kill all the nearby rats.

The rodents have invaded some of the islands of the Chagos Archipelago in the Indian Ocean, producing a surprisingly negative impact on the neighboring reefs.

The total tally showed that rat-free islands were home to 750 times more seabirds, which deposited nitrogen at a much higher rate.

By examining soil samples, algae, and counting fish numbers close to the six rat-free and six rat-infested islands, scientists uncovered evidence of severe ecological harm caused by the rats, which extended way beyond the islands and into the sea.

An worldwide team of scientists led by Lancaster University is reporting that rats must be eliminated on many tropical islands in an effort to protect coral reefs.

"These results not only show the dramatic effect that rats can have on the composition of biological communities but also on the way these vulnerable ecosystems function (or operate)", said study co-author Dr. Andrew Hoey, from the ARC Centre of Excellence for Coral Reef Studies in Australia.

"Rat eradication should be a high conservation priority on oceanic islands".

"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".

Therefore, there's little wonder that seabirds have learned to avoid these islands and no longer nest here, depriving the ecosystem of the rich nutrients found in guano, Graham told Newsweek. "And we're desperately trying to find ways to enhance the resilience of coral reefs and allow them to cope with climate change".

This in turn boosts the health of reefs, with more algae, seaweed and fish able to flourish thanks to the natural fertiliser provided by the bird's droppings. "It could tip the balance for the future survival of these reefs and their ecosystems".

It is estimated that invasive predators like rats, which feed on bird eggs and chicks, have hugely impacted bird populations on about 90 percent of the world's tropical islands, but this is the first time rats have been identified as the enemies of reefs too.

Invasive rats that decimate the population of island seabirds have unwanted consequences on the health of coral reefs.

Eradicate rats to bolster coral reefs