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Eradicate rats to bolster coral reefs

Eradicate rats to bolster coral reefs

July 11, 2018, Lancaster University

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Researcher surveying a coral reef in the Chagos Archipelago. Credit: Guy Stevens | Manta


Rat control should be considered an urgent conservation priority on many

remote tropical islands to protect vulnerable coral reefs, according to an

international team of scientists.

New research has confirmed that invasive rats decimate seabird populations,

with previously unrecognised consequences for the extensive coral reefs that

encircle and protect these islands.

Invasive predators such as rats—which feed on bird eggs, chicks, and even

adults birds—are estimated to have decimated seabird populations within

90% of the world's temperate and tropical island groups, but until now the

extent of their impact on surrounding coral reefs wasn't known.

The new study, published today in the journal Nature, examined tropical

ecosystems in the northern atolls of the Chagos Archipelago to uncover how

rats have impacted surrounding reefs.

Lead author Professor Nick Graham of Lancaster University, UK, said:

"Seabirds are crucial to these kinds of islands because they are able to fly to

highly productive areas of open ocean to feed. They then return to their island

homes where they roost and breed, depositing guano—or bird droppings—on

the soil. This guano is rich in the nutrients, nitrogen and phosphorus. Until

now, we didn't know to what extent this made a difference to adjacent coral


An extraordinary set of remote tropical islands in the central Indian Ocean,

the Chagos islands provided a perfect 'laboratory' setting as some of the

islands are ratfree,

while others are infested with black rats—thought to have

been introduced in the late 1700s and early 1800s. This unusual context

enabled the researchers to undertake a unique, largescale

study directly

comparing the reef ecosystems around these two types of islands.

By examining soil samples, algae, and counting fish numbers close to the six


and six ratinfested

islands, scientists uncovered evidence of severe

ecological harm caused by the rats, which extended way beyond the islands

and into the sea.

2018 Eradicate rats to bolster coral reefs 2/3

Journal reference: Nature

Provided by: Lancaster University feedback to editors

Parrotfish feeding on a coral reef in the Chagos Archipelago. Credit: Nick Graham


islands had significantly more seabird life and nitrogen in their soils,

and this increased nitrogen made its way into the sea, benefiting macroalgae,


sponges, turf algae, and fish on adjacent coral reefs.

Fish life adjacent to ratfree

islands was far more abundant with the mass of

fish estimated to be 50% greater.

The team also found that grazing of algae—an important function where fish

consume algae and dead coral, providing a stable base for new coral growth

—was 3.2 times higher adjacent to rat free islands.

"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 coauthor

Dr. Andrew Hoey from the

ARC Centre of Excellence for Coral Reef Studies ,Australia.

"Critically, reductions in two key ecosystem functions (grazing and bioerosion)

will likely compromise the ability of these reefs to recover from future


Professor Graham said: "The results of this study are clear. Rat eradication

should be a high conservation priority on oceanic islands. Getting rid of the

rats would be likely to benefit terrestrial ecosystems and enhance coral reef

productivity and functioning by restoring seabird derived nutrient subsidies

from large areas of ocean. It could tip the balance for the future survival of

these reefs and their ecosystems."

Associate Professor Aaron MacNeil from Dalhousie University, Canada, said:

"These results show how conservation can sometimes be a bloody business,

where doing right by the ecosystem means there is a time to kill. For these

invasive rats, that time is now."

The paper "Seabirds enhance coral reef productivity and functioning in the

absence of invasive rats," is published in the journal Nature.

Explore further: Remote corals pay the price of climate change

More information: Nicholas A. J. Graham et al, Seabirds enhance coral reef

productivity and functioning in the absence of invasive rats, Nature†(2018).

DOI: 10.1038/s4158601802023


About the author

Dr. Howard Dryden

Dr. Howard Dryden

Dr. Dryden has unique knowledge combination of biology, chemistry and technology and is the inventor of the activated, bio-resistant filter media AFM®. Dr. Dryden is one of the world`s leading experts in sustainable water treatment.

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