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What do rats have to do with the number of fish on coral reefs?
The Black Rat – Rattus rattus – wreaks havoc on island seabirds around the world, including in the Great Barrier Reef, where it has been harmful for over 200 years.
Animals eat breeding bird eggs and attack young, removing the number of birds on the islands that they inhabit.
An article in Nature Today shows how this triggers a series of events that not only damage the surrounding coral reefs. but also has an impact on fish and other forms of marine life.
It's all about poo.
![A school a blue and yellow fusiliers A blue and yellow rifle school](http://www.abc.net.au/cm/rimage/9957666-3x2-thumbnail.jpg?v=2)
Researchers found that fish biomass was much higher on reefs around rat-free islands.
(Provided: Nick Graham)
![A school a blue and yellow fusiliers Researchers found that fish biomass was much higher on reefs around rat-free islands. </p>
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<h2> An Ideal Test </h2>
<p> In the Chagos Archipelago of the Indian Ocean near the Maldives, the islands are shared between introduced rats and those According to researcher James Cook University and One of the authors of the paper, Dr. Andrew Hoey </p>
<p> researchers had the unique opportunity to study their impact on island ecosystems. where you have six islands that have rats and six others next door that do not have rats, "he says. </p>
<aside class=](http://www.abc.net.au/cm/rimage/9957666-3x2-thumbnail.jpg?v=2)
" So you really could not conceive of the experience much better. "
Dr. Hoey was part of a team that compared the abundance of aberrations and nitrogen levels in the soil between rat-infested and rat-free islands.
the rats were absent, they found that the abundance of seabirds was 760 times greater than on the islands with rats.
As a result, the rates of nitrogen deposition of the poop of birds, known as guano, were 251 times higher.
The impact of rats extends to external reefs
Birds are an important source of new nutrients for isolated islands
"The most important thing for seabirds is that they travel offshore and bring these ocean sources of nutrients to the islands," says Dr. Hoey
![A reef crest in the Chagos Archipelago A Reef Ridge in the Chagos Archipelago](http://www.abc.net.au/cm/rimage/9958484-3x2-thumbnail.jpg?v=2)
The reduction of nutrient concentrations had an effect on reef ridges
(Provided: Nick Graham)
![A reef crest in the Chagos Archipelago A reef ridge in the Chagos Archipelago](http://www.abc.net.au/cm/rimage/9958484-3x2-thumbnail.jpg?v=2)
Researchers have specifically studied nitrogen-delta-15, which is present in seabird droppings and can be traced back to their oceanic regime.
![A booby chick on the nest over a coral reef lagoon A crazy chick on the nest above a lagoon of coral reefs](http://www.abc.net.au/cm/rimage/9958398-3x2-thumbnail.jpg?v=2)
Rats eat eggs and young birds
(Provided: Nick Graham)
![A booby chick on the nest over a coral reef lagoon A chick on the nest above a coral reef Rats eat eggs and young birds </p>
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<p> Although it was previously understood that the nitrogen from the poo of the birds enters the reef lagoons, Dr. Selina Ward of the University of Queensland, who did not participated in the study, said "incredible" to see until it penetrates through the reef. </p>
<p> Macroalgae, filter sponges, peat eaters and fish on adjacent reefs all showed high levels of nitrogen where the rats were absent. </p>
<p> Damselfish Herbivores were found significantly faster, and the s fish populations had almost 50% higher biomass on reefs where nitrogen levels were high. </p>
<p> And the difference continued in the structure of the reef itself. </p>
<p> The reefs affected by rats carried fewer parrotfish such as seaweed. </p>
<p> "O One of the unique things with the parrot fish is that you can go down and measure their feeding range, you can measure their bite sizes, and you can … get an estimate of the amount of reef how they are grazed and how much "The ability of fish communities to kill and maintain algae in a state of culture and to prevent these algae from growing is critical" </p>
<h2> for Conservation </h2>
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![Black rats have been introduced to numerous coral islands Black rats have been introduced into many coral islands](http://www.abc.net.au/cm/rimage/9011018-3x2-thumbnail.jpg?v=2)
Black rats have wiped out many species of birds on Lord Howe Island
(Getty: Michael Leach)
![Black rats have been introduced to numerous coral islands Black ships have wiped out many species of birds on Lord Howe Island. </p>
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<p> Although it is believed that black rats arrived in Australia aboard the First Fleet, their origin remains mysterious, according to Professor Peter Banks of "Univ" They were found in wreck cannons of ships sunk in the west of Australia aboard Dutch ships, "he said. </p>
<p> Shortly after 1788, they spread rapidly on the mainland and coastal islands, including </p>
<p> Their impact was exaggerated on islands that were not used by predators <strong> </strong> says Professor Banks . </p>
<p> "We have more than 60 species of native rodents here, so our wildlife in Australia is not. But Lord Howe Island is distinct in that they've never been Mammals. "</p>
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<p> On Lord Howe Island, 600 kilometers east of Port Macquarie, off the coast of New South Wales, damage after stranding From an American mothership in 1918, a few rats failed on the shore and hunted five endemic birds and 13 invertebrate species </p>
<div class=](http://www.abc.net.au/cm/rimage/9011018-3x2-thumbnail.jpg?v=2)
![A rat-baiting program on Lord Howe Island has divided opinions .The Island Has Shared Views](http://www.abc.net.au/cm/rimage/9010392-3x2-thumbnail.jpg?v=2)
A rat-baiting project
(Source: Sarah Oxenham)
![A rat-baiting program on Lord Howe Island has divided opinions A rat-priming program on Lord Howe Island divided opinions](http://www.abc.net.au/cm/rimage/9010392-3x2-thumbnail.jpg?v=2)
In 1964, climber and scientist David Roots discovered Lord Howe's stick-shaped insect, which we thought was extinct, on a rocky outcrop about 30 kilometers from the island
. reintroducing the stick insect, known as the Lord Howe tree lobster, is approaching a start date.
The plan would see tons of poisoned pellets dropped from the helicopter and hand-held on the almost virgin island.
![A lesser noddy A Small Bald-headed Gray Nodule Bird](http://www.abc.net.au/cm/rimage/9957738-3x2-thumbnail.jpg?v=2)
Bird droppings or guano provide high levels of nitrogen to island ecosystems
(Provided: Guy Stevens)
![A lesser noddy A Small bald-headed gray bird-nodule](http://www.abc.net.au/cm/rimage/9957738-3x2-thumbnail.jpg?v=2)
It has been proven that the local population feared that the poison could affect them. Other native wild species.
Researchers will follow the program closely. If it works, it could serve as a model for similar projects in other Australian islands
In the case of uninhabited islands, the removal of rats should be a conservation goal in the near future, according to Dr. Hoey . "There is more and more evidence, like on the island of Macquarie, near Antarctica, where they have also managed to eradicate rats and foxes," he said.
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Tags coral fish havoc News number Rats reduce reefs Science wreak