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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.
An ideal test
On the Chagos Archipelago of the Indian Ocean near the Maldives, the islands are divided between those that were introduced and those that did not. not.
According to James Cook University researcher and one of the authors of the paper, Dr. Andrew Hoey
"It's really a natural setting, totally blank where you have six islands that have rats and six "So you could not really better design the experience."
Dr. Hoey was part of a team that compared the abundance of seabirds and Nitrogen levels in the soil between rat-infested and rat-free islands
When rats were absent, they found the abundance of seabirds was 760 times greater only 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 spread to outer reefs
Birds are an important source of new nutrients for isolated islands
"The Thing Most important for seabirds is that they travel offshore and bring these oceanic sources of nutrients to the islands, "says Dr. Hoey.
Researchers specifically studied nitrogen-delta-15, which is present in seabird droppings and can be traced back to their oceanic regime.
"The guano that infiltrates it then escapes through the rain and then into the surrounding reef environment," says Dr. Hoey. Dr. Selina Ward of the University of Queensland, who was not involved in this study, said that it was "amazing" to see where she enters the reef.
Macroalgae, filter sponges, turf Fish and fish from adjacent reefs all had high levels of nitrogen when rats were absent.
Herbivorous damsels grew much faster, and fish populations had almost 50% higher biomass on reefs with high levels of nitrogen
. The reefs affected by the rats carried fewer parrots, which fed on algae.
"One of the unique things with parrot fish is that you can go down and measure their feeding area. you can measure their bite size, and you can … get an estimate of the amount of reefs that they graze and the amount of reef carbonates that they eliminate, "said Dr. Hoey
. It is essential that the fish communities eliminate these algae and keep them in a state of culture and prevent the development of larger algae.
Black rats are considered conservation birds
th According to Professor Peter Banks of the University of Sydney, the first fleet is still mysterious: "They were found in cannons of ships sunk in Western Australia on Dutch ships, "he said. 19659002] It does not matter, after 1788, they spread rapidly across the continental and littoral islands, including in the Great Barrier Reef
Their impact is exaggerated on islands that are not used for predators, says Professor Banks. We have more than 60 species of native rodents here, so our wildlife in Australia is not so naive, "he added.
" But Lord Howe Island is distinct in that They have never had mammals. "
Lord Howe Island, 600 kilometers east of Port Macquarie, off the coast of New South Wales, has witnessed the damage done by rats introduced into the sea.
After the stranding of an American mothership in 1918 endemic birds and 13 species of invertebrates
In 1964, climber and scientist David Roots discovered a stick-shaped insect of Lord Howe , which we thought was extinct, on a rocky outcrop about 30 kilometers from the island.
Now a controversial program to rid the island of rats and reintroduce the insect -Button, 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 at the hand on the almost virgin island.
It has proved controversial among locals who fear that the poison may affect other native wildlife 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 managed to eradicate things like rats and foxes," he said [19659026]. target the rats and get rid of them without harming the rest of the ecosystem, so great. "
ABC
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