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In the uninhabited Chagos Archipelago, in the middle of the Indian Ocean, rats arrived in the eighteenth century with Europeans became masters of most of the 55 islands. According to one study, its presence has completely altered the territory's ecosystem and caused a chain effect that harms seabirds, and coral reef fish.
A common seabird breeding in the tropical oceans in its nest near a coral reef. Nick Graham
At first glance the 55 islands of the depopulated Chagos Archipelago halfway between Africa, Asia and the Middle East , seem to be the same, and yet the difference is obvious. In some, the noise is deafening because of the abundance of birds and the intense smell of their depositions. In others, silence reigns and the sky is empty.
"The size of the islands and their geology is similar to each other, but the difference in the seabird population is dramatic ," notes Nicholas Graham of Lancaster University, who presented a study with Aaron MacNeil, from Dalhousie University (Canada), at the Euroscience Open Forum which was held in Toulouse (France) this week.
Without natural predators, rats took control of islands devouring eggs from birds and their chickens
The team of scientists, led by Graham, took five days to reach this remote location, and immediately found the culprits: rats who arrived with the Europeans between the eighteenth and nineteenth centuries.
Rats vs. birds
Without natural predators, the rats seized the islands an ecosystem that does not belong to them, devouring the eggs of birds and their chickens . "They decimate the number of seabirds," says Graham. Rodents prevent nesting and reproduction of birds.
In the book, published today in the journal Nature researchers, who focused on 12 islands of the northern atolls of the archipelago, reveal that the [1 990 901] Ratless islands have 750 times more birds than those with these rodents.
But the presence of rats causes a cascading effect throughout the entire ecosystem of the islands. Without the birds, organisms living on coral reefs no longer receive nutrients through the droppings of birds that fall to the ground and are released into the sea.
promptly when they live near the islands with seabirds, compared to islands with rats, and this results in a total amount of fish which is almost 50% higher ", says expert at Syn. [19659005] An altered ecosystem
The droppings deposited in the soil help fertilize the islands and nearby coral reefs, but this flow of nutrients and phosphorus are altered by rat infestations. "Rats on the islands decrease the life of fish in coral reefs and alter the health of ecosystems ," says Graham.
According to the l. study, coral reefs near islands without rats (and with many seabirds), they are much healthier than the coral reefs that are near the islands with rats. "Nitrogen deposits are 250 times lower in the islands with rats," says Graham.
The absence of birds mbadively decreases the contribution of nutrients to the terrestrial environment, and consequently to adjacent corals. Researchers propose a deratting strategy to preserve the environment of these islands
"The eradication of rats in these tropical islands should be a priority for conservation and management. The elimination of rats is likely to benefit both animals and birds that use the islands, as well as animals that live in coral reef ecosystems, "concludes the expert. 39, moment, only one of the islands was able to eradicate rodents
A controversial archipelago
Reason for territorial conflict since the defeat of Napoleon in 1815, the 39 Chagos archipelago in the Indian Ocean was ceded by the French to the English, but its location in the middle of the sea between Africa, the Middle East and Asia would make it a coveted object of military desire during the Cold War for the United States [19659005] In 1966, the British decided to abandon one of the atolls – called Diego García – to the Americans to install their military base. For this, they took the disputed decision of to expel the population formed by descendants of African slaves who were growing coconut, in a process that lasted from 1968 to 1973.
Chagossians, sent since then to Mauritius, are still fighting today to recover their homes. Currently, 37 of the 55 islands are populated by rats .
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