Rat-free islands had significantly more bird life, resulting in greater amounts of nitrogen from bird droppings entering the soil and ending up in the sea. Invasive rats are killing off seabirds in large numbers, and the researchers have identified previously undetermined consequences for the coral reefs that surround and protect the islands.
An extraordinary set of remote tropical islands in the central Indian Ocean, the Chagos islands provided a flawless "laboratory" setting as some of the islands are rat-free, while others are infested with black rats - thought to have been introduced in the late 1700s and early 1800s.
Rats are voracious bird predators, feeding on eggs, chicks and even adult birds. They realized that the issue of introduced rats decimating the local bird populations was having an unforeseen effect on the health of the reefs.
This positive effect spilled over into the sea - with almost 50 per cent more fish living near islands fertilised by seabirds than those infested with rats.
"This is one of the clearest examples so far, where eradicating rats will lead to increased numbers of seabirds and this will bolster the coral reef", coauthor Nick Graham of Lancaster University in the United Kingdom tells the BBC.
Rats on tropical islands are damaging surrounding coral reefs by depriving them of nutrients from seabird droppings, according to a study.
"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".
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.
Professor Graham and his term verified that the nutrients present in seabird droppings, also known as guano, were derived from the fish that they ate.
The nitrogen fuelled the growth of micro-algae, which in turn benefited filter-feeding sponges and fish further up the food chain.
"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.
"Coral reefs are also hugely threatened", said Prof Graham.
Save the coral reefs by saving the birds by eradicating rats, scientists say in a study that exposes how rat infestation impacts deteriorating reefs.
"Until now, we didn't know to what extent this made a difference to adjacent coral reefs", Graham continues.
The reefs and their abundance of marine life provide livelihoods for millions of people around the world, so the decline in coral reefs is poised to become a humanitarian crisis.