The impact was clear up and down the coastal food chain

When Carolyn Kurle first visited Alaska's Hawadax Island, then known as Rat Island, she immediately noticed the silence. “When you're on an island that's never had rats, it's just like birds everywhere—it's really loud,” she says. “So when you get to an island that does have rats, you really notice because it's cacophony versus quiet.”

Nowadays Hawadax is once again a noisy place. Roughly a decade after a successful effort to rid the island of its predatory rodents, a bounty of seabirds has returned. And the benefits have extended across the island's entire seashore ecosystem, which again teems with diverse life. These findings, published in Scientific Reports, show that certain ecosystems can recover with surprising speed if given the chance.

“This study is an example of something positive that can happen when we humans take action to clean up after ourselves,” says Kurle, who is lead author of the study and a conservation ecologist at the University of California, San Diego. “It also highlights how everything is interlinked, especially in coastal systems.”

Kurle originally began studying rats' ecological effects on the remote Aleutian archipelago for her doctoral research. The voracious rodents colonized Hawadax after a Japanese shipwreck in the 1780s, and they quickly wiped out seabird communities. Kurle's first findings, published in 2008, showed that the rats affected not just birds but the entire food chain—all the way down to algae. Without birds to eat seashore invertebrates, populations of snails, limpets and other herbivorous species exploded and gobbled up much of the marine kelp, which provides crucial habitat for other organisms. “Certain invasive species can have impacts beyond those that are most obvious,” Kurle says.

Those early findings inspired the U.S. Fish and Wildlife Service, in partnership with The Nature Conservancy and Island Conservation, to eradicate the rats by dropping poison on Hawadax. Kurle and her colleagues secured funding to survey the island five and 11 years after the intervention. They found that its intertidal ecosystem had steadily recovered and now resembles that of other Aleutian Islands that were never invaded by rats, with significantly fewer marine invertebrates and much more kelp cover.

“Very few rat-eradication projects have focused on the impact on marine ecosystems, so the Hawadax Island case is really noteworthy,” says University of Tennessee, Knoxville, ecologist Daniel Simberloff, who was not involved in the study. “This is a very cool, elegant result from an academic ecology standpoint and, of course, is important in terms of conservation.”

This article was originally published with the title "Ratted Out" in Scientific American 324, 6, 15 (June 2021)

Rachel Nuwer is a freelance science journalist and author who regularly contributes to Scientific American, the New York Times and National Geographic, among other publications. Follow Nuwer on Twitter @RachelNuwer Credit: Nick Higgins

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