When humans set forth on the seas to explore new lands, they often bring with them unintended stowaways: rats. If the animals gain a foothold on an island, they can devastate local fauna. And a study published yesterday (July 11) in Nature finds that the rodents’ destruction extends into the seas surrounding islands, starving the ecosystems around coral reefs of nutrients.
“The depth of this research shows just how much ecosystems impacted by invasive rats have to lose,” Holly Jones of Northern Illinois University who was not involved in the study tells The Atlantic.
In the study, researchers compared six rat-infested islands in the Indian Ocean with six nearby islands that are rat-free. Soil and plants on the rat-free islands had more of a nitrogen isotope that’s common in marine food sources, which birds commonly consume and then poop out on islands. The research team also found seabird densities were 760 times higher on the uninfested islands. Fewer birds on the invaded islands means less guano, the researchers write, which leads to less nitrogen seeping into the surrounding ocean to feed organisms such as plankton that form the basis of the food web. Overall, there was 48 percent more fish biomass in coral reefs adjacent to the rat-free islands than in reefs near islands with invasive 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 U.K. tells the BBC.