On a small island in Palau, getting rid of rats did more than protect native birds. It triggered a cascade of recovery that reached the coral reefs offshore.
Researchers found that one year after removing invasive rats from Ulong Island, the land and sea both rebounded in ways they did not expect.
A single pest was choking the island's life
Ulong Island, part of Palau's Rock Islands, had been overrun with rats for decades. The rodents ate seeds, destroyed plants, and preyed on seabird eggs and chicks. With fewer seabirds, less bird droppings reached the soil, which meant fewer nutrients washed into the surrounding waters.
In 2023, conservation groups led by Island Conservation and partners including the Palau government and OneReef carried out a rat eradication program. They used helicopters to drop bait across the island. By 2024, the rats were gone.
Plants, seabirds, and fish all bounced back
Within a year, the changes were visible. Native plants like the beach cabbage and sea trumpet began to spread. Seabirds, including the brown noddy and black noddy, returned to nest in higher numbers. Their guano, rich in nitrogen, again reached the soil and flowed into the ocean.
That nutrient boost helped algae and tiny organisms near the reef. Herbivorous fish, such as parrotfish and surgeonfish, increased in number. Their grazing kept the reef clean and helped corals stay healthy. Researchers measured a 12 percent rise in herbivorous fish biomass and a 16 percent increase in coral cover in waters near the rat free island.
Why local communities took notice
For Palauans, Ulong Island is not just a tourist destination. It is a place tied to traditional fishing and cultural practices. The reef surrounding the island supports fish that local people depend on. Seeing the reef improve so quickly after rat removal gave communities a tangible reason to support further eradication efforts on other islands.
The project also showed that land based invasive species can harm marine ecosystems in ways that are not always obvious. Removing rats did not just protect birds. It restored a nutrient cycle that fed the reef.
A fast fix with lasting effects
The Ulong Island case is one of the fastest documented recoveries after rat eradication. Most similar projects take years to show measurable results. Here, the ecosystem responded within months.
Scientists caution that not every island will react the same way. But the findings offer a clear example of how removing a single invasive species can set off a chain of positive effects across both land and sea.
