CLIMATE WIRE | Just a year ago, the tiny islet of Irooj in the Marshall Islands was teeming with invasive rats. Hungry rodents have been rampaging there for decades, gobbling up native seabird eggs and threatening local biodiversity.
But since March, the small island has been declared rat-free. This is thanks to a year-long campaign to eradicate rodents and restore the island to its natural state.
The effort was led by the Ministry of Natural Resources and Commerce of the Republic of the Marshall Islands, with assistance from the Secretariat of the Pacific Regional Environment Program, an intergovernmental organization focused on climate and environmental issues on small islands in the Pacific, and the non-profit Island Conservation, which works to remove invasive species from islands around the world.
“The island feels alive again,” Kennedy Kaneko, national invasive species coordinator for the Republic of the Marshall Islands, said in a statement. “Careful monitoring showed no signs of rats on Irooj. In fact, seabirds and crabs were found in abundance.”
Irooj is just a small islet in the long chain of volcanic islands and coral atolls that make up the Marshall Islands, which dot the central Pacific Ocean between Hawaii and the Philippines. Yet it represents a small success in a series of global efforts to eradicate invasive species from small islands, especially in the tropics.
These efforts, experts say, can help protect fragile island ecosystems, which are often home to threatened or endangered species, including plants and animals that may not exist anywhere else in the world. They can also help strengthen the diverse coral reef ecosystems that surround many tropical islands.
And they can promote resilience to climate change in the process.
Small islands and coral reefs both face existential threats from the effects of climate change, including sea level rise, warming waters and ocean acidification. Limiting greenhouse gas emissions and curbing climate change is the only way to truly stem these threats. But by removing additional environmental stressors, such as harmful invasive species, it can make ecosystems healthier, more robust and better able to withstand the pressures of global warming.
Small islands around the world have historically contributed little to global warming greenhouse gas emissions, added Chad Hanson, assistant vice president of conservation at the nonprofit Island Conservation. Yet they experience disproportionate impacts from climate change.
“Your island communities are not the ones contributing to climate change,” he said. “But they are the ones experiencing sea level rise, they know invasive species which are often more adaptable to increases in temperature or changes in soil chemistry, and they can survive many native and endemic species. .”
Island Conservation is one of the organizations helping to lead the charge against invasive island species. The organization works at sites around the world, with projects in South America, North America, the Pacific and Indian Oceans and the Caribbean, aimed at preventing the extinction of native species. He treats a variety of invasive species, including plants and animals, but specializes in vertebrates – like rats.
Rats have traveled the world for centuries as stowaways on ships. By some estimates, they have reached 90% of the world’s islands – and they have wreaked havoc in many places they have invaded. They have a particularly devastating impact on island seabird populations, many of which had few or no natural predators before their arrival.
“Rodents are a generalist,” Hanson said. “In order for them to feed on vegetation, they may feed on protein sources – which could directly attack a bird or eggs or crabs or any of these native species which can be incredibly vulnerable.”
And it’s not just terrestrial organisms that suffer when rats invade. Nearby coral reefs are also threatened.
Indeed, corals and seabirds are closely related. Seabirds feed in the open ocean, then return to islands to rest, breed and nest. While on land, they deposit copious amounts of guano – a fancy name for bird poo – all over the island.
This guano is rich in useful nutrients, such as nitrogen and phosphorus. Nutrients eventually flow off the island and into the water, where they are used by corals and algae. The fish come in and eat the algae, and the nutrients move up the food chain. In this way, they help support the entire coral reef ecosystem.
But once the rats move in, everything changes.
“Once you lose seabirds, you lose that nutrient connection,” said Casey Benkwitt, a researcher at Lancaster University who studies coral reefs and other marine ecosystems. “There are far fewer nutrients entering the system.”
This often leads to problems such as fewer fish, slower growing fish and lower productivity in reef communities, she added.
A recent study, published in January, demonstrated some of the unintended consequences of rat-related declines in seabirds. The study looked at sites around the Chagos Archipelago in the Indian Ocean, focusing on a small fish known as the jewel damselfish.
It is normally an aggressive and territorial species. It lives around coral reefs and spends much of its time monitoring and protecting the patches of algae it prefers to graze on, a practice scientists call “farming”. But the study found that damselflies become less territorial when living around rat-infested islands.
These islands have fewer seabirds and fewer nutrients flowing into the water. As a result, fish’s favorite algae is less nutritious. And that means it’s not worth it for the fish to expend so much precious energy to keep their little algae farms going.
“Fish from the ‘ratty’ islands need to spend more time feeding to get the equivalent amount of nutrients,” said Rachel Gunn, coral reef ecologist at the University of Tübingen in Germany and lead author of the study.
Getting rid of invasive rats from an island, on the other hand, can help restore nutrient balance and increase the productivity of coral reef ecosystems. Research indicates that once an island is free of rats, its nutrient flows can rebound in about 15 years, Benkwitt said.
“You’re probably not going to see instant success,” she said. “But 15 years is not bad.”
In general, it is good for island ecology and native biodiversity. Hanson of Island Conservation noted that eradication campaigns sometimes push native species back from the brink of extinction.
In one notable case, he said, Island Conservation helped eradicate invasive rats from the Galápagos Islands of Rábida and Pinzón. After the rats left, a tiny gecko appeared on Rábida – an animal that hadn’t been documented in the fossil record for 5,000 years.
“It had been suppressed to levels where it just didn’t exist,” Hanson said. But as the island bounces back, so does the gecko.
Removing invasive species and restoring natural nutrient flows can also help nearby islands and coral reefs better withstand the pressures of global warming and bounce back from climate-related disasters.
One example is coral bleaching events, Benkwitt noted. When corals are stressed – often from sea heat waves – they expel the colorful symbiotic algae that live inside and bleach in the process. Bleaching does not necessarily kill all corals instantly, and reefs can recover given sufficient time once the source of stress has died down.
There are a few specific types of crusty algae that can help coral reefs recover, Benkwitt noted. These can help hold reefs together and provide a platform for new baby corals to settle in and grow. And a 2019 paper found that islands with lots of seabirds tended to have more of this algae after coral bleaching events, compared to islands infested with rats.
“It could speed up recovery,” she said.
The study also found that the reefs around the rat-free islands harbored more species of herbivorous fish. These fish can help control algae levels – a good thing for corals, which often compete with algae for resources.
Scientists believe that healthy coral ecosystems can also help protect islands from erosion and sea level rise – or at least slow their effects. Healthy coral reefs can help mitigate the impact of storm surges, Hanson pointed out, by protecting islands from violent waves.
And some types of reef fish produce sand, which can spill onto islands and help feed their sandy shores. Parrotfish, for example, feed on algae and dead coral, digest the crusty reef material, and then excrete it as sand.
Providing a healthy environment for these types of fish could help strengthen islands against the effects of erosion and rising sea levels, Benkwitt said.
“We don’t know if that’s happening yet,” she warned. “But it’s a reasonable assumption.”
None of these positive side effects can replace meaningful climate action, Benkwitt added. Sea level rise, sea heat waves, ocean acidification and all the consequences of climate change will continue to worsen as long as greenhouse gases continue to increase in the atmosphere.
But these efforts can help buy the islands a bit more time and give them a better chance in the meantime.
Island Conservation has set a goal to restore 40 islands by 2030.
“Ocean health is a shared issue,” Hanson said. “Biodiversity and extinctions are a common problem. Climate change, without a doubt – I’m preaching to the choir here, is a huge shared issue. There is no one who will avoid the impacts of this.
Work, he added, “really is more important than any group or individual”.
Reprinted from E&E News with permission from POLITICO, LLC. Copyright 2023. E&E News provides essential information for energy and environmental professionals.
