Islands are often celebrated for their beauty, biodiversity, and deep cultural heritage. But they are also on the front lines of two of the fastest-growing environmental threats worldwide: climate change and invasive species. For US and US-affiliated islands—from Hawaiʻi and Puerto Rico and the US Virgin Islands, to Guam, the CNMI, American Samoa, and the countries in free association with the United States—these threats are already reshaping ecosystems, food systems, and local economies. A new paper in BioScience takes a closer look at why invasive species impacts are so severe on islands—and what needs to change to reduce those risks and build resilience in a rapidly changing world.

One key finding is just how disproportionate the impacts are. Between 1980 and 2019, invasive species caused more than $11.7 billion in damages across US and US-affiliated islands. When adjusted for land area, that’s five times higher per square kilometer than on the US continent. Islands import most of their food and goods, rely heavily on tourism and military transport, and often have limited resources to respond when new pests arrive.

But the paper also shows that the biggest challenges are not about a lack of tools or knowledge. This research, led by Pacific RISA PI Laura Brewington as part of her service on the US Invasive Species Advisory Committee, identifies three lessons that apply not only to US islands, but to island nations around the world. First, local capacity and trust determine whether efforts succeed. Programs that invest in local jobs, training, and community engagement are more likely to detect invasions early, while long-term support of island-led research, workforce development, and implementation supports sustained management as climate extremes intensify. Second, prevention at ports of entry matters. Airports, seaports, and shipping routes are the main gateways for invasive species. When inspections are inconsistent or under-resourced, new pests slip through—and the costs multiply later. Third, long-term control tools are essential but often underused. Islands have successfully applied biological control, targeted chemical treatments, and ecosystem restoration, but these approaches are frequently limited by short-term funding or regulatory delays. Expanding access to conservation-relevant tools and investing in restoration infrastructure also both increase ecosystem resilience following disturbance.

“In many cases, the science exists and the solutions are known,” says lead author Laura Brewington. “The real challenge is making sure systems are in place to prevent invasions in the first place and to act quickly and effectively when they occur.”

The paper also highlights promising examples, from interagency agreements in the Pacific to biofouling controls in Australia and community-driven biosecurity efforts in Mexico. These cases show that coordination and sustained investment can make a real difference. Islands are often described as “sentinels” for environmental change. But in the case of invasive species, they are also shields—protecting surrounding regions from further spread. Strengthening island biosecurity isn’t just an island issue. It’s a global one. Download the paper here.

Featured image: Sunset over Tumon Bay, Guam. Credit: Laura Brewington