Stranded

Biodiversity hotspots at risk

Because of their isolation, these islands have developed unique and wildly different ecosystems, ranging from tropical rainforests to grass savannahs, freshwater lakes, salt marshes, coral reefs, and more. It makes them perfect hosts for a large variety of species. The region encompasses three global biodiversity hotspots with more than 30,000 plants and 3000 vertebrate species.^{1Kumar et al. (2020). Climate Change and Impacts in the Pacific.} However, a range of factors is putting them at risk.

The environmental vulnerability index (EVI) measures the relative severity of various types of environmental issues experienced by countries based on 50 different indicators.^{2Kaly, Pratt & Mitchell (2005). The Environmental Vulnerability Index (EVI) 2004.} These include exposure to natural disasters, level of biodiversity and the impact of human interventions through settlements or agriculture and fishing. In 2004, 10 of the 22 Pacific nations were rated extremely vulnerable and ranked in the bottom 10% of all countries.

Biodiversity loss through the global extinction of species is among the greatest challenges facing humanity today. That's especially true for islands. While island isolation promotes specialised flora and fauna, that isolation is also what makes their species so vulnerable: many live on a single island, sometimes a single valley, with nowhere else to go if the habitat changes. A recent study by Saban and Wiens^{3Saban & Wiens (2025). Unpacking the extinction crisis: rates, patterns and causes of recent extinctions in plants and animals.} explored global extinction patterns and found that the majority of recent extinctions were species endemic to islands.

The IUCN Red List tracks the global extinction risk status for more than 175,900 animal, fungus and plant species. It forms the basis of the Red List Index that shows trends in overall extinction risk for species. A value of 1 indicates that there is no current extinction risk to any of the included species, while a value of 0 means that all included species are extinct.

Since 1993, the Red List Index has been declining for all Pacific nations, except Niue (slight improvement) and American Samoa (stable). It indicates that species living there, on average, are more at risk of extinction now than they were 30 years ago. Compared to most other countries worldwide, the scores of Pacific countries are much lower.^{4UN SDG Indicators Database (2025). BirdLife International and IUCN.} It means the region experiences higher levels of biodiversity loss and extinction risk among species.

The decline has been most rapid in Guam, which has fallen below 0.4 in 2024. The loss of biodiversity is largely linked to the brown tree snake, which was accidentally introduced to Guam after World War II. Guam had no native snakes and no natural predators on the island. Its population grew rapidly and put many native birds at risk of extinction. Efforts to control the brown tree snake population on Guam have been ongoing for decades, but progress has been slow.

According to Saban and Wiens^{3Saban & Wiens (2025). Unpacking the extinction crisis: rates, patterns and causes of recent extinctions in plants and animals.}, the most common causes for past extinctions were linked to invasive species, habitat loss, and exploitation. On islands, invasive species were the reason for more than half of the researched extinctions (52%).

The role of climate change

While climate change wasn't found to be a major reason for past extinctions, this might not reflect future threats. In fact, another study^{5Urban (2024). Climate change extinctions.} estimated that climate change will threaten 7.6% of all species with extinction (average across all scenarios) - a number that is estimated to be even higher for island species (12%).

Particular factors make species of the Pacific Islands more vulnerable to climate change.

Smaller islands in the Pacific are much more vulnerable due to exposure to the surrounding oceans. Species living on such islands lack the opportunity to migrate once their habitat has become inhabitable. For example, the Tuvalu Forest Gecko is found only on two small, low-lying islands in Tuvalu, with an average elevation below 2m. It is facing a significant threat from sea level rise and erosion.

It's not too late

So if these trends are irreversible, is there any hope for species at risk of extinction?

For one, the IUCN Red List isn't comprehensive - it doesn't cover every animal or plant on the planet, and for some groups, data might be biased towards extinct species.^{3Saban & Wiens (2025). Unpacking the extinction crisis: rates, patterns and causes of recent extinctions in plants and animals.} Second, the data is a lagging indicator and based on past, not future, changes. The good news is that these time lags provide a buffer for some species, during which time climate change might reverse, or conservation efforts might succeed.

Climate change is predicted to play an increasing and more certain role in causing extinctions in the coming decades. We need urgent action to address greenhouse gas emissions and slow down global warming to ensure the worst case scenarios don't become reality. But a bigger threat for many species right now is invasive species and habitat loss - things that can be, and have been, successfully managed with conservation efforts.

For example, a conservation programme to reverse declining numbers of Fiji Crested Iguanas led to the creation of a protected sanctuary on Yadua Taba Island. Research, breeding efforts and removal of goats from the island have shown signs of success, but more is needed to secure populations in other locations.^{8Wikipedia (2026). Fiji crested iguana.}

Data will remain crucial for monitoring levels of biodiversity and identifying species at risk. The work to map these species - to know which islands, which animals, which zones of risk - is what makes targeted action possible. Explore threatened species of the Pacific Islands on the interactive map