Climate Change Clues From Monitoring in Pacific Island Parks

Change is a powerful force in nature, and islands are especially vulnerable to it. The Park Service's Pacific Island Inventory and Monitoring Network describes the climate change of recent decades as unprecedented, and climatologists expect it to speed up. Shifting rainfall, more extreme storms, changing bird migration, spreading invasive species and declining coral reefs all follow. The network carries out systematic long-term monitoring of many natural resources to determine whether change is happening and why.

Rainfall in Kalaupapa National Historical Park's lush valleys is projected to decline, affecting ecosystems from the ridges to the ocean. Image from the National Park Service's page.

Weather and climate

• Average temperatures on Pacific islands have risen 0.5°F over the past century.
• At higher elevations in Hawaiʻi, temperatures are now rising 0.48°F per decade.
• Hawaiʻi's rainfall has declined statewide over the past two decades, and the decline is expected to continue.

A warming climate brings more frequent and intense tropical storms and droughts. Forecasting future climate depends on models built from existing weather data, which weather stations in and near every park in the network record routinely. Several new park stations now allow near real-time tracking and give modelers more data.

Forests and landbirds

In Pacific island parks, the higher elevations are the main refuge for native plants and animals. In Hawaiʻi, native birds survive there because few mosquitoes carrying avian malaria reach those heights, and across the Pacific, native plants do best where people have disturbed little and conditions do not suit the invaders that have transformed the lowlands. Warmer weather lets disease-carrying mosquitoes live higher up, pushing native birds even higher or toward extinction. Ninety-three percent of Hawaiian birds and 62% of all U.S. Pacific island birds are considered vulnerable to climate change.

Avian malaria in Hawaiʻi doubled from 1995 to 2005. The ʻapapane has shown some tolerance for the disease; other native honeycreepers have not. Image from the National Park Service's page.

The network completed its first cycle of landbird monitoring at Haleakalā National Park, Hawaiʻi Volcanoes National Park and the National Park of American Samoa; the cycle repeats in each park every five years. It also monitors vulnerable plant communities, wet forests, mangroves, coastal strand and subalpine shrublands, on a five-year cycle. Rising seas and more big storms may hit coastal strand and mangrove forests, while inland vegetation may face hotter, drier conditions. Invasive plants may gain ground, especially at higher elevations, so the network tracks both established and newly arriving invaders in the same places.

A mangrove forest in American Memorial Park on Saipan occupies a small strip of low land between the town and the sea. As the sea rises, the mangroves have nowhere left to go. Image from the National Park Service's page.

Fresh water

Fresh water is the most valuable natural resource on Pacific islands, for people and for the unusual animals that live in it. As rainfall drops and warmth increases evapotranspiration, both groundwater and surface water may suffer. Sea level is rising faster, by more than an inch per decade in Hawaiʻi, and pumping upslope can cut the flow of groundwater to the coast. Hawaiʻi's rare coastal anchialine pools and wells on Guam may grow saltier as a result.

Year-round streams are rare on these islands, and many still hold native animals, especially in upper reaches where invasive species are less established. The network monitors groundwater, water quality and freshwater animals every year, giving managers what they need to protect those waters and their native crustaceans, fish and snails, such as the ʻōpae ʻoehaʻa.

Coral reefs

Oceans may absorb up to 90% of the carbon dioxide in the atmosphere over the next 1,000 years, a huge buffer against even faster climate change. But that uptake is already acidifying the oceans. Coral reefs, and the great variety of life that depends on them, are especially at risk, because stony corals cannot build their skeletons in water that is too acidic. Corals are also very sensitive to heat: when the water warms, they expel the colorful algae that live in them, which is called bleaching. Bleaching from warmer seas is increasing in the Pacific, and disease, slowed growth and death often follow. Within 50 years, temperature and carbon dioxide levels are expected to exceed anything reefs have experienced in half a million years.

Bleached coral in Guam during a mass bleaching event in 2013. Image from the National Park Service's page.

The network surveys reef fish and coral reefs every year at Kaloko-Honokōhau and Kalaupapa National Historical Parks, the National Park of American Samoa and War in the Pacific National Historical Park, tracking changes in fish, corals, invertebrates and algae. These reefs are among the most immediate and reliable indicators of climate change in the region.

Reef fish such as the pink anemonefish depend on healthy reefs for shelter and food. Image from the National Park Service's page.

Sources

• National Park Service, Pacific Island Inventory and Monitoring Network, "Climate Change Clues from Monitoring." https://www.nps.gov/articles/pacn-climate-change.htm
• The page asks how native species will "fair"; the word meant is fare.