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Global warming: Sea level rise threatens Hawaii biodiversity

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Pelagic birds do need a bit of land, and some nesting areas in Hawaii may be threatened. Bob Berwyn photo.

USGS study says sea bird rookery in outlying Hawaiian Islands at risk

By Summit Voice

SUMMIT COUNTY — Sea level rise could threaten the breeding areas of numerous sea bird breeding areas in the northwestern Hawaiian Islands, according to a new U.S. Geological Survey study that analyzed the combined effects sea-level rise and wave action.

Most climate change models predict a 1-meter rise in global sea level by 2100, with larger increases possible in parts of the Pacific Ocean. Those rising sea levels may inundate low-lying islands across the globe, placing island biodiversity at risk.

The Northwestern Hawaiian Islands, which extend 1,930 kilometers beyond the main Hawaiian Islands, are a World Heritage Site and part of the Papahānaumokuākea Marine National Monument. These islands – comprising the Hawaiian Islands National Wildlife Refuge, Midway Atoll National Wildlife Refuge, and Kure Atoll State Wildlife Sanctuary – support the largest tropical seabird rookery in the world, providing breeding habitat for 21 species of seabirds, four endemic land bird species and essential foraging, breeding or haul-out habitat for many other resident and migratory wildlife species.

“These magnificent seabirds spend the majority of their adult lives at sea: soaring vast distances over open water searching for food in an over-fished ocean. The one thing they cannot do at sea is reproduce,” said USGS cirector Marcia McNutt. “And now their breeding ground is in peril.”

The USGS team was led by biologist Michelle H. Reynolds of the USGS Pacific Island Ecosystems Research Center. The study modeled what is known as passive sea-level rise (excluding wave-driven effects such as wave flooding and erosion) for islands in this biologically important region.

General climate models that predict a temperature rise of 1.8–2.6 degrees Celsius and an annual decrease in rainfall of 24.7–76.3 millimeters by 2100 were applied across the study area.  For the most biologically diverse low-lying island of Laysan, dynamic wave-driven effects on habitat and wildlife populations were modeled for a range of sea-level rise scenarios.

Given a passive sea-level rise of 1 meter, they found about 4 percent of the land mass of the Northwestern Hawaiian Islands will be lost. If sea level rises 2 meters, 26 percent of the land mass will be lost. On Laysan Island, within the Hawaiian Islands National Wildlife Refuge, impacts from storm waves as well as groundwater rise were found to greatly amplify the effects of sea-level rise: from 4.6 percent to 17.2 percent inundation in the 2-meter scenario, for instance.

Thus habitat loss would be most dramatic in the wave-exposed coastal habitats and most devastating to species with global breeding distributions primarily on the low-lying Northwestern Hawaiian Islands, such as the Black-footed Albatross (Phoebastria nigripes), Laysan Albatross (Phoebastria immutabilis), Bonin Petrel (Pterodroma hypoleuca), Gray-backed Tern (Onychoprion lunatus), Laysan Teal (Anas laysanensis), Laysan Finch (Telespiza cantans), and Hawaiian monk seal (Monachus schauinslandi).

The publication, “Predicting Sea-Level Rise Vulnerability of Terrestrial Habitat and Wildlife of the Northwestern Hawaiian Islands,” by Michelle H. Reynolds, Paul Berkowitz, Karen N. Courtot, Crystal M. Krause, Jamie Carter, and Curt Storlazzi is available online. 

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