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The Northwestern Hawaiian Archipelago

Geography and history

The NWHI is an archipelago which consists of a series of islands, atolls, reefs, shallow water banks, and seamounts that start with Nihoa Island and stretch 1,193 miles (1,920 km) west-northwest to Kure Atoll. They are part of the Hawaiian Ridge-Emperor Seamounts chain that extends approximately 3,700 miles (6,000 km) from the island of Hawai'i to the Aleutian Trench off the coast of Siberia.

The named islands, shoals , banks and atolls (from east to west) are: Nihoa, Necker, French Frigate Shoals, Gardner Pinnacles, Maro Reef, Laysan Island, Lisianski Island, Pearl and Hermes Atoll, Midway Island, and Kure Atoll.

Northwestern Islands and Banks of the Hawaiian Archipelago
Table coral (Acropora) at French Frigate Shoals (Photo: James Watt)

The NWHI were formed by volcanic action over the past 70-75 million years as the Pacific tectonic plate moved slowly northwestward over a stationary magmatic hotspot in the Earth's crust (a location on the Earth's surface which has had volcanic activity for a long period of time). This hotspot has its origin in the convection of molten lava from the upper mantle (Ref. 2). Kure is the oldest island in the Hawaiian Archipelago; the Main Hawaiian Islands (MHI) are the youngest.

A beautiful coral in the NWHI
A beautiful coral in the NWHI (Photo: Bishop Museum/ NOWRAMP Expedition)

A significant percentage of reef-building corals within the waters of the United States are contained within the NWHI. While elsewhere in the world coral reefs are threatened and stressed by human activities such as coastal development, pollution, and resource over-exploitation, the remote location of the NWHI has helped protect its coral reefs from adverse human impact. The shallow-water coral reefs of the NWHI are truly unique. They are still pristine ecosystems with a much greater diversity in reef habitats than in the MHI.

Algae

Scientists have recorded 366 described species of algae from The NWHI, with new endemic species (species native to the area) more recently discovered. The NWHI provide habitats for many Indo-Pacific algal species that are not found in the MHI.

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Birds, mammals, and turtles

A distinctive group of marine mammals, fishes, sea turtles, birds, and invertebrates inhabit the NWHI. They include species that are endemic, rare, threatened, and endangered, including the Hawaiian monk seal and the green, leatherback, and hawksbill sea turtles. The majority of the highly endangered Hawaiian monk seals breeds and feeds in the NWHI, as do over 90 percent of the Hawaiian population of threatened green sea turtles. Four other species of sea turtles are sometimes seen in the waters of the NWHI. The NWHI also provide the nesting habitats for more than 14 million Pacific seabirds. Nearly all of the world's Laysan albatross and black-footed albatross reproduce there. Seventeen other species of seabirds also nest in the islands. Many of these birds rely on the coral reefs for food. Many of these atolls also provide protection for Hawaiian spinner dolphins to safely rest during daylight hours. Other marine mammals, such as the Hawaiian humpback whale, also travel through this region.

A pristine coral reef in the NWHI
A pristine coral reef in the NWHI (Photo: Bishop Museum/ NOWRAMP Expedition)

Corals

More than 7,000 marine species have been recorded from the Hawaiian Islands, including corals and other benthic (bottom-dwelling) invertebrates, algae, plants, fishes, sea turtles, and marine mammals. It has been estimated that as many as one quarter to one half of the species in some of these groups exist only in the NWHI. These islands also serve as a source of marine species that helps restock the MHI. Among the 57 recorded stony coral species in the NWHI, 11 were first records and 29 were species range extensions. Coral endemism is high (30 percent), with three genera accounting for 88 percent of the endemic species and most of the endemic abundance in the NWHI. Live coral cover is highest on Maro Reef and lowest on Necker Island. Coral abundance and diversity are highest on the large open atolls (French Frigate Shoals, Maro Reef, Lisianski/Neva Shoals) and decline through the remaining atolls to the northwest.

A list of NWHI coral species (pdf,30kb) adapted from: Maragos, J., G. Aeby, D. Gulko, J. Kenyon, D. Potts, D. Siciliano, and D. VanRavensway. 2004. The 2000-2002 Rapid Ecological Assessment of Corals in the Northwestern Hawaiian Islands, Part I: Species and Distribution. Pacific Science 58(2):211-230.

Squirrelfish inhabiting crevices and holes in a reef in the NWHI
Squirrelfish inhabiting crevices and holes in a reef in the NWHI (Photo: Bishop Museum/ NOWRAMP Expedition)

Fishes

The average fish standing stock (the total biomass of fishes in a given area) in the NWHI was almost 300 percent greater than in similar habitats of the MHI. The deeper waters surrounding these islands support commercially important fishes such as large sea basses and deep sea snappers. Remarkably, the NWHI have an abundance of sharks and other large apex predators, species at the top of the food chain. More than 54 percent of the total fish biomass on forereef habitats in the NWHI consisted of apex predators, compared to less than 3 percent in the MHI. About 30 percent of the fish species are endemics. Most of the dominant species by weight in the NWHI are either rare or absent in the MHI.. Overfishing has not taken a devastating toll on these species as it has done on most coral reef ecosystems that are more accessible to humans.

Online Encyclopedia for Flora and Fauna of the Northwestern Hawaiian Islands http://www8.nos.noaa.gov/onms/park/parks/?pID=12

Early human influences

The NWHI also possess a great cultural significance to native Hawaiians. During their trans-Pacific voyages, ancient Polynesians sailed these waters and used these islands for centuries as places of residence and worship. By the time European explorers discovered these islands, the early Polynesians had already stopped visiting them.

Some of the island ecosystems, for example, Laysan, suffered in the late 1800's and early 1900's when humans exploited seabird guano deposits for use as fertilizers. They also introduced rabbits and guinea pigs as food supplements and for business ventures. Soon the island was overrun with rabbits which ate most of the vegetation, nearly turning the island into a desert. Without vegetation for shelter, the great populations of birds on the islands were threatened with extinction. The great numbers of birds also attracted poachers, which slaughtered hundreds of thousands of birds for their feathers. As a result of this wholesale slaughter of birds, President Theodore Roosevelt, on February 3, 1909, by executive order, set aside all of the islands from Kure to Nihoa, with the exception of Midway, as the Hawaiian Islands Bird Reservation, Within this Sanctuary it is unlawful to kill or molest the birds.

NOAA’s Remote Sensing Team led development of the first benthic habitat maps made for the Northwest Hawaiian Islands. The satellite data used was IKONOS multispectral (blue/green/red/near-infrared bands) and panchromatic imagery from Space Imaging, collected between 2000 and 2002. Landsat 7 Enhanced Thematic Mapper Plus (ETM+) imagery was also obtained for all ten atolls as well as for most of the bank areas

NWHI: Maps and Imagery

NOAA's Remote Sensing Team led development of the first benthic habitat maps made for the Northwest Hawaiian Islands. The satellite data used was IKONOS multispectral (blue/green/red/near-infrared bands) and panchromatic imagery from Space Imaging, collected between 2000 and 2002. Landsat 7 Enhanced Thematic Mapper Plus (ETM+) imagery was also obtained for all ten atolls as well as for most of the bank areas

http://ccma.nos.noaa.gov/ecosystems/coralreef/nwhi/

Bathymetry of the Northwestern Hawaiian Islands

The Pacific Islands Benthic Habitat Mapping Center provides an assortment of bathymetric maps for the Northwestern Hawaiian Islands.

http://www.soest.hawaii.edu/pibhmc/pibhmc_nwhi.htm

NWHI Multi-Agency Education Project

This site provides educational materials and web reports from NWHI expeditions.

http://www.hawaiianatolls.org/

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