| Northwestern Hawaii scrub | |
|---|---|
 | |
 Location of the ecoregion | |
| Ecology | |
| Realm | Oceanian |
| Biome | tropical and subtropical grasslands, savannas, and shrublands |
| Geography | |
| Area | 15 km2 (5.8 sq mi) |
| Country | United States |
| States | Hawaii and Midway Atoll (territory) |
| Conservation | |
| Conservation status | Vulnerable [1] |
| Protected | 100% [2] |
The Northwestern Hawaii scrub is a tropical and subtropical grasslands, savannas, and shrublands ecoregion on the Northwestern Hawaiian Islands in the Pacific Ocean.
The ecoregion covers the Northwestern Hawaiian Islands, a chain of low atolls and islets that extend 1350 kilometers northwest from the high volcanic islands of Hawaii. The atolls are the remnants of ancient volcanic islands created by the same geologic hotspot that created all the islands in the Hawaiian chain. As the movement of the Pacific Plate to the west-northwest carried the volcanic islands past the hotspot, volcanic activity ceased and the islands eroded and sank. Hard corals built up layers of coralline limestone to create a protecting barrier reef around the shallow lagoon where the central island used to be, and the action of wind, waves, and tides build small islands of coral sand.
Most of the ecoregion is in the state of Hawaii. Midway Atoll, near the northwestern end of the chain, is a territory of the United States.
Five plant species are endemic to the ecoregion and listed as endangered. Three plants, the Nihoa fan palm (Pritchardia remota), Schiedea verticillata , and Amaranthus brownii , are native to Nihoa. The fan palm has been introduced to Laysan Island. Cyperus pennatiformis ssp. bryanii is known only from Laysan. Cenchrus agrimonioides var. laysanensis was historically known from Laysan Island, Midway Atoll and Kure Atoll, but has not been seen since about 1980 and may be extinct. The endangered Sesbania tomentosa or ‘ohai is native to Nihoa, Necker, and the larger Hawaiian Islands. [3]
The ecoregion is home to a distinct fauna, including the endangered Hawaiian monk seal (Neomonachus schauinslandi), three endemic species of birds – the Laysan duck (Anas laysanensis), Laysan finch (Telespiza cantans), and Nihoa finch (Telespiza ultima) – and the Nihoa millerbird (Acrocephalus familiaris kingi), an endemic subspecies. [4]
The Northwestern Hawaiian Islands are an important feeding, nesting, and nursery habitat for seabirds, sea turtles, and cetaceans. 5.5 million seabirds nest in the islands every year, and 14 million seasonally reside there. It is collectively the largest tropical seabird rookery in the world. 99% of the world's Laysan albatross (Phoebastria immutabilis) and 98% of the world's black-footed albatross (Phoebastria nigripes) breed here. [4]
The entire ecoregion is in protected areas. Papahānaumokuākea Marine National Monument was created in 2006, and protects the islands and the surrounding oceans. [5]
Midway Atoll is a 2.4-square-mile (6.2 km2) atoll in the North Pacific Ocean. Midway is an insular area of the United States and is an unorganized and unincorporated territory. The largest island is Sand Island, which has housing and an airstrip. Immediately to the east of Sand Island across the narrow Brooks Channel is Eastern Island, which is uninhabited and has no facilities. Forming a rough, incomplete circle around the two main islands and creating Midway Lagoon is Spit Island, a narrow reef.
Kure Atoll or Ocean Island is an atoll in the Pacific Ocean 48 nautical miles west-northwest of Midway Atoll in the Northwestern Hawaiian Islands at 28°25′N178°20′W. There is a coral ring six miles across that encloses a shallow lagoon several meters deep. The only land of significant size is called Green Island and is a habitat for hundreds of thousands of seabirds. A short, unused and unmaintained runway and a portion of one building, both from a former United States Coast Guard LORAN station, are located on the island. Politically, it is part of Hawaii, although separated from the rest of the state by Midway, which is a separate unorganized territory. Green Island, in addition to being the nesting grounds of tens of thousands of seabirds, has recorded several vagrant terrestrial birds including snow bunting, eyebrowed thrush, brambling, olive-backed pipit, black kite, Steller's sea eagle and Chinese sparrowhawk. It is currently managed as a Wildlife Bird Sanctuary by the State of Hawaii's Department of Land and Natural Resource--Division of Forestry and Wildlife as one of the co-trustees of Papahānaumokuākea Marine National Monument with support from Kure Atoll Conservancy.
Located about 2300 miles (3680 km) from the nearest continental shore, the Hawaiian Islands are the most isolated group of islands on the planet. The plant and animal life of the Hawaiian archipelago is the result of early, very infrequent colonizations of arriving species and the slow evolution of those species—in isolation from the rest of the world's flora and fauna—over a period of at least 5 million years. As a consequence, Hawai'i is home to a large number of endemic species. The radiation of species described by Charles Darwin in the Galapagos Islands which was critical to the formulation of his theory of evolution is far exceeded in the more isolated Hawaiian Islands.
Nihoa, also known as Bird Island or Moku Manu, is the tallest of ten islands and atolls in the uninhabited Northwestern Hawaiian Islands (NWHI). The island is located at the southern end of the NWHI chain, 296 km (160 nmi) southeast of Necker Island. Nihoa is the closest NWHI in proximity to the eight main windward Hawaiian Islands at approximately 240 km (130 nmi) northwest of the island of Kauaʻi. The island has two peaks, 272 m (892 ft) Miller's Peak in the west, and 259 m (850 ft) Tanager Peak in the east. Nihoa's area is about 171 acres (0.69 km2) and is surrounded by a 142,000-acre (57,000 ha) coral reef. Its jagged outline gives the island its name, Nīhoa, which is Hawaiian for "tooth".
The French Frigate Shoals is the largest atoll in the Northwestern Hawaiian Islands. Its name commemorates French explorer Jean-François de La Pérouse, who nearly lost two frigates when attempting to navigate the shoals. It consists of a 20-mile (32 km) long crescent-shaped reef, twelve sandbars, and the 120-foot (37 m) high La Perouse Pinnacle, the only remnant of its volcanic origins. The total land area of the islets is 61.508 acres (24.891 ha). Total coral reef area of the shoals is over 232,000 acres (94,000 ha). Tern Island, with an area of 26.014 acres (10.527 ha), has a landing strip and permanent habitations for a small number of people. It is maintained as a field station in the Hawaiian Islands National Wildlife Refuge by the United States Fish and Wildlife Service. The French Frigate Shoals are about 487 nautical miles northwest of Honolulu.
The Northwestern Hawaiian Islands or Leeward Islands are the small islands and atolls in the Hawaiian island chain located northwest of the islands of Kauai and Niihau. Politically, they are all part of Honolulu County in the U.S. state of Hawaii, except Midway Atoll, which is a territory distinct from the State of Hawaii, and grouped as one of the United States Minor Outlying Islands. The United States Census Bureau defines this area, except Midway, as Census Tract 114.98 of Honolulu County. Its total land area is 3.1075 square miles (8.048 km2). All the islands except Nihoa are north of the Tropic of Cancer, making them the only islands in Hawaii that lie outside the tropics.
The Pearl and Hermes Atoll is part of the Northwestern Hawaiian Islands, a group of small islands and atolls that form the farthest northwest portion of the Hawaiian island chain. The atoll consists of a variable number of flat and sandy islets, typically between five and seven. More were noted in historical sources but have since been lost to erosion and rising sea levels.
Laysan, located 808 nautical miles northwest of Honolulu at N25° 42' 14" W171° 44' 04", is one of the Northwestern Hawaiian Islands. It comprises one land mass of 1,016 acres (4.11 km2), about 1 by 1+1⁄2 miles in size. It is an atoll of sorts, although the land completely surrounds a shallow central lake some 8 feet (2.4 m) above sea level that has a salinity approximately three times greater than the ocean. Laysan's Hawaiian name of Kauō means egg.
The Laysan finch is a species of Hawaiian honeycreeper, that is endemic to the Northwestern Hawaiian Islands. It is one of four remaining finch-billed Hawaiian honeycreepers and is closely related to the smaller Nihoa finch. The Laysan finch is named for Laysan, the island to which it was endemic on its discovery. It was subsequently introduced to a few other atolls, and its historical range included some of the main islands.
The Laysan albatross is a large seabird that ranges across the North Pacific. The Northwestern Hawaiian Islands are home to 99.7% of the population. This small gull-like albatross is the second-most common seabird in the Hawaiian Islands, with an estimated population of 2.5 million birds, and is currently expanding its range to new islands. The Laysan albatross was first described as Diomedea immutabilis by Lionel Walter Rothschild, in 1893, on the basis of a specimen from Laysan Island.
Kīlauea Point National Wildlife Refuge is a National Wildlife Refuge on the northwest coast of the island of Kauaʻi in Hawaiʻi.
The Nihoa finch is one of the two endemic bird species of the tiny Hawaiian island Nihoa, the other being the Nihoa millerbird. When it was classified in 1917, scientists thought that it would be the last endemic species named. This was later found untrue. The island's population is 1000–3000 birds. The Nihoa finch was added to the Endangered Species List by the U.S. Fish and Wildlife Service on March 11, 1967. An attempt to protect the species against extinction was made by starting a colony on French Frigate Shoals, another leeward island. This would ensure its continued existence in the event that the Nihoa population was wiped out. This attempt, however, failed. Nihoa is part of a group of islands that make up the Hawaiian Islands National Wildlife Refuge which provides protected land for the Nihoa finch to roam on.
The Laysan millerbird was a subspecies of the millerbird, similar in appearance to the remaining subspecies, the Nihoa millerbird. Its dorsal side was brown, and its belly was grayish. Its name derives from its favorite food, several species of moths of the genus Agrotis commonly referred to as "millers".
The Papahānaumokuākea Marine National Monument is a World Heritage listed U.S. National Monument encompassing 583,000 square miles (1,510,000 km2) of ocean waters, including ten islands and atolls of the Northwestern Hawaiian Islands. Created in June 2006 with 140,000 square miles (360,000 km2), it was expanded in August 2016 by moving its border to the limit of the exclusive economic zone, making it one of the world's largest protected areas. It is internationally known for its cultural and natural values as follows:
"The area has deep cosmological and traditional significance for living Native Hawaiian culture, as an ancestral environment, as an embodiment of the Hawaiian concept of kinship between people and the natural world, and as the place where it is believed that life originates and to where the spirits return after death. On two of the islands, Nihoa and Mokumanamana, there are archaeological remains relating to pre-European settlement and use. Much of the monument is made up of pelagic and deepwater habitats, with notable features such as seamounts and submerged banks, extensive coral reefs and lagoons."
The TanagerExpedition was a series of five biological surveys of the Northwestern Hawaiian Islands conducted in partnership between the Bureau of Biological Survey and the Bishop Museum, with the assistance of the U.S. Navy. Four expeditions occurred from April to August 1923, and a fifth in July 1924. Led by Lieutenant Commander Samuel Wilder King on the minesweeper USS Tanager (AM-5), and Alexander Wetmore directing the team of scientists, the expedition studied the plant animal life, and geology of the central Pacific islands. Noted members of the team include archaeologist Kenneth Emory and herpetologist Chapman Grant.
Tern Island is a tiny coral island located in the French Frigate Shoals in the Northwestern Hawaiian Islands, at 23.870°N 166.284°W, approximately 490 miles west north west of Oahu. It has a land area of 105,276 m2. The island provides a breeding habitat to 18 species of seabirds, threatened Hawaiian green sea turtles, and endangered Hawaiian monk seals. It is maintained as a field station in the Hawaiian Islands National Wildlife Refuge by the United States Fish and Wildlife Service.
Eragrostis variabilis is a species of grass known by the common names variable lovegrass, kawelu, emoloa, and kalamalo. It is endemic to Hawaii, where it occurs on all the main islands plus Kure Atoll, Midway Atoll, Pearl and Hermes Atoll, Lisianski Island, Laysan, and Nihoa.
The Central Polynesian tropical moist forests is a tropical and subtropical moist broadleaf forests ecoregion in Polynesia. It includes the northern Cook Islands, the Line Islands in Kiribati, and Johnston Atoll, Jarvis Island, Palmyra Atoll, and Kingman Reef which are possessions of the United States.