Midway atoll (28°15' N, 177°20' W) consists of three sandy islets (Sand Island: 4.56 km2, Eastern Island: i.36 km2, and Spit Island: 0.05 km2), for a total of 5.98 km2 in terrestrial area, lying within a large, elliptical barrier reef measuring approximately 8 km in diameter (Fig. 1). Although geographically part of the Hawaiian archipelago, Midway is not part of the State of Hawaii and is an unincorporated territory of the United States.
The climate of Midway is influenced by the marine tropical or marine Pacific air masses, depending upon the season. During the summer, the Pacific high pressure system becomes dominant with the ridge line extending across the Pacific north of Kure and Midway. This places the region under the influence of easterly winds, with marine tropical and trade winds prevailing. During the winter, especially from November through January, the Aleutian low moves southward over the North Pacific, displacing the Pacific high before it. The Kure-Midway region is then affected by either marine Pacific or marine tropical air, depending upon the intensity of the Aleutian low or the Pacific high pressure system.
Nowhere else on the planet is the tropical island evolution process, with examples of every stage of development, illustrated so beautifully and linearly as in the northwestern Hawaiian Islands. The 1200-mile-long string of islands represents the longest, clearest, and oldest example of island formation and atoll evolution in the world. The ten islands and atolls extending northward from Kauai represent a classic geomorphological sequence, consisting of highly eroded high islands, nearatolls with volcanic pinnacles jutting from surrounding lagoons, true ring-shaped atolls with roughly circular rims and central lagoons, and secondarily raised atolls, one of which bears an interior hypersaline lake. These islands are also surrounded by over 30 submerged banks and seamounts. This geological progression along the Hawaiian ridge continues northwestward beyond the last emergent island northwest of Midway, Kure atoll, as a chain of submerged platforms. Numerous patch reefs formed by reef-building coralline algae and 16 species of corals provide habitat for a wide variety of coral reef species.
Midway is at the northern end of the Hawaiian archipelago. The atoll, which is 28.7 million years old, is surrounded by more than 356 km2 of coral reefs.
The biota of Midway is a combination of native and introduced species that are a product of its land-use history. The islands boast enormous nesting colonies of Laysan albatrosses (Phoebastria immutabilis; ~450,000 breeding pairs) (Fig. 2) and black-footed albatrosses (Phoebastria nigripes; ~24,000 breeding pairs), making the atoll the largest single colony of albatrosses in the world. Another 14 species of tropical seabirds also breed in abundance at Midway. Introduced canaries breed among historic buildings that mark the beginning of cable communication across the Pacific in the early twentieth century.
Currently, the land cover on all of the islands at Midway is approximately 30% paved or structures, 23% grass and forbs, 18% woodland, 7% sand and bare ground, 22% shrublands, and less than 0.23% wetland. Of the at least 354 species of plants that have ever been observed at Midway, only 14 are considered indigenous, and only three of those are endemic to the Hawaiian Islands. There are no plant species considered endemic to Midway atoll alone. A total of 508 species of terrestrial arthropods are listed from Midway. Only 41 of these species (8%) are endemic to Midway, and 50 additional species (10%) are indigenous to the tropical Pacific. The large number of alien species that have been introduced and the failure to re-collect three of the four native seed bugs and all three native moths in recent years suggests that the high rate of alien species introductions has reduced the numbers of native insects.
Hawaiian monk seals and green turtles forage in the waters offshore but come to the sandy beaches of the atoll to breed. There are 163 species of reef fish reported from Midway, and the shallow-reef fish community is remarkable in the abundance and size of fish in the highest trophic levels. Recent research efforts in the Hawaiian Islands and the Line archipelago have demonstrated that coral reef communities with low levels of human exploitation and disturbance are characterized by fish communities dominated by apex predators.
There are no records yet discovered of Polynesian visits to Midway, but Captain N. C. Brooks of the Gambia first claimed it under the Guano Act of 1856 after discovering it on July 5, 1859. Midway atoll's central location in the Pacific made it a critical link in communications and transportation history in the Pacific in the early twentieth century. One of the most important battles of World War II in the Pacific, the Battle of Midway, was fought both at Midway atoll and in the waters beyond it. Midway continued to have a significant military role after World War II; it was an active Navy installation during the Cold War and served as an aircraft and ship refueling station during the Vietnam War.
Noteworthy is the role that Midway played in the early history of wildlife conservation in the United States. In 1903 President Theodore Roosevelt sent in the U. S. Marines to stop the slaughter of seabirds at Midway atoll by feather hunters.
In 1988 the atoll was designated an overlay national wildlife refuge, and in 1993 the Navy closed the naval air facility and embarked on a major environmental cleanup in which many buildings and underground fuel tanks were removed. In 1996 the Navy formally transferred Midway atoll and the ocean waters out to 19 km to the Department of Interior as Midway Atoll National Wildlife Refuge. In 1999, the U. S. Navy identified the Battle of Midway as one of the two most important events in its history, and in 2000, the U. S. government designated Midway as the Battle of Midway National Memorial. Papahānaumokuākea Marine National Monument was established by Presidential Proclamation 8031 on June 15, 2006. This resulted in bringing waters out to 80 km around Midway atoll, along with the rest of the northwestern Hawaiian Islands waters, into the largest fully protected marine conservation area in the world.
Midway's terrestrial native vegetation and insect communities have been greatly altered by more than a century of human occupation. The U. S. Navy, the U. S. Fish and Wildlife Service, and the U. S. Department of Agriculture successfully eradicated black rats (Rattus rattus), introduced in 1943, from all of Midway, and invasive ironwood trees (Casuarina equisetifolia) have been entirely removed from Eastern Island. An active program of invasive weed eradication and native plant propagation is ongoing to restore the plant community present prior to human occupation. This has improved living conditions for the 16 species of tropical seabirds that breed at the atoll as well as for migrant shorebirds such as bristle-thighed curlews (Numenius tahitiensis) and Pacific golden plovers (Pluvialis fulva) that winter there. A translocated population of Laysan ducks (Anas laysanensis, an endangered species whose sole remaining population was at Laysan Island until the translocation) is thriving as it forages on the introduced insect community at Midway. Tragically, the Laysan rail population that was moved to Midway prior to its extirpation at Laysan Island in the 1920s went extinct in 1943 when Rattus rattus arrived at Midway and before individuals could be returned to repopulate Laysan Island.
Today, Midway serves as a window to the rest of the Marine National Monument as the only atoll in the chain open for public visitation. It is the site of active ecological restoration efforts and research for conservation science.
Atolls / Hawaiian Islands, Geology / Invasion Biology / Reef Ecology and Conservation / Seabirds
- natural history of Pearl and Hermes Reef, northwestern Hawaiian Islands. Atoll Research Bulletin 174. Washington, DC: Smithsonian Institution. , Jr., , and . 1974. The
- Growth and subsidence of the Hawaiian-Emperor volcanic chain, in The origin and evolution of Pacific Island biotas, New Guinea to eastern Polynesia: patterns and processes. and , eds. Amsterdam: SPB Academic Publishers, 35–50. 1996.
- Midway 1942, turning point in the Pacific. Oxford, UK: Osprey Publishing. 1993.
- Pacific Island battlegrounds of World War II: then and now. Honolulu, HI: The Bess Press. 1995.
- Midway terrestrial arthropod survey. Final report prepared for the U. S. Fish and Wildlife Service. Honolulu, HI: Hawaii Biological Survey, Bishop Museum. 1998.
- Isles of refuge: wildlife and history of the northwestern Hawaiian Islands. Honolulu: University of Hawaii Press. 2001.
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