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Restoring habitat at Pearl Harbor.

At first glance, the area resembles an African savanna, but one marked with invasive species such as mesquite (Prosopis spp.), Indian marsh fleabane (Pluchea indica), and bufflegrass (Cenchrus ciliaris) dominating the landscape. A closer inspection reveals an ancient raised limestone coral reef and remnants of the last remaining coastal dryland plant communities on the Hawaiian island of O'ahu.


This harsh, sun-drenched landscape is home to the Kalaeloa Unit of the Pearl Harbor National Wildlife Refuge. Located west of Honolulu on the 'Ewa Plain, Kalaeloa was part of the former Barbers Point Naval Air Station until it was added to the National Wildlife Refuge System to protect native plants, including two endangered species--an 'akoko (Chamaesyce skottsbergii var. kalaeloana) and the 'Ewa hinahina (Achyranthes splendens var. rotundata).


Although Kalaeloa has been heavily altered by agricultural, military, residential, and commercial activities, U.S. Fish and Wildlife Service biologists and land managers are working to restore the unique habitats native to this once pristine subtropical dry forest. Continuing habitat restoration activities include the removal of invasive plant species and the propagation and out-planting of native dryland plants, including endangered and threatened species.

In addition to subtropical dry forest restoration, the Service is restoring another unique and rare habitat known as anchialine pools. Anchialine pools are landlocked brackish ponds located close to the shoreline and connected to the ocean by subterranean tunnels. On O'ahu, anchialine pools are generally found in karst formations rather than lava fields like those found on Maui and the island of Hawai'i. Karst is the type of topography that forms when raised limestone reefs are subjected to the movement of groundwater over and through the reef. The weak carbonic acid found in ground water slowly dissolves the limestone, creating large holes, channels, and bumpy surfaces. One of the largest such formations on O'ahu is the 'Ewa karst.

The major threats to anchialine pools and the shrimp species that inhabit them are habitat degradation and destruction, nonnative invasive species, and over-collection of the shrimp for the aquarium trade. In the past, most of Kalaeloa's anchialine pools have been filled in with sediment and coral rubble.

In 2005, Phase I of a project to restore anchialine pools within the Kalaeloa Unit rehabilitated an anchialine pool and led to the successful recruitment of two color phases of an anchialine pool shrimp known as 'opae 'ula (Halocaridina rubra), a species at risk. Found only in Hawai'i, 'opae 'ula can reach 10 to 15 years of age, an unusually long lifespan for a tiny crustacean. This species is approximately 0.5 inches (1.27 centimeters) in length and occurs in a range of colors--red, pink, white, light yellow/clear, and banded (red/clear). Kalaeloa is the only location in Hawai'i where two distinct genetic lineages of 'opae 'ula are found to coexist at the same site.


Based on the success of Phase I, Phase II sought to expand the number of restored pools at sites that would benefit both 'opae 'ula and another anchialine pool shrimp, Metabetaeus lohena, which is a candidate for Endangered Species Act protection. Restored pools were also targeted as potential translocation sites for the orangeblack Hawaiian damselfly (Megalagrion xanthomelas), another listing candidate.


In March 2008, Lorena Wada and Aaron Nadig, biologists with the Service's Pacific Islands Fish and Wildlife Office, and Jason Hanley, Invasive Species Strike Team Leader with the Hawai'i and Pacific Islands National Wildlife Refuge Complex, led the project to restore 12 anchialine pools. Personnel from the Service's Hawaiian Refuges and Ecological Services offices, the Hawai'i Division of Aquatic Resources, and the State Natural Area Reserve contributed over 800 hours of work during the first 6 months of the project.

Using heavy equipment, pumps, and hand tools, they removed coral rubble and soil blocking the pools. This work successfully restored natural tidal fluctuations in the pools, which allowed native anchialine pool shrimp to quickly recolonize the sites. In May 2008, the first 'opae 'ula were observed in one of the newly restored pools. 'Opae 'ula have now been seen in eight of the restored sites. As of September 1, 2009, 11 anchialine pools have been restored.


Future plans include monitoring 'opae 'ula, continuing data collection on water quality, evaluating the pools as potential reintroduction sites for the orangeblack damselfly, and evaluating future translocation sites for Metabetaeus lohena. The work being accomplished at anchialine pools also provides a unique opportunity for partnerships and educational outreach.


RELATED ARTICLE: Treasures from an ancient past.

The restoration of anchialine pools at Kalaeloa uncovered some hidden treasures that are just beginning to open a window to the area's ancient past. While removing the debris, Service personnel found fossilized bird bones, some from species never before seen. To date, scientists have uncovered fossilized bones of an extinct hawk (first time reported as a fossil on O'ahu), a long-legged owl, Hawaiian sea eagle, petrel, two species of crow, Hawaiian finches, Hawaiian honeyeaters, and the moa nalo (a turkey-sized, flightless gooselike duck- the largest native Hawaiian bird). Further work is needed to confirm the identification and age of each species. The Service is working with representatives from the Smithsonian Institution and Bernice P. Bishop Museum to properly clean, store, preserve, and identify the bones.


Ken Foote, an information and education specialist with the Pacific Islands External Affairs office, can be reached at 808-792-9535 or
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Title Annotation:Pearl Harbor National Wildlife Refuge
Author:Foote, Ken
Publication:Endangered Species Bulletin
Geographic Code:1U9HI
Date:Sep 22, 2009
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