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Johnston Atoll National Wildlife Refuge

small state map showing location

Johnston Island, Pacific Islands


Ecology

JPG -- Picture of Johnston Atoll Fish and Coral.

As the only shallow water and dry land area in millions of square miles of ocean, Johnston is an oasis for reef and bird life. Corals and coralline algae are responsible for the existence of the atoll. Though corals are true animals, colonies of microscopic symbiotic algae are contained in their tissues. The algae contribute their photosynthetic production to the coral, receiving in return secure space in the sun and the coral's wastes as nutrients. Johnston is home to 32 species of coral, with the most impressive being the table Acropora forming massive colonies up to 10 feet in diameter.

About 300 species of fish have been recorded from the reefs and inshore waters of Johnston Atoll. The majority of the fishes are edible, though some may very rarely retain a poison within their flesh known as ciguatoxin. The poison is produced by a microscopic alga that is eaten by fishes browsing along the bottom. It causes the fishes no harm, but the poison can concentrate in the flesh of many reef fishes, especially the carnivores such as eels, jacks, and sharks. Unsuspecting humans and even seals can then be poisoned when they eat their catch.

Due to the atoll's isolation, small size, and lack of habitat diversity, the number of species of coral, fish, and reef life are not as great as in Hawaii. However, western and southern Pacific species of coral, fish, and other fauna, including mollusks, crabs, and urchins, exist here but not in Hawaii. Johnston marine life has been little studied and may yet contain species unknown to science.


Return to Bird Checklist of Johnston Atoll National Wildlife Refuge

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