Northern Prairie Wildlife Research Center
Johnston Island, Pacific Islands
Near the center of the North Pacific between the Hawaiian Islands and the Marshall Islands lies one of the most isolated atolls in the world: Johnston Atoll. The formation of Johnston Atoll began about 70 million years ago when volcanic eruptions forced lava to the surface of the ocean. It cooled to form a small island, and coral began to grow around the edge of the island and over the sunlit shallows.
Over millions of years, the island slowly sank back into the sea. As the land mass disappeared under the water, the coral around the outer edge of the island continued to grow, eventually forming a coral ring around the island. When the island sank, only the continually growing expanse of coral-covering flats, small coral islands in the blue central lagoon, and a ring of coral reef remained.
Today, Johnston Atoll is a broad, shallow platform about 50 square miles in size, with a marginal coral reef emergent only on the north and west sides. Four small islands--Johnston, Sand, North, and East--emerge from the lagoon.
In comparison to the shallow reefs, which are lush and varied, the deep surrounding ocean supports much less marine life. In the warm, westward flowing stream of the North Equatorial Current, few nutrients rise to the surface, and the microscopic plant life that supports all other marine creatures is sparse. As it flows around the atoll, the current is diverted, and turbulence brings the nutrients of deeper water to the surface. The richer marine life this supports creates a feeding ground for the thousands of seabirds that roost and breed on the islands.