Biology and Ecological Functioning of Coral Reefs in the Main Hawaiian Islands

The eight main Hawaiian Islands (MHI) are the emergent volcanic islands of the Hawaiian Archipelago (Fig. 12.1). The Hawaiian Archipelago is located in the center of the north Pacific Ocean and consists of islands, atolls, submerged banks and shoals, trending northwest by southeast in the between latitudes 19° N and 29° N. The island chain extends approximately 2,400 km (1,500 miles) from the Island of Hawaii in the southeast to Kure Atoll in the northwest. Hawaii is among the most isolated island groups on the planet being located approximately 3,000 km (1,860 miles) from the nearest continent. These islands are the emergent portion of the undersea Hawaiian-Emperor seamount chain that was formed continuously over the past 70–75 million years as the Pacific tectonic plate moved north and northwest over a stationary magma “hot spot” (Clague and Dalrymple 1994) at a rate of from 5 to 10 cm/year. Molten lava breaking through the thin rigid crust slowly creates volcanic mountains that eventually reach the surface of the ocean and emerge as islands (Macdonald et al. 1983). As the islands move off the hot spot they undergo erosion and subsidence. Eventually they are worn down and gradually sink, forming low islands and atolls and ultimately submerged seamounts. The eight MHI at the southeastern end of the archipelago represent approximately 5 million years of that cycle. The island of Hawaii is the youngest island with the oldest rocks dating to only about 430,000 years ago. Its youngest volcano, Kilauea, is currently active, along with a newly forming submerged volcano named Loihi located to the southeast of the Island of Hawaii.