The Hawaiian Islands, a remote archipelago in the Pacific Ocean, are home to extensive and diverse coral reef ecosystems. The waters surrounding Hawaii contain a significant portion of the coral reefs found under U.S. jurisdiction, making them a prominent feature of the region’s ocean landscape.
Where Hawaii’s Coral Reefs Are Found
Coral reefs in Hawaii are widely distributed across the archipelago, from the main Hawaiian Islands to the distant Northwestern Hawaiian Islands. The main islands, including Oahu, Maui, Kauai, and the Big Island (Hawaiʻi), host approximately 410,000 acres of living reef. These reefs often manifest as fringing reefs, which grow close to the shoreline and are separated from the land by a shallow lagoon or reef flat. For example, Hanauma Bay on Oahu is a well-known marine sanctuary with a pristine reef ecosystem.
Beyond fringing reefs, some areas exhibit barrier reef characteristics, such as parts of Kaneohe Bay on Oahu and the southern coast of Molokai, where reefs begin further from shore and expand seaward. These formations create a lagoon between the reef and the coastline. The prevalence and structure of reefs can vary between islands, influenced by factors like wave exposure, freshwater runoff, and geological history.
A substantial portion of Hawaii’s coral reefs, over 85% of the total U.S. coral reef area, is found within the Northwestern Hawaiian Islands (NWHI). This remote stretch of islands, atolls, and submerged banks extends over 1,200 miles northwest of the main islands. The NWHI are largely encompassed by the Papahānaumokuākea Marine National Monument, one of the largest marine conservation areas globally. This monument protects vast, undisturbed reef systems, including atolls like Midway and Kure.
The reefs in this monument span more than 2,000 kilometers. These remote locations often feature healthier and more developed reef structures due to reduced human impact compared to the more populated main islands.
Distinctive Features of Hawaiian Coral Reefs
Hawaiian coral reefs are notable for their high degree of endemism, meaning a significant number of species found here exist nowhere else on Earth. This unique biodiversity is largely a result of Hawaii’s extreme isolation in the central Pacific Ocean. Over 1,250 marine species, including various corals, fish, and invertebrates, are found exclusively on Hawaii’s reefs. This represents over 25% of all marine life in the region, with new species still being discovered regularly.
For instance, deep coral reefs in the Hawaiian Archipelago, particularly mesophotic coral ecosystems (often called the “Coral Reef Twilight Zone”), exhibit even higher levels of endemism. In these deeper waters (around 160-300 feet), up to 43% of fish species can be endemic, more than double the endemism found in shallow Hawaiian reefs. In the northern reaches of the Papahānaumokuākea Marine National Monument, endemism levels can approach 100%, making it one of the highest recorded for any marine ecosystem globally.
The geological history of the Hawaiian Islands also influences the distinctiveness of their reefs. Volcanic activity and lava flows have created unique underwater landscapes that provide diverse substrates for coral growth and habitat for marine organisms. The proximity of deep oceanic waters to the shallow reef environments further contributes to the unique conditions supporting these ecosystems.