Bleaching in Oahu's Hanauma Bay

Published 2017-05-30

Photo: Catlin Seaview

Over 1 million people visit the Hanauma Bay Nature Preserve on Oahu, Hawaii every year to snorkel over the reef and see diverse assemblages of fish and invertebrates. Although state laws protect the fish and invertebrate populations of Hanauma Bay, coral cover on the reef is in decline. In addition to local impacts, including damage from human interaction, corals in Hanauma Bay are at risk of decline due to rising ocean temperatures. Since 1999, the Coral Reef Assessment and Monitoring Program (CRAMP) has been monitoring corals in Hanauma Bay. Most recently, researchers from the Hawaii Institute of Marine Biology in the Coral Reef Ecology Lab have tracked the severity of recent bleaching events in the summer of 2014 and the summer of 2015. In a recently published study, they report that 47% of corals on the reef flat exhibited bleaching during these events while 9.8% died. The researchers suggest that rising ocean temperature, which can lead to coral bleaching, is the most influential factor contributing to the decline of coral reefs in this location.

Water flow patterns also play a large role in bleaching patterns in Hanauma Bay. HIMB researchers found that bleaching occurred more severely in certain areas of the bay than others. Bleaching and mortality were more severe in areas with low water flow, while areas with higher flow and consistent flushing were less prone to bleaching. This research demonstrates that the impacts of rising ocean temperatures are strong, even in areas that lack direct human fishing and harvesting pressures.

Journal Reference:
1. Ku‘ulei S. Rodgers, Keisha D. Bahr, Paul L. Jokiel, Angela Richards Don�. Patterns of bleaching and mortality following widespread warming events in 2014 and 2015 at the Hanauma Bay Nature Preserve, Hawai‘i. PeerJ, 2017; 5: e3355 DOI: 10.7717/peerj.3355