Climate Change and Ocean Acidification

photo of coral
Blue rice coral. Credit: Claire Fackler, NOAA

Why is it a concern?

Over the next century, climate change is projected to profoundly impact coastal and marine ecosystems around the globe including the Papahānaumokuākea Marine National Monument. Concerns for the Monument related to climate change include coral bleaching, diseases affecting marine organisms, ocean acidification, increased frequency and severity of storms, and loss of habitat due to sea-level rise.

Problems associated with increased sea surface temperatures have been reported in the Northwestern Hawaiian Islands. Sea surface temperature information obtained from NOAA demonstrated that water temperatures at Midway rose nearly two degrees centigrade over the usual summer maxima in August of 2002. Corresponding with this warm water event, substantial coral bleaching was observed—a process whereby coral colonies lose their color due to the expulsion of symbiotic microscopic algae (zooxanthellae) from most coral tissues—on reefs at the three northwestern most atolls: Kure, Midway, and Pearl and Hermes.  A similar thermal anomaly centered over Lisianski Island in 2014 resulted in significant bleaching in shallow waters and mortality of nearly four square kilometers of coral.

Climate models predict that global average sea level may rise considerably this century, potentially affecting species that rely on coastal habitat. Most of the Northwestern Hawaiian Islands are low lying and therefore potentially vulnerable to increases in global average sea level. The effects of habitat loss on Northwestern Hawaiian Islands biota are difficult to predict, but may be greatest for endangered Hawaiian monk seals and threatened Hawaiian green sea turtles at Pearl and Hermes Reef (Baker et al. 2006).

Atmospheric carbon dioxide is rising at an unprecedented rate. The ocean absorbs approximately one-third of all carbon dioxide from the atmosphere, therefore increased atmospheric levels of carbon dioxide expose the ocean to higher levels as well, resulting in changes to the chemical composition of the ocean. These changes in ocean chemistry can lead to impacts on organisms with calcium carbonate skeletons such as corals, including slower growth rates, weaker skeletons, increased susceptibility to erosion, malformations, and in the most severe scenarios, dissolution of their skeletons. Acidification is projected over the next century to affect calcification by shallow and deep corals as well as other calcifying organisms, including plankton and the reef building coralline algal Species. Managers need to understand the process and impacts of ocean acidification in the Monument to better plan for the future of the remote reef system.

Overview of Research

Project Name PI and contacts Links

Seawater carbonate chemistry monitoring

Dr. Chris Winn and Dr. Sam Kahng, Hawaii Pacific University

Coral reef health and Climate Change

Dr. Paul Jokiel and Dr. Kuulei Rodgers, Hawaii Institute of Marine Biology


Science Needs and Questions

  • How much land habitat is likely to be lost due to sea-level rise at each island or atoll in the PMNM?
  • Which species (marine and terrestrial) are likely to be impacted by increases in sea level?
  • What are the impacts of sea-level rise to various species of the NWHI?
  • How will Midway Atoll be impacted by sea-level rise in terms of historic resources, buried contaminants and existing and planned infrastructure?
  • What options are available to managers to address and potentially mitigate sea-level rise in the Monument?
  • How will cultural resources of each island or atoll be affected by sea-level rise?
  • How much monk seal haul-out and pupping habitat is in danger of being lost due to sea-level rise?
  • How much sea turtle nesting grounds is in danger of being lost due to sea-level rise?
  • How does a carbonate reef affect the surrounding seawater?
  • What are the fluctuations of seawater inside the atoll lagoons?
  • What measures are available to managers to address or mitigate CO2 emissions?
  • How are calcifying organisms affected by acidification?
  • Which calcifying organisms are most severely affected by acidification?
  • What oceanographic characteristics confer resistance or susceptibility to bleaching?
  • What species specific characteristics confer resistance, resilience and susceptibility to bleaching?
  • How widespread are bleaching events in the Monument?
  • How far in advance can bleaching events be predicted using currently available tools?
  • What is the predictability of bleaching events in terms of duration and geographic scope?
  • How do bleaching events affect the ecosystem as a whole?
  • What role do the zooxanthellae play in a bleaching event and in coral recovery?
  • What percent of corals survive bleaching events of different severity in the Monument?


Education and Outreach Material

Office of National Marine Sanctuaries Climate Change Website


Baker, J.D., C.L. Littnan ,D.W. Johnston. 2006. Potential effects of sea level rise on the terrestrial habitats of endangered and endemic megafauna in the Northwestern Hawaiian Islands. Endangered Species Research 2:21-30.

Friedlander, A.M., G. Aeby, R. Brainard, A. Clark, E. DeMartini, S. Godwin, J. Kenyon, R. Kosaki, J. Maragos, P. Vroom. 2005. The sate of coral reef ecosystems of the Northwestern Hawaiian Islands. pp. 270-311. In: J. Waddell (ed.), The state of coral reef ecosystems of the United States and Pacific freely associated states: 2005. NOAA Technical Memorandum, NOS NCCOS 11. NOAA/NCCOS Center for Coastal Monitoring and Assessment’s Biogeography Team. Silver Spring, MD. 522 pp.

Hoeke, R., R. Brainard, R. Moffitt, M. Merrifield. 2006. The role of oceanographic conditions and reef morphology in the 2002 coral bleaching event in the Northwestern Hawaiian Islands. Atoll Res. Bull. 543:489-503.

Kenyon J.C. and R.E. Brainard. 2006. Second recorded episode of mass coral bleaching in the Northwestern Hawaiian Islands. Atoll Res. Bull. 543:505-523.

Kenyon J.C., G.S. Aeby, R.E. Brainard, J.D. Chojnacki, M.J. Dunlap, C.B. Wilkinson. 2006. Mass coral bleaching on high-latitude reefs in the Hawaiian Archipelago. In: Y. Suzuki, T. Nakamori, M. Hidaka, H. Kayanne, B.E. Cassareto, K. Nadooka, H. Yamano, M. Tsuchiya (eds.) Proceedings of the 10th International Coral Reef Symposium Okinawa, Japan. 1950 pp.

National Marine Sanctuary Program (NMSP). 2005. Northwestern Hawaiian Islands coral reef ecosystem reserve final reserve operations plan. 255 pp.