Ocean & Coastal Ecosystems


Chubs (Kyphosus bigibbus) in foreground and goatfish (Mulloidichthys sp.) in distance. Northwest Hawaiian Islands. September, 2004. ©NOAA Photo Library, photo by Dr. Dwayne Meadows, NOAA/NMFS/OPR.

The Pacific Islands region contains some of the most diverse ocean and coastal ecosystems in the U.S., and some of the most pristine, including the Pacific Remote Islands Marine National Monument and Papahānaumokuākea Marine National Monument. These ecosystems contain communities of species and groups of species of value economically, culturally, and for conservation, protection, and global biodiversity. These species include, among others, pelagic fish (such as tuna), reef fish, corals, endangered sea turtles and monk seals, marine mammals, and plankton, which form the base of the food web.

Climate variability and change threaten marine and coastal ecosystems through rising air and sea-surface temperatures, sea-level rise, changes in seasons, changes in the frequency and intensity of extreme weather events (such as tropical cyclones and heavy rain events), changes in solar radiation, and increasing ocean acidification. Given the complex interconnections among ecosystems, we can only begin to understand how they will change as climate change advances and how these changes will impact economies, subsistence, culture, and the way of life of peoples of the Pacific Islands

Key Messages

Higher sea-surface temperatures will increase coral bleaching, leading to a change in coral species composition, coral disease, coral death, and habitat loss.

Increasing ocean acidification and changing ocean chemistry will have negative consequences for the entire marine ecosystem. Although potentially dramatic, the exact nature of the consequences is not yet clear.

Distribution patterns of coastal and ocean fisheries will be altered due to changes in ocean circulation, with potential for increased catches in some areas and decreased catches in others. Overall in the long term, open-ocean fisheries will decline.

Observed trends

  • Average sea-surface temperature across the region has risen over the last century, with more rapid warming since the 1970s.
  • Carbon dioxide is absorbed by sea water, resulting in a series of chemical reactions that increase sea-water acidity, carbonate ion concentration, and the availability of the biologically important calcium carbonate minerals through a process known as ocean acidification.
  • Reefs across the Pacific have shown varying responses to changes in temperature and sea-water acidity, some showing resilience to high acidity and increased sea-surface temperature.
    • Reef-building corals in several pools on Ofu Island, American Samoa, are exposed to high temperature variability and exhibit higher resilience to thermal stress than corals in other pools that experience less temperature variability. (Palumbi et al. 2014, Barshis et al. 2012, Birkeland et al. 2008)
    • Reefs in the Rock Islands of Palau are exposed to continually low local pH and exhibit high coral biodiversity and coral cover, despite high levels of erosion of reef structures (Shamberger et al. 2014, Barkley et al. 2015)

Future projections and impacts

  • Surface temperatures across the region are projected to increase at levels that will impact key marine ecosystems.
  • Increasing ocean temperatures, changing ocean currents and decreased primary productivity in the Central North Pacific are projected to cause a decline in pelagic fisheries by 2100 (Howell et al. 2012, Woodworth-Jefcoats et al. 2012, Woodworth-Jefcoats et al. 2016).
  • The biological impacts of ocean acidification to key organisms, including larval fish, coral reefs, phytoplankton, zooplankton, and other calcifying organisms, are anticipated to have potentially devastating effects and must be better understood to prepare for and prevent impacts.
  • For sensitive ecosystems like coral reefs, with high vulnerability and potentially low adaptive capacity, greenhouse gas reduction is the only meaningful response. High levels of local protection will only buy time for these ecosystems and do not provide immunity to significant climate change impacts.
  • Key habitats such as mangroves, coastal wetlands, and dunes could also be negatively impacted by erosion and inundation, made worse by sea-level rise.
    • Loss of low-lying land due to sea-level rise in the Northwestern Hawaiian Islands is projected to diminish habitat for endemic and endangered species, including several seabird species, the Hawaiian green sea turtle and the Hawaiian monk seal (Baker et al. 2006, Storlazzi et al. 2013, Reynolds et al. 2015).
  • Changes in precipitation patterns may lead to increased coastal erosion, decreased coastal water quality, and changes in aquatic species distribution.
  • A projected increase in tropical cyclone intensity could impact the physical features of coastlines and marine ecosystems (coral reefs, seagrasses, and mangroves), influencing the spread of invasive species and reducing shoreline protection for coastal communities.

Download “Marine, Freshwater, and Terrestrial Ecosystems on Pacific Islands” Chapter from the 2012 PIRCA Report

This chapter should be cited as:

Parker, B., & Miller, S. E. (2012). Marine, Freshwater, and Terrestrial Ecosystems on Pacific Islands. In V. W. Keener, J. J. Marra, M. L. Finucane, D. Spooner, & M. H. Smith (Eds.), Climate Change and Pacific Islands: Indicators and Impacts. Report for the 2012 Pacific Islands Regional Climate Assessment (PIRCA). Washington, DC: Island Press.


Content: Ocean & Coastal Ecosystems