NOAA awards $2.4 million for mesophotic coral ecosystem research in American Samoa

October 2019

Most ocean enthusiasts are familiar with shallow coral reefs: colorful ecosystems teeming with life that support more species than any other marine environment. But what many people don’t know is that these reefs can extend to depths of over 500 feet. These deeper reefs are known as mesophotic coral ecosystems, or “twilight reefs.”

Mesophotic coral ecosystems are not easy to access, and not as well studied as shallow coral reefs. However, NOAA is working with partners to change this. This month, NOAA is announcing $2.4 million in funding for a four-year research project studying mesophotic coral ecosystems in American Samoa, including reefs within National Marine Sanctuary of American Samoa and National Park of American Samoa.

diver swimming near a mesophotic reef
Diver Jason Leonard photographs a mesophotic coral ecosystem at 80 meters (262 feet) off Larsen's Bay in National Marine Sanctuary of American Samoa. Click the image to download a larger version. Photo: R.L. Pyle, under Creative Commons License

The first year of research represents $599,673 of the anticipated $2.4 million four-year project. The competitive research program is called the Deep Coral Reef Ecosystem Studies (Deep-CRES) Program: American Samoa. It seeks to improve our scientific understanding of mesophotic coral ecosystems, so that resource managers like National Marine Sanctuary of American Samoa can better protect them.

The funding comes from NOAA’s National Centers for Coastal Ocean Science (NCCOS) Competitive Research Program, in cooperation with the Office of National Marine Sanctuaries and Office of Ocean Exploration and Research.

Twilight reefs

Mesophotic coral ecosystems are located below conventional scuba diving depths, at about 100 to 500 feet or more. Due to their depth, they remain relatively understudied. They share some coral and fish species with shallow reefs, in addition to other species that are unique to these depths.

With the health of shallow coral reef ecosystems in decline, it is important to understand the value and role of mesophotic coral ecosystems in tropical and subtropical waters. These ecosystems serve as essential habitat for economically and ecologically important species to spawn, breed, feed, and grow to adulthood.

pink and brown soft corals
These soft corals (Dendronephthya spp.) were photographed at 45 meters (148 feet) in American Samoa. Photo: Anthony Montgomery, under Creative Commons License

Why American Samoa?

To improve knowledge of mesophotic coral ecosystems, this project targets American Samoa, the only U.S. territory in the South Pacific. American Samoa includes five volcanic high islands (Tutuila, Aunu‘u, Ofu, Olosega, and Ta‘u) and two atolls (Rose and Swains). Due to the region’s volcanic and coral topography, nearly 80 percent of potential coral reef habitat in American Samoa is within the depth range of mesophotic coral ecosystems. Yet it remains relatively unexplored.

map of american samoa
American Samoa is located in the South Pacific and consists of five volcanic high islands (Tutuila, Aunuʻu, Ofu, Olosega, and Tāʻu) and two atolls (Rose and Swains). Click the image to download a larger version. Image under Creative Commons License

There is only modest knowledge of the fish and corals found within mesophotic coral ecosystems in American Samoa. We have little to no information about the physical environment, habitat characteristics, water quality, or distribution of mesophotic coral ecosystems in the region. Improving our scientific understanding of these poorly-known habitats will help resource managers proactively develop strategies to manage and protect these ecosystems.

American Samoa has several marine protected areas that contain mesophotic coral ecosystems, including National Marine Sanctuary of American Samoa, National Park of American Samoa, Rose Atoll Marine National Monument, and community-based marine protected areas managed by the American Samoa Department of Marine and Wildlife Resources. In addition to protecting fragile ecosystems, these marine protected areas serve as hubs for science projects like this one.

Partnering to understand mesophotic coral reefs

gorgonian growing from a rock wall
A large gorgonian coral grows along a reef drop-off at a depth of about 70 meters (230 feet) off Vaitogi, American Samoa. Click the image to download a larger version. Photo: R.L. Pyle under Creative Commons License

The project is led by the U.S. Fish and Wildlife Service, in partnership with Bishop Museum, the Hawai‘i Institute of Marine Biology at the University of Hawai‘i, Old Dominion University, and Papahānaumokuākea Marine National Monument.

The U.S. Fish and Wildlife Service’s Pacific Islands Fish and Wildlife Office will lead the overall project and research related to coral ecology and describing physical habitat characteristics. Bishop Museum will lead fish taxonomy and reproduction studies, conduct research on the diversity of algae and non-coral invertebrates, and identify environmental water characteristics. Papahānaumokuākea Marine National Monument will lead the fish diversity and ecology research. University of Hawai‘i will lead the study of evolutionary relationships among organisms and environmental DNA research. Old Dominion University will lead bleaching studies on the susceptibility of mesophotic corals to changes in ocean temperature and water quality.

Research for the future

This research will provide resource managers with an inventory of species associated with mesophotic coral ecosystems in American Samoa and their habitat preferences. It will include distribution and abundance data for key species and reproductive characteristics for commercially important fish. The research will help identify local and regional threats to mesophotic coral ecosystems in American Samoa, as well as predict distribution of these ecosystems across American Samoa.

Our global ocean is under threat from changes and human impacts. By studying mesophotic coral ecosystems, we improve our understanding of these fragile habitats so we can better protect them for current and future generations.

green coral
This stony coral, Galaxea fascicularis, was photographed at 46 meters (151 feet) off Tutuila, American Samoa. Click the image to download a larger version. Photo: Anthony Montgomery, under Creative Commons License

For more information, contact Sarah Marquis, West Coast/Pacific Islands media coordinator for NOAA's Office of National Marine Sanctuaries:, (949) 222-2212.