Taking Stock of Coral Reefs at War in the Pacific National Historical Park, Guam

Picture snorkeling over a vibrant coral reef, fish darting in and out of strong, healthy coral — then picture the same reef faded and silent, its life gone. That is what happens when reefs give way to the stresses they now face.

Coral reefs provide habitat for marine life but face threats from climate change and pollution (NPS).

Why reefs matter

Reef-building corals are living animals that are also home to many other marine species, supporting rich biodiversity. Reefs buffer shorelines from storms and big waves, protecting people onshore from wave energy, storm surge and coastal erosion. At War in the Pacific National Historical Park in Guam, they also let swimmers and divers see the wonders of the ocean up close.

The threat of bleaching

Bleaching is a serious and ongoing threat to corals worldwide. Rising ocean temperatures stress corals until they expel the helpful algae living in their tissues, leaving the coral white — bleached. Corals that survive bleaching become more vulnerable to disease and death. Warmer oceans driven by climate change are the leading cause.

Healthy (brown) coral tissue beside bleached (white) tissue (NPS).

Guam's reefs also suffer from land-based pollution and erosion, so good watershed management and waste disposal are critical. Reducing waste and spreading the word about protecting corals can make an immediate difference.

Nurseries — and the need for data

One strategy under study is planting heat-tolerant corals raised in nurseries; Guam has two coral nurseries, where fragments are grown until they can be replanted where coral needs to be reestablished. But managers need to know the state of the reefs first — planting in places where corals already struggle with erosion, for example, may fail.

The inventory

The National Park Service's Inventory and Monitoring Division sent scuba divers to photograph the park's reefs at various depths, so coral could later be identified and mapped.

• They recorded 245 hard coral species, including two listed under the U.S. Endangered Species Act. Among the corals observed was the threatened Acropora globiceps.
• They noted signs of stress, including stress caused by erosion and areas of significant bleaching. Research has shown a significant link between coral death and bleaching.

The threatened coral Acropora globiceps, recorded during the inventory (NPS / Burdick).

The findings point to the need for better stewardship on land and a stronger connection between land and sea. Scientists and park managers will use them to track reef health over time and choose the best ways to protect the park's many corals. Threats to reefs can seem overwhelming, but continued monitoring and proactive management can help keep their colors alive.

Sources

• National Park Service, Inventory and Monitoring Division: "Keeping Color in the Corals: Research Informs Decisions at War in the Pacific National Historical Park," by Summer Boulais (June 2024), summarizing O'Connell K, Burdick D, Vaccarino M, Lock C, Zimmerman G, Bhagat Y, Coral species inventory at War in the Pacific National Historical Park: Final report, Natural Resource Report NPS/WAPA/NRR—2024/2619 (2024).