Study Outlines Path to Restore Reef Health in Hawai‘i

A team of scientists has announced new guidelines to better support herbivore populations who help maintain the health of coral reef ecosystems.

Herbivores like uhu, manini, palani, kole and kala prevent algae from taking over the habitats coral rely on to reproduce. Algae overgrowth can smother reefs and negatively affect the immediate ecosystem’s overall health. Reefs with flourishing herbivore populations are thought to be more resilient to pollutants, heavy fishing, and the effects of climate change like coral bleaching and heavy storms.

“Establishing management areas that restrict herbivore harvest is a common recommendation for protecting coral reefs, but there is limited information on how to do that,” said Dr. Anne Chung, the lead author of the study and a recent graduate of the University of Hawai‘i at Mānoa who now works for NOAA. “Based on the latest science, our team developed design principles for establishing an herbivore management area network that builds reef resilience in Hawai‘i.”

The team’s key recommendations include:

• Protecting ecologically important areas—particularly diverse reefs that provide nursery, shelter, feeding and spawning habitats for herbivores;
• Building connectivity so fish and their larvae can travel between areas and take advantage of critical food resources and habitats;
• Protecting reefs that have shown resilience to disturbance in the past while avoiding degraded areas.

The health of herbivore populations in management areas also depends on community engagement and support.

“Fishing is an important part of our island culture, so this work was born out of a practical need to protect our reefs while still allowing fishing to occur,” Chung said. “Herbivore management areas would not prevent fishing for other kinds of fish such as ulua, omilu, weke and ‘u‘u.”

Currently, less than 5% of the Hawaiian Island coastlines throughout the state effectively protect reef fish through managed areas, according to the study’s co-author Dr. Alan Friedlander, a University of Hawai‘i researcher. Only one area is specifically designated to manage herbivore populations: the Kahekili Herbivore Fisheries Management Area offshore of Kāʻanapali on Maui.

Management areas show proven, significant positive results. Within the Fisheries Management Area, parrotfish populations have recovered by 368%, algae have decreased, and coral habitats—which were once being smothered by algae—are no longer declining despite a mass bleaching event in 2015. In a 2018 survey led by The Nature Conservancy that examined 22,000 coral colonies at 51 sites in south and west Maui, Kahekili was ranked as one of leeward Maui’s five most resilient reefs.

“Herbivore management areas can help build reef resilience to climate change, but they should be used in conjunction with other management strategies, such as reducing sediments coming from land,” said co-author Dr. Alison Green of The Nature Conservancy.

Watershed management initiatives at Kahekili are reducing the amount of land-based sediment and nutrients that flow to the ocean.

“Practical guidance like these design principles is helping to equip government agencies and community groups with the tools they need to meet the State’s goal of effectively managing 30% of nearshore waters by 2030,” said Kim Hum, marine program director for The Nature Conservancy in Hawai‘i. “Maintaining healthy coral reefs around the Hawaiian Islands is a tough job. Rising and warming seas make it even tougher. But together, we can build healthier reefs and more abundant fisheries to support local livelihoods and feed our families into the future.”

The study’s paper, Building Coral Reef Resilience Through Spatial Herbivore Management, was published in the journal Frontiers in Marine Science.