Protected waters are best for reefs, Maui survey finds

A study of 22,000 coral colonies at 51 sites along Maui’s south and west shores found formally protected reefs near managed areas were among the most likely to show resilience to climate change.

Five of the most resilient reefs are situated within or adjacent to state-managed areas or offshore of a federal wildlife refuge, according to the 2018 survey by The Nature Conservancy.

A peer-reviewed copy of the study was unavailable for online review Thursday but is expected to be available in a few weeks on the website of the National Atmospheric and Oceanic Administration’s Coral Reef Conservation Program.

The study involved an analysis of thousands of photographs and observations taken during two weeks in March 2018 by a 10-person research team.

The survey’s healthiest reef was found offshore of Kealia Pond National Wildlife Refuge, one of the state’s last remaining natural wetland habitats, located north of Kihei.

“I don’t think it was a coincidence that it was the most resilient,” said Eric Conklin, director of marine science for The Nature Conservancy of Hawaii. “Wetlands are natural filters of sediment.”

Sediment runoff is one of the biggest threats to the health of coral reefs, along with nutrient pollution, fishing pressures, coastal development, warming waters and increasing ocean acidification.

Scientists said coral reefs are among the most vulnerable of ecosystems to ocean temperature rise resulting from global warming. Coral bleaching is expected to be an annual event by 2040, according to some projections.

But the results of the study suggest coral reefs can be managed to build resilience and the ability to survive in an uncertain future.

“Healthy, functioning reefs should be able to grow and adapt to sea level rise,” Conklin said.

Also among the healthiest reefs, according to the survey, were the state’s Molokini and Honolua Marine Life Conservation Districts, Kahekili Herbivore Fisheries Management Area and the Ahihi Kinaʽu Natural Area Reserve.

Sites with high fishing pressure included North Kaanapali and Hanakaoo north of Lahaina, the study said, while Kihei and North Kaanapali were areas with more pronounced nutrient and water quality issues.

Maui’s coastal reefs have been in the news recently because the U.S. Supreme Court agreed to hear an ongoing dispute linked to pollution from the Lahaina Wastewater Reclamation Facility.

The plant disposes of millions of gallons of treated sewage a day into underground injection wells, and environmentalists have argued for decades that pollution from the plant is contaminating groundwater that seeps into the ocean, killing coral and triggering algae blooms in West Maui waters.

The closest site to the plant included in the survey was the Kahekili Herbivore Fisheries Management Area, which was farther offshore and in good shape, said Conklin.

Elsewhere, sediment was a problem up and down the leeward coast, including reefs around Olowalu, Kihei and Lahaina, he said.

Concern for coastal water quality on Maui has led to the formation of the West Maui Ridge 2 Reef Initiative and Hui o Wai ka Ola, a group that assists the state with monitoring water quality.

The state maintains a goal of having 30 percent of its nearshore waters under effective management by 2030. However, Conklin said, only 3.4 percent of shores are currently managed.