saving hawaii's coral reefs

Michelle Liu
October 02, 2023

Hanauma Bay is one of Hawaii’s best-known natural wonders. Its iconic keyhole lagoon with calm, crystal-clear water and colorful fish would draw up to 6,000 people daily. But COVID-19 changed that. For nearly nine months in 2020, the bay was closed to visitors. It ended up being a blessing.

Hanauma Bay is one of Hawaii's most popular attractions.

“Overtourism and sunscreen pollution have impacted Hanauma’s fragile ecosystems and wildlife for decades,” explains Ron Bregman, a Friends of Hanauma Bay board member. “But this pause in human usage allowed the bay to experience an unprecedented natural resurgence. Marine animals had a chance to thrive without the pressure of human disturbance and sunscreen contaminants.”

Hanauma Bay has since reopened to visitors, but with new restrictions emphasizing conservation over commercialization. A reservation system enforces a daily visitor cap and the bay is closed twice a week. Daily visiting hours have also been reduced.

In addition to these measures, efforts are underway to restore coral in Hanauma Bay. Six coral colonies were installed on the southern side of the bay this spring, where a large log damaged coral in 2020.

A coral module planted in Hanauma Bay. Photo courtesy Friends of Hanauma Bay

“These modules each represent 20 to 25 years of natural coral growth,” says Bregman. “They should be large enough to survive and thrive in the bay’s natural environment.”

That’s important because a variety of marine life depend on coral reefs for survival. Reef fisheries also provide a significant food source for people and protect shorelines from severe erosion.

But the reefs around Hawaii are dying. Poor coastal development practices have buried corals in mud and silt. Fertilizers from agriculture and sewage have caused an overgrowth of seaweed that smother corals. While certain fish species would normally eat the seaweed and keep it from killing the coral, they’ve been overfished. Coral bleaching is also a significant issue. It’s caused by climate change – when the ocean waters are too warm, corals eject the algae living in them, depriving them of their food source. Corals then lose their color, turning white. If their environment remains stressful, the coral will die.

That’s why there’s a push to restore coral around Oahu. While this is the first large-scale coral restoration project in Hanauma Bay, there have been other pilot projects. In 2016, the Hixon Lab at the University of Hawaii at Manoa added “fish condos” made of concrete blocks to the outer sand flats of Hanauma Bay. Their goal was to determine if these condos would provide enough shelter for fish to colonize, clean the nearby seafloor of seaweeds, and result in replenished coral growth.

Progress of coral growth using "fish condos." Photo courtesy Hixon Lab at UH Manoa

“Off Waikiki Beach, we learned that providing shelter for fish enhances the local abundance of coral,” says Mark Hixon, Ph.D., Hsiao Endowed Professor of Marine Biology in the School of Life Sciences at UH Manoa. “We also found that living fragments of colonies dislodged by storms, waves, or other disturbances thrived when attached to these artificial structures.”

The miniature versions that Hixon created for the pilot project are being tested on a much-larger scale. The REEFrame project will build two coral nurseries off Waikiki – each about 100-by-100-feet and seven feet tall. They’ll help restore reefs in the area, where most of the coral has died and collapsed.

Preliminary visualization of 3D-printed concrete module. Photo courtesy Natrx

“The organic shapes of the structures will attract colonizing fishes and other organisms, stimulating natural growth of corals,” says Hixon. “The structures will eventually become coral reefs in their own right.” 

They’ll be built about three-quarters of a mile off the beach, so surf spots and boating won’t be affected. The REEFrame project is also working with Waikiki fishermen, surfers, residents, and hotels to design and build the coral nurseries in ways that will best serve the community.

“This and other coral restoration projects will help ensure that our children and grandchildren will enjoy the same benefits of a thriving ocean ecosystem as previous generations,” says Hixon. 

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