Off the coast of Olowalu in West Maui, hundreds of acres of coral cover the ocean floor. It's home to many different species of marine life, including one of the largest known populations of manta rays in the world.
That unique ecosystem and its inhabitants are under constant threat.
Like many of Hawaiʻi's reefs, Olowalu's corals have struggled through multiple mass coral-bleaching events in the last decade. During a 2015 bleaching episode, it experienced up to 45% coral loss.
But the main harm to the Olowalu reef system comes from the land above.
"The primary stressor for the Olowalu-Ukumehame reef is sedimentation," said Scott Paul Crawford, director of the Maui Marine Program with the Nature Conservancy.
"And the primary cause of sedimentation in Olowalu-Ukumehame is fire."
Brush fires regularly break out in the Olowalu area, including one fire that burned 120 acres this past June.
Those fires burn through the vegetation that holds soil in place on Olowalu's steep slopes. When rain comes, it washes that soil into the ocean below, where it smothers the vulnerable reef.
"You do that to a coral, it's not going to survive," said John Starmer, chief scientist with the Maui Nui Marine Resource Council.
His organization has been battling the same problem in North Kīhei, another fire-prone area on Maui's leeward coast.
"We were getting five or six inches of mud covering the nearshore environment," Starmer said. That sediment can take months to clear completely, clouding water and further disrupting the corals' photosynthesis.
The Maui Nui Marine Resource Council and the Nature Conservancy, along with local and state partners, are working to better protect Maui's reefs from the impacts of wildfires.
"This happens to Maui every year. It's the dry side of the island," Starmer said.
Just because it's routine doesn't mean it's natural, Starmer said. Tropical environments that host coral reefs typically aren't adapted for wildfires. But they are becoming more of a problem across the Pacific, especially in parts of southern Guam and the Federated States of Micronesia.
The fire that burned through Lāhainā in August introduced a completely new set of risks to reef systems.
"When you have an unfortunate situation where you have structure fires, especially at the scale that we've seen here on Maui, it is almost certainly releasing heavy metals," Starmer said.
Broadly speaking, Starmer said scientists aren’t yet sure what the exact impact of those metals may be on ocean health.
"We don't really know, but it's scary as heck," Starmer said. One concern is that those contaminants could bioaccumulate and travel up the food chain until they eventually make their way back onto our plates.
"Maybe they get sucked up by some little piece of plankton and then something that nibbles on the plankton ingests that, and you keep moving up the food chain until you get to the point where you're catching an ulua that has been snacking on things in a contaminated area," Starmer said.
The state Department of Land and Natural Resources is currently conducting testing in the nearshore waters off Lahaina to check for the presence of heavy metals and other volatile chemicals. Barriers have also been set up around Lahaina’s storm drains to prevent further run-off of contaminants into the ocean.
It's especially important to keep these contaminants out of the ocean in the first place, said Starmer, since "heavy metals are persistent. They don't really go away."
The Olowalu reef sits just a few miles south of Lahaina, but Crawford said its neighboring islands need to be concerned.
"The current generally goes to the north, and so it's not as likely to affect the Olowalu-Ukumehame reef," Crawford said "It's more likely for those contaminants to end up across the channels on the Lānaʻi and Molokaʻi reefs."
"We just don't know what the effect is," Crawford said, "I think that we're gonna have to be monitoring that area for a long time."
