If coral reefs aren’t growing, they’re decaying.

The bleak assertion comes amid efforts to help Maui County’s reef systems survive climate change effects, such as bleaching, that are predicted to worsen in future decades. Looking at coral reefs as living homes for marine species — and what would happen if they’re gone — is one way to grasp the magnitude of the impact that scientists, as well as Hawaii residents and visitors, are facing should corals die.

“Corals, when healthy, are growing and creating complex habitats,” said Russell Sparks, aquatic biologist for the state Department of Land and Natural Resources’ Division of Aquatic Resources. “These habitats are critical for fish and other critical reef animals. When corals die or become stressed, these structured habitats start to erode away toward flat, featureless areas, which will not support the same amount of marine life. On a reef, if corals are not growing then they are eroding.”

Maui-based Sparks is among the local experts busy at work to combat coral reef deaths. His division assisted a recent study that looked at more than 22,000 coral colonies at 51 sites along Maui’s south and west shores.

With highlights released last month, the 2018 report showed that five of the most resilient (defined as the reef’s ability to resist or recover from climate change) reefs can be found in or near state marine managed areas. The five are Molokini and Honolua conservation districts, Kahekili Herbivore Fisheries Management Area, Ahihi Kinau Natural Area Reserve and the reef offshore U.S. Fish & Wildlife Refuge at Kealia.

The least resilient reefs were a deep-water site Puamana and a shallow-water site Awalua near the Olowalu refuse collection location.

The Nature Conservancy study, with support from the DLNR’S Division of Aquatic Resources, the University of Hawaii and National Oceanic Atmospheric Administration, sought to identify sites most and least resilient to climate change to help guide conservation efforts on Maui. The findings are also meant to inform the state’s Marine 30×30 Initiative, a commitment to manage 30 percent of nearshore waters by 2030.

The study suggests that with the right management, coral reefs can build resilience and increase survivability — all good news, right?

“Not really that good of news,” said Sparks. “It is all referenced off of the best reefs locally. So it is all relevant to our best reef. If they are all struggling, it just shows which ones are doing better than other ones.”

Sparks is focused on the bigger picture for coral reefs in Maui and Hawaii, which remain under duress from mass bleaching events in 2014 and 2015 that wiped out up to 90 percent of coral living on some reefs, according to The Nature Conservancy.

A NOAA 2018 status report on Hawaii’s coral reefs rated the Maui Nui area as “fair,” a moderate assessment, with corals, algae, fish and climate conditions listed in the “impaired” zone, which is one level above the lowest “critical” score.

Resiliency also does not equal coral health, but it does give the system a fighting chance, Sparks said. In reducing coral reef stressors, reefs can hopefully sustain future climate change events, recover and reproduce, Sparks said.

The scientist said NOAA issues watches and warnings for bleaching events. By 2030, bleaching may happen every four years. By 2040, the frequency will become much more common, he said.

“If corals are going to get hit year after year, then it will be hard to recover,” he said. “If other stressors are reduced, then we’re hoping they can survive and spread to other areas.”

The Nature Conservancy study showing resiliency in some state managed areas is a mix of both good and bad news.

“It is both things,” said Emily Fielding, director of marine programs for TNC-Maui. “The managed areas are doing better but we are still facing a lot of problems.”

Maui’s south- and west-side reefs experience a combination of human-controlled threats, including sediments, nutrients and high fishing pressure.

Threats such as overfishing and land-based sources of pollution can be managed at a local level, while coral reefs would also benefit from the reduction of greenhouse gases that fuel climate change and ocean acidification, NOAA said. Overfishing reduces vital fish species that help coral reefs grow and disrupt the delicate ecological balance for the reef.

Land-based sources of pollution along Maui’s leeward shores come from coastal development and stormwater transported by impervious surfaces. Pollution forms include sedimentation, which smothers coral, and nutrient enrichment, which leads to seaweed overgrowth and an introduction of toxins and disease into the system.

If these threats are alleviated, coral reefs have a better chance for survival when future bleaching events occur, Sparks said.

If we are going to go out and manage certain areas, we want to pick the ones that are the most resilient,” he said. “If these (climate) changes come, at least we can get those places to survive.”

The state’s goal is to manage 30 percent of its nearshore waters by 2030. Only 3.4 percent of shores are currently managed, according to TNC.

Saving Maui and Hawaii’s underwater ecosystem requires an all-hands-on-deck approach, Fielding said. She encouraged residents to support state marine management, join community-based groups such as Napili Bay and Beach Foundation, Save Honolua Coalition, Maui Nui Marine Resource Council and Hui O Wai Ka Ola, and learn about impacts such as overfishing and human pollution. Only in working together can Hawaii’s unique and delicate marine life be conserved.

“Hawaii is the most isolated archipelago in the world, resulting in coral reef ecosystems with a quarter of all its life found nowhere else,” NOAA said. “This means Hawaii has a high rate of endemism. Corals and fishes here create a marine assemblage that is uniquely distinct from those found elsewhere.”

* Kehaulani Cerizo can be reached at kcerizo@mauinews.com.