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Protecting the next generation of corals

New research shows the major factors that help coral larvae settle and survive are the nearshore current and the physical features of the seafloor. The work could help identify sites where future reefs will be most viable and highlights a need to better protect these coral nurseries.

Aerial image of coral reef and coastline in the South Kona, Hawaiʻi region. (Image credit: ASU Global Airborne Observatory)

Protecting areas of the seafloor where young corals prefer to settle and grow is essential for sustaining reefs, a new study finds. 

Reef conservation efforts typically focus on preserving established coral and protecting them from known stressors such as pollution, overfishing, and runoff from coastline populations.

However, research published Jan. 8 in Proceedings of the National Academy of Sciences shows that identifying and protecting marine ecosystems both down-current and up-current of coral reefs, specifically areas where coral larvae are more likely to survive and thrive, is crucial to future coral health, especially as reefs face increasing pressure from the devastating effects of climate change.

The study took place near Miloliʻi in the southwestern part of the island of Hawaiʻi and was supported by the ʻĀkoʻakoʻa Reef Restoration Program, a regional effort that fuses cultural leadership, multi-modal education, advanced science, and government engagement.

Lead author Rachel Carlson, PhD ’23, completed the study as an affiliate scientist at Arizona State University and a PhD student in the Emmett Interdisciplinary Program in Environment and Resources (E-IPER), part of the Stanford Doerr School of Sustainability. According to Carlson, collaborative work that combines local, Indigenous knowledge and Western science is crucial to mapping out a future that ensures the survival of coral populations.

“There’s a lot of Indigenous knowledge about coral spawning and fish populations in West Hawaiʻi. In this study, we addressed an open question: How connected are coral populations between embayments along this coastline?” said Carlson, whose co-authors on the study include her PhD advisors, Stanford Doerr School of Sustainability professor Larry Crowder and Arizona State University professor Greg Asner. “What we essentially found is that the major factors in helping the coral keiki, known as larvae, settle down and survive are the nearshore current and the structure of the reef,” she said.

The study shows that the larvae more often settle in and inhabit areas with large boulders and uneven surfaces, or “chunky features,” said Carlson, who is now a Chancellor’s Postdoctoral Fellow at the University of California Davis Bodega Marine Laboratory. Adult coral will spawn millions of larvae into the water column and those larvae prefer to settle in places with large knolls and boulders.

A colony of the native Hawaiʻian coral Pocillopora meandrina settles and grows on a rock along the reef of South Kona on the island of Hawaiʻi. (Image credit: Greg Asner)

This discovery is good news: These kinds of seafloor features have been mapped via Arizona State University’s Global Airborne Observatory, a highly specialized aircraft that uses several types of remote sensing technologies to track both underwater and land-based habitats. This means that the researchers have the capability to help find and map priority reefs for conservation and restoration.

“This is foundational research in several important ways,” said Asner, the study’s senior author and the director of Arizona State University’s Center for Global Discovery and Conservation Science in the Julie Ann Wrigley Global Futures Laboratory. “First, it gives us an understanding of the connectivity of different parts of reefs along our coastline and tells us the level of connectivity in the context of the birth, settlement, and growth of corals miles apart. Second, our unique remote sensing capabilities can identify reef sites where coral restoration could be most viable in the future. Finally, these findings provide a critical building block for future restoration efforts by our ʻĀkoʻakoʻa team and collaborators.”

Protecting coral keiki

The group’s goal is to preserve and restore vitality to Hawaiʻi’s coral reefs and coastline health. 

“We as lineal descendants of the Miloliʻi area have always relied on the reef for our ʻOhana (families). Our reef is our sustenance and is of enormous cultural value to us,” said Kaʻimi Kaupiko, president of the nonprofit organization Kalanihale, which manages the Miloliʻi Community-Based Subsistence Fishing Area where the study took place.

Asner said the intertwined nature of reefs along Hawaiʻi’s coastlines is crucial to consider in reef protection strategies. Narrowing in on one area without consideration for the reproductive corridors of corals, he said, would be akin to worrying about planting trees in a certain place and not thinking about the forest as a whole. This sentiment is echoed by co-author Robin Martin, associate professor with the Arizona State University School of Ocean Futures in the Julie Ann Wrigley Global Futures Laboratory, who said reef connectivity is an underutilized tool in reef restoration efforts globally. 

“In Hawaiʻi and worldwide, we’re trying to figure out where we should place protections and restore areas to help reefs,” said Martin. “This study is highly technical, but it needs to be part of that conversation and part of that work, because if you aren’t protecting the upcurrent reefs, you are cutting off important reproductive areas.” 

Martin said reef restoration could, for example, expand a protected area of reefs beyond just the spots that have more dense coral coverage on the ocean floor; protection efforts would also be needed in the upcurrent path that the coral larvae traveled through before they settled in a new location.

Asner adds that this research could very well help conservation efforts expand to much greater distances than have been achieved previously.

A close-up view of coral polyps, specifically the Hawaiʻian coral Porites compressa, growing on a reef in South Kona, Hawaiʻi. (Image credit: Greg Asner)

“These kinds of studies of connectivity, flow, and movement are needed because the west Hawaiʻi island coastline is longer than the whole circumference of any other island,” Asner said. “We have a lot of degraded reefs along our coastline, so knowing where and how to help baby corals thrive is fundamental to the ʻĀkoʻakoʻa restoration effort.”

“Our students participated in the coral study, and that also helped us to connect the dots between cultural knowledge and Western science,” Kaupiko said. “The study supports our community-based subsistence fishing area by showing that our area is ecologically connected, and thus it needs to be managed and protected as one connected reef and coastline.” 

This story was adapted from a press release originally published by Arizona State University.

Crowder is the Edward Ricketts Provostial Professor, a professor of oceans, and a professor (by courtesy) of biology at Stanford. He is also a senior fellow at the Stanford Woods Institute for the Environment

Coral recruitment fieldwork for this research was supported by the Dorrance Family Foundation. Global Airborne Observatory (GAO) data collection was supported by the Lenfest Ocean Program of Pew Trust. The GAO is made possible by support from private foundations, visionary individuals, and Arizona State University. Rachel Carlson was further supported by the NSF Graduate Research Fellowship Program (DGE-1656518), a David and Lucile Packard Graduate Research Fellowship, and an International Coral Reef Society Graduate Fellowship.

Media Contacts

Sandra Leander

Arizona State University

Katie Jewett

Stanford Doerr School of Sustainability

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