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Research Spotlight: Mapping Corals from the Sky Guides Reef Conservation

Asner G.A., Vaughn N.R., Heckler J., Knapp D.E., Balzotti C., Shafron E., Martin R.E., Neilson B.J., and J.M. Gove. (2020) Large-scale mapping of live corals to guide reef conservation. PNAS. DOI: 10.1073/pnas.2017628117

The Upshot

Coral reefs are one of the most biodiverse ecosystems on the planet supporting an estimated 25 percent of all marine species. According to current estimates, 75 percent of the world’s coral reefs could face critical threat levels by 2050. Scientists widely agree that immediate and well-targeted action must be taken to preserve coral reefs for future generations. However, without a clear understanding of where live corals are found, management and conservation efforts will remain hampered at best and ineffective at worst. A critical case in point is the Hawaiian Islands, an icon of the natural world and the modern-day stresses underway on reef ecosystems. Coastal development has resulted in hotspots of sedimentation, waterborne pollutants, and reef removal, while fishing and other resource uses have generated declines in reef resilience. Marine heatwaves, driven by a warming global climate, have also periodically engulfed the Hawaiian Islands, with the 2015 and 2019 coral bleaching events being the most recent. The 2015 event caused widespread coral death, but the geographic extent of coral loss or resistance has remained poorly understood, as it has in reef regions throughout the world.

The Discovery

Using a new airborne mapping approach developed by researchers at Arizona State University’s Center for Global Discovery and Conservation Science (GDCS), the geographic distribution of live corals was, for the first time, quantified to 16 meters (51 feet) of water depth across the main Hawaiian islands. The mapping data were collected by the ASU Global Airborne Observatory, an aircraft-based laboratory developed by Asner and his team that houses advanced Earth mapping technology. By combining laser-guided imaging spectroscopy and artificial intelligence, the new approach reveals unprecedented views of coral reefs below the ocean surface. The maps show where live corals persist as well as areas of degraded reef.

The Impact 

“We undertook this first-ever mapping of a large archipelago to determine where corals live in Hawaiian waters despite repeated heatwaves and problematic coastal development issues,” said Greg Asner, lead author of the study and director of GDCS. “It’s this basic information that is needed by partner organizations to drive more cost-effective protections, restoration activities, and public engagement.” The results of the analysis revealed that nearshore development has a major negative relationship with live corals. The new mapping approach also pointed out areas where corals show resilience to human-driven environmental stressors. These regions of coral survival, deemed ‘refugia’, suggest that some corals and some sites are more resilient, and are thus prime locations for enhanced coral conservation. Garnering a greater understanding of coral survivorship could also alter predictions of whether corals will survive in the current and future ocean climate.

The Researchers

Researchers are from the Arizona State University Center for Global Discovery and Conservation Science, Hawaii’s Division of Aquatic Resources, Department of Land and Natural Resources, and the National Oceanic and Atmospheric Administration Pacific Islands Fisheries Science Center.