ASU center announces first-ever global coral reef maps


September 9, 2021

When people think of Arizona State University and the Sun Devils, desert landscapes and simmering Phoenix days come to mind. But for one ASU research team, their setting is tropical islands and beaches — Hawaii to be exact. 

The Center for Global Discovery and Conservation Science — located in Tempe, Arizona, and in Hilo, Hawaii — does not call this paradise home just for the views. This team is leading the way in groundbreaking research to inform climate and biodiversity action around the world. And one of its projects, the Allen Coral Atlas, continues to reach new heights for what is possible.  Dr. Alexandra Ordonez collects georeferenced reef data with GPS overhead. Credit: Chris Roelfsema Alexandra Ordonez collects georeferenced reef data with GPS overhead. Photo by Chris Roelfsema Download Full Image

On Sept. 8, the Allen Coral Atlas met a major milestone by completing global habitat maps of the world’s tropical, shallow coral reefs. A combination of satellite imagery, advanced analytics and global collaboration has resulted in maps that show the marine ecosystems' benthic and geomorphic data in unprecedented detail. With eyes in the sky, the technology recognizes geomorphic, or seascape structures, up to about 15 meters (52 feet) underwater and benthic data, or the composition of the ocean floor, up to about 10 meters (33 feet) underwater. 

The Allen Coral Atlas is a collaborative project led by the Center for Global Discovery and Conservation Science in partnership with Vulcan Inc., Planet Labs Inc., the University of Queensland (UQ) and the National Geographic Society. Drawing on satellite imagery, the Allen Coral Atlas maps and monitors the world's coral reefs. And with this newest accomplishment, conservation users will have a resource for globally comparable coral reef data, at a scale never before available.

“We now have the highly detailed maps needed to create new spatial plans and marine protected areas,” said Wen Wen, a marine spatial analyst in Indonesia. “The Allen Coral Atlas is playing a large role in prioritizing 30 million hectares of a new MPA (marine protected area) and providing alternative locations for a coastal economic development project of a shoreline airport. This tool is a blessing to our country.”

A marine protected area is an area of the ocean set aside for economic resources, biodiversity conservation and species protection. Basically, it limits human activity to support the reef and ocean ecosystem, and, in effect, the nearby communities that rely on these reefs.

Innovation and collaboration are key to crafting the maps

Before becoming a game-changing conservation tool, the journey of a habitat map begins as satellite imagery from Planet Labs. ASU calculates the water depth, and these calculations are sent with the imagery to the Remote Sensing Research Center at UQ, where scientists use machine learning and analysis to craft the habitat maps. 

Machine learning uses algorithms to classify the pixels in an image into different reef classifications. Just like any student, these algorithms need to learn how to recognize the different pixels. Local teams have contributed more than 450 datasets that “train” the algorithms to do just that. 

After classifying the reefs, these datasets are used to assess the reef maps and check that the classifications are accurate. While turbidity — think sand or sediment in the water — and atmospheric conditions, such as clouds, create barriers when mapping coral reefs, the Allen Coral Atlas leverages collaboration by engaging with teams for feedback and organizing expeditions for additional reef data.

After the regions have been validated and a local expert provides feedback, the habitat maps are sent to the software engineering team at ASU, where they are transformed into visual and downloadable data available to anyone with internet access. Check them out at the Allen Coral Atlas website.

Informing action

With these maps, organizations have a new tool to guide their conservation efforts. 

“It is a gratifying milestone after years of dedicated nonstop teamwork to bring this global map to fruition, but the true value of the work will come when coral conservationists are able to better protect coral reefs based on the high-resolution maps and monitoring system,” said Greg Asner, managing director of the Allen Coral Atlas at ASU. “We must double down and use this tool as we work to save coral reefs from the impacts of our climate crisis and other threats.”

Already, officials from 14 countries are engaged with Allen Coral Atlas team members, working on 48 new marine planning projects using the atlas maps as their foundational data set. 

Vatu Molisa, Vanuatu Project liaison officer for the IUCN Marine Program, explained how the Allen Coral Atlas will be used to inform the region’s efforts to protect coral.

“We will be utilizing this very valuable and important dataset to contribute to our continuing National Marine Spatial Plan and efforts, and look forward to future and continuing collaborations," Molisa said.

The use of the habitat maps goes beyond marine spatial planning, with organizations using the Allen Coral Atlas for disaster recovery, proposed policies for fishing regulations, and the identification and documentation of local threats to coral reef habitats.

Combined with recent innovation — a monitoring system capable of detecting coral bleaching in biweekly increments — the Allen Coral Atlas is now the most complete, consistent, accurate and continually updated resource for coral scientists, policymakers and regional planners. 

In addition to the Allen Coral Atlas, the Center for Global Discovery and Conservation Science team’s research continues to awe the conservation community — from groundbreaking studies, including Shawna Foo’s recently published study on coral and algae relationships, to the first high-resolution mapping of live corals on the Hawaiian Islands, to educational coral videos shot under the waves.

Makenna Flynn

Digital communications intern, Center for Global Discovery and Conservation Science

Scientists report new findings on the role that fish play in balancing coral, algae on reefs


August 23, 2021

When people think of coral reefs, images of beautiful colors and structures come to mind. But beyond aesthetic pleasure, coral reefs provide numerous benefits, ranging from food security and coastline protection to their role in coastal traditions and cultures. Although reefs cover less than 1% of the ocean floor, they support about 25% of marine life and earn their nickname: the rainforests of the sea.

A major challenge to reefs today is whether corals can persist under changing climate. One way that climate affects corals is by stimulating the overgrowth of algae that can smother the reef, making life tough for new corals to survive. Herbivore fish, such as Yellow Tang, help to prevent algae from overgrowing coral on reefs, credit: Shawna Foo Herbivore fish, such as yellow tang, help to prevent algae from overgrowing coral on reefs. Photo by Shawna Foo Download Full Image

To better understand the balance between coral and algae, scientists at Arizona State University’s Center for Global Discovery and Conservation Science explored the role of herbivorous fish in keeping check on one of the main antagonists in coral-algae fight for reef space, known as “turf algae.” Their findings were published on Aug. 9 in Coral Reefs, the Journal of the International Coral Reef Society.

Led by postdoctoral researcher Shawna Foo, the team utilized 1,476 fish and benthic surveys from 2010 to 2019 across the eight main Hawaiian Islands.

“We found that control of turf algae cover differs by water depth, and herbivore fish numbers were the best indicator of reductions in turf algae cover," Foo said. “Smaller fish exerted greater control on turf algae than larger fish.”

A mixture of many algal species and usually less than 2 cm (less than 1 inch) in height, turf algae grows quickly and occupies new spaces on the reef. It can also overgrow and kill coral. Herbivores protect coral by grazing on the turf algae, reducing their overall cover, like cattle on a grass pasture.

Prior to this study, the role of herbivorous fish in controlling algae was well known, but there was limited understanding of how this role changed by reef depth and with different types of fish. The new study revealed patterns between different types of herbivore fish — scrapers like parrotfish, browsers like angelfish and grazers like tangs — and their relationship with how much turf algae covered the ocean floor on shallow, mid and deep reefs.

“Overgrown algae is a critical issue for coral reefs globally,” said Greg Asner, study co-author and director of of the center. “This research sheds new light that directly supports the need for conserving herbivore reef fish in a warming climate, for reefs that otherwise will continue to lose to turf algae.”

The fish surveys were conducted by National Oceanic and Atmospheric Administration divers who counted, sized and classified fish at each site. They also estimated what covered the ocean floor, allowing the researchers to distinguish between coral and different types of algal cover. With these surveys, the ASU team investigated factors related to fish and turf algae, including how the composition of herbivorous fish changed at different depths and how fishing intensity changed across depths.

“Our findings also indicate that fishing on deeper parts of Hawaiian reefs may be the most detrimental because deeper reefs are naturally inhabited by fewer fish compared to shallower reefs,” Foo said. “So deeper reefs would be more vulnerable to fishing pressure on herbivores”.

The findings provide new input to reef managers in Hawaii and beyond. Herbivore fish management is a key strategy that can reduce turf algae and boost coral survival. While past management has often focused on the total biomass of herbivore fish present on a reef, the new research indicates that the number of fish — literally the number of mouths on the reef — is the more important goal in the effort to battle turf algae and to protect corals in a warming climate.

Makenna Flynn

Digital communications intern, Center for Global Discovery and Conservation Science