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Conservation

For Coral Reef Restoration to Work, Remote Sensing Technology is Key

Original Article: “Scaling Up Coral Reef Restoration Using Remote Sensing Technology.” Shawna A. Foo, Gregory P. Asner. Front. Mar. Sci., 13 March 2019 | https://doi.org/10.3389/fmars.2019.00079

The loss of staghorn coral and other formerly abundant corals across the Caribbean has profoundly affected coral reef ecosystems. Coral restoration projects plant coral species like staghorn onto reefs with the ultimate goal of helping reefs recover some of their lost biodiversity, structure, and genetic diversity. [Image is Figure 2 from “Jackson JBC, Donovan MK, Cramer KL, Lam VV (2014) Status and Trends of Caribbean Coral Reefs: 1970-2012. Global Coral Reef Monitoring Network, IUCN, Gland, Switzerland.”; A by Phillip Dustan, C by Robert Steneck]

When I recently planted nursery-raised staghorn corals onto a Caribbean reef, I couldn’t quite imagine that the elegant, branching corals had covered the reef just four decades ago. Like many parts of the Caribbean, huge patches of the reef that were crowned with coral during the 70s and 80s had been supplanted by algae-coated coral rubble. My small outplanting onto the coral reef was part of an effort across dozens of countries and hundreds of sites to try and restore the Caribbean reefs’ former biodiversity and structure.

Coral restoration, or intentionally growing and replanting certain coral species onto a degraded reef, is commonplace on Caribbean reefs still reeling from their staggering decline to just 10% coral cover on average in the last three decades. But with coral reefs facing global threats like warming seas and ocean acidification, the practice is likely to grow across the world as a hardline tactic to reverse coral loss. It’s a daunting challenge, made practical in part by remote sensing technology. Advances in remote sensing have made coral restoration more efficient and effective—and can improve coral restoration science even further in the near future.

Remote sensing is a catch-all term for any technology that collects physical data from a distance, like satellite sensors, sonar, radar, or the laser scanning LiDAR (Light Detection And Ranging). It  can give us detailed data about sea surface temperature, the texture of the seafloor, salinity, or even how many fish are present on a reef, among many other ocean qualities. Scientists and managers working in coral restoration already have plenty of opportunities to use remotely sensed data in every step of the coral restoration process. Yet remote sensing technology has the potential to do even more for coral restoration.

 

Zoomed-out aerial views of our planet from imaging satellites are commonplace today. But they’re just one of many remote sensing products that collect information about the ocean from afar. (Image from Pixabay).

 

For example, remote sensing can help with expensive and difficult decisions in the coral restoration process, such as choosing where to plant nursery-raised corals back onto the reef. Coral restoration managers have half a dozen factors to consider when picking where to plant new colonies, including depth, algae cover, and even whether enough herbivores live nearby. Common remote sensing technologies can assess all these considerations, and help managers pick the best sites.

 

Remote sensing includes a wide range of technologies that operate on both large and small scales. (Graphic is Figure 1 in Foo and Asner, 2019.)

 

The most underused possibility for reef restoration with remote sensing may be monitoring nursery corals after they’re planted onto the reef. Because only half of coral restoration sites monitor how their outplants are doing for more than a year, it’s difficult to compare how much the restoration helps the reef in the long term. Monitoring a reef the old-fashioned way often means deploying researchers in scuba gear to detail what they observe, a painstaking and expensive prospect when monitoring a large area over time. Today, low-flying aircraft like drones can detect what’s growing on a reef area with 4 cm resolution, sometimes down to the exact coral species.

A scientist takes thousands of photos of the reef floor to be combined into a single image and analyzed for coral cover. Imaging for remote sensing can be large scale and far away, or fine-resolution and detailed. (Image from Bermuda Institute of Ocean Sciences/Stacy Peltier)

Of course, remote sensing is not an instant solution to all of the challenges in coral restoration—each specific remote sensing technology has its own limitations, like poor data quality in deep water or with glare from the ocean surface. Some factors, like how much coral in a certain area is diseased, are still best estimated by trained human eyes (for now). But deploying a wide range of technologies combined with cutting-edge science will be essential for coral restoration to work in the long run.

I hope to return to the Caribbean restoration site I planted in a decade or two and find thriving staghorn colonies where today there are only modest nursery outplants. But if I don’t make it back, I hope that seeing how the restoration has changed the reef will be as simple as checking its growth with a remotely sensed dataset.

 

 

References

Jackson JBC, Donovan MK, Cramer KL, Lam VV (editors). (2014) Status and Trends of Caribbean Coral Reefs: 1970-2012. Global Coral Reef Monitoring Network, IUCN, Gland, Switzerland.

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