Scientists create giant atlas of the world's most remote reefs



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Coral reefs are spread all over the world, but they are sometimes difficult to spot because they are under water. At present, a group of researchers has discovered that satellite imagery is capable of mapping reefs on a global scale. They have used this technology, as well as field studies, to create the world's most comprehensive coral reef atlas to date, including some of the world's most remote reefs.

A study describing the atlas, published last week in the Coral Reefs journal, confirms that a mapping method generally reserved for individual reefs extending over hundreds or thousands of square kilometers can map the reefs on a much larger scale. Maps like this are essential for reef conservation: before we can understand how to save the reefs, we need to know where they are and how big they are.

Using satellites and field observations, the authors mapped more than 25,000 square miles of coral. They published these maps in an online database called World Reef Map, where viewers can visit the reefs of Fiji in Seychelles. In some places, the map offers real underwater images of what the reefs look like.

Gathering all these pieces was not easy. The team, whose researchers came from the Rosenstiel School of Marine and Atmospheric Science of the University of Miami and the Khaled bin Sultan Living Oceans Foundation, who funded exhibitions and provided the ship to reach all the reefs, spent 10 years traveling in 11 countries to compile information in the field. about more than a thousand coral reefs. The authors have not listed popular places like the Great Barrier Reef in Australia; they searched for the least studied reefs, said author Sam Purkis, chairman of the department of marine geosciences at the University of Miami.

"We went to the most remote reefs, so mapping those that we have not mapped should be much easier because they are more accessible," he told Earther. "We did the hardest first."

They also sought the highest level of detail, even going so far as to map reefs to a single square meter using satellites. The online atlas also includes information on the surrounding habitat to provide a more complete picture of the reef situation. For example, users can look at the density of nearby seagrasses and mangroves. The researchers wanted to know if satellites were a good tool for analyzing reefs on a global scale, but they also wanted to collect as much information as possible about these ecosystems.

"We can better monitor their situation, then we can better apply our solutions to the coral reef crisis, which may be marine protected areas or a reef rehabilitation area or non-fishing areas," Purkis said. Earther. "We can make these decisions now on a global scale."

However, the use of satellites to remotely assess reefs has its limitations. The study showed that satellite imagery could misclassify some habitats, but the maps still showed an accuracy of 85%.

And the team was able to recheck satellite analysis with observations in the field. While they were there, the researchers analyzed the corals by wearing a wetsuit and diving into the water with a video camera in hand. The team dropped more than 22,000 cameras during its expedition. The purpose of all this data collection was to better prepare the next group of cartographers to continue to monitor the reefs of the world.

All this work comes at a critical time. Rising ocean temperatures can cause coral bleaching, which has affected more than 70% of the world's corals during a bleaching event between 2014 and 2017. Reefs known as the Great Barrier Reef are: again suffering from this event.

Meanwhile, new corals continue to be discovered. By better mapping them, scientists can assess their situation in a warmer world and determine how to deploy solutions to the crisis they are facing.

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