7 Aug

Map of the Week: Coral Reefs

By Nigel Jaffe

Google Street View provides curious navigators with the ability to take photographic tours of an ever-growing portion of the world’s roads; meanwhile, thorough maps of Mercury, Mars, and the Moon (as spotlighted in the July 24 Map of the Week) are available for the curious extraterrestrial explorer. Despite the growing detail of maps depicting our world and other planets, one domain remains glaringly unexplored— the ocean. According to the Schmidt Ocean Institute, only about 5% of the world’s seafloor has been topographically mapped, and since the ocean comprises around 70% of the Earth’s surface, approximately two-thirds of the planet’s surface remains therefore unexplored.

Another stunning statistic: coral reefs, often called the “rainforests of the sea,” cover less than 1 percent of the ocean floor, yet 25 percent of all known fish rely on them for food and shelter. Due in large part to their small numbers, healthy reefs are incredible for their biodiversity. For example, the Northwest Hawaiian Island coral reefs, which are part of the Papahānaumokuākea National Marine Monument near Hawaii, support more than 7,000 species of birds, plants, and marine animals.

Despite their vital importance to ecosystems across the ocean, reefs are in grave danger. Threats on both local and global scales—including acidifying seas, changing water temperatures, pollution, toxic runoff, and overfishing—have contributed to the widespread decline of coral reefs around the world. And though many of the most imperilled reefs are located in relatively shallow areas, efforts to monitor reefs remotely are hindered by the general inability of satellite and airborne cameras to generate detailed topographical maps of anything beneath the waves.

The Global Airborne Observatory aims to change that. Developed by a team of scientists led by Greg Asner, director of Arizona State University’s new Center for Global Discovery and Conservation Science, and Robin Martin, a biochemist and remote-sensing expert, the system can map the seafloor to a depth of 50 feet. While standard mapping methods either require swimming with sonars or attaching them to a boat, both inefficient tactics, the Global Airborne Observatory, which surveys bodies of water from a low-flying plane, can map 250,000 acres a day.

By taking samples of different types of coral by hand, the team searches for matching spectral signatures from above. Cameras mounted to the plane pick up colors outside the range of human vision that correspond to the chemistry of the corals, generating a map accordingly.

The equipment on board the plane includes an imaging spectroscopy device designed by NASA, a lidar instrument, and high-resolution cameras. Combined, the measurements from these three tools create a 3-D image of the seafloor below. 

These maps may provide valuable insight into the precise locations of coral reefs that might otherwise go undiscovered; meanwhile, reefs that are known to be in bad health can be closely examined without requiring scuba expeditions. The Global Airborne Observatory maps have already been used in Peru to identify locations for new national parks and in the Dominican Republic to design a marine preserve. Future conservation efforts will have a powerful new tool as mapping continues across (literally) uncharted terrain.

Sources: 1, 2