The Sudanese coast of the Red Sea is a well-known destination for diving due to clear water and abundance of coral reefs (or shia’ab in Arabic). Reefs are formed primarily from precipitation of calcium carbonate by corals. (In addition to its commonly used meaning, precipitation can also describe how something dissolved in a solution becomes “undissolved” through chemical or biological processes.) Massive reef structures are built over thousands of years of succeeding generations of coral. In the Red Sea, fringing reefs form on shallow shelves of less than 50 meters depth along the coastline. This astronaut photograph illustrates the intricate morphology of the reef system located along the coast between Port Sudan to the northwest and the Tokar River delta to the southeast.
The Great Barrier Reef is the largest reef system on Earth, with more than 3,000 separate reefs and coral cays. It is also one of the most complex natural ecosystems.
In one frame International Space Station astronauts were able to capture the evolution of fringing reefs to atolls. As with the Hawaiian Islands, these volcanic hot spot islands become progressively older to the northwest. As these islands move away from their magma sources they erode and subside.
In February 2017, the Great Barrier Reef continued to be exposed to warm ocean water—the main stressor on this coral system and the reason for its bleaching.