A reef is a rock, sandbar, or other feature lying beneath the surface of the water (80 meters or less beneath low water). Many reefs result from abiotic processes - deposition of sand, wave erosion planing down rock outcrops, and other natural processes - but the best-known reefs are the coral reefs of tropical waters developed through biotic processes dominated by corals and calcareous algae. Artificial reefs such as shipwrecks are sometimes created to enhance physical complexity on generally featureless sand bottoms in order to attract a diverse assemblage of organisms, especially fish. Read more ...

World's oceans have gone 'crazy haywire,' officials warn, with majority of coral reefs in peril   NBC - May 17, 2024

Conditions last year were so unusually warm in some waters that heat stress levels were literally off the charts of NOAA's alert system. Daily monitoring of ocean conditions around the world, released by NOAA’s Coral Reef Watch, shows zones of Bleaching Alert Level 4 in the central Pacific Ocean and off the Atlantic coast of South America, with some ribbons of Alert Level 5 in the southern Atlantic.