<P> However, the "topography of coral reefs is constantly changing . Each reef is made up of irregular patches of algae, sessile invertebrates, and bare rock and sand . The size, shape and relative abundance of these patches changes from year to year in response to the various factors that favor one type of patch over another . Growing coral, for example, produces constant change in the fine structure of reefs . On a larger scale, tropical storms may knock out large sections of reef and cause boulders on sandy areas to move ." </P> <P> Coral reefs are estimated to cover 284,300 km (109,800 sq mi), just under 0.1% of the oceans' surface area . The Indo - Pacific region (including the Red Sea, Indian Ocean, Southeast Asia and the Pacific) account for 91.9% of this total . Southeast Asia accounts for 32.3% of that figure, while the Pacific including Australia accounts for 40.8% . Atlantic and Caribbean coral reefs account for 7.6% . </P> <P> Although corals exist both in temperate and tropical waters, shallow - water reefs form only in a zone extending from approximately 30 ° N to 30 ° S of the equator . Tropical corals do not grow at depths of over 50 meters (160 ft). The optimum temperature for most coral reefs is 26--27 ° C (79--81 ° F), and few reefs exist in waters below 18 ° C (64 ° F). However, reefs in the Persian Gulf have adapted to temperatures of 13 ° C (55 ° F) in winter and 38 ° C (100 ° F) in summer . There are 37 species of scleractinian corals identified in such harsh environment around Larak Island . </P> <P> Deep - water coral can exist at greater depths and colder temperatures at much higher latitudes, as far north as Norway . Although deep water corals can form reefs, very little is known about them . </P>

The optimum temperature for coral formation occurs where the average annual temperatures are between