Query: On a world scale coral reefs are in decline.

Relevant passages:
Coral reef <=SEP=> Coral reefs are diverse underwater ecosystems held together by calcium carbonate structures secreted by corals . Coral reefs are built by colonies of tiny animals found in marine waters that contain few nutrients . Most coral reefs are built from stony corals , which in turn consist of polyps that cluster in groups . The polyps belong to a group of animals known as Cnidaria , which also includes sea anemones and jellyfish . Unlike sea anemones , corals secrete hard carbonate exoskeletons which support and protect the coral polyps . Most reefs grow best in warm , shallow , clear , sunny and agitated waters .   Often called `` rainforests of the sea '' , shallow coral reefs form some of the most diverse ecosystems on Earth . They occupy less than 0.1 % of the world 's ocean surface , about half the area of France , yet they provide a home for at least 25 % of all marine species , including fish , mollusks , worms , crustaceans , echinoderms , sponges , tunicates and other cnidarians . Paradoxically , coral reefs flourish even though they are surrounded by ocean waters that provide few nutrients . They are most commonly found at shallow depths in tropical waters , but deep water and cold water corals also exist on smaller scales in other areas .   Coral reefs deliver ecosystem services to tourism , fisheries and shoreline protection . The annual global economic value of coral reefs is estimated between US$ 29.8-375 billion . However , coral reefs are fragile ecosystems , partly because they are very sensitive to water temperature . They are under threat from climate change , oceanic acidification , blast fishing , cyanide fishing for aquarium fish , sunscreen use , overuse of reef resources , and harmful land-use practices , including urban and agricultural runoff and water pollution , which can harm reefs by encouraging excess algal growth .

Conservation biology <=SEP=> Conservation biology is the management of nature and of Earth 's biodiversity with the aim of protecting species , their habitats , and ecosystems from excessive rates of extinction and the erosion of biotic interactions . It is an interdisciplinary subject drawing on natural and social sciences , and the practice of natural resource management .   The conservation ethic is based on the findings of conservation biology .

Coral <=SEP=> Corals are marine invertebrates in the class Anthozoa of phylum Cnidaria . They typically live in compact colonies of many identical individual polyps . The group includes the important reef builders that inhabit tropical oceans and secrete calcium carbonate to form a hard skeleton .   A coral `` group '' is a colony of myriad genetically identical polyps . Each polyp is a sac-like animal typically only a few millimeters in diameter and a few centimeters in length . A set of tentacles surround a central mouth opening . An exoskeleton is excreted near the base . Over many generations , the colony thus creates a large skeleton that is characteristic of the species . Individual heads grow by asexual reproduction of polyps . Corals also breed sexually by spawning : polyps of the same species release gametes simultaneously over a period of one to several nights around a full moon .   Although some corals can catch small fish and plankton using stinging cells on their tentacles , most corals obtain the majority of their energy and nutrients from photosynthetic unicellular dinoflagellates in the genus Symbiodinium that live within their tissues . These are commonly known as zooxanthellae and the corals that contain them are zooxanthellate corals . Such corals require sunlight and grow in clear , shallow water , typically at depths shallower than 60 m. Corals are major contributors to the physical structure of the coral reefs that develop in tropical and subtropical waters , such as the enormous Great Barrier Reef off the coast of Queensland , Australia .   Other corals do not rely on zooxanthellae and can live in much deeper water , with the cold-water genus Lophelia surviving as deep as 3000 m . Some have been found on the Darwin Mounds , north-west of Cape Wrath , Scotland . Corals have also been found as far north as off the coast of Washington State and the Aleutian Islands .

Marine protected area <=SEP=> Marine protected areas ( MPA ) are protected areas of seas , oceans , estuaries or large lakes . MPAs restrict human activity for a conservation purpose , typically to protect natural or cultural resources . Such marine resources are protected by local , state , territorial , native , regional , national , or international authorities and differ substantially among and between nations . This variation includes different limitations on development , fishing practices , fishing seasons and catch limits , moorings and bans on removing or disrupting marine life . In some situations ( such as with the Phoenix Islands Protected Area ) , MPAs also provide revenue for countries , potentially equal to the income that they would have if they were to grant companies permissions to fish .   On 28 October 2016 in Hobart , Australia , the Convention for the Conservation of Antarctic Marine Living Resources agreed to establish the first Antarctic and largest marine park in the world encompassing 1.55 million km2 ( 600,000 sq mi ) in the Ross Sea . Other large MPAs are in the Indian , Pacific , and Atlantic Oceans in certain exclusive economic zones of Australia and overseas territories of France , the United Kingdom and the United States , with major ( 990,000 km2 or larger ) new or expanded MPAs by these nations since 2012 -- such as Natural Park of the Coral Sea , Pacific Remote Islands Marine National Monument , Coral Sea Commonwealth Marine Reserve and South Georgia and the South Sandwich Islands Marine Protected Area . When counted with MPAs of all sizes from many other countries , as of August 2016 there are more than 13,650 MPAs , encompassing 2.07 % of the world 's oceans , with half of that area -- encompassing 1.03 % of the world 's oceans -- receiving complete `` no-take '' designation .