Query: Coral atolls grow as sea levels rise.

Relevant passages:
Climate change in Tuvalu <=SEP=> Global warming (recent climate change) is particularly threatening in Tuvalu. This is because the average height of the islands is less than 2 metres (6.6 ft) above sea level, with the highest point of Niulakita being about 4.6 metres (15 ft) above sea level. Between 1971 and 2014, during a period of global warming, Tuvalu islands have increased in size, according to aerial photography and satellite imagery. Over four decades, there was a net increase in land area in Tuvalu of 73.5 ha (2.9%), although the changes were not uniform, with 74% of land increasing in size and 27% of land decreasing in size. The sea level at the Funafuti tide gauge has risen at 3.9 mm per year, which is approximately twice the global average.Tuvalu could be one of the first nations to be significantly impacted by rising sea levels. Not only could parts of the island be flooded but the rising saltwater table could also destroy deep rooted food crops such as coconut, pulaka, and taro. Research from the University of Auckland suggests that Tuvalu may remain habitable over the next century. However, as of March 2018, Prime Minister Enele Sopoaga stated that Tuvalu is not expanding and has gained no additional habitable land. Sopoaga has also said that evacuating the islands is the last resort.

Tuvalu <=SEP=> Tuvalu ( -LSB- tᵿˈvɑːlu -RSB- or -LSB- ˈtuːvəˌluː -RSB- ) , formerly known as the Ellice Islands , is a Polynesian island nation located in the Pacific Ocean , about midway between Hawaii and Australia , lying east-northeast of the Santa Cruz Islands ( belonging to the Solomons ) , southeast of Nauru , south of Kiribati , west of Tokelau , northwest of Samoa and Wallis and Futuna and north of Fiji . It comprises three reef islands and six true atolls spread out between the latitude of 5 ° to 10 ° south and longitude of 176 ° to 180 ° , west of the International Date Line . Tuvalu has a population of 10,640 ( 2012 census ) . The total land area of the islands of Tuvalu is 26 km2 .   The first inhabitants of Tuvalu were Polynesians . The pattern of settlement that is believed to have occurred is that the Polynesians spread out from Samoa and Tonga into the Tuvaluan atolls , with Tuvalu providing a stepping stone to migration into the Polynesian Outlier communities in Melanesia and Micronesia .   In 1568 , Spanish navigator Álvaro de Mendaña was the first European to sail through the archipelago , sighting the island of Nui during his expedition in search of Terra Australis . In 1819 the island of Funafuti was named Ellice 's Island ; the name Ellice was applied to all nine islands after the work of English hydrographer Alexander George Findlay . The islands came under Britain 's sphere of influence in the late 19th century , when each of the Ellice Islands was declared a British Protectorate by Captain Gibson of between 9 and 16 October 1892 . The Ellice Islands were administered as British protectorate by a Resident Commissioner from 1892 to 1916 as part of the British Western Pacific Territories ( BWPT ) , and then as part of the Gilbert and Ellice Islands colony from 1916 to 1974 .   A referendum was held in December 1974 to determine whether the Gilbert Islands and Ellice Islands should each have their own administration . As a consequence of the referendum , the Gilbert and Ellice Islands colony ceased to exist on 1 January 1976 and the separate British colonies of Kiribati and Tuvalu came into existence . Tuvalu became fully independent within the Commonwealth on 1 October 1978 . On 5 September 2000 Tuvalu became the 189th member of the United Nations .

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 .