The Coral Sea is a marginal sea of the South Pacific off the northeast coast of Australia, and classified as an interim Australian bioregion. The Coral Sea extends 2,000 kilometres (1,200 mi) down the Australian northeast coast. The sea was the location for the Battle of the Coral Sea, a major confrontation during World War II between the navies of the Empire of Japan, and the United States and Australia.
The sea contains numerous islands and reefs, as well as the world's largest reef system, the Great Barrier Reef (GBR), which was declared a World Heritage Site by UNESCO in 1981. All previous oil exploration projects were terminated at the GBR in 1975, and fishing is restricted in many areas. The reefs and islands of the Coral Sea are particularly rich in birds and aquatic life and are a popular tourist destination, both domestically and internationally.
The Australian shore of the Coral Sea is mostly composed of sand. The GBR is too far away to provide significant coral deposits, but it effectively screens the coast from the ocean waves. As a result, most land vegetation spreads down to the sea, and the coastal waters are rich in underwater vegetation, such as green algae. The most common genera of seagrasses are Halophila and Halodule.
The islands of the GBR contain more than 2,000 plant species, and three of these are endemic. The northern islands have 300–350 plant species which tend to be woody, whereas the southern islands have 200 which are more herbaceous; the Whitsunday region is the most diverse, supporting 1,141 species. The plants are spread by birds.
The sea hosts numerous species of anemones, sponges, worms (e.g. Spirobranchus giganteus shown in the photograph), gastropods, lobsters, crayfish, prawns and crabs. Red algae Lithothamnion and Porolithon colour many coral reefs purple-red and the green alga Halimeda is found throughout the sea. The coastal plants consisting of only about 30–40 species, and mangroves occur in the northern part of the sea. Four hundred coral species, both hard corals and soft corals inhabit the reefs. The majority of these spawn gametes, breeding in mass spawning events that are triggered by the rising sea temperatures of spring and summer, the lunar cycle, and the diurnal cycle. Reefs in the inner GBR spawn during the week after the full moon in October, while the outer reefs spawn in November and December. Its common soft corals belong to 36 genera. There are more than 1500 fish species in the reef systems. Five hundred species of marine algae or seaweed live on the reef, including thirteen species of the genus Halimeda, which deposit calcareous mounds up to 100 metres (110 yd) wide, creating mini-ecosystems on their surface which have been compared to rainforest cover.
Crown-of-thorns starfish (Acanthaster planci) is the major predator of the reefs, as it preys upon coral polyps by climbing onto them, extruding its stomach over them, and releasing digestive enzymes to absorb the liquefied tissue. An individual adult can eat up to 6 m2 of reef per year. In 2000, an outbreak of crown-of-thorns starfish contributed to a loss of 66% of live coral cover on sampled reefs. Changes in water quality and overfishing of natural predators, such as the giant Triton, may have contributed to an increase in the number of crown-of-thorns starfish.
There are at least 30 species of whales, dolphins, and porpoises, including the dwarf minke whale, Indo-Pacific humpback dolphin, humpback whale and dugongs. Six species of sea turtles breed on the GBR – the green sea turtle, leatherback sea turtle, hawksbill turtle, loggerhead sea turtle, flatback turtle and the olive ridley.
More than 200 species of birds (including 22 species of seabirds and 32 species of shorebirds) visit, nest or roost on the islands and reefs, including the white-bellied sea eagle and roseate tern. Most nesting sites are on islands in the northern and southern regions of the GBR, with 1.4–1.7 million birds using the sites to breed.
Seventeen species of sea snake, including Laticauda colubrina (pictured), live on the GBR in warm waters up to 50 metres (160 ft) deep and are more common in the southern than in the northern section; none of them are endemic or endangered. The venom of many of these snakes is highly toxic; for example, Aipysurus duboisii is regarded as the world's most venomous sea snake.
There are more than 1,500 fish species, including the clownfish (Amphiprioninae), red bass (Lutjanus bohar), red-throat emperor (Lethrinus miniatus), coral trout (Plectropomus leopardus) and several species of snapper (Lutjanidae). Forty-nine species mass spawn and eighty-four other species spawn elsewhere in their range. With a maximum total length of 0.84 cm (0.33 in), Schindleria brevipinguis, which is native to the GBR and Osprey Reef, is one of the smallest known fish and vertebrate. There are at least 330 species of ascidians on the reef system with the diameter of 1–10 cm (0.4–4 in). Between 300 and 500 species of bryozoans live on the reef.
Saltwater crocodiles live in mangrove and salt marshes on the coast. Around 125 species of shark, stingray, skates or chimaera live on the GBR, in addition to about 5,000 species of mollusc. The latter include the giant clam and various nudibranchs and cone snails.
One study of 443 individual sharks gives the following distribution of their species on the Australian side of the Coral Sea: grey reef shark (Carcharhinus amblyrhynchos, 69%), whitetip reef shark (Triaenodon obesus, 21%), silvertip shark (Carcharhinus albimarginatus, 10%), tiger shark (Galeocerdo cuvier, <1%) and great hammerhead (Sphyrna mokarran, <1%). The interaction rate (free diving) at the Coral Sea reefs ranged from a few to 26 sharks perhour. The rare Etmopterus dislineatus shark species is endemic to the central part of the Coral Sea. It has been observed at depths of 590–700 m on or near the continental slope.