Blue coral, Helicopora coerulea, below, is found in the Pacific and Indian Oceans below 2 m on reefs exposed to wave action. It is the iron salts that give the coral its blueish colour and, hence, its common name. It has remained unchanged since the Cretaceous. Each polyp has eight tentacles. It is often found in marine aquaria, and is now (2016) classed as vulnerable due to collection, bleaching, habitat destruction and climate change.
Above is Lophelia pertusa. It is classed as a reef-building, stony, deep sea coral, and is the only species in the genus. This particular one was taken between the Hebridean islands of Barra and Coll at a depth of around 22 metres, but it is more usually found from 80 - 3000 metres deep. Because of the depth it has no symbiotic algae, and filters food from the water, so is found in areas with fast currents. It can be found in the North Atlantic, Caribbean, Pacific. It requires a substrate to anchor to, but is not fussy and will make do with man-made structures such as oil rigs. It is slow-growing and can be harmed by certain methods of fishing, and also by oil exploration.
Some Lophelia reefs off the North Carolina coast have been radio carbon dated which shows them to be 40,000 years old, with individual clumps up to 1000 years old. Reefs can grow up to 35 metres height, and one off the Norway coast was recorded as 3 kilometres by 35 kilometres in length. Such reefs form a habitat for a number of fish and invertebrates.
Boulder brain coral, Colpophyllia amaranthus, above, can grow up to two metres in diameter. It is found in tropical waters of the Western Atlantic.
The Starlet coral, Siderastrea siderea above is a stony coral usually found in shallow waters of around 10 m deep, although it can be found as deep as 70 m. It is fairly common in the Caribbean, Gulf of Mexico, around Florida, Bahamas and Bermuda. It is also resilient and can recover from coral bleaching if conditions improve. When alive it is a reddish brown colour.
Maze coral, Meandrina meandrites, above is a stony coral found in the tropical Atlantic in the Caribbean and Gulf of Mexico. It is mainly located on the outer edges of reefs, where colonies can grow up to one metre in diameter. It is usually found at 8 - 30 m deep, but colonies have been found as deep as 80 m. This coral is unusual in that it undergoes natural bleaching. Its symbiotic algae vanish in the autumn, but the coral recovers usually by the end of the year. When alive it is pale grey or brown.
Related pages, main Cnidaria page - main Anthozoa page - main coral page