Кораллы-столбы: описание и распространение.

Species of coral

Pillar coral (Dendrogyra cylindrus) is a hard coral (order Scleractinia) found in the western Atlantic Ocean and the Caribbean Sea. It is the only species in the monotypic genus Dendrogyra. It is a digitate coral that is, it resembles fingers (Latin digites) or a cluster of cigars, growing up from the sea floor without any secondary branching. It is large and can grow on both flat and sloping surfaces at depths down to 20 m (65 ft). It is one of the few types of hard coral in which the polyps can commonly be seen feeding during the day.

Pillar coral forms an encrusted base from which grow vertical cylindrical, round ended columns. This coral can grow to a height of with pillars more than wide but is usually much smaller than this. The corallites from which the polyps protrude are smaller than in diameter and arranged in shallow meandering valleys with low ridges in between. The skeleton of the coral is not usually visible because the polyps are typically extended during the daytime, unlike most other coral species.

Pillar corals are found in the warmer parts of the western Atlantic Ocean and the Caribbean Sea. Within its range, D. cylindrus is common in some places, but rare in other seemingly suitable locations. Some of the islands in the Bahamas have plentiful numbers of colonies as does the north coast of Jamaica. It used to be common on the reefs off the coast of Florida but has suffered from over collection there. It seems to be absent from Bermuda and the coasts of Panama and Colombia. It usually grows on level or slightly sloping parts of the reef at depths between .

Pillar coral is a zooxanthellate species, with symbiotic dinoflagellate algae living within the tissues. In sunlight these undergo photosynthesis and most of the organic compounds they produce are transferred to their host, while they make use of the coral's nitrogenous wastes. These algae give the coral its brownish colour and restrict it to living in shallow water into which the sunlight can penetrate. Sexual reproduction takes place with gametes being released into the water column where fertilisation takes place. The larvae that develop from the eggs are planktonic and drift with the currents before settling on the seabed to found new colonies. Finally, it is a gonochoric species which was never particularly common within its range, making its reproductive potential lower than might otherwise be expected. The species is functionally extinct in Florida, USA, and mostly survives in captivity.