Dendrogyra

Lore & Background

Pillar coral forms an encrusted base from which grow vertical cylindrical, round-ended columns. It can reach a height of 3 m (10 ft) with pillars more than 10 cm (4 in) wide, though usually much smaller. The corallites are smaller than 1 cm (0.4 in) in diameter and arranged in shallow meandering valleys with low ridges. The skeleton is not usually visible because polyps are typically extended during the daytime, unlike most other coral species. The mass of undulating tentacles gives the coral a furry appearance, and it is usually some shade of beige or brown.

Pillar coral is a zooxanthellate species, with symbiotic dinoflagellate algae living within its tissues. These algae give the coral its brownish colour and restrict it to shallow water where sunlight can penetrate. It is a slow-growing, long-lived species. If the whole colony is dislodged and topples over, new cylindrical pillars can grow vertically from the fallen coral. Some specimens show evidence of this happening more than once, and the history of the colony can be deduced from its shape. If a pillar gets detached and becomes lodged in a suitable position, it can continue to live, sending up new pillars from the base and other parts of the column.

Each pillar coral clonal colony is either male or female (gonochoric), though hermaphroditic events have been recorded. Sexual reproduction takes place with gametes released into the water column where fertilisation occurs. The larvae are planktonic and drift with currents before settling on the seabed to found new colonies.

Reader's Guide

Pillar coral is listed as Critically Endangered on the IUCN Red List under criteria A2bce. This status reflects low recruitment and survival rates of juveniles, and its particular susceptibility to both bleaching and white plague disease. It is resistant to strong wave action but can be wrecked by hurricanes and tropical storms; however, broken fragments regenerate well. The advent of stony coral tissue loss disease in Florida and the Caribbean is causing local extinctions and may have species-level effects, as this species is infected at an early stage of the disease progression. The species is functionally extinct in Florida, US, and mostly survives in captivity. It is a gonochoric species that was never particularly common within its range, making its reproductive potential lower than might otherwise be expected. Some localities where it is found are in marine parks, where it should be safe from human disturbance. The species is the only member of its genus, making its loss particularly significant for biodiversity.

Did You Know?

• Pillar coral is one of the few hard corals in which polyps can commonly be seen feeding during the day.
• It is the only species in the monotypic genus Dendrogyra.
• If a colony topples over, new vertical pillars can grow from the fallen coral.