A coral specialist from the Netherlands has reported the discovery of a new coral species that lives on the ceilings of caves in Indo-Pacific coral reefs.

Reef corals in shallow tropical seas normally need the symbiotic algae for their survival and growth. Without these algae, many coral reefs would not exist. During periods of elevated seawater temperature, most reef corals lose their algae, which is visible as a dramatic whitening of the reefs, a coral disease known as bleaching.

Most reef corals generally do not occur over 40 m depth, a twilight zone where sunlight is not bright anymore, but some species are exceptional and may even occur much deeper. At greater depths, seawater is generally colder and corals here may be less susceptible to bleaching than those at shallower depths.

The new coral, named Leptoseris troglodyta, was described in a paper in the journal ZooKeys by Dr Bert Hoeksema of Naturalis Biodiversity Center in Leiden. The word troglodyta is derived from ancient Greek and means ‘one who dwells in holes,’ a cave dweller.

L. troglodyta differs from its closest relatives by its small polyp size and by the absence of symbiotic algae, so-called zooxanthellae. Its distribution range overlaps with the Coral Triangle, an area that is famous for its high marine species richness.

The discovery sheds new light on the relation of reef corals with symbiotic algae. The new species has adapted to a life without them. Consequently, it may not grow fast, which would be convenient because space is limited on cave ceilings.

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Bibliographic information: Hoeksema BW. 2012. Forever in the dark: the cave-dwelling azooxanthellate reef coral Leptoseris troglodyta sp. n. (Scleractinia, Agariciidae). ZooKeys 228: 21; doi: 10.3897/zookeys.228.3798