Shade-Dwelling Corals of the Great Barrier Reef

Shade-dwelling corals were studied from 127 caves, tunnels, and overhangs from a variety of reefs within the Great Barrier Reef Province.Over 3,000 coral colonies were recorded from these shaded habitats, and more than 150 species, mostly herrnatypic, were represented.Three groups of shade-dwelling corals are tentatively distinguished: generally skiophilous (shade-loving) corals, found both in deep water and in shallow but shaded conditions; preferentially cavernicolous corals, growing mostly in shallow, shaded habitats; and shade-tolerant corals, common also in better illuminated parts of the reef, but tolerant of a wide range of conditions.Hermatypic shade-dwelling corals usually have thin, flattened growth forms, and the coralla are generally small, suggesting that low light intensity is restricting both the shape and size of colonies.Apart from an abundance of ahermatypic corals on the ceilings of some cavities, particular fauna1 zones were not detected in different sectors of cavities or at different irradiance levels.This lack of zonation is attributed principally to 2 factors.Firstly, the coral fauna represents only a well shaded but not 'obscure' (dark) aspect of skiophilous communities; secondly, ahermatyplc corals were not found in conditions darker than those tolerated by some hermatypic species.