Cactus Coral

Colonies of this species have vertical, irregular, two-sided fronds about 5 cm (2 in) tall and not more than 5 mm (0.2 in) thick. The corallites housing the polyps are very shallow and form widely separated rows parallel to the margins of the fronds. The bases of these fronds may be dead while the upper parts are still alive supported by the skeletal tissue below. The fronds may be clustered together in a supercolony formed from one or more individual colonies and extending for several metres (yards) across the seabed. This is a zooxanthellate species of coral, with symbiotic microscopic algae living in its tissues. It is an olive green or a brownish colour.

Pavona cactus is found in the tropical Indo-Pacific, its range extending from the Red Sea and East African coast to Japan, Tahiti and Australia. It is found in turbid but calm waters, on upper reef slopes and in shallow lagoons at depths down to 40 metres (130 ft).

Although this coral is common and has a wide range, the International Union for Conservation of Nature lists this species in its Red List of Threatened Species as being "Vulnerable". Under adverse conditions, such as a rise in sea temperature, this coral may expel its zooxanthellae and become bleached. It is then much more susceptible to disease. Coral reefs in general are under threat from a decline in the quality of the habitat through mechanical damage, pollution, sedimentation, ocean acidification and global warming and Pavona cactus faces another threat in that it is collected for the aquarium trade.