by B. N. Sullivan
Although the appearance of these corals may look similar to the underside of a mushroom cap, the resemblance stops there. These are stony corals; they are not soft.
While most hard coral species live as colonies of polyps that aggregate and form calcareous structures, most species of corals in the Fungiidae family live as solitary corals rather than as colonies. In addition to being solitary, most of the corals in this family are free-living -- that is, they are not attached to the substrate.
The photos on this page show two examples of solitary, free-living corals from the Fungiidae family. Both of these are Indo-Pacific species, widely distributed across the region from the Red Sea in the west, to the islands of the central Pacific. Both of the corals shown here were photographed in Hawaii.
The image near the top of this page is Fungia scutaria, the most common mushroom coral in Hawaiian waters. F. scutaria also is the largest of the mushroom corals found in Hawaii. It typically grows into an oblong or oval shape that can reach a size of about seven inches (18 cm) in length, although most of the individuals we have seen are about half that size.
Both of these species begin the post-larval stage of their lives attached to the substrate by a stem-like structure. As the juveniles mature and take on their adult form, the stem gradually dissolves, and they become free-living adults.
Mushroom corals usually are found in sandy areas near the base of stands of reef-building corals, and on rubble slopes at the outer edges of fringing reefs. They are found less frequently in shallow areas where they would be subject to being tumbled about by waves and surge. They prefer more sheltered environments.
Mushroom corals are known to feed on plankton and the metabolic by-products of the symbiotic algae that live in their tissues, but a team of Israeli scientists carrying out a reef survey in the Gulf of Aqaba (Red Sea) recently witnessed mushroom corals feeding on -- of all things -- rather large jellyfish! They documented the species Fungia scruposa feeding on a Moon Jelly (Aurelia aurita). You can read about this amazing discovery in this article (with photos) published by the BBC: Predatory coral eats jellyfish.
See also: Alamaru, A, et al. (2009). Opportunistic feeding by the fungiid coral Fungia scruposa on the moon jellyfish Aurelia aurita. Coral Reefs. DOI: 10.1007/s00338-009-0507-7