Calicoblastic neoplasms in Acropora palmata, with a review of reports on anomalies of growth and form in corals.

Colonies of the elkhorn coral (Acropora palmata), possessing raised, whitened, irregularly shaped skeletal protuberances, were discovered at Carysfort Reef and Grecian Rocks, Key Largo National Marine Sanctuary, Key Largo, FL. These lesions exhibited relatively rapid growth and spread along the branches, as polyps were overlaid by coenosteal skeletal material. Histopathological examinations of the soft tissues surrounding and extending into the skeletal masses revealed proliferation of gastrovascular canals and associated calicoblastic epidermis, with loss of normal polyp structures and zooxanthellae. The slightly atypical tumor calicoblasts were cuboidal to columnar, resembling those found in the rapidly growing apical tips. Stable carbon isotope ratios of skeletal samples revealed that the tumor skeleton was isotopically lighter than the skeleton in the normal or apical track regions, indicative of higher tissue metabolic rates and lack of carbon isotope fractionation by zooxanthellae. This condition appears to be a neoplasm of the coral, and it is proposed that it be classified "calicoblastic epithelioma." Several different types of abnormal skeletal deposition, possibly the result of neoplastic processes, have been reported to occur in stony corals and are here reviewed.