Pathology of growth anomalies in massive Caribbean corals of the family Faviidae

Abstract

Growth anomalies (GAs) are a morphologically diverse and poorly understood group of lesions affecting corals. The aim of this study was to describe the prevalence and morphology of GAs affecting the faviid corals Diploria labyrinthiformis, Pseudodiploria strigosa, Psudodiploria clivosa, and Colpophyillia natans on St. Kitts. Three gross morphological variants of GAs (exophytic, nodular, and ruminate) were equally prevalent, together affecting 7.8% of corals surveyed across 5 reefs. Prevalence varied by reef and coral species, being highest in C. natans (35.7%). Median colony diameter was larger in corals with GAs relative to those without (Mann-Whitney U test, P < .001). Histopathological examination of exophytic GAs consistently showed corallite and polyp gigantism ( n = 7), characterized by polyp enlargement and retained microanatomical structures. In contrast, nodular GAs ( n = 9) were consistently hyperplasia of the basal body wall with skeletal dystrophy, composed of micronodular skeletal deposits with abundant hyaline lamellae, bordered by calicoblastic epithelial hyperplasia, interspersed with distorted gastrovascular canals and islands of mesoglea. Endolithic organisms, particularly fungi and algae, were common among GA and apparently healthy biopsies. While pathogenesis of these lesions remains uncertain, a neoplastic basis for GAs on Caribbean faviids could not be established using diagnostic criteria conventionally applied to tumors of vertebrate taxa, in line with other recent observations of coral GAs.