Green and non-green fluorescing forms of the Caribbean coral Montastrea faveolata (Ellis and Solander, 1786), and their roles in photoprotection

The common Caribbean hermatypic coral Montastrea faveolata (Ellis and Solander, 1786) is found in both green fluorescing and non-green fluorescing morphs. Spectrophotometric analyses of aqueous, fluorescent pigment extracts indicated the presence of a green pigment fluorescing at 504nm in green fluorescing (G) M. faveolata that is absent in non-green fluorescing (nG) M. faveolata. Epifluorescence microscopy revealed that the green fluorescing pigment is localized in the oral ectoderm of G M. faveolata. These observations led to the hypothesis that the green fluorescent pigment serves a photoprotective function, helping protect these corals from bleaching. However, several tests of this hypothesis were unable to confirm a photoprotective role for this green fluorescing pigment and did not support separation of G and nG M. faveolata into 2 morphospecies. These conclusions are based on data indicating no differences between G and nG M. faveolata in their relative abundances at different depths; no differences in their bleaching responses to experimental stressor conditions; no fixed genetic differences based on restriction fragment length polymorphism analyses of coral internal transcribed spacer regions or in preliminary studies of their green fluorescent protein-like genes; no differences in their associated symbionts; no differences in corallite morphometric comparisons and no differences in the presence and distribution of a turquoise fluorescing pigment (peak emission ∼483nm) found throughout the oral ectoderm of the coral host. Overall, while the data cannot dismiss outright the possibility of a photoprotective function for the green fluorescing pigment in M. faveolata, it seems likely that these morphotypes are best explained by another, yet undiscovered, function in these corals.