Endolithic algae in living stony corals: algal concentrations under influence of depth-dependent light conditions and coral tissue fluorescence in Agaricia agaricites (L.) and Meandrina meandrites (L.) (Scleractinia, Anthozoa)

DELVOYE, L., 1992. Endolithic algae in living stony corals: Algal concentrations under influence of depth-dependent light conditions and coral tissue fluorescence in Agaricia agaricites (L) and Meandrina meandrites (L.) (Sclereactinia, Anthozoa). Studies Nat. Hist. Caribbean Region 71, Amsterdam 1992: 24-41. The relation between Scleractinians and their endolithic algae was studied in the depth range of 10 to 35 m in Curaçao. Endolithic algal concentrations are found in the skeleton under the living tissue of stony corals and never in dead parts or in coral rubble. The influences of depth-dependent light conditions and coral tissue fluorescence on endolithic algal concentrations were studied in a non-fluorescent and a fluorescent form of both Agaricia agaricites and Meandrina meandrites. Spectroscopy shows that this fluorescence has a photosynthetic potential for both their zooxanthellae and their endolithic algae. The hypothesis that the width of the algal concentrations and their depth below the tissue are correlated with depth on the reef could not be confirmed, with one exception. This only can be explained by the redistribution of zooxanthellae in the coral tissue with increasing depth, making it more transparent. No evidence was found that fluorescence is indeed enhancing the photosynthesis in the endolithic algae of both corals. Ground section histology shows that endolithic algae are in contact with soft coral tissue and are associated with fungi.