Scleractinian Coral Evolution, Resilience and Disease with a Histological Study of Dark Spot in Agaricia agaricities and Siderastrea siderea

Defense Date


Document Type


Degree Name

M.S. Marine Biology

First Advisor

David Gilliam

Second Advisor

Patricia Blackwelder


Corals made their first appearance in the geologic record during the Triassic period over 237 million years ago. Undoubtedly coral disease has existed since their evolution, but its record can only be examined directly in growth anomalies in preserved skeletons. However, genetics and molecular work has revealed that the evolutionary history of corals and their symbiotic dinoflagellates, Symbiodinium spp. may be important in the ability of corals to survive stress and resist disease. For example, Porties spp. have evolved ultrastructural characteristics which may account for their disease resistant qualities. In addition, in areas of environmental perturbations certain clades of symbiotic algae (clade D) may be present, which are more resistant to stress than other clades. In modern corals, studies of stony coral disease began in the 1970s and histological examination of diseased tissue in corals may provide a measure of coral disease. The number of described coral diseases has grown to the thousands, and distribution worldwide includes the Indo- Pacific and Red Sea. This review initially discusses the evolution of scleractinian corals over geologic time. It is followed by a discussion of coral disease with a focus on Dark Spot Disease, and its description, distribution and host species. A laboratory histological examination of Dark Spot Disease in two species of coral, Agaricia agaricities and Siderastrea siderea is presented. The corals were prepared according to standard histological protocols which revealed an unidentified species of endolithic fungi. Samples infected with Dark Spot Disease displayed tissue changes including breakdown, loss of cellular organization, zooxanthellae expulsion and mucocyte degradation.

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