Dark Spots Syndrome: invasion by an endolithic fungus

Coral diseases have become a cause for concern on coral reefs worldwide. However, for most diseases/syndromes, specifics about pathogenesis are lacking. This study involved a histopathological analysis of dark spots syndrome (DSS), also called dark spots disease. Tissue samples from affected and reference colonies were analyzed both macroscopically (dissecting scope) and microscopically (light microscope). The macroscopic analysis revealed that the characteristic dark purple/brown color of DSS lesions was limited to the aboral region of polyp tissue. The calicodermal cells in DSS lesions were hypertrophied and exhibited an increase in eosinophilic granules, which are involved in skeletogenesis. These changes indicated an increase in the metabolic activity of the calicodermal cells and a response to irritation. The density of endolithic fungal filaments was dramatically increased in DSS tissue, and the filaments were observed penetrating the coral tissue in some areas. Thus, the DSS pathogen is believed to be an opportunistic endolithic fungus that presumably invades the coral tissue when the balance between rapid aragonitic deposition (coral defense mechanism), coral host, and endoliths is disrupted. Therefore, DSS may be a good indicator of natural and anthropogenic stress related to coral reef health and skeletogenesis, such as eutrophication, elevated sea surface temperatures, and increases in CO2.

Contact Information

Dr. Jill Borger
University of Miami
Undergraduste Marine Science Program
Coral Gables Florida