Identification of a protist-coral association and its possible ecological role

Recent investigations of coral-associated microbial communities have revealed that coral surfaces are replete with microorganisms that may play important roles in colony wellbeing. In this study we show that the surfaces of a number of large polyped coral species are covered by a layer of aggregate-like microorganisms. These microorganisms are embedded in the mucus and in the tissue of solitary coral Fungia granulosa and in a number of faviid species. They are found on the coral surface and in the coral tissue. They are dispersed in a patchy distribution, with the highest density occurring in the area of the polyp mouth. Microscopic investigation revealed that the microorganisms found on and in tissues of F. granulosa are approximately 5 to 30 μm in diameter and are made up of unique coccoid bodies of approximately 1 μm in diameter. Transmission electron microscopy (TEM) revealed that they contain a nucleus, mitochondria and golgi, indicating they are eukaryotic in nature. The morphological data lead us to identify these organisms as stramenopile protists. This premise was strengthened by molecular investigation of samples taken from the surface mucus of the coral F. granulosa. The possible role of these protists is discussed.