Endolithic Microbes in Coral Skeletons: Algae or Bacteria?

Abstract

Microbial endoliths exist ubiquitously, in several terrestrial and marine environments, including inside pores of coral skeletons. Although coral skeletons provide a harsh environment due to limited light and circadian fluctuations in pH and oxygen, visible green, black, brown, and red bands comprised of cyanobacteria, fungi, bacteria, and red and green algae, respectively, are usually observed in the skeletons of corals. Based on microscopic observation and culture-based methods, many studies showed algae, fungi, and cyanobacteria as dominant microorganisms in coral skeleton and also suggested that the endolithic microbes may be nutrient source of their coral hosts. Recently, various bacteria in coral skeletons have been illustrated, thanks to culture-independent methods. This chapter focuses on (1) challenges of environment in coral skeleton to endolithic microbes, (2) the endolithic microorganism and potential roles in coral skeletons, and (3) perspectives.