Appearance
Great star coral colonies form massive boulders and domes over 5 feet (1.5 m) in diameter in waters of shallow and moderate depths. In deeper waters, this coral has been observed growing as a plate formation. It is found throughout most reef environments, and is the predominant coral at depths of 40–100 feet (12.2–30.5 m).
This coral occasionally has a fluorescent red or orange color during daytime; it has recently been suggested that this hue is due to phycoerythrin, a cyanobacterial protein. It appears that, in addition to symbiotic zooxanthella, this coral harbors endocellular symbiotic cyanobacteria, possibly to help it fix nitrogen. However more recently, Oswold et al. (2007) showed an absence of functional phycoerythrin in M. cavernosa.