Light and the bioenergetics of a symbiotic coral [Symbiodinium microadriaticum, zooxanthellae, dinoflagellates]

Colonies of the coral Stylophora pistillata growing at high light can obtain all the reduced carbon needed for animal respiration from photosynthesis by symbiotic zooxanthellae. In contrast, colonies in shaded reef areas must acquire 60% of their reduced carbon heterotrophically. More than 90% of the carbon fixed by zooxanthellae is translocated to the animal host in both light regimes, but very little is assimilated, apparently because the translocated products are deficient in nitrogen. Thus, the coral's overall growth efficiency is similar to that of aquatic herbivores that forage actively.