Abstract
The illuminated parts of many hermatypic corals have higher levels of photosynthetic pigments and symbiotic dinoflagellates belonging to the genus Symbiodinium than the shaded parts that often appear pale. In the field, we observed that the perforate coral Montipora capitata restored this original pattern after being overturned by disturbance. Here, two hypotheses were tested to account for this phenomenon, using experimentally overturned M. capitata plates in the laboratory. Our results indicated that restoration of the original pattern was not due to changes in chlorophyll a content per Symbiodinium cell or alterations in symbiont density through differential division rates. Instead, Symbiodinium cells appear to be translocated within the colony. This finding demonstrates an additional photoacclimatory process for hermatypic corals, whereby new Symbiodinium cells proliferate in shaded parts of the colony where they are protected from potentially high levels of solar irradiance and are then transported to illuminated parts of the colony (and possibly released from the colony when damaged). Additional studies in other species are required to determine if this dynamic spatial and temporal process is a general property of the hermatypic coral-Symbiodinium relationship.
