ECOLOGICAL AND PHYSIOLOGICAL DIFFERENCES BETWEEN 2 COLOR MORPHS OF THE CORAL POCILLOPORA-DAMICORNIS

Pocillopora damicornis (Linnaeus) is a ubiquitous branching coral foun d throughout the Indo-Pacific region. Like many other species of coral , P. damicornis displays a large range of morphologies. At One Tree Is land, it occurs as two distinct morphs that are easily distinguished b y the presence or absence of pink pigmentation. The two colour morphs of P. damicornis were found to differ in their distribution and abunda nce in the One Tree Island Lagoon. The brown morph was more abundant t han the pink morph in the shallows (<1 m), whereas the pink morph was more abundant at deeper sites (>3 m). The two morphs also differed phy siologically. The brown morph tended to have a greater calcification r ate than the pink morph, regardless of environmental conditions. Howev er, the difference in the calcification rate between the two morphs be came non-significant under shaded conditions (5% full sunlight), indic ating some degree of physiological plasticity of the morphs. The pink colour in P. damicornis was due to a hydrophilic pigment with a major peak absorbance at 560 nm. The expression of pink pigment had both gen etic and phenotypic components. The brown morph has a reduced genetic capacity to express the pigment relative to the pink morph. On the oth er hand, pigment expression could be induced by light in the pink morp h. Although genetic differences ultimately determine the differences b etween the two morphs of P. damicornis, the extent of pigment expressi on is under some degree of environmental influence.