MORPHOLOGY AND TRACE METAL CONTENT: A PROXY FOR BLEACHING IN PORITES DIVARICATA

Morphology and trace metal content of scleractinian corals have previously been used as proxies for past environmental conditions, but no proxies for the health of corals currently exist. Skeletal material associated with bleached and non-bleached tissue from Porites divaricata was analyzed with SEM and ICPMS. Differences in both morphology and trace metal content were noted between samples associated with bleached and non-bleached tissue.

SEM analysis showed that skeletal corallites associated with unbleached tissue appeared normal, with well-defined septal denticles. Skeletal corallites associated with bleached tissue had weakly-defined septal denticles, many appearing rudimentary. Statistically significant differences in trace metal/Ca ratios were found for seven elements between skeletal material associated with bleached and non-bleached tissue, when analyzed with ICPMS. The presence of these differences suggests that the processes of skeletogenesis and the uptake and deposition of trace metals in the skeleton are affected by bleaching. It is possible that such indicators may be observed in the fossil record as indicators of environmental stress and bleaching in scleractinian corals.