- Mediated by algal symbionts, calcification in reef building corals is one of the important processes, which enable coral's growth. In the present study, we used a buoyant weighing technique to study calcification of two coralline species, Stylophora pistillata and the hydrocoral Millepora dichotoma . The colonies were grown in a tank system, in which light, nutrition and water motion were kept constant and temperature was elevated by means of a computerized controlled apparatus. An almost constant rate of calcification was observed in the two species at 22–28 °C. Elevation of the temperature above this range to 29–31 °C caused a slow down in calcification in both species. A grater number of S. pistillata colonies became bleached at temperatures of ≥29 °C, whereas M. dichotoma colonies suffered from bleaching only after three days at 31 °C. For both species, control groups, remained viable during the experimental period. The differences in responses to changes in temperature of the two species may be as a consequence of different adaptive mechanisms or to different susceptibilities of the corals to elevated temperatures. We have shown that elevating temperatures above annual maximal ranges have a significant effect on coral calcification. We also demonstrated that sessile calcified marine organisms having ecological and biomedical significance could be cultured and manipulated under laboratory conditions.