Factors affecting calcification processes in the hermatypic corals Pocillopora damicornis and Porites compressa

Temperature affects coral distribution and it also affects rates of physiological processes. Little attention has been given through, to the relation between the basic effect of temperature on reaction rates at the molecular level and its effect on coral distribution at the organismic level. Incubating coral samples in sea water containing 45Ca incorporation as a measure of calcification rate, I studied the effects of temperature on calcification in two coral species, P. damicornis and P. compressa. CaCO3 deposition was chosen because of its basic importance in reef formation. Immediate effects of temperature on calcification rates were studied, as well as temperature adaptation to seasonal and geographic changes in natural temperature. Temperature has a marked effect on rate--an effect that varies depending on the temperature history of the coral (i.e., temperature adaptation occurs). P. damicornis showed both at 27°C and 31°C temperature optimum--one or the other being dominant depending on the natural water temperature to which the coral was adapted. P. compressa may also have two optima but the data are not as conclusive. The optimum temperatures may indicate two isoenzymes or two alternate metabolic pathways involved in the calcification process. The laboratory method for study of growth in corals seems to be the most practical quantitative approach. A possible disadvantage of this method however, is that calcification rates obtained in the laboratory may not be comparable to natural rates. Possible sources of error in estimating growth rates from the laboratory calcification rates were investigated. During long incubations (several hours or more) a significant decrease in rate was observed. However, very short incubations proved feasible and were used. Inorganic exchanges of 45Ca across the living coenosarc was not significant. Time of day, light conditions, and position of samples within the colony may affect calcification rate. Terminal parts of branches calcified serveral times more rapidly than lateral parts. P. damicornis calcified less rapidly at night than in the day. The calcification rate of P. damicornis seemed more sensitive to ecological factors than P. compressa. Being aware of these factors I estimated growth from calcification rates and found that the rates obtained in the laboratory were comparable to those in the field.