CELL PROLIFERATION AS AN INDEX OF GROWTH IN CORALS; INCORPORATION OF ^3H-THYMIDINE

Abstract

Preliminary experiments are described which are designed to quantify the rates of DNA synthesis in corals. Whole colonies or small sections of Pocillopora damicornis and other corals were incubated in up to 1 μCi ^3H-thymidine/ml sea water under field and laboratory conditions. The tissue was extracted with hot 2N NaOH and solubilized, and the ^3H-DNA activity was measured with a liquid scintillation spectrometer. Activity was expressed as CPM/mg dry or wet weight or CPM/calice. Specificity and site of the label was confirmed and studied with autoradiography and DNAse extraction. The label was primarily concentrated in the epidermis with maximum activity in the polyp columns and coenosarc. Labeling indices in the tentacles appeared to increase 5 to 7 days after ^3H-thymidine incorporation and this increase was probably due to migration of labeled cells from the polyp column. No ^3H-thymidine uptake occurred in zooxanthellae and very little was taken up by planulae. Labeling between different calices of the coral species was uniform; however, decreasing rates of 3H-thymidine incorporation were seen from apical polyps to basal branches in ramose forms. DNA synthesis in P. damicornis is markedly influenced by minor variations in incubation temperature. Optimum labeling occurred at an acclimation temperature of 31℃ with a rapid decline in rate on both sides. Indirect evidence demonstrates that the temperature optimum for the incorporation of ^3Hthymidine increases in parallel with the temperature of the habitat.