THE PHYSIOLOGY OF SKELETON FORMATION IN CORALS. I. A METHOD FOR MEASURING THE RATE OF CALCIUM DEP-OSITION BY CORALS UNDER DIFFERENT CONDITIONS THOMAS F. GOREAU 1 Department of Physiology, University College of the Wcsi Indies, and The New York Zoological Society The purpose of this study is to examine the rate of growth of reef-building corals by measuring the calcium deposition in the skeleton with the aid of a new method using radioactive calcium-45 as tracer. With this procedure it was possible to determine calcification rates in the different parts of coral colonies, and to estimate quantitatively the effect of light and darkness, zooxanthellae and carbonic anhydrase inhibitors on skeletogenesis. Numerous attempts have been made in the past to estimate the growth rates of reef-building corals, mostly by letting weighed and measured coral colonies grow in their natural habitat for periods of months to years (Agassiz, 1890; Abe, 1940; Boschma, 1936; Edmondson, 1929; Kawaguti, 1941; Ma, 1937; Mayor, 1924; Motoda, 1940; Stephenson and Stephenson, 1933; Tamura and Hada, 1932; Vaug-han, 1919). Recently, Kawaguti and Sakumoto (1948) tried, by a chemical method, to determine the rate of calcium uptake of corals in light and darkness. Using calcium-45 as tracer, we have developed a rapid and precise method for measuring the rate of incorporation of calcium into the coral skeleton under con-trolled laboratory conditions (Goreau, 1957). The preliminary experiments, de-scribed here, were carried out on the following coral species : Manicina areolata (Linne), Cladocora arbuscula (Lesueur), Porites divaricata (Lesueur), Acropora prolijcra (Lamarck), Madracis decactis (Lyman) and Oculina diffnsa (Lamarck) from Jamaica, B.W.I.; Acropora conferta (Quelch) from Eniwetok Atoll; and Montipora vcrrucosa (Lamarck), Porites compressa (Quelch), Pocillopora dami-cornis (Linne) and Porolithon sp., a coralline alga, from Hawaii. All the madreporarian corals used in these experiments are shallow-water forms which contain zooxanthellae. Among these, Oculina diffnsa is the only species which has not been collected from reefs, but it is common in Kingston Harbour where it grows on rocks on a muddy bottom (Goreau, 1958). The Hawaiian Porolithon listed above is a calcareous alga of the family Corallinaceae, representa-tives of which are important reef builders in the Central Pacific (Emery, Tracey andLadd, 1954). PROCEDURE Freshly collected coral colonies in good condition were put into glass vessels containing filtered sea water and fitted with tight covers. Aeration, circulation and pH were maintained by bubbling a slow stream of air through the water. The 1 Mailing address : Department of Physiology, University College of the West Indies, Mona St. Andrew, Jamaica, B.W.I. 59
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