The relation of temperature to calcification in Montepora verrucosa

Abstract

Reef-building or hermatypic corals are limited in their geographical distribution to the warmer waters of tropical oceans. Significant coral growth occurs only in water ranging from 180 C to 330 C, and massive reefs form only at temperatures toward the upper end of this temperature range (Wells, 1957). The coral skeleton is composed almost entirely of calcium carbonate (CaC03) with the crystalline structure of aragonite; calcite is completely absent. H. Lowenstam (1954) has suggested that the failure of corals to produce any calcite may be the factor influencing the smaller number of scleractinian species in cooler water. Organisms that can produce both aragonite and calcite tend to produce calcite during colder seasons and aragonite during warmer seasons. Thus, by their nature of calcification, corals may physiologically limit their geographical distribution. Physiological study of corals began in the early nineteenth century. Towards the latter part of the century, some work with growth rates of reef corals was started by Alexander Agassiz (1890). Similar studies have since been made by others (Abe, 1940; Boschma, 1936; Edmondson, 1929; Kawaguti, 1941; Ma, 1937; Mayor, 1924; Motoda, 1940; Stephenson and Stephenson, 1933; Tamura and Hada, 1932; and Vaughan, 1919). All of these stud ies involved the technique of allowing the coral to grow for long periods, days to years, in its natural environment, with size and weight measurements being taken at periodic intervals. However, more recent attempts to estimate growth rates have involved chemical methods of measuring the incorporation of calcium into the skeleton under controlled laboratory conditions (Kawaguti and Sakumoto, 1948; Coreau, 1959; and Goreau and Goreau, 1959, 1960a, 1960b). The present study employed a procedure involving the incorporation of radioactive calcium-45 into the coral skeleton to determine the optimum temperature for calcium deposition in Montipora verrucosa, a common Indo-Pacific hermatypic sc leractinian. In contrast to previous studies, short periods of one-half to six hours were used. These shorter periods were used in order to reduce adverse environmental laboratory conditions.