Calcification in Montipora Verrucosa

LOMA LINDA UNIVERSITY Graduate School THE RELATION OF TEMPERATURE TO CALCIFICATION IN MONTIPORA VERRUCOSA by Wa 1te r W. Cox A Thesis in Part1al Fulfillment of the Requirements for the Degree Master of Arts in the Field of Biology August 1971 Each person whose signature appears below certifies that he has read this thesis and that in his opinion it is adequate, in scope and quality, as a thesis for the degree of Master of Arts. , Chairman Ariel A. Roth, Professor, Department of Biology Leonard R. Brand, Assistant Professor, Department of Biology i i I wish to dedicate this thesis to my wife, Sharon, who through her support, patience, and many hours of typing has made this thesis and my education possible. iii ACKNOWLEDGMENTS I wish to thank Dr. Ariel A. Roth, Chairman of my committl~e, for his knowing guidance and pertinent comments during the progress of the research and the writing of this thesis. I, also, sincerely appreciate the helpful suggestions which I received from Conrad Clausen while we were in Hawaii and during our later discussions. I am indebted to Dr. Paul Yahiku for his invaluable assistance with the statistical analysis and to the facilities made available by the University of Hawaii's Institute of Marine Biology. Computational assistance was received from the Lorna Linda Univer sity Scientific Computation Facility supported in part by NIH Grant #RR00276-06. iv TABLE OF CONTENTS PAGE . INTRODUCTION .••• e .. II • • • • • • • II. • • • II • • • • • GENERAL EXPERIMENTAL CONDITIONS 3 LOCATION OF CALCIFICATION 6 INORGANIC EXCHANGE OF CALCIUM 12 RELATION OF CALCIFICATION TO TEMPERATURE. 22/ LITERATURE CITED •.•. 26 v LIST OF TABLES TABLE PAGE , L Calcification rates for three experiments with living coral. • • • • • •••• 6 2. Calcification rates of upper and lower coral surfaces • • • • • 9 3. Inorganic exchange values for three experiments with living and dead coral .••••• 14 4. Inorganic exchange values for dead coral . 18 5. Inorganic exchange values for corals killed with hot and cold sea water • • • • • • • • •••••••• 20 6. Calcification rates for a series of increasing temperature values ••.••••••••••• 23 vi LIST OF FIGURES FIGURE PAGE 1. Diagram of a typical coral sample 7 2. Diagram of a coral branch showing sampling areas 7 3. Percent calcification of sampling areas 10 ~. Inorganic exchange in dead coral 13 5. Inorganic exchange in living coral 16 6. Calcification response to increasing temperature in M. verrucosa . 0 • • • • • • • • • • • • • • • 2~ vii I NTRODUCT ION Reef-building or hermatypic corals are limited in their geographi cal distribution to the warmer waters of tropical oceans. Significant coral growth occurs only in water ranging from 180 C to 330 C, and mas sive reefs form only at temperatures toward the upper end of this temp erature range (Wells, 1957). The coral skeleton is composed almost entirely of calcium carbon ate (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 th~t 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 2 methods of measuring the incorporation of calcium into the s.!<eleton 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 scleractinian. In contrast to previous studies, short per iods of one-half to six hours were used. These shorter periods were used in order to reduce adverse environmental laboratory conditions. GENERAL EXPERIMENTAL CONDITIONS living specimens of M. verrucosa~ three to four inches in diameter, were collected fresh each day from a patch reef in Kaneohe Bay, Oahu, Hawaii, during the Spring of 1970. They were collected in containers under water and brought to the laboratory without being exposed to air. The experiments were started at the same time each day to minim i ze any possible circadian effects. The coral was placed in a clear pl ,exiglass vessel, 6" x 4/1 X 3/1, containing 750 ml of fresh sea water. Air was slowly bubbled through the water to help maintain the pH, oxygen ten sion, and circulation du r ing the experiments (Goreau, 1959). The coral was acclimated to the experimental temperature by placing the plexiglass vessel in a water bath previously adjusted to the desired temperature, and allowing the water in the vessel to adjust to the temperature of the water bath during a one-hour period. A second identical incubation ves sel containing a small amount of Ca-45 approximately (250 ~c) was placed in the water bath adjacent to the acclimation vessel and allowed to come to temperature equi librium at the same time. In a l l experiments, con stant temperature was maintained withint . 50 C. Light was supplied during all experiments by ten 20-watt daylight fluorescent tubes arranged in a semi-circle directly above the water bath. This gave a total light intensity reading comparable to that found on a clear day in mid-afternoon on the reef at an average depth of ten feet. light intensity was determined in each case by using a specially equipped ISCO Model SR spectroradiometer. After the one-ho~r acclimation period, the coral was transferred 3 4 to the incubation vessel containing the Ca-4S. The uptake oJ the ra dioactive calcium should be proportional to the rate of calcification by the coral. The initial radioactivity of the sea water was determin ed by counting two 50 ~l aliquots with a Packard, model 2002, Tri-Carb liquid scintillation spectrometer. Calculations of carbonate deposit ions were based on a normal calcium concentration of 400 mg per liter of sea water (Hill, 1963). The coral was left in the radioactive sea water for one hour and then immersed in distilled water to stop calci fication and kill the polyps (Edmondson, 1928). After 30 to 45 minutes, samples of approximate dimensions 0.5 x 1.5 cm were cut from each piece (Fig. 1) with a Dremel el~ctric cutting tool and rinsed with four chan ges of distil led water, the pieces remaining approximately five minutes in each change. This was done to remove excessive amounts of radioact ive isotope from the tissue. Each sample was then placed in a separate test tube and the tissue was dissolved with two 10-minute washes in 5 ml of IN NaOH in a boiling water bath. The remaining skeletal material was rinsed four times with distilled water to remove all traces of dissolved tissue before drying ~t 10Soc for 1 1/2 to 2 hours. The skeletal samples were dissolved' in 4 ml 3N Hel to which had been added five drops of octyl alcohol to retard violent foaming (Go reau and Goreau, 1960b). The radioactivity of 200 ~l aliquots of each dissolved sample was determined with a liquid scint illation spectrometer as previously mentioned. The observed activity was corrected for radio active decay since, in most instances, there was a period of several days between the time the experiment was run and the time the samples 5 were counted. Other workers have used a variety of methods to express growth in corals. Mayor (1924) measured coral respiration per tissue weight after the corallum had been dissolved in nitric acid. Kawaguti and Sakumoto (1948) compared calcium deposition to coral weight. In M. verruaosa~ the corallum is extremely porous with the tissue extending throughout mos.t of the skeleton. It does not just cover the surface a's is found in several other species (Vaughan and Wells, 1943). Considering this, the methods mentioned above were considered unsatisfactory and a method of expressing calcification per unit of area in contact with the exter nal' medium was devised. Several measurements of the length, width and thickness were made for each sample and a mean value calculated for each. A formula was derived: (2W-T)L+1rTaL (Fig. 1), to express sur face area, where W = width, T = thickness, and L = length. Calcium de position is expressed as fig CaC03 deposited per mm 2 of tissue covering the sample surface and exposed to the surrounding water. LOCATION OF CALCIFICATION Montipora verrucosa is highly variable in growth form. However. large. flat. fan-shaped colonies can be found. usually at depths below 20 feet in Kaneohe Bay. This form is presumably due to the photosyn- (hetic requirements of the symbiotic dinoflagellate algae (zooxanthel- lae) that are found in the tissues of all reef-building corals (Goreau. 1959; Goreau and Hartman. 1963). As light begins to diminish with depth. corals tend to grow so as to expose as much surface area as possible to what light is available; this usually results in spreading and flattening of the corallum.

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