166 



MARSH 



dark. Goreau concluded that the effect of light on coral 

 growth is at least partly mediated through the zooxanthel- 

 lae. A few experiments were also done with the calcareous 

 red alga Porolithon^ Goreau's pioneering study greatly 

 influenced the thinking and research of later researchers. 



Clausen and Roth (1975) looked at the effect of tem- 

 perature and temperature adaptation on calcification rates 

 in the coral Pocillopora damicornis^ They reported that 

 temperature has a marked effect on the rate of ^^Ca 

 uptake but that the effect varies depending upon the tem- 

 perature history of the coral (interpreted as meaning that 

 temperature adaptation occurs). The temperature optimum 

 shifted from 27°C to 31 °C, depending upon the tempera- 

 ture at which the corals had been previously held. Clausen 

 and Roth also noted the great variability in rates of Ca 

 uptake even when all experimental material and conditions 

 were as constant as could be achieved. 



Chalker (1976) studied the mechanism of calcium 

 transport during skeletogenesis in the corals Acropora cer- 

 uicornis and A. formosa. He found that light-enhanced cal- 

 cification results from the active transport of calcium ions 

 and shows saturation enzyme kinetics. On the other hand, 

 dark calcification, as simulated by the addition of the pho- 

 tosynthetic inhibitor DCMU, results from enzyme-mediated 

 isotopic exchange. Strontium was found to be a competi- 

 tive inhibitor of both light-enhanced and dark calcification. 

 Chalker concluded that his data refuted the diffusional 

 model for calcium movement in hermatypic corals. He also 

 reported that light-enhanced calcification creates a signifi- 

 cant energy demand which may possibly be satisfied by 

 the oxidation of low-molecular weight compounds translo- 

 cated from the symbiotic algae to animal tissue. In refer- 

 ence to the earlier work of Muscatine and subsequent 

 researchers, Chalker suggested that other organic com- 

 pounds besides glucose, glycerol, and alanine should be 

 examined for such possible translocation. 



Knutson et al. (1972) and Buddemeicr et al. (1974), 

 working at a different level of biological organization, 

 reported cyclic variations in the radial density of coral 

 skeletons, as revealed by X-radiography of thinly sliced 

 samples. The presence of bands of radioactivity deposited 

 in the coral structure by atomic testing at known dates 

 allowed calibration of these growth bands, which were thus 

 found to be annual. This "retrospective analysis" of coral 

 growth opened up a new area of research which was then 

 followed up by Buddemeier et al. The calibration pro- 

 cedure took advantage of the unusual situation created by 

 previous atomic testing at Enewetak and could not have 

 been accomplished at most other sites. 



Knutson and Buddemeier (1973) followed up on the 

 initial work by examining the distributions of radionuclides 

 in reef corals. They reported that historic variations in the 

 specific activity of surface oceanic ^Sr and ^''C could be 

 reconstructed from band-dated colonies. Studies of the *^Sr 

 content of Enewetak corals suggested that the lagoon com- 

 munity was acting as a long-term source of that radioiso- 

 tope. Knutson and Buddemeier further reported that they 

 could detect no significant changes in coral growth rates, 



patterns, or skeletal structures related to previous nuclear 

 weapons tests. 



Highsmith (1979) studied the relationship between 

 coral growth rates and the environmental control of density 

 banding in the massive species Favia pallida, Goniastrea 

 retiformis, and Pontes lutea. Of these species, Goniastrea 

 has the densest skeleton but an intermediate growth rate; 

 Pontes grows more rapidly. All three species grow indeter- 

 minately and at a declining growrth rate with increasing 

 depth. Favia was found to have a linear growth rate of 5.7 

 mm yr^' and a mass growth rate of 0.82 g cm~^ yr '; 

 Goniastrea had rates of 6.8 mm yr~^ and 1.16 g cm~^ 

 yr~', resfsectively; and Pontes, rates of 7.6 mm yr~' and 

 1.07 cm~ yr~\ respectively. 



Highsmith found that the high-density portion of 

 annual-band couplets is produced during late summer and 

 fall when water temperature is highest and light is possibly 

 reduced; low-density portions of the annual couplets are 

 formed during seasonally lower temperatures and possibly 

 higher light availability In deep>er water, the high-density 

 portions of the skeletons account for a greater proportion 

 of linear and mass growth than in shallower water; the 

 high-density portions of the skeletons also account for a 

 greater proportion in those corals with slower growth 

 rates. This led to the prediction that linear growth will be 

 highest where conditions are most favorable for deposition 

 of low-density skeletal material. Highsmith further 

 proposed that matrix production in the skeleton is more 

 closely linked to activities of the zooxanthellae than is 

 extracellular calcification and that the former tends to 

 decline sharply at temperatures above or below the 

 optimum of 27°C or with decreasing light. On the other 

 hand, extracellular calcification is [Xjsitively correlated with 

 temperature, at least up to 31°C to 32°C. 



Nitrogen Flux in Individual Populations 



Interest in the nitrogen flux of individual populations 

 has been slower to develop than interest in oxygen metab- 

 olism and calcification and has followed the previously dis- 

 cussed studies of nitrogen flux in reef communities as a 

 whole. Aside from nitrogen-fixing algae and bacteria, 

 interest has focused primarily on corals (e.g., D'Elia and 

 Webb, 1977; Muscatine and D'Elia, 1978), with the large 

 reef-flat populations of holothurians being the only other 

 major population to be studied (Webb et al., 1977). 



D'Elia and Webb (1977) studied dissolved nitrogen flux 

 in corals and focused primarily on rates of nitrate uptake. 

 Working with intact coral colonies in incubation chambers, 

 they found uptake to be light-dependent. Uptake was local- 

 ized in the coral tissue or its algal symbionts and did not 

 occur in the bare skeletons left when living coral tissue 

 with its contained zooxanthellae was removed. Uptake was 

 found to fit the active-transp>ort model of enzyme kinetics, 

 with a half-saturation constant of 249 ± 247 nM and a 

 maximum uptake rate of 5.69 ± 1.11 ng-atoms mg N~' 

 min~' (29.9 ± 7.1 ng-atoms N mg chl a~^ min~'). 

 There appeared to be a threshold ambient nitrate concen- 



