ECOLOGY AND TAXONOMY OF Halimeda 165 



The lower intensities of this range were initially chosen because they 

 were similar to those commonly used in algal culture including work 

 with siphonaceous algae. Puiseux-Dao (1970) gives a range of approxi- 

 mately 100-300 ft-c for Acetabularia, and Chen and Jacobs (1966) used 

 100 ft-c in their culture of Caulerpa. 



Better growth is obtained, at least initially, at intensities such as 

 700 ft-c. This improvement is often paralleled by increased epiphy-te 

 growth, and the epiphytes can become very difficult to control. The 

 water of small self-contained aquaria also becomes overheated at the 

 higher intensities, necessitating a cooling system. 



Light intensities of approximately 375-500 ft-c are somewhat of a 

 compromise in the range given. Growth as well as vegetative and sexual 

 reproduction occur at these intensities. It is realized, however, that they 

 are considerably below the light intensities of the shallow reef, some of 

 which are recorded in Table XII, using a Gossen Tri-Lux foot-candle 

 meter in an underwater case at two of our north shore Jamaican work 

 sites, Runaway Bay and Glory Be (Section X). They indicate that plants 

 growing at — l-5m to —2m receive approximately 47-73% of the 

 surface light which, on three sunny Jamaican days, about midday, 

 averaged 7530 ft-c. 



It is realized too that the unusual segment shapes often obtained in 

 culture (Fig. 16; Colinvaux et al., 1965, Fig. 3) may be the result of 

 growing these plants in intensities equivalent to those of the blue- 

 lighted regions in the reef at about — 40 m to — 50 m. 



7. Epiphyte control 



A wide range of organisms, plant and animal, are introduced on the 

 cleaned Halimedae thalli. A number of them grow very well in the 

 system, and if uncontrolled will usually overgrow the Halimeda popula- 

 tion eventually. Some of the introduced organisms also grow on the 

 sand and rock substrates, as well as on the glass sides of the aquaria. 

 Epiphyte control is important for aquaria which will be maintained 

 longer than about six weeks, and for shorter-term aquaria when light 

 intensities are 1000 ft-c or higher. 



The contaminant plants include a number of soft red and green, as 

 well as blue-green, algae. There have also been occasional dense 

 dinofiagellate blooms. 



Phytoplankton blooms, if troublesome, can be controlled by chang- 

 ing the water and using a filter system. Since some inoculum remains on 

 the Halimedae and on the sand or rock substrate, the improvement may 

 only be temporary. 



