ECOLOGY AND TAXONOMY OF Holimeda 211 



available because of the difficulty of maintaining them in culture) it is 

 not possible to calculate their contribution, but there is clearly the 

 possibility for a large component of total production to be included. 



And to the pinnacle Halimedae must be added those of the deep 

 fore-reef. In Jamaica, at depths of —61*5 m to —91 m, there are very 

 dense populations of cryptica and lesser populations of copiosa (an 

 Opuntioid form) which locally attain 60% cover (Moore et al., 1976). It 

 seems likely that similar growths are prevalent outside the fore-reef of 

 atolls, though no census data are available because of the difficulties 

 of diving operations at these sites. Some considerable part of the 

 production of the deep fore -reef, which contributes heavily to the 

 sediments of the island slope of Jamaica (Fig. 86), may be swept up in 

 the vigorous onshore currents of these atolls, to be deposited later in the 

 still waters of lagoons. 



In conclusion it may be said that the bimodal production suggested 

 by Smith and Kinsey (1976) seems to accord with the drill-core data 

 and the scanty Holimeda production figures. It is necessary to look at 

 the older literature describing very high production figures for the 

 whole reef, like those collected by Chave etal.{\^l\), with the realization 

 that they do not imply actual growth of coral reef ridge itself, but the 

 carbonate accumulations of the whole reef system. The largest part of 

 this accumulation is probably in the large areas of the quiet lagoons. 

 Halimeda is a very significant contributor to this accumulation both 

 from the production of sand-dwelling plants in shallow water, and 

 from the rock-hanging forms of the pinnacles and possibly of the deep 

 fore-reef. 



X. Halimeda Distribution in two Reef Systems 



This chapter describes two reef systems from the point of view of 

 Halimeda, or at least from the point of view of an investigator asking 

 questions about reefs as the habitat of Halimeda. As with all reef 

 studies there are constantly in the background questions of how the 

 reefs were built, but these questions are again likely to be phrased 

 from the point of view of Halimeda: "In what way have the Halimeda 

 populations contributed to the structure and mass of the reef?" It is 

 suggested that this might be a timely bias, since the great majority of 

 studies on coral reef systems have been designed on the unspoken 

 assumption that the essential process in reef-building is the construc- 

 tion of the coral framework. It has already been mentioned (Section 

 IX) that the classic studies on reef productivity, like those of Sargent 

 and Austin (1954) and Odum and Odum (1955), are of small sections 



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