ECOLOGY AND TAXONOMY OF Halimedci 



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Fig. 93. Part of a buttress. Halimedae are rare in this region of Jamaican reefs. They 

 are also absent from the sand at the bases of the buttresses. 



On the hard surfaces provided by the fore -reef slope and deep fore- 

 reef, the genus is more successful, and at depths of— 61-5mto — 91m 

 on the deep fore-reef of Discovery Bay cover by Halimeda was estimated 

 as 10%, with cryptica occupying up to 60% of the available space on 

 parts of promontories (Moore et al., 1976). 



(b) Unconsolidated substrates. The Halimedae of sands and muds are 

 principally members of the Rhipsalis section, although opuntia and 

 gracilis, in their sprawling growth, are sometimes associated with such 

 substrates. The greatest cover achieved by these Halimedae for the 

 parts of the Glory Be reef surveyed was in the shallow sandy flats of 

 regions 3 and 4. These flats, although sometimes barren of macro- 

 vegetation, generally supported large populations of sea grasses, the 

 Halimeda species monile and incrassata, and the related calcareous 

 green algae Penicillus (often capitatus) and Udotea flabellum. The 

 resultant cover was essentially closed, and although the sea grass 

 Thalassia testudinum Konig was a clear areal dominant, about 40% 

 cover was provided by the above three genera of calcareous green algae, 

 with the two Halimeda species accounting for about 15%. A fairly 

 closed plant cover also existed in the sandy patches of the inshore reef 

 flat (4), but much of it was provided by a spongy turf of about 16 cm 



