ECOLOGY AND TAXONOMY OF Halimeda 



297 



though relative abundance and diversity appear to decrease with 

 depth. 



Rock habitats for the species with this habitat strategy are available 

 on the reef crest, much of the back-reef, in the inter-island channels, at 



Table XXXIV. Species and Abundances of Halimeda and Tydemania at 

 Enewetak Atoll, December 1975" 



« From Hillis-Colinvaux (1977). 



** 1 = a few species found by diligent searching; 2 = common, but a minor part of 

 Halimeda community; 3 = abundant, a major part of the Halimeda cover. 



the lagoon borders, and on the pinnacles and mounds of the lagoon 

 floor. Unconsolidated material floors most of the lagoon, but there is 

 little sand habitat elsewhere except for patches in the reef and its 

 channels. Significantly for the distribution of the Rhipsalis group of 

 Halimeda, the windward back-reef lacks the extensive sand terrain so 

 important for Halimeda production in the Caribbean. It may be that 

 the absence of an extensive sand flat along the back-reef is a character- 

 istic of atolls, which makes the basis of their carbonate budgets 



