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L. HILLIS-COLINVAUX 



Fig. 103a. A part of the grove shown m Fig. 102a, showing the spreading algal mat over 

 loose substrate in the foreground, and overgrowth of the older thalh. The animal 

 mound in the upper left indicates some of the disturbances of the substrate in these 

 communities which might effect the extent of cloning of Rhipsalian Halimedae by 

 "runners" through the sand. Height range of the thalli in this and Fig. 103b is 

 approximately 9 cm. 



on the flanks of 2000 pinnacles may be the solution to this problem of 

 the Halimeda sediments at Enewetak. We need Halimeda production 

 data from pinnacles. 



(f ) The lagoon shallows. Coming to an atoll with the experience of a 

 fringing reef, it would be logical to expect the unconsolidated sediments 

 of shallows, with associated coral rock, to be a prime site of Halimeda 

 and carbonate production. There is certainly some, but not what might 

 be expected if the measure is the inshore reef of the Jamaican north 

 shore at Glory Be. At Enewetak the densities of Rhipsalian Halimedae 

 growing on sand are much less striking than on the Jamaican fringing 

 reef. There are more hard-substrate species, but even these do not seem 

 abundant by the standards of a fringing reef. 



The shallows on the lagoon sides of the islets have much living or 

 dead coral and rock debris, among which sandy surfaces are not 



