177 



of sea cucumbers, as % of 

 total C 



pH of parrotfish guts 



6.4 to 7.5 



Smith and Paulson, 1974 



of that element, with the symbiotic algae implicated as the 

 major agents in this update. Research on nitrogen cycling 

 through reef-flat populations of sea cucumbers was 

 reported to be a significant portion of total release by the 

 whole community. Exchange of phosphorus between reef- 

 flat organisms and overlying waters has been studied by 

 several workers, leading to the general conclusion that 

 exchange rates are slow and that there is a tight internal 

 cycling in most (but not all) cases. 



There have been a number of studies of trophic rela- 

 tionships and transfers, although no subsequent study has 

 been as broad as that of Odum and Odum (1955). A 

 number of fish groups, in particular, have been dis- 

 tinguished at various trophic levels. The role of detritus, 

 both coral mucus and algal fragments, exported from the 

 reef flats into the lagoon has been emphasized but not 

 completely worked out, particularly with regard to its 

 importance for various fish populations. 



Overall, there have been a large number of studies of 

 energy and materials flux at Enewetak, many of them of a 

 pioneering nature which pointed the way to a general 

 understanding of reef processes. However, ihe dominant 

 theme must be the preliminary nature of what has been 

 accomplished; a truly integrative understanding of reef 

 processes probably lies a long way in the future. 



ACKNOWLEDGMENTS 



I thank S. V. Smith, R. E. Johannes, and N. Marshall 

 for their reviews of the paper, although they may not 

 necessarily agree with everything in it. This is Contribution 

 No. 227 from the University of Guam Marine Laboratory. 



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