statistical significance is indicative of the time required for competitive effects 

 to become evident and of the patchy nature of recruitment. The very small sample 

 sizes of corals larger than 9mm prevents thorough statistical treatment of differ- 

 ences in corals of this size. It seems unlikely that the trends toward greater 

 survival in the corals of intermediate size on the exposed reefs would cease to be 

 significant statistically as the community matures. For Agaricia spp. and Porites 

 astreoides , Fitz (unpublished data) measured mean linear growth rates of 0.6 

 (±0.2)mm/mo for corals 5-10mm diameter, 0.9 (±0.3)mm/mo for corals 10-15mm diameter, 

 and 1.3 (±0.3)mm/mo for corals 15-20mm diameter (n=45, 41 and 17, respectively). 

 Few corals would be expected, therefore, to attain sizes greater than 9mm in the 

 year-long immersion period. 



Some manipulations of the coral reef community are feasible and provide insights 

 into the processes shaping that community. This caging experiment implies that the 

 herbivores present at moderate depths play a crucial role in the survival of juve- 

 nile corals. As has been shown in shallow water areas (e.g., Sammarco 1980), 

 herbivory can reduce the deleterious effects of the algae on the corals by reducing 

 the biomass of the algal competitor. Though not as abundant in deeper as in shallow 

 waters, herbivores nevertheless appear to control the survival of coral recruits and 

 determine the structure of this epibenthic sessile community. 



ACKNOWLEDGEMENTS 



Special appreciation goes to Jane Dominquez for many hours of cold saturation 

 diving, and to the very competent surface support staff of the NOAA Hydrolab oper- 

 ation. We also thank Frank Pecora, Cheryl Van Zant, Hugh Reichardt, Miriam Smyth, 

 and Joseph Dinneen, who assisted in building the reefs either as aquanauts or as 

 part of the scientific surface support team. This work was made possible by grants 

 from NOAA (NA81AAA01500, NA82AAA01286) and NSF (0CE-78-26605) to Marjorie L. Reaka. 

 This is Contribution No. 110 from the West Indies Laboratory. 



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