was that net coral growth rates do not vary much with depth. Although 

 calcification rates decrease with increasing depth, rates of injury to colonies 

 are much higher in shallow water. This results in several examples of deep 

 corals at 35 or 55 m growing faster than corals of the same species at 10 or 

 20 m. These data suggest that we should exercise caution when using calcifica- 

 tion rates to evaluate coral reef growth. 



In our third presentation, Suchanek discussed the relative abundances and 

 interaction frequencies of corals and demosponges over a 40 m depth range 

 (Suchanek, et a! . , 1983). He emphasized the high frequency of demosponge-coral 

 interactions at 40 m and the increasing prevalence of demosponges as aggressive 

 spatial competitors with increasing depth. Aggressive interactions in shallow 

 water involved encrusting gorgonians, hydrocorals, and zoanthids. 



The effect of spatial competition on coral or demosponge growth, depth 

 distribution, and life history variation remains to be determined. Even though 

 deep hermatypic corals experience relatively low injury rates, a significant 

 amount of this injury is caused by sponge overgrowth (Hughes, 1983; Suchanek, 

 et al . , 1983; Hughes and Jackson, in review). Lang (1974) has previously noted 

 the prevalence of demosponges in deep fore-reef (below 55 m) and island slope 

 zones off Discovery Bay, Jamaica. Hermatypic corals growing under light-limited 

 conditions near their lower distributional limit may be more susceptible to 

 overgrowth by demosponges than corals growing at shallower depths. 



Wahle presented his data on the relationship between injury, colony size, 

 and life history variation in the gorgonian Plexaura homomalla (Wahle, 1983). 

 Between-colony analysis of variation in fecundity indicated that only colonies 

 taller than 20 cm contained eggs. Natural and experimentally induced injuries 

 to large female colonies resulted in physiologically isolated colony branches 

 which exhibited size-related variation in fecundity. This work demonstrates 

 that: 1) "colony size and not age controls both onset and continuation of 

 gametogenesis" ; 2) "injury can subtly reduce fecundity without noticeably 

 affecting (colony) size"; and 3) injuries can alter the level of colony integrity 

 and "create mosaics of different life history stages coexisting within the same 

 colony." 



My own presentation dealt with an analysis of divergent life history 

 patterns in Zoanthus sociatus and Z^ solanderi . Since these data do not appear 

 elsewhere, I present them here in more detail than that given to the other five 

 presentations. Both of these zoanthids are very common at several locations 

 throughout the Caribbean Sea. These sessile colonial organisms generally 

 inhabit shallow subtidal and lower intertidal zones where they occasionally are 

 exposed to extreme wave action (e.g., Hurricane Allen, see Woodley, et al . , 

 1981) or to desiccation (Sebens, 1982a; Fadallah, et al . , 1984). Both species 

 may successfully escape from such extremes by dispersing gametes and/or fragmented 

 clusters of adult polyps. 



Highsmith (1982) has suggested that fragmentation is an important part of 

 the life history of many corals, and that one characteristic typical of 

 fragmenting species is delayed sexual reproduction. The data in table 1 were 

 collected from 101 zoanthid colonies to determine if either Z. sociatus , Z. 

 solanderi, or both species delay sexual reproduction. Both species have been 



18 



