50 T. F. CORKAIT AND W. D. IIAKTMAN 



colonies (Fig. 13) of a type never seen in any other part of the 

 coral reef biotope. The deposition of coarse reef material on the 

 fore-reef slope appears to be an essential requirement for the subse- 

 quent establishment of these deep-water Agaricia communities. In 

 a more general sense it seems that detrital slides and avalanches 

 must constitute an important mechanism whereby conditions favor- 

 able for the development of corals are extended into environments 

 normallv inaccessible to manv sessile organisms because of the lack 

 of a stable, well drained substrate. 



It is remarkable that on the fore-reef slope there is no formation 

 of a primary framework (Goreau, 1963) despite the productive reef- 

 building fauna and flora. The immense coral-encrusted detritus 

 heaps described above are not in any sense to be thought of as 

 primary coral framework comparable to, sav, the buttresses of the 

 reef crest, since they are predominantly not the result of /'/] situ coral 

 deposition, and there is almost no structural consolidation by ce- 

 menting organisms. The lack of framework growth on the outer 

 slope is due to ( 1 ) slow rate of calcification with flattening of 

 corals, (2) paucity of frame-cementing biota, (3) intensive erosion. 

 Of all these factors, there is no doubt that the erosional processes 

 initiated, and facilitated, bv the boring sponges are most important. 

 Bv weakening their attachment to the substrate, the boring sponges 

 preferentiallv accelerate the loss of the larger and more massive 

 corals which are also the major potential frame builders. 



Not enough information is yet available to determine whether the 

 ecological triad described above, i.e., steep topography plus re- 

 duced frame-building capacity plus boring sponge activitv, occurs 

 elsewhere: the sharp offshore precipices bordering coral reefs in 

 the Red Sea (Nesteroff, 1955) and the Pacific Ocean (Emery et ah, 

 1954) suggest that the processes we have observed in Jamaica mav 

 be much more widespread than is now believed. 



Summary 



1. Intensive invasion of corals bv boring sponges has been ob- 

 served in reef communities at depths below 30 meters on the fore- 

 reef slope in Jamaica. In this habitat the consequences of large-scale 



