42 T. F. GOREAU AND W. D. IIARTMAN 



coenia, and Pontes, all of which normally build large, massive 

 rounded heads in well illuminated environments. Foliose and 

 branching genera, such as Agaricia, Acropora, and Madracis, become 

 thinner and more spindly but do not undergo marked changes in 

 geometry. The outstanding consequence of flattened growth is that 

 such colonies are much lighter in proportion to their surface area 

 than round forms of the same radius (Goreau, 196-3). 



Attachment of Corals to the Substrate 



The base of shallow-water corals is usually skirted by a layer of 

 living polyps, so that the attachment grows in proportion to the bulk 

 of the corallum: the larger the corals, the better cemented they are 

 and the more difficult it is to separate them from their substrate. In 

 deep water, however, only the upper surfaces of the flattened 

 colonies are alive, and the holdfast is not covered by a layer of 

 polyps; the growth of these colonies therefore is not accompanied 

 by a proportional increase in thickness and strength of the base, 

 so that large individuals are often precariously perched on a thin 

 neck which is easily broken. 



Encrusting Biota 



The dead, exposed undersurfaces of deep-water corals also fonn 

 ideal sites for sponges, hydroids, algae, Bryozoa, Gorgonacea, Anti- 

 patharia, Foraminifera, worms, and mollusks. The majority of these 

 organisms merely use the coral as a foothold, but they often reach 

 such large sizes that the supporting colonies are overwhelmed. 

 Indeed, the thin attachment of the coral can become so overloaded 

 that it will break when the mass becomes too heavy. Figures 14 and 

 15 show the characteristic narrow base of flattened, sponge-en- 

 crusted corals growing on the outer fore-reef slope. 



The Effect of Boring Sponges on the Corals 

 OF THE Fore-Reef Slope 



Damage by boring sponges is widespread in all reef zones; most 

 corals show evidence of penetration at sites where the skeleton is 

 not protected by living polyps. Deep-water corals, with their thin- 



