CONTROL OF CORAL REEFS BY BORING SPONGES 35 



crystalline calcite when this serves as a substrate for the sponge. 

 Instead, the chips are bounded by curved faces and ha\'e the same 

 shape whether the sponge bores into mollusk shells, corals, lime- 

 stone, or Iceland spar. It is highly probable that the removal of 

 chips from the substrate by clionids results from localized chemical 

 dissolution of the calcareous matter where cell processes come in 

 contact with it. The nature of the chemical process involved has 

 not yet been demonstrated. It is possible, as Nassonow (1883) and 

 Vosmaer (1933-1935) have noted, that the contractilitv of the 

 sponge cells plays an auxiliary role in the removal of the chips along 

 with a chemical process. 



Structure and Ecology of Coral Reefs in Jamaica 



The field studies described here were made by SCUBA-equipped 

 divers on the north coast of Jamaica, between Rio Nuevo and Dun- 

 cans. The reefs of this area are heavily buttressed (Goreau, 1959, 

 1961; Zans, 1958) and are built up on the edge of a near-vertical 

 offshore slope which falls to oceanic depths within a kilometer from 

 the shore. The submarine topography of these reefs and their associ- 

 ated structures is shown on the fathogram profiles in Fig. 10. The 

 principal characteristics of the major biotic zones are summarized 

 below. 



The Reef Crest, to 20 Meters 



The reef crest includes the shallow rampart, the surf zone, and 

 the buttress zone to a depth of about 20 meters on the seaward side. 

 The environment is of the high-energy, high-light-intensity type, as 

 it lies in the shallow, well illuminated region above the wave base. 

 The dominant organisms are the reef corals, which reach very large 

 sizes (see Fig. 11) and build a massive wave-resistant framework 

 raised above the surrounding sea bottom ( Lowenstam, 1950 ) . Coral 

 and algal CaCOs production is so high in this region that the over- 

 flow governs the pattern of carbonate sedimentation over a wide- 

 spread area outside the reef. The accessory fauna of sponges, Gor- 

 gonacea, and Bryozoa is reduced; boring organisms are common but 



