3. WESTERN ATLANTIC REEFS 



CORAL REEFS in the Western Atlantic have in 

 most cases been built under conditions some- 

 what different from the majority of those 

 discussed previously. A great part of this 

 area lies within what Davis (1928) has 

 called the marginal belt. The characteristics of such 

 an area are related to conditions which are supposed to 

 have existed there during the glacial periods. While 

 the true coral seas did not become too cold for the 

 continued life and growth of corals, there were certain 

 areas between them and the cold seas in which the reef 

 corals died during glaciation. These are known as the 

 marginal seas. During glaciation the seas dropped and 

 the land emerged from the water. In the true coral seas 

 new reefs grew and protected the land from abrasion. 

 In the marginal belt, however, no reefs existed during 

 glaciation and the shore remained unprotected during 

 that period. As a result the waves were able to wear 

 away the coast and form a platform around it, just 

 below the sea level. Part of this platform was due to 

 the sea cutting into the land and part due to the debris 

 thus formed settling down further out from shore (see 

 Fig. 9). 



Towards the end of the glacial period, when the seas 

 once more became warm, reef corals were again able 

 to live and reefs were formed upon these platforms. 

 Such reefs are called bank reefs and are characterized 

 by being further from shore than a fringing reef but 

 at the same time possessing a shallower lagoon channel 

 than a barrier reef. Moreover the reef is often at some 



36 



