result of suppression of tlie growth of corals in the area where the 

 loose sediment and clastic material, carried away from the reef flat by 

 the surf and tide, drifts down. Since active growth of coral proceeds 

 lower down the slope, in the Mix zone, a moat is formed between the Br 

 and Mix zones. Its bottom is covered with sand and a mass of fragments 

 of coral, among which are living solitary coral s/ Fungia . The clastic 

 material is densely populated with periphyton, which is eaten by the 

 large mollusks ( Lambis , Bursa , Murex , Turbo , Trochus ) . 



The main mass of the macrobenthos consists of infauna, which 

 inhabits the colonies and large lumps of dead corals accumulated on the 

 bottom. Here dre masses of polychaetes, decapods, amphipods, isopods, 

 ol igochaetes, sipunculides and Ophiuroidea. 



The Mix (mixed) zone, 4-8 m deep. It occupies the slope, with 

 rather abundant growth of corals, which extend to the next zone. 



The Bu (buttress) zone, 8-20 m deep. This is one of the most 

 important and rapidly growing elements of the reef. Here the most 

 intensive growth of corals occurs and the greatest taxonomic variety is 

 seen (Table 4). The growth of corals occurs in strips, located 

 perpendicular to the edge of the reef. It is divided by slots, through 



Table 4. Distribution of massive species of coral over an area of 90 m 

 in the main zones of the frontal part of reef at Heron Island, Great 

 Barrier Reef (Grassle, 1073). 



Zone Species cm 



Total dred of colonies, 

 ^•10-^ in an area of 90 m'^ 



Fl Acropora cuneata 14.0 



9.7 



3.4 

 2.6 



Br Acropora corumbosa 5.5 



4.5 

 1.6 

 1.4 



Mix + FR Acropora formosa 196.9 



65.7 



36.1 



5.3 



2.2 



which the sediment and clastic material mo>'e. As a result of this 

 localization of the active growth of coral, rows of large, limestone 

 humps are formed. Their surfaces are densely covered with corals, which 



169 



