sediments and clastic niaterial is transported. The flat is a zone of 

 active calcification. In most reefs, the primary role in this 

 calcification process is played by the calcareous algae ( Neogoniol ithon , 

 Porol ithon , Li thotamnium ) . In some reefs, they construct a purely algal 

 limestone reef flat (Kornicker, Boyd, 1962; Glynn, 1973). The growth of 

 the limestone mass of the reef flat is accomplished by the algae and 

 also by polychaetes (Dendrostomidae, Sabellidae), which construct the 

 limestone tubules. The entire porous surface of the reef flat is 

 covered with a dense cover of periphyton, consisting of filamentous 

 macrophytes, filamentous blue-green algae and diatoms. Stands of 

 macrophytes with short, strong thalli are also seen (Turbinaria , 

 Laurencia , Chnoospora , Hydroclarthus , Sargassum , Padina ), plus large 

 colonies of soft coral s~ TZoantus ) 7~col onial sea anemones ( Palythoa ) . 

 various individual sea anemones, Ascidia and sponges. Living coral 

 ( Acropora , Siderastrea , Pocil lopora , fentastrea , Pi ploria , Mil lepora , 

 Favia , Coeloria , Dicoenia , Leptastrea ) grow on the surface of the reef 

 flat sparsely in the form of massive crusts or low colonies. The rocky 

 plateau and the "niggerheads" are populated by Gastropoda ( Li ttorina , 

 Neri ta , Trochus , Gonus , f-tnetaria , Cypraea , Murex , Bursa , Turbo , 

 Lunel la , Astraea , Hal iotis , Mancinella ), various crabs, stars, 

 Ophiuroidea, Polychaeta ( Capital 1 idae, Nereidae, Phyl lodocidae) . The 

 periphyton and rich fauna serve as food for many fish which come to feed 

 on the reef flat during high tide. 



The Br (breaker) zone is the frontal edge of the reef where the 

 waves break, 1-2 m deep. The population of corals living here is 

 constantly subjected to the powerful mechanical effects of the surf. 

 Their growth is determined by their strength. If the reef is in the 

 path of tropical cyclones, the tremendous waves which arise during these 

 storms may crush off all living coral on the outer edge of the reef down 

 to a depth of 5-8 m (Goreau, 1959; Glynn, 1973; Stoddart, 1974). The 

 underlying zones (Mix, But, Fr) , after the cyclone passes, Are buried in 

 fragments and colonies of broken coral (personal observation of the 

 author on the Lau Islands). Strong typhoons sometimes break down even 

 the rocky reef plateau or bury it in clastic material, as a result of 

 which new islands arise. This occurred at Funafurti Atoll (Ellis 

 Islands) in 1971. 



In spite of the strong mechanical action of the surf, conditions 

 for the growth of coral here Are optimal, due to the high turbulence and 

 good illumination. Therefore, a dense population of young coral usually 

 arises in the breaker zone, with strong, massive colonies withstanding 

 the waves. Such are the colonies of coral Acropora ( Acropora palmata , 

 _A. cuneata , _A. corumbosa ) , as well as Stylophora pistillata , 

 Millepora platyphilla , H. complanata , Mjntipora hoffmeisteri , 

 Porites lutea , P_. asteroides , Pocillopora damicornis , Diploria strigosa , 

 and Favia fragum . The calcareous algae Li thothamnium and Porol ithon , 

 which form massive colonies in the breaker zone, are very significant in 

 strengthening this zone. Among the benthic fauna, forms which live in 

 cracks in the rocky base and in the colonies of dead corals are 

 predominantly ascidians, sponges, crabs, and various polychaetes. 



f-b (moat) zone--3-5 m deep. This zone has the shape of a long 

 moat, along the edge of the breaker zone. The moat is formed as a 



168 



