2.1 Reef-Bui1d1ng Organisms 



A coral reef is a limestone structure capable of resisting wave 

 action, formed of hermatypic organisms on shallow platforms in the 

 tropical oceans and seas. A variety of benthic fauna and flora occupies 

 the limestone structures and accompanying porous limestone sediment of 

 corallogenic origin. The hermatypic organisms are both animals and 

 plants. Animal hermatypes include the reef-forming corals and certain 

 mollusks (Vermetidae, Tridacnidae) . In most reef builders, the active 

 deposition of the carbonates of calcium and magnesium is functionally 

 related to photosynthesis; hermatypic corals, as well as Tridacnidae, 

 carry many symbiotic algae, capable of photosynthesis, within their 

 tissues. Hermatypic plants in coral communities include the red and 

 green algae. Other groups with calcareous skeletons play a significant 

 role in the formation of the reef material : calcareous sponges, sea 

 urchins, polychaetes, ostracods, mollusks and foramini fera . 



Usually 30-50 species of madrepore corals inhabit a coral reef, 

 primarily members of the families Agaricidae, Pocilloporidae, 

 Acroporidae, Poritidae, Faviidae, Asterocoenidae, Nbandrinidae, 

 Mussidae, as well as hydrocorals (family Mil leporidae) and octocorals 

 (family Hel ioporidae) . The plant hermatypes on reefs are represented by 

 30-40 species of calcareous algae: red ( Li thotamnium , Peyssonel 1 ia , 

 Porol ithon , Goniol i thon . Corall ina . Li thophyl lum , Sporol ithon , Tenarea ) 

 and green algae ( Halimeda , Penicillus , Udotea ). The coral reef includes 

 a rocky calcareous structure and loose limestone sediment. The process 

 of formation of the rocky reef structure includes two successive stages, 

 performed by different species of hermatypes. First, the massive corals 

 ( Favia , Siderastrea , Hydropora ) or corals with massive, strong 

 appendages (Porites , Acropora , Pocil lopora ) create the basic skeleton of 

 the growing portion of the reef. Certain calcareous algae also 

 participate in this process, forming massive outgrowths (Li thotamnium , 

 Porol ithon ) , which, however, play a secondary role (Goreau, Goreau, 

 1973). 



The second phase in the formation of the rocky structure of the 

 reef consists of cementation of its skeletal basis and transformation 

 into a continuous, monolithic structure. This function is primarily 

 performed by the red calcareous algae ( Lithotamnium , Porol ithon , 

 Peysonel 1 ia ) , as well as the foraminifera , calcareous sponges 

 ( Astrasclera ) , mollusks ( Tridacna , Vermetidae) and polychaetes 

 (Sabell idae) . 



The calcareous algae are characterized by high rates of growth and 

 metabolism. The rate of formation of lime in these plants is much 

 higher than in corals. Therefore, it is these plants which form most of 

 the carbonaceous rock of the reef. The living corals usually cover only 

 a small portion of the rocky surface of the reef: not over 30-50% in 

 zones of active growth, and less than 5% on the reef plateau (reef 

 flat), occupying most of its surface. The loose calcareous sediment 

 (coral sand) covers most of the surface of the bottom of the lagoon. 

 The red Amphirhoa , Coral! ina , Goniol ithon ) and green (Hal imeda ) 

 calcareous algae are most significant in its formation. The Halimeda is 

 one of the primary agents involved in the formation of the lime material 



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