2.4 Perlphyton, Phytobenthos , Primary Production and Microflora 

 In Reef Blotopes 



When we speak of the algoflora of a reef and Its production, we generally 

 mean macrophytes and calcareous algae. However, most of the primary 

 production In coral biogeocenoses is created, apparently, not by the 

 macrophytes, but rather by the periphyton and microphytobenthos. The 

 perlphyton abundantly overgrows all rocky surfaces of the reef flat, the 

 porosity of the calcareous material of the flat significantly increasing the 

 Area and mass of the overgrowth. The perlphyton develops particularly 

 intensively on colonies of dead coral and their fragments, fbst of the 

 perlphyton consists of filamentous and mucous forms of bluegreen algae and 

 diatoms ( Osterobium , Calotrix , Microcoleus , Shizotrix , Rivularia , Ni tzschia , 

 Navlcula , Cymbella ). In addition to these, we also see certain macrophytes 

 with short, filamentous thalloms (dwarf forms of Laurencia , Sargassum , 

 Polysiphonia and Gelidella ). The biomass of algae in the periphyton is 2-5 

 mg/g (Sorokin, 1973d). The photosynthesis of the periphyton over the dead 

 corals amounts to 100-500 iig C/g dry weight of dead colony per day (Table 7). 



The photosynthesis of the periphyton on dead corals expressed as dry 

 weight of the colony, averages close to that on living coral of the same 

 species and configuration. The daily production of photosynthesis of 

 perlphyton over dead corals is about 3% of the total content of organic 

 matter, averaging 3-5 g C/m'^. The production is equally intensive In 

 periphyton over the clastic material and over the reef flat rocks (Tables 5, 

 7). The production of macrophytes on the Great Barrier Reef averages about 

 0.3 g C/m^ per day (Grassle, 1973). 



The respiration of the periphytonic community is also rather intensive, 

 50-100% of the production by its photosynthesis. The same relationship 

 between photosynthesis and respiration was also found for living corals 

 (Tables 5, 6). Thus, the periphyton community, like the living corals, fully 

 supplies itself with energy by photosynthesis, in spite of a significant 

 quantity of heterotrophic organisms in it. It is quite probable that some 

 closed cycles of nutrients exist in the perlphyton community, since the 

 primary producers and reducers are combined into single agglomerates by mucus 

 excreted by the algae. This, in particular, may explain the richness of the 

 periphyton, even on the outer side of the reef, which is washed with water 

 that is practically devoid of the inorganic forms of nutrients. 



The coral sand which occupies most of the area of the atolls and of 

 certain barrier reefs Is also abundantly populated with microscopic algae. 

 The sand particles are fragments of coral skeletons or coralline algae of the 

 shells of foramlnifera and ostracods. They are covered with a mucous film 

 containing algae and bacteria. The wet biomass of phytobenthos In the sands, 

 based on the results of direct measurements (Sorokin, 1973d, e) , was 0.5-1 

 mg/g, based on calculations of the intensity of photosynthesis, about 2 

 mg/g. Measurements of the photosynthesis of the phytobenthos by the 

 radiocarbon and oxygen methods (Sorokin, 1971b, 1973d, e, 1975a) have yielded 

 similar values: 30-60 pg C/g per day. The thickness of the photosynthesis 

 layer in the coral sand on Funafuti Atoll is 3 cm, but it decreases rapidly in 

 the first centimeter of sand. Calculation of the production by photosynthesis 

 of the phytobenthos in the sand yields a value of about 1 g C/m , which is 3-5 

 times higher than the primary production of photosynthesis by phytopl ankton in 

 the 100-meter euphotic layer of tropical waters. 



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