NET PRODUCTION OF CORAL REEF ECOSYSTEMS 



S. V. Smith 

 Hawaii Institute of Marine Biology 

 P.O. Box 1346, Kaneohe, Hawaii 96744 



INTRODUCTION 



How do coral reefs survive as rich and diverse ecosystems generally found in 

 nutrient-deficient water? This fundamental question has directed much research on 

 the community metabolism of coral reefs towards two ancillary questions: 



1. Does the high biomass of coral reef communities indicate high gross 

 organic carbon production? 



2. Are coral reef communities net importers or exporters of organic 

 material? 



If coral reefs were found to produce organic carbon very slowly, then their 

 survival in nutrient-deficient waters would be more easily understood; their 

 nutritional requirements would be minimal. However, early work (Sargent and 

 Austin, 1949, 1954; Odum and Odum, 1955) through to recent research (see 

 references in Kinsey, 1979; Smith, 1981) has consistently demonstrated that the 

 gross production rate of these reef communities is relatively high. The best 

 estimate for the average gross production rate of these communities is 7 gC m _ 2 

 d"l , not an entry to the Guinness Book of Records, but impressive nevertheless. 



The organic and inorganic nutritional requirements of any biological system 

 are determined by the difference between the amount of organic material produced 

 and that which it consumes. We therefore turn to the second question. Can we 

 learn something about the survival mechanisms and ecosystem requirements of 

 coral reefs by considering their net trophic status? 



The flow respirometry model advanced by Sargent and Austin (1949) and popularized 

 by Odum and Odum (1955) to study the community metabolism of coral reef flats 

 was an elegant approach to community metabolism. Much has been done to refine 

 the model and to adapt it to communities besides reef flats. Probably to the 

 detriment of the original question about the survival of reefs in nutrient- 

 deficient waters, the flow respirometry model and its extensions have focused 

 attention on the metabolic performance of coral reef communities , not coral 

 reef ecosystems . 



By now we know that individual coral reef communities can be net producers 

 or consumers of organic material, by substantial margins in either direction 

 (Smith and Marsh, 1973; Kinsey, 1979). However, net community production is 

 not directly relevant to the question of net ecosystem performance, because we 

 know that the transfer of particulate and dissolved materials across boundaries 

 between adjacent autotrophic and heterotrophic communities tends towards an 

 intercommunity trophic balance. Such a tendency towards trophic balance has 

 been demonstrated by examining groups of distinct communities (or zones) on 

 coral reefs (Smith and Marsh, 1973; Kinsey, 1979) and is discussed in some 

 detail for a non-reef ecosystem that is metabol ical ly dominated by seagrass and 

 soft bottom communities (Smith and Atkinson, 1983). This characteristic also 

 has been noted as a general characteristic of adjacent communities in flowing 

 water (Odum, 1956). 



But do we really have a firm notion about the metabolic balance among the 

 entire consortium of biotic communities which form a coral-reef ecosystem? I 



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