Table 1. Organic carbon production (+) or consumption (-) rates for atoll 

 lagoon reef ecosystems. Note that the calculated rates reflect the budgets 

 adjusted to the presently estimated piston coefficient based on other budgetary 

 data presented in the original reference citations. 



Location Rate Reference 



mgC m"2 d~l 



Canton 1973 170 Smith and Jokiel (1978) 



Christmas 1983 70 Smith, et al_. (1983) 



Fanning 1983 Smith (unpublished data) 



Fanning 1972 -10 Smith and Pesret (1974) 



It should be noted that Canton, by its proximity to equatorial upwelling and 

 because of its ocean/lagoon exchange characteristics, has the highest nutrient 

 concentration and loading of these sites. Moreover, it is clearly demonstrated 

 in Table 1 'that this site exhibits the highest net ecosystem production observed 

 according to this model. 



Shark Bay, although not a coral reef, is another confined ecosystem showing 

 a very low net production rate (15 mgC m _ 2 d _ l ; Smith and Atkinson, 1983). The 

 Abrolhos lagoon is an open atoll lagoon surrounded by oceanic reefs. The slopes 

 of these oceanic reefs have a very large standing crop of typically temperate- 

 water macroalgae (kelp), much of which gets swept into the lagoon during storms 

 (Crossland, ejt a]_. , 1983). Based on dissolved nutrient export from that lagoonal 

 reef system, we concluded that that system is marginally heterotrophic. We 

 could not quantify the degree of heterotrophy there, although research on that 

 question continues (B. Hatcher, personal communication). 



DISCUSSION 



Based on this very limited set of data from a particular subset of coral 

 reefs, I suggest that the net organic carbon metabolism of coral reefs and 

 related ecosystems in low-nutrient waters is very low, probably generally 

 averaging well less than 100 mgC m" 2 d - l . The available data show a slight 

 bias towards net autotrophy, but it seems likely that individual systems can be 

 influenced to swing one way or the other. This swing will reflect variations 

 in availability (and lability) of inorganic and organic materials used for 

 metabol ism. 



The important conclusion to be drawn from these calculations does not 

 ultimately concern the trophic status of coral reefs and related systems. 

 Rather, note the very low absolute values of net organic carbon flux in these 

 ecosystems. Let us compare, for example, the net nutritional requirements of 

 coral reefs with the requirements of the surrounding ocean. 



Eppley and Peterson (1979) defined "new production" of plankton to be that 

 production in the surface waters supported by external nutrient inputs, mostly 

 from upward nutrient flux out of the aphotic zone. Those authors estimated an 

 ocean-averaged new production rate of about 30 mgC m - 2 d _ l , within the range 

 for net coral-reef production (Table 1). 



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