believe that the answer to this question in any explicit fashion must be "No!" 

 We simply cannot expect to weight and sum the component estimates for individual 

 communities in most ecosystems to a quantitatively satisfying estimate of net 

 ecosystem production. Neither the sizes of communities within the ecosystems 

 nor the community production rates can be measured with sufficient accuracy or 

 precision to accomplish such a summation to within a few percent. At least 



such precision is required. 



RESULTS 



I have recently revisited a subset of my own research papers (and have 

 literally revisited one site and added another) in an attempt to derive an 

 explicit answer about the net production rate of entire coral reef ecosystems. 

 This subset deals with coral atoll lagoons. The lagoons in question are a 

 special case of atoll lagoons: I have examined lagoons virtually surrounded by 

 land (rather than by the more usual oceanic reef rim). Within the lagoons are 

 reef flats, slopes, and inter-reef communities--al 1 of the essential units of 

 more classical "open" coral reefs. The advantage of these confined lagoonal 

 reef ecosystems over more open reef ecosystems is the clear definition of 

 ecosystem boundaries and fluxes. These lagoonal reef systems apparently function 

 as self-contained entities with little communication (with respect to carbon 

 flow, at least) with the oceanic reefs beyond the enclosing islands. 



The sites being considered are Fanning (Smith and Pesret, 1974, plus new 

 data), Canton (Smith and Jokiel, 1978), and Christmas (Smith, et aK , 1983), 

 all in the central Pacific Ocean. I will also include some relevant discussion 

 with respect to a more open atoll lagoonal system in the Indian Ocean (the 

 Abrolhos Islands; Crossland, et al. , 1983) and a seagrass-dominated coastal 

 lagoon in Western Australia (Shark Bay; Smith and Atkinson, 1983). These last 

 two systems provide additional insight into material processing at the scale of 

 enti re ecosystems. 



I have used water, salt, and CO2 budgets to examine the net metabolism of 

 these confined lagoonal systems for clues about the total system metabolism of 

 coral reef ecosystems. Shark Bay provides the clue that my suggestions about 

 the metabolism of coral-reef ecosystems may be generalized to other well-defined 

 ecosystems with little input from the surroundings, and the Abrolhos lagoon is 

 an anomaly which strengthens our understanding of the mechanisms controlling 

 these systems. 



The initial work at Fanning and Canton resulted in values for CaC03 production 

 and total CO2 flux, but failed to separate organic metabolism from gas flux 

 across the air-water interface. In that early work, we were initially very 

 conservative about the gas transfer coefficient. Expressing this coefficient 

 in terms of "piston coefficients," we assumed a possible range between and 20 

 m d"l. More recent assessment of available data suggests that at wind speeds 

 below 7 m s~* (i.e., about the median wind speed on most coral reefs), the 

 piston coefficient lies in the much narrower range of 0.3 to 3 m d~l (Smith and 

 Atkinson, 1983). If the average piston coefficient is applied to the data set 

 previously mentioned, we derive the following organic carbon production rates 

 (Table 1): 



128 



