in South Carolina, we will assume the 

 ''(net) °^ 1,000 kcal/m^/yr is a conserva- 

 tive estimate. 



The ingestion rate (I) of a reef pop- 

 ulation, as expressed by the "functionally 

 average" 60-mm oyster, approximates the 

 ability of oysters in the population to 

 filter about 100 ml of water per minute 

 (extrapolated from values reported by 

 Walne [1972] for C^. qiqas of the same 

 height). The feeding experiments by Walne 

 were carried out at temperatures approxi- 

 mating the median level for our study area 

 (19° C). During one day (12 hours of pump- 

 ing time), the oysters occupying a typical 

 square meter of reef could filter 288,000 

 liters of water (4,000 oysters x 0.1 li- 

 ter/mi n X 12 hr x 60 min). With an aver- 

 age POC load of 0.01 g/liter assumed (Odum 

 and de la Cruz 1967), this would equal a 

 potential maximum ingestion rate of 300 

 gC/m2/day, or 1 x 106gC/m2/yr (5 x 105 

 kcal/m^/yr) if the oysters filtered at 

 100% efficiency. If filtration is 40% 

 efficient (Haven and Morales-Alamo 1970), 

 ingestion of organic carbon would occur at 

 the rate of about 2 x 10^ kcal/m2/yr. Only 

 a small fraction of this cartjon would be 

 assimilable, however. The remainder would 

 be egested and biodeposited as feces or 

 pseudofeces, or excreted as organic nitro- 

 gen. Mathers (1974) reported that large 

 oysters of the species £. anqulata could 

 completely filter water at the- rate of 

 54 ml/g (wet wt)/hr or about 0.45 liter/g 

 (afdw)/hr. This translates to about 

 2 X lO^'gC/m^/yr or 1.0 x 10^ kcal/m Vyr 

 for reef oysters, twice the estimate of 

 Walne (1972). These two estimates illus- 

 trate the approximate nature of this meas- 

 urement. 



Egestion, excretion, and pseudofecal 

 production (E) by reef oysters can be 

 expressed in terms of a reef population of 

 60-mm oysters. Bernard (1974) reported 

 that large specimens of C^. gigas ( '^10 g 

 dry wt of meat) produced about 5.9 x IC* 

 kcal per oyster per year as biodeposits. 

 If an extrapolation were made to the 60-mm 

 reef oyster (dry meat weight = 0.18 g), we 

 could conservatively predict that it would 



biodeposit the equivalent of 1,000 kcal/ 

 yr, or 4 x 10^ kcal/m^/yr for the entire 

 oyster population. If one judges by the 

 estimated maximum ingestion rate, however, 

 (see above) this estimate is equal to 80% 

 of ingestion, implying a 20% assimilation 

 rate (A = I-E). This estimate may be high 

 because only a small portion of the total 

 of all ingested carbon can be assimilated 

 by oysters. 



Of the terms in Equation (1), respi- 

 ration rates (R) are best known for reef 

 oysters. Bahr (1974, 1976) calculated that 

 the reef oyster population accounted for 

 approximately 48% of the mean oxygen up- 

 take of the total reef community, or about 

 3,900 g02/m2/yr. This estimate was derived 

 by combining individual oyster respirome- 

 try experiments (carried out seasonally at 

 ambient temperatures and on different 

 sized animals) with the relative propor- 

 tion of the reef oyster biomass repre- 

 sented by each size class. 



From data reported by Dame (1970) and 

 Bahr (1974), the following equation de- 

 scribes the relationship between oyster 

 oxygen uptake and biomass at the approxi- 

 mate median water temperature in the study 

 area (20° C). 



0.53X 



0.71 



(5] 



where Y = mg O2 used per hour and 

 X = total afdw 



Solving this equation for a function- 

 ally typical oyster of 0.25 g afdw, one 

 would predict that a single oyster would 

 consume 0.20 mg 02/hr. When this figure is 

 multiplied by 12 hours of inundation time/ 

 day, 365 days/yr, and 4,000 oysters/m^, 

 the resulting estimate of oxygen require- 

 ments is 3,500 g Oa/m^/yr, very close to 

 the above estimate of 3,900 g Oa/m Vyr 

 (Bahr 1974). 



The final estimates of the parameters 

 in the energy budget Equation (1) are pre- 

 sented in Section 2.5 and illustrated in 

 Figure 12. 



105 



