The effect of feeding on the carbon isotopic composition of zooxanthellae, animal tissue and skeleton was investigated in the scleractinian coral Stylophora pistillata. Two sets of corals were grown with filtered seawater under controlled conditions. One group of colonies was fed Artemia sp. nauplii and compared to a control group that was starved. Fed corals exhibited higher concentrations of chlorophyll (60% more), soluble protein (4 times more) and calcification rates (29% more) than starved colonies. The net photosynthetic rate was higher in starved than in fed corals (18.53 +/- 6.99 and 6.78 +/- 2.06 mumol O-2 cm(-2) h(-1) respectively), whereas dark respiration was not significantly different (8.74 +/- 2.27 and 6.66 +/- 0.40 mumol O-2 cm(-2) h(-1)). The average delta(13)C value of Artemia sp. nauplii used for feeding was -12parts per thousand. delta(13)C was significantly heavier in zooxanthellae than in animal tissues, for both fed (-10.1 vs -11.7parts per thousand) and starved colonies (-10.9 vs -13.2parts per thousand.). Artemia sp. carbon was incorporated into the coral tissue as shown by the heavier delta(13)C in fed than in starved colonies (- 11.7 to -13.2parts per thousand, respectively), although there was no difference in the delta(13)C of the zooxanthellae fraction. Skeletal delta(13)C was similar in fed and starved colonies (mean -4.6parts per thousand). Skeletal delta(18)O composition was, however, significantly different between the 2 treatments (-4.24 to -4.05parts per thousand. for fed and starved colonies, respectively), which may have been due to differences in the calcification rates of fed and starved corals. These data are used to establish a conceptual model of the carbon flow between the various compartments of a symbiotic coral. It suggests that the skeletal delta(13)C is not sensitive to heterotrophic food supply.
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