Uptake of ammonium by the scleractinian coral Stylophora pistillata : Effect of feeding, light, and ammonium concentrations

Abstract

Experiments were designed to assess the uptake rates of 0.2, 1, and 5 μM ammonium by the scleractinian coral Stylophora pistillata maintained under different feeding regimes (highly fed, slightly fed, and starved) for 4–8 weeks. 15 NH 4 was used to follow the incorporation of nitrogen in the zooxanthellae or in the animal tissue and to calculate uptake rates. After 4 or 8 weeks, fed corals contained significantly higher concentrations of protein, chlorophyll, and zooxanthellae than starved nubbins. They also contained significantly higher amounts of carbon and nitrogen per unit surface skeleton. Results obtained showed that the algal fraction was enriched with 15 N at up to 10 times the rate of the host, which suggests that the zooxanthellae are the primary site of assimilation. Uptake rates (measured in the algal fraction) varied according to the nitrogen concentration in seawater. They were ~20 times lower at 0.2 than at 1 or 5 μM 15 NH 4 enrichment (2–30 vs. 120–510 ng N h −1 cm −2 ) for both fed and starved nubbins. These rates were also affected by the feeding history of the host, because they were significantly lower for fed than for starved nubbins (analysis of variance, P

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