Cook, Clayton B.;
Muller‐Parker, Gisèle;
D'Elia, Christopher F.
Ammonium enhancement of dark carbon fixation and nitrogen limitation in symbiotic zooxanthellae: Effects of feeding and starvation of the sea anemone Aiptasia pallida
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Media type:
E-Article
Title:
Ammonium enhancement of dark carbon fixation and nitrogen limitation in symbiotic zooxanthellae: Effects of feeding and starvation of the sea anemone Aiptasia pallida
Contributor:
Cook, Clayton B.;
Muller‐Parker, Gisèle;
D'Elia, Christopher F.
Description:
<jats:p>The nutrient status of algae symbiotic with marine invertebrates is controversial. We assessed the nitrogen status of zooxanthellae symbiotic with the sea anemone <jats:italic>Aiptasia pallida</jats:italic> using NH<jats:sub>4</jats:sub><jats:sup>+</jats:sup> enhancement of dark C fixation; enhancement increases with N limitation in other microalgae. Freshly isolated symbionts obtained from laboratory populations of known feeding history and from field populations were assayed: NH<jats:sub>4</jats:sub><jats:sup>+</jats:sup> enhancement depended on the nutritional history of the host anemones. Zooxanthellae from well‐fed laboratory populations showed little enhancement of dark <jats:sup>14</jats:sup>C fixation by NH<jats:sub>4</jats:sub><jats:sup>+</jats:sup>, while mean dark enhancement ratios (NH<jats:sub>4</jats:sub><jats:sup>+</jats:sup> rates: seawater rates) exceeded 2.3 for zooxanthellae from anemones unfed for 1–6 weeks. Photosynthetic rates of the isolated algae declined with starvation. <jats:italic>V<jats:sub>D′</jats:sub> </jats:italic>: <jats:italic>V<jats:sub>L</jats:sub></jats:italic>, an index which includes both dark NH<jats:sub>4</jats:sub><jats:sup>+</jats:sup> enhancement and photosynthesis, increased markedly with time since feeding. Three of four field samples of <jats:italic>A. pallida</jats:italic> yielded zooxanthellae with dark enhancement ratios similar to those of fed laboratory populations; <jats:italic>V<jats:sub>D′</jats:sub> : V<jats:sub>L</jats:sub></jats:italic> values were somewhat higher. Symbionts from anemones collected on a fourth date had a mean enhancement ratio of 2.88, and <jats:italic>V<jats:sub>D′</jats:sub></jats:italic> : <jats:italic>V<jats:sub>L</jats:sub></jats:italic> values similar to those from laboratory anemones that had not fed for 1–2 weeks, indicative of increased N limitation.</jats:p>