Symbiotic anemones can grow when starved: nitrogen budget for Anemonia viridis in ammonium-supplemented seawater

The ability of endosymbioses between anthozoans and dinoflagellate algae (zooxanthellae) to retain excretory nitrogen and take up ammonium from seawater has been well documented. However, the quantitative importance of these processes to the nitrogen budget of such symbioses is poorly understood. When starved symbiotic Anemonia viridis were incubated in a flow-through system in seawater supplemented with 20 mu M ammonium for 91 d under a light regime of 12 h light at 150 mu mol photons m(-2) s(-1) and 12 h darkness, they showed a mean net growth of 0.197% of their initial weight per day. Control anemones in unsupplemented seawater with an ammonium concentration of