Assimilation and partitioning of prey nitrogen within two anthozoans and their endosymbiotic zooxanthellae

The movement of nitrogen from zooplankton prey into the temperate scleractinian coral Oculina arbuscula and the anemone Aiptasia pallida was measured using ¹⁵N-labeled brine shrimp. The efficiency with which prey nitrogen was incorporated into cnidarian tissues was species-specific. O. arbuscula with a full complement of zooxanthellae had an assimilation efficiency of nearly 100%, compared to only 46% for corals containing few zooxanthellae. In A. pallida, symbiont density had no effect, and nitrogen assimilation was 23 to 29%. In both species, the host retained the bulk of the ingested label. Complete digestion was rapid (