MEPS 262:125-136 (2003)  -  doi:10.3354/meps262125

ABSTRACT: 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 (<4 h), as was the partitioning of the label between host amino acids and macromolecules. The label was primarily in the low-molecular weight-amino acid pool in O. arbuscula, where it remained for 30 h. A maximum of ca. 20% of the ¹⁵N appeared in the zooxanthellae, where it was rapidly converted into macromolecules. Individual amino acids in A. pallida tissues were highly labeled with ¹⁵N within 4 h and showed no subsequent enrichment with time; however, zooxanthellae amino acids became increasingly enriched over 30 h. Differences in ¹⁵N enrichment among amino acids were consistent with known synthesis and transformation pathways, but it was not possible to discriminate between host feeding and de novo synthesis.

KEY WORDS: Nitrogen · ¹⁵N · Assimilation efficiency · Oculina arbuscula · Aiptasia pallida