Nutrient Uptake by a Deposit-Feeding Enteropneust: Nitrogenous Sources

We measured carbon, nitrogen, protein, bacterial and microalgal abundance, and minerals p e c ~ f ~ c surface area m sediments from the feeding zone of undisturbed Saccoglossus korualewskyi, as well as In their fresh egesta. Comparison of results using surficial material (> 1 mm) and the top 3 mm of sediments indicated ingestion of surficial material by the enteropneusts. Assuming the surficial s e h ment as a food source results in apparent absorption efficiencies of 15 % for TOC, 35 % for TON, 60 % for protein and 86% for microalgae. The C:N ratio of the apparently absorbed material was 4.2, consistent with an amino acid-rich diet. Protein-nitrogen uptake, however, accounted for only about 28% of total nitrogen absorption, indicating a dominant use of non-protein nitrogen. Bacter~al and microalgal contributions to dietary nitrogen uptake were no more than 3 % and 4 "/o respectively Active worms maintain 2 foraglng areas with an average total foraging volume of 0.9 cm3 and a volume ingestion rate of 0.06 to 0.12 cm3 ind.-' h-' If the preferred feeding zone of these enteropneusts is the nitrogen-enriched surficial layer, we estimate that their feeding activities will deplete the available food resources every 8 to 16 h and they may rely on biological and tidal redistribution of surface material.