The relative importance of sloppy feeding, excretion, and fecal pellet leaching in the release of dissolved carbon and nitrogen by Acartia tonsa copepods

Crustacean zooplankton produce dissolved organic matter (DOM) and inorganic nutrients via sloppy feeding, excretion, and fecal pellet leaching. These different mechanisms of the release of metabolic products, however, have never been individually isolated. Our study was designed to determine the relative importance of these different modes on release of dissolved organic carbon (DOC), ammonium (NH4+), and urea from Acartia tonsa calanoid copepods feeding on the diatom Thalassiosira weissflogii. Excretion and sloppy feeding were the dominant modes of DOC production (80 and 20% of total DOC release, respectively) and NH4+ release (93 and 7% of total NH4+ release, respectively). Urea, however, was predominately produced via sloppy feeding and fecal pellet leaching (25% and 62% of total urea release, respectively). Urea contributed 20% of total measured nitrogen (TMN; NH4+ + urea) released from copepods, and constituted 100% of TMN released via fecal pellet leaching, 47% of TMN released via sloppy feeding, and only 3.5% of TMN released via excretion. TMN release was > 100% of copepod body N d− 1, resulting in low DOC:TMN release ratios (4.1 for sloppy feeding, 2.1 for cumulative release of sloppy feeding, excretion, and fecal pellet leaching). Our results suggest that the mechanism of release plays an important role in the amount of different forms of DOM, NH4+, and urea available to bacteria and phytoplankton.

Research highlights
► Relative importance of sloppy feeding, excretion, and fecal pellet leaching varied.
► Excretion and sloppy feeding were the dominant modes of DOC and NH4+ release.
► Sloppy feeding and fecal pellet leaching were dominant modes of urea release.
► Ingestion and sloppy feeding were highest in the first 20 min of the 3 h incubation.
► Excretion and fecal pellet leaching were consistently lower in non-feeding copepods.