THE PRODUCTION AND INGESTION OF FECAL PELLETS BY NAUPLII OF MARINE CALANOID COPEPODS

The downward transport of organic matter as zooplankton faecal material is influenced by copepods which fragment, ingest and recycle some of the pellet contents. Most of this activity has been attributed to the later copepodite stages and the adults, but little is known about the role of nauplii. Stage-related defaecation rates during the naupliar development of two species of copepod, Calanus helgolandicus and Pseudocalanus elongatus, were quantified in a series of laboratory experiments. The production of faecal material commenced soon after the appearance of the NIII in both species and increased throughout naupliar development. The causes of the increase were the formation of larger pellets by later stages in Calanus and an increased rate of production by Pseudocalanus. Calanus nauplii, when supplied with algal food at concentrations that would support full naupliar development, ingested or broke up the pellets of the smaller Pseudocalanus species at rates of 1.15 pellets nauplius-1 h-1. This consumption increased to 2.96 pellets nauplius-1 h-1 when the concentration of algal food was reduced to a limiting level. Pseudocalanus was not able to consume the pellets of Calanus. Ingestion of Pseudocalanus faecal pellets by Calanus could supply a nutritional benefit to a food-limited nauplius.