Feeding behavior of nauplii of the genus Eucalanus (Copepoda, Calanoida)

Abstract

The goals of this and following studies were to describe how nauplii of related calanoid copepods gather and ingest phytoplankton cells, and to compare their feeding behavior with that of copepodids and adult females of the same species. Nauplii of the calanoids Eucalanus pileatus and E. crassus draw particles towards themselves creating a feeding current. They actively capture diatoms > 10 pm width with oriented movements of their second antennae and mandibles. The cells are displaced toward the median posterior of the mouth and then are moved anteriorly for ingestion. The nauplii gather, actively capture, and ingest particles using 2 pairs of appendages, whereas copepodids and females use at least 4 of their 5 pairs of appendages (second antennae, maxillipeds, first and second maxillae) to accomplish the same task. These nauplii are not able to passively capture small cells efficiently like copepodids and females because they lack a fixture similar to the second maxillae. Gathering and ingestion by late nauplii of E. crassus and E. pileatus require together an average of 183 ms for a cell of Thalassiosira weissflogii ( l 2 pm width) and 1.17 S fox Rhizosolenia alata (150 to 500 pm length). Although na.uplii of related species show little difference in appendage morphology, they differ markedly in feeding and swimming behavior. Their behavior is partly reflected in the behavior of copepodids and adult females.