© 2004 by ICES/CIEM International Council for the Exploration of the Sea/Conseil International pour l'Exploration de la Mer
Radiotracer determination of the diet of calanoid copepod nauplii and copepodites in a temperate estuary
a Department of Zoology, University of Guelph Guelph, Ontario N1G 2W1, Canada
b Environmental Science, Acadia University Wolfville, Nova Scotia B4P 2R6, Canada
*Corresponding author. e-mail: john.roff{at}acadiau.ca; kerrifin{at}uoguelph.ca.
Many studies have focused on the consumption of specific prey items and clearance rates on natural food particles by copepod adults and copepodites, but few have addressed the feeding habits of the youngest stages, the nauplii. Because of the difference in size and shape between copepod developmental stages, corresponding differences in diet would be expected. This subject was addressed using a modification of a new method offering radiolabelled natural food particles (with 3H for heterotrophs and 14C for autotrophs) to nauplii and copepodites of the copepods in a temperate estuary. By measuring the uptake of the radiolabel by the copepods it was possible to determine clearance rates on different sizes and types of food particles. All copepods began feeding on food sources >2 µm in size, and feeding on heterotrophs by all species and stages was considerably lower than feeding on autotrophs. Overall, it appears that copepod nauplii have a comparable diet to the later stages in terms of food type and size and therefore it is unlikely that nauplii are a more efficient link between the microbial foodweb and the classical foodweb, at least in temperate estuarine waters.
Keywords: clearance rates, copepod nauplii, copepodites, natural food assemblage, radiotracers