Radiotracer determination of the diet of calanoid copepod nauplii and copepodites in a temperate estuary

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Abstract 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.