In order to define the niche of copepod nauplii relative to copepodites and explain previously observed differences in food limitation between stages, several aspects of copepod naupliar feeding and growth were evaluated both experimentally, using the copepods in Passamaquoddy Bay, NB, and by reviewing previous studies. Feeding experiments using fluorescent latex beads of a range of sizes demonstrated that nauplii have a lower maximum food size than copepodites do, but the lower size limit of all stages is comparable. A synthesis of previously published ingestion rates of nauplii indicated that their optimal food size is lower than that of copepodites, and that the optimal food size to predator size ratio was 18:1. Food type differences between stages were explored by radiolabelling autotrophic and heterotrophic prey: nauplii and copepodites fed preferentially on autotrophs, and both appeared capable of consuming heterotrophs. Experiments examining possible alternative feeding mechanisms (mucous traps and drinking) indicated that neither method is frequently used by any stage. Therefore, nauplii must obtain food using mechanisms similar to those of copepodites and adults. Thus, there is little evidence for significant differences in food type consumed between stages.

The artificial cohort method was used to monitor growth rates of nauplii and copepodites over a range of food concentrations. The growth rates of the nauplii did not vary considerably, despite a wide range of food concentrations, while the growth rates of the copepodites were much more variable. There was no strong evidence that nauplii or copepodites were experiencing food limited growth in terms of food quantity, but the lower growth rates of the copepodites may have been a response to low food quality. One site in Passamaquoddy Bay was monitored bi-weekly for copepod abundance and chlorophyll concentration to measure grazing and production rates of the different developmental stages. These analyses found that copepod nauplii in Passamaquoddy Bay contributed significantly to total copepod grazing (25 - 54 %), and production (10 - 50 %). Thus, additional studies examining the precise niche of copepod nauplii are imperative before a full understanding of their trophodynamic role is possible.