Vertical distribution and abundance of Calanus pacificus and Pseudocalanus newmani in relation to chlorophyll a concentrations in Dabob Bay, Washington

Recent evidence suggests that diatoms may induce reproductive failure in planktonic copepods, either through ingestion of diatoms by females or contact of embryos with diatom extracts. Therefore, the co-location of copepods and diatoms in situ may affect copepod reproductive success. As part of a study to determine the effect of diatoms on copepod reproductive effort, we measured the abundance and nighttime vertical distribution of two species of copepods, Calanus pacificus and Pseudocalanus newmani, as well as vertical distribution of chlorophyll a, during winter–spring in Dabob Bay, Washington State, USA, in 2002 and 2003, with limited observations in the summer of both years. Populations of both species declined throughout the winter–spring but rebounded by summer. While C. pacificus females, males, and CV copepodites were not strongly co-located with chlorophyll a concentrations, those same stages of P. newmani were consistently found within the layer containing the chlorophyll maximum. Our limited data on vertical migration show that female and CI–CII copepodites of C. pacificus exhibited normal diel vertical migration behavior, but adult P. newmani exhibited reverse diel migration. Overall, these data suggest that the patterns of reproductive success observed for the two species may be related to their different vertical distributions and may affect their population dynamics.