Phytoplankton growth rate and nitrogen content: implications for feeding and fecundity in a herbivorous copepod

Abstract

Observations of natural feeding and egg-production rates of plankton copepods, have revealed distinct responses, independent of phytoplankton biomass, to oceanographic processes that fertilize the photic layer. The diatom Thalassiosira weissflogii , grown in continuous cultures at different dilution rates and different nitrogen concentrations in the growth medium, was offered to the copepod Acartia tonsa at a concentration of 1.5 ppm. Over more than 2 orders of magnitude increase in algal growth rate, the ingested cell volume increased by less than a factor of 2, ingested carbon remained constant whereas ingested nitrogen as well as rate of egg production increased by a factor of ca 6.