Natural ingestion rates of the copepods Neocalanus plumchrus and N. cristatus calculated from gut contents

Abstract

Gut contents of copepodid stage V Neocalanus plumchrus and N. cristatus from 5 depth strata were measured with a gut fluorescence method, every 3 to 7 h, during five 24 h stations in the Bering Sea. Levels of gut fullness were generally higher during the phytoplankton bloom in May than post-bloom in June. However, within each 24 h period, levels of gut fullness varied with depth and time, and were not related to ambient chlorophyll concentrations. This probably indicates that individuals of both species were vertically mobile. Gut evacuation rate, used to convent gut-content data to feeding rates, was exponential and temperature dependent. Short-term feedng rates varied within each 24 h period and sometimes were much higher than rates measured by more traditional methods which involve 12 to 24 h incubations. This work is part of a multi-disciplinary study titled 'pro-the ingested chlorophyll is quickly degraded to cesses and Resources of the Bering Sea Shelf' or PROBES; it