Importance of ciliates as prey of the euphausiid Euphausia pacifica in the NW North Pacific

Abstract

We investigated the feeding of Euphausia pacifica on ciliates, especially naked ciliates, in laboratory and field experiments in which cultured Strombidium conicum, or natural food assemblages, or both were given, and estimated the importance of ciliates as prey. E. pacifica ingested cultured S. conicum at rates of 0.04 to 0.07 μgC krill -1 h -1 at low ciliate concentration and 1.01 to 3.24 μgC krill -1 h -1 at high ciliate concentration, when S. conicum was given as the sole prey. The daily ration on naked ciliates ranged from 0.02 to 1.8% of body carbon when natural food assemblages enriched with S. conicum were given, and from 0.05 to 2.3 % of body carbon when S. conicum was given as the sole prey. Our results provide indirect evidence that E. pacifica ingests naked ciliates and plays a role in linking microbial food webs to the classical grazing food chains.