Experimental studies on the deep-water pelagic community of Korsfjorden, Western Norway. Prey-size preference and feeding ofEuchaeta norvegica(Gopepoda)

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Abstract
Three species of copepods, with an average individual dry weight of 7, 430, and 1360 μg respectively, were used as prey for Euchaeta norvegica adult females and stage V copepodids. The type of prey had no significant influence on the mortality rate which was close to the mortality rate of starving animals under comparable laboratory conditions. Stage V copepodids had a somewhat higher mortality rate than females, probably depending on a sensitive period at the state of moulting. The average time before feeding and faecal-pellet production started was shortest when the smallest prey organism, Pseudocalanus elongatus, was used, and this prey also gave the highest production of faecal pellets by E. norvegica. Stage V copepodids began feeding sooner than adult females when offered P. elongatus but later when offered the two other prey organisms. On an average 0.18 C. finmarchicus or 0.09 C. hyperboreus per day was ingested by adult females, the values for stage V copepodids being somewhat lower. Maximum predation rate ever observed was 2 C. finmarchicus or 1 C. hyperboreus during a day for adult females, while stage V managed 1 C. finmarchicus during a day at the most. Remaining parts of the prey organisms indicated that P. elongatus was eaten with the urosome first, while C. finmarcicus was taken preferably with the anterior part first. The assimilation effciency was 92 % for adult females and 94 % for stage V copepodids and differed very little between animals fed on different prey organisms. Starvation experiments on animals from autumn, winter, and summer respectively gave somewhat different results, but as a whole indicated a weight loss mainly determined by the utilization of stored lipids.