Experimental feeding of copepod Calanus finmarchicus (Gunner) on phytoplankton cultures 1 ] 3 



Of sea water on a planchette. Owing to self-absorption, this was not a satisfactory 

 method, giving results which were too low, and it was therefore impossible to calculate 

 the percentage digested. If we assume that this is the same as in a later experiment (see 

 Table I), a figure can be obtained for the volume filtered which will be approximately 

 correct for the richer concentration but minimal for the weaker. The estimated 

 volume filtered in 24 hours in a concentration of 106,000 Skeletonema cells per ml 

 varied from 1-6 to 40 ml in 24 hours, and in a concentration of 10,600 cells per ml 

 from 5-7^2-5 ml. It is usual to find that in high concentrations of food cells filtration 

 falls off, and the figures obtained compare well with our earlier experiments using '^?. 



Table I 

 Feeding experiments with Calanus using cultures grown with "C 



Species 



Concentratiuns 



Cal- 

 anus 



o 



Time 

 of 



expt. 

 in 



hours 



iFaecal pellets 



I No 



Skeletonema 



costatum 

 Culture 



Filtrate 



Cryptomonas 

 Culture 



Filtrate 



1615 counts ml min 

 144000 cells ml 

 001 counts cell 



35 counts/ml /min 



1 



T 



3 

 4 

 5 

 A 

 B 



I7i 

 17-1 

 \1\ 

 Ml 

 17* 



1275 counts /ml /min 

 12600 cells ml 

 010 counts cell 



60 counts/ml/min 



1 



2 

 3 

 4 

 5 

 A 

 B 



in 

 in 



in 



in 



21i 



m 

 in 



54 



17 



47 







10 



4 







Syracosphaera 



carterae 

 Culture 

 Filtrate 



840 counts/ml/min 1 



13500 cells/ml 2 



06 counts 'cell 3 



8 counts ml min A 



38 

 51 

 80 

 56 



57 

 2 



Lost 



Body Total 

 I less removed 

 Countsfiltrate, c min | 

 Imin cimin ' 



ml 

 °o filtered 

 used in 24 hr 



lis 



192 

 301 



59 

 36 



170 



465 

 449 

 220 

 516 



817 

 283 

 673 

 

 119 



}«. 



1095 



475 



974 







178 



74-6 

 59-6 

 69- 1 



090 

 0-38 

 0-81 



66-9 14 



289 



86 



392 



The results of a second experiment with Skeletonema are shown in Table I. In this 

 and subsequent experiments all the bodies and faecal pellets were disintegrated. As 

 is usual in feeding experiments, individual variation was considerable; the number 

 of faecal pellets varied from 10-54, and one Calanus did not feed at all. The amount 

 digested varied from 60-75%, a figure very similar to that obtained with cultures 

 labelled with ^^P. Unfortunately the Calanus v/ere in poor condition and the volume 

 filtered, less than 1 ml in 24 hours, was low. The activity of the culture was not high 

 enough to give very accurate results. In both experiments with Skeletonema, the cell 

 concentration was high compared with what is found in the sea. 



In an experiment with Cryptomonas, which has cells about 20ix long, all the females 

 fed well, although they filtered on an average only about I ml in 24 hours (Table 1). 

 The digestion ranged from 53-78%, as compared with 51-89% in cultures labelled 

 with 3 2p. 



Finally, the experiment with Syracosphaera was carried out using three Calanus 

 in a concentration of 13,500 cells/ml. Judging by faecal pellet production, they fed 



