1 ] 2 S. M. Marshall and A. P. Orr 



the use of a small disintegrator. This consisted of a narrow tube (diameter 9 mm) about 7 cm long, 

 into which was fitted a perspex piston of almost the same diameter as the tube, and shaped at the 

 foot to fit the bottom of the tube. The Calanus or the faecal pellets were put in the tube in about 0-5 

 ml of sea water, and the piston rotated by a small motor. By raising and lowering the tube the water 

 and the Calanus or faecal pellets were forced past the rotating piston and thus disintegrated. After 

 washing down the piston and tube and making the volume up to 3 ml, five aliquot samples were 

 taken for measurement of activity. Microscopical examination showed that disintegration was almost 

 complete. No fragments of a Calanus body could be recognized, and there were very few recognizable 

 bits of faecal pellet. The disadvantage of the disintegration method is the dilution of the activity, 

 since only 0-2 ml samples were used from the 3 ml of fluid. This can be countered by taking more 

 sub-samples, or by making much longer counts. 



In a feeding experiment a number of bottles of about 70 ml capacity were filled with the diluted 

 culture prepared as described, and sampled for a count of cell number and activity. Into each bottle 

 was introduced a single Calanus. Since females feed better than either Stage V or male Calanus they 

 were always used. Each bottle was then tied in a black cloth bag (because Calanus feeds better in the 

 dark than in the light), and attached to a wheel revolving about once every three minutes in a vertical 

 plane. This keeps the culture cells from sinking to the bottom and so giving the Calanus an accumula- 

 tion to feed on. Control bottles containing filtrate from the culture used were also set up to measure 

 any uptake of ^*C from solution. Other control bottles, containing culture but no Calanus, were used 

 to measure the^*C returned to solution by the respiration of the plant cells. 



After leaving them to feed for a suitable time, usually 15 to 18 hours, each Calanus was removed, 

 washed three times to free it from radioactive water, disintegrated and sampled. The contents of the 

 bottle were then poured into a flat-bottomed perspex dish with the inside angles bevelled, and the 

 faecal pellets picked out under a binocular microscope. These too were washed, disintegrated, and 

 sampled and their activity was measured. 



The activity of the Calanus body added to that of the faecal pellets gives a measure of the total i*C 

 removed from the culture. From these and the culture reading can be calculated the number of cells 

 ingested, the percentage digested and the volume of water swept clear. The results can be expressed 

 either as counts per minute or as cell equivalents. The cell equivalent is a useful figure when consider- 

 ing the total amount taken up, but if we express the activity of the faecal pellets as cell equivalents, 

 it must be remembered that each " cell equivalent " really represents several cells, the number varying 

 according to the percentage digested. 



EXPERIMENTAL WORK 



Feeding experiments with female Calanus were made, using cultures of the diatom 

 Skeletonema costatum, one of the more important spring diatoms in the sea, and the 

 flagellates Cryptomonas sp. (Plymouth strain 23) and Syracosphaera carterae. The 

 cultures when used were only a few days old, and were probably in the exponential 

 growth phase. It was thought that some of the "C might be present in the inorganic 

 form, either adsorbed on the cells or in solution inside. This was tested with Skele- 

 tonema by exposing samples on planchettes to the fumes of hydrochloric acid 

 (Steemann Nielsen, 1952), and comparing the activity before and after exposure. 

 About 7 % of the total disappeared with this treatment. With Syracosphaera, which 

 possesses large numbers of calcareous coccoliths, the loss seemed to be greater but 

 accurate measurements were not made. 



The control bottle containing culture but no Calanus showed that, as a result of 

 the respiration of the plant cells, the i*C content of the filtrate had risen by 2-5%. 

 This will cause a slight underestimate of the amount taken up by the Calanus. 



A preliminary experiment was done with a culture of Skeletonema costatum in 

 two different concentrations. It was thought that the activity of the faecal pellets and, 

 in the lower concentrations, of the bodies also, would be too weak for the disintegra- 

 tion method, so they were torn up as finely as possible with needles and put in 0-2 ml 



