46 



PLANKTON OF THE SUPPLY TANKS OF THE 

 DOVE MARINE LABORATORY. 



By OLGA M. JORGENSEN. 



An investigation of the contents of the supply tanks was 

 made from May, 1917, to May, 1918, in the hope that it would 

 yield a satisfactory indication, both quantitatively and quali- 

 tatively, of the micro-plankton of the sea at Cullercoats, but 

 as the method has been found to have many disadvantages, and 

 owing to too little time being available for the work, only a very 

 general account can be given. 



At first the water to be examined was drawn from the 

 Laboratory taps, and a certain amount, usually 1,000 cc, filtered. 

 The contents of the filter paper were washed in a known quantity 

 of filtered sea-water, and either examined straight away or 

 centrifuged fir.st. This was found to be tedious and unsatis- 

 factory, after which the centrifuge only was used, the method 

 employed by Dr. Marie Lebour at Plymouth being adopted.* 



Samples of sea-water were obtained by lowering a large can 

 into the supply tank until it dipped just sufficiently below the 

 surface to become filled. The water was then well stirred before 

 being drawn o& with a pipette and run into the centrifuge tube. 

 Samples were taken and examined once a week whenever possible, 

 the temperature, height of water in the tank, and the weather 

 conditions being noted. No samples were taken during the month 

 of December. 



The samples were found to consist almost entirely of Diatoms, 

 Peridiniales and Protozoa, with an odd Nemertine, Copepod 

 or Pygnogon appearing occasionally. 



DIATOMS. 



On the whole, the average number of diatoms for each month 

 gives a curve similar to that recorded for Plymouth* and the 

 Irish Sea,f that is to say, there is a smaller autumn maximum 

 and a considerably higher spring one {see fig. 1). The autumn 



* " The Microplankton of Plymouth Sound." By Marie V. Lebour, D.Sc. 

 t Herdman in " Lane. Sea Fish. Lab. Reps." for yearis 1907-1917. 



