however, it was found that it was most efficient to prepare 

 no more than two samples at a time. 



COUNTING 



Microplankton counts were made under a compound 

 microscope at 200 diameters. Size estimates of all orga- 

 nisms greater than 10 microns in diameter were made with 

 a Whipple ocular disc. The collecting area of the mounted 

 filter membrane was fixed by the diameter of the Millipore 

 apparatus. The diameter of the collecting area was found 

 to contain 36 square fields (fig. 6) delineated by the grid of 

 the Whipple ocular disc. The total number of fields per 

 slide was computed; each slide had a total area of 1017 fields. 



Concentrations as great as 10^ per ml of naicro- 

 constituents made total counts, which had been made in the 

 analysis of macroplankton, impractical. Consequently, a 

 valid sampling technique had to be developed for micro- 

 constituents. Counts of all recognizable organisms, to- 

 gether with inorganic particles and debris 10 microns or 

 larger, were made by means of a random-sampling technique. 

 Organisms in five percent (51 fields) and in 2|^ percent (25 

 fields) of the collecting area were counted. The following 

 method was used. All particles contained in 1 field, 25 

 fields, and 50 fields were counted and recorded by two 

 people. Each count by each person was repeated 10 times. 

 Variation in results of one individual's counts and differences 

 between results obtained by the two individuals were analyzed. 

 Both comparisons revealed differences in the number of 

 organisms which approached 20 percent in isolated instances. 

 In every case, however, the rank order of particles remained 

 the same. The largest difference in counts involved those 

 particles which were either present in large numbers, such 

 as Gymnodinium flavum, or were not only numerous but also 

 difficult to recognize. A further difficulty was that the 

 distribution of particles following Millipore filtration is not 

 even. Clumping of organisms and apparent adsorption of 

 particles to glass filtration tubes tend to form a ring on the 

 filter, a difficulty also encountered by Holmes (1962), 

 Whereas most counts were within 12 percent, no greater 



12 



