Effect of Plankton 



The attenuation as a function of the plankton content is 

 shown in figures 17 to 2 for the fundamental mode. Two 

 groups of organisms were dominant during the bloom, the 

 dinoflagellate Gonyaulax polyedra (fig. 17) and dinoflagel- 

 lates of the genus Peridinium (fig. 18). The attenuation in 

 figure 19 has been plotted as a function of the remaining 

 particulate matter containing chlorophyll. Finally, figure 

 2 gives the sum of the counts in the previous three figures. 



The plankton samples had a volume of 1 ounce. The 

 count was performed by first shaking the sample well, and 

 then, using an eye dropper, filling a Sedgwick-Rafter 

 counting cell with a portion of the sample. The dimensions 

 of the chamber are 50x20x1 mm, and the volume contained 

 is therefore 1 cm 3 (or 1 ml). The count was accomplished 

 at 100 power with a microscope equipped with a Whipple 

 micrometer disk. All the particles within the horizontal 

 lines of the disk were counted during three complete passes 

 in the length direction of the chamber. The calibration 

 showed that the number obtained should be multiplied by 

 5. 9 to give the number of particles per ml. It should be 

 noted that only a small fraction of the particulate matter 

 present was accounted for by the described procedure. 



Influence of Sampling Methods 



The rather poor correlation of attenuation and plankton 

 count might well be attributed to nonrepresentative sampling 

 Plankton determinations for biological investigations are 

 often accomplished by towing a plankton net at a chosen 

 depth for a given time. The count can then be performed 

 as described above. However, the accuracy will be much 

 greater since all of the plankton from the large volume of 

 water swept out by the net will be concentrated in a small 

 sampling jar. This method was attempted during the pres- 

 ent investigation by letting the discharge from the pump 



