Relative Importance of Groups of Protozoa and Algae 237 



200 per inch is arbitrary, as cells of less diameter than the net 

 pores may be caught, while organisms of the same group or even 

 of the same species may differ greatly in size, sufficiently to be 

 classed as nannoplankton in one case and net-phytoplankton in 

 another. The diatoms Skeletonema costatum and species of 

 Chaetoceros are cases in point. However, if an arbitrary limit of 

 20/.1 in greatest dimension is chosen, most of the net-phytoplank- 

 ton will be above this. 



Wood and Davis (3) found that the nannoplankton greatly 

 outnumbered the net phytoplankton in the onshore waters east 

 of Cronulla. In the Coral and North Tasman Seas, where counts 

 were recently made from a large number of stations, and at depths 

 to 150 m, the nannoplankton is, on the average about 13 times 

 as numerous as the phytoplankton over 20^1 in diameter, and 

 ranges from 1 to 100 times as numerous, except on rare occasions 

 when the larger organisms may outnumber the nannoplankton. 

 In the Southern Tasman, however, the ratio of nannoplankton 

 to net phytoplankton ranges from 140 to 1 to 1 to 15, and the 

 net phytoplankton exceeded the nannoplankton at 35 per cent 



TABLE 1 



Composition of Phytoplankton in Random Samples from (a) Coral Sea, 

 (b) Southern Tasman Sea 



Diatoms and Larger 

 Microflagellates Gymnodinium, etc. Dinoflagellates 



\-5ti 5-10;U 110/i 



a. 10 

 19 

 16 

 30 

 10 

 20 



b. 10 

 30 



3 

 6 

 8 

 10 

 0.3 



