Discussion 



The Yellowstone River net plankton reported here (Tables 1 and 

 2) and the nannoplankton reported in earlier and ongoing studies (5, 

 9, 16) differ considerably in composition, except that in all cases 

 diatoms were reported as the dominant group. None of the filamentous 

 Chlorophyceae in Table 1 were reported in the nannoplankton by other 

 workers nor were any of the five dominant non-diatom plankton taxa 

 listed in Table 2, including Cladophora glomerata . The reason is 

 primarily because the net plankton drift method employed here selects 

 for larger (filamentous) forms as opposed to the smaller cells, which 

 may pass through the meshes of the net. On the other hand, a water 

 bottle sample would select for the smaller organisms occurring at 

 higher densities in a given volume of water, and against the occasion- 

 al detached and drifting filament. 



It is evident from all Yellowstone algae studies that suspended 

 algae of benthic origin make up the bulk of both the net plankton and 

 the nannoplankton. Very few of the algae observed in the plankton are 

 typical or "true" plankters, but these may be well concentrated in 

 some reaches (9). However, many of the detached and suspended benthic 

 forms are either dead or dying. The Public Health Service (9) reported 

 more dead than living diatoms in the plankton and much of the suspended 

 filamentous Chlorophyceae appeared degenerate in the present study. 

 (Recently developed staining techniques could be employed to more 

 accurately determine the ratio between synthesizing and decomposing 



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