plankters.) Nevertheless, it is likely that a considerable number of 

 suspended diatoms, green and blue-green algae are viable and capable 

 of synthesis as they drift in the current. Consequently any primary 

 production study on the Yellowstone must take the suspended peri- 

 phyton into account and should partition plankton synthesis from 

 benthic synthesis. 



Not only do benthic forms dominate the plankton, but all the 

 typical plankters were encountered in the periphyton, some more 

 frequently than in the plankton. Two reasons account for this: 

 (i) the net method underestimated the small plankters and (ii) even 

 many true plankters arise from the periphyton (4). This situation 

 illustrates the interconnectivity and indistinct boundaries of these 

 two communities in the Yellowstone River. 



In 1952 it was observed that Cladophora and diatoms dominated 

 the periphyton from Laurel to Glendive, with Cladophora most abundant 

 from Laurel to Huntley and diatoms most abundant from Custer to 

 Glendive (9). This was at a time when the river was receiving a much 

 larger organic waste load than it is today. Now, with less organic 

 pollution, it appears that diatoms and Cladophora are evenly matched 

 as co-dominants of the periphyton throughout the length of the river 

 (Table 2). 



Among the non-diatom algae, C ladop hora glomerata is far and away 

 the most important taxon in the Yellowstone River in terms of frequency 

 and abundance. In other waters, Cladophora often becomes a nuisance. 



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