930 East i ' 

 Introduction **%*, ^ 



Algae — small, often microscopic aquatic plants — are responsible for the major 

 share of primary production within the Yellowstone River ecosystem. Together with 

 organic matter contributed by terrestrial plants along the river banks, algae form 

 the base of the aquatic food pyramid that culminates in the production of such con- 

 sumers as osprey and trout or sauger. Many algae are rather specific in their 

 tolerance of habitat conditions and therefore serve as reliable indicators of com- 

 munity health and water quality. 



With the imminent potential for massive coal development in the Yellowstone 

 basin, including possible large-scale diversions and a major impoundment, a thorough 

 knowledge of the existing biological system is an urgent must both for defining 

 existing conditions and for predicting future changes. Benthic algae, along with 

 aquatic bacteria and fungi, belong to the periphyton or aufwuchs community. Rela- 

 tively little is known of the periphyton community of the Yellowstone River system. 

 Roeder (2) studied the diatom assemblage of the Gardner River, a tributary of the 

 Yellowstone in Yellowstone National Park. Wright and Soltero (6) described the 

 algal flora of Bighorn Lake on the Bighorn River. Stadnyk (3) measured biomass 

 standing crop and autotrophic index of the periphyton community at three stations 

 between Gardiner and Billings but did not determine species composition. Westinghouse 

 (4) identified the suspended algae and counted organisms of the "phytoplankton" 

 community at two stations near the mouth of Armells Creek. And Williams (5) de- 

 termined the percent occurrence of plankton algae at Sidney over a one year period. 



The present report concerns three net samples taken on April 2, 1973 at the 

 following locations: Yellowstone River at Myers Bridge (001), Bighorn River at 

 Bighorn (002), and the Yellowstone River at Custer (003). The samples were collected 

 at midafternoon by suspending a small net from a bridge for five minutes. The 



