One of the most dramatic examples of a cold-water stenotherm is the mountain- 

 stream-dwelling chrysophyte Hydrurns foetidus . This macroscopic, brown, gelatinous, 

 unpleasant-smelling alga is relatively abundant in both the eastern and western mountain 

 streams of North America. The gelatinous envelope in which the cells are embedded is 

 exceedingly tough and the plant frequently covers the entire surface of submerged rocks 

 and has caused more than one hiker to lose his or her footing when crossing a stream. It 

 normally begins to disappear when water temperatures rise much above 10°C. . .Other 

 requirements for this species apparently include low pH and bright sunlight. 



Hydnirus foetidus often dominates the winter and spring algal communities of glacier- fed 

 streams of the Swiss Alps, which exhibit unstable channels and wide seasonal fluctuations in 

 flow, temperature, and turbidity (Hieber et al. 2001). Elsewhere, Kawecka (1990) reported that 

 Hydrurus foetidus dominated the algal communities of unregulated streams in a study of paired 

 regulated and unregulated streams. 



Diatoms were common in Jennies Fork and ranked 2" , while Oscillatoria sp. was 

 occasional and ranked 3'^''. Like Jackson Creek, Jennies Fork supported only 2 genera of non- 

 diatom algae (Table 3). 



Granite Creek. The filamentous green alga Cladophora was abundant and ranked 1^' in 

 biovolume in Granite Creek (Table 3). Streams that support large amounts of filamentous algae 

 typically have more stable flows, firmer substrates, and larger concentrations of inorganic 

 nutrients than streams that do not support these algae. Diatoms were frequent and ranked 2"'' in 

 biovolume here, followed by Nostoc (frequent) and the desmid Cosmarium (common). This site 

 supported at least 5 genera of non-diatom algae, including occasional cells of Oscillatoria and 

 the filamentous red alga Audouinella. 



The presence o( Nostoc in Granite Creek, especially ear-shaped colonies of Nostoc 

 parmelioides (see discussion under Sample Notes above), indicates that nitrogen was likely the 

 limiting nutrient at this site. Large stands of filamentous macroalgae (e.g., Cladophora) are 

 known to release surplus PO4 into the ambient water, thereby decreasing the local N:P ratio and 

 conferring a competitive advantage on nitrogen-fixing algae, such as heterocyst-bearing blue- 

 green algae (e.g., Nostoc) (Lowe 2003). 



