32 



Further Notes on Communities of Blue-Green Algae 



Helen Foot Buell 



In two previous papers^ the author described a fresh-water com- 

 munity of bhie-green algae collected in Minneapolis, Minnesota. 

 This community develops in bottom ooze and later floats to the 

 water surface. It is a globular, gelatinous mass, disagreeable in odor, 

 varying in color from greenish-black to black or reddish-black. The 

 community consists of an outer layer composed of species of Oscil- 

 latoriaceae, some having a violet color, and surrounding an oozy 

 inner portion containing pseudo-vacuolate, unicellular Cyan- 

 ophyceae. As far as I know there have been no other published re- 

 ports of such communities. 



During the summer of 1938, however, collections were made^ 

 in Lake Itasca, Itasca Park, Minnesota, of communities which are 

 practically identical with those previously described. They appeared 

 likewise to be developing in similar sitviations — bays of the lake 10 

 to 20 feet deep, offering some protection against water movement, 

 and having the bottom composed of a deep deposit of fine black 

 mud. These communities were from 2 to 5 cm. in diameter, some- 

 what smaller than those found earlier at Minneapolis, which were 

 from 2 to 8 cm. and occasionally 12 cm. 



There appears, however, to be a slight dissimilarity in the tem- 

 perature conditions under which the communities develop. As far 

 as was determined, the Minneapolis communities never developed 

 at mean temperatures lower than 21° C, and those having a red- 

 dish-black color, dominated by violet-colored Cyanophyceae, de- 

 veloped only at temperatures 2 to 3° higher. The Lake Itasca com- 

 munities were reddish-black in color and were composed mainly of 

 violet-colored Cyanophyceae. The mean temperature for the period 

 beginning 10 days prior to their first observance and ending the 

 last day of their observance (i.e., from July 28 to August 16) was 

 22° C, indicating development at slightly lower temperatures than 



■'■ Buell, H. F. A community of blue-green algae in a Minnesota pond. 

 Ecology 19:224-232. 1938. 



. The taxonomy of a community of blue-green algae in a Minnesota 



pond. Bull. Torrey Bot. Club 65:377-396. iy3cS. 



^ By Dr. Murray F. Buell and students at the Biological Station of the 

 University of Minnesota at Itasca Park, Minn. 



