Fresh-Water Invertebrates 



The Aleutian Islands are dotted with shallow pools. In only 

 a few cases are the pools larger than 5 or 10 acres, and most of 

 them are depressions only a few feet across. Standing on a hill- 

 side on Agattu Island, and looking over an expanse of about 2 by 

 5 miles, we estimated that there were 200 pools in sight. 



In 1937, collections of fresh-water organisms were made in 24 

 lakes scattered along the Aleutian chain. Crustaceans were col- 

 lected with a plankton net; mollusks and aquatic insects were 

 collected by hand. (A discussion of the insects is presented later 

 in the section devoted to land invertebrates.) 



The pools and lakes may be classed loosely in three groups, ac- 

 cording to their size and the amount of vascular plant life present, 

 as follows : 



Type 1: Small, clear pools (fig. 14). Shallow; vegetation absent 



rrlfa'rrtui - 



* 



Figure 14. — A fresh-water pool of type 1 (small and clear). Attu Island, 



August 17, 1938. 



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