In contrast to conditions at Station 126 we may cite the 

 example shown by Stations 252 and 25I4 in the Maumee Bay Section. 

 Here phytoplankton was extremely abundant; the mean abundance for 

 a period of three months in 193C was 26 times as great as at 

 Station 126 (Table 62) . Accompanying the great abundance of 

 phytoplankton there was a great abundance of plankton Crustacea; 

 for the same period of time in 1930 the mean count was 20 times as 

 great as at Station 126. Similar but less pronounced differences 

 in both phytoplankton and zooplankton are evident in comparing the 

 Detroit River Section with other sections of the lake. 



The data of 1930 permit the demonstration of a still closer 

 relationship between the abundance of the Crustacea and the phyto- 

 plankton. For a period of three months, the sections, listed in 

 descending order according to the abundance of both algae and 

 Crustacea, were: Maumee Bay, River Raisin, Island, and Detroit River 

 (compare Tables 82 and 62). In vievj of this agreement, it is dif- 

 ficult to escape the conclusion that the marked inequalities in 

 horizontal distribution of the Crustacea are the result of the 

 irregular distribution of the phytoplankton. 



The relationship between the plants and animals probably is 

 not entirely direct. Naumann (I9I8) found that fine organic detritus 

 was a more important item of food for the Crustacea than the living 

 algae, but Klugh (192?) found the opposite to be true. The relation- 

 ship between the abundance of phytoplankton and zooplankton, which 

 has been observed many times, seems to be partly indirect, that is, 

 through the organic detritus derived from disintegrating algal cells. 

 In Western Lake Erie detritus derived from domestic sewage probably 

 is an important part of the food of the Crustacea, and probably, too, 

 the relative positions of the different sections with respect to 

 abundance of detrital food from sewage was the same as with respect 

 to that derived from the algae. 



It should be pointed out that the correlation between abun- 

 dance of plants and of animals was not perfect. For example Maumee 

 Bay had 26 times as much phytoplankton as the Detroit River Section, 

 but only 20 times as many Crustacea, In the Island Section there was 

 four t-'mps as much phytoplankton, but 13 times as many Crustacea, as 

 in the Detroit River Section. The lack of perfect agreement is to be 

 expected because the number of samples was not large enough to de- 

 termine the mean abundance of plankton with great exactitude, and 

 because sources of food for the Crustacea other than the plankton 

 algae and their products of disintegration tend to disturb the normal 

 relationship. Station 1^9, in the Portage River Section, offers another 

 example of lack of agreement. In the period of three months in 1930 



218 



