the mean abundance of phytoplankton was 11 times as great as in the 

 Detroit River Section, which would place the section somewhat below 

 the River Raisin Section in order of abundance. Exactly comparable 

 data are not available for the Crustacea, but for five of the six 

 two-week periods the mean abundance was 57 per liter, which was well 

 above the mean abundance in the River Raisin Section for the same 

 five periods. Thus this section held third place among the different 

 sections in abundance of phytoplankton, but second in abundance of 

 Crustacea. Here, again, too few samples probably explain the dis- 

 crepancy, for conditions are unusually changeable at Station 1$9» 



In 1929 the sampling program was too irregular to allow a 

 satisfactory comparison of the different sections with regard to 

 the abundance of both phytoplankton and zooplankton. As far as com- 

 parisons can be made, they seem to confirm the broad conclusions 

 reached from the data of 1930. 



It was pointed out in the chapter on phytoplankton that the 

 differences in abundance in the sections were in part the result of 

 natural conditions, but that the differences have been accentuated 

 by pollution. In view of the anparent relationship between the abun- 

 dance of phytoplankton and Crustacea," it is reasonable to suppose 

 that there were differences in abundance of Crustacea under natural 

 conditions, and that these have been accentuated bj' pollution. That 

 is, in all probability, the increase of phytoplankton and organic 

 detritus resulting from pollution has made possible an increase of 

 the Crustacea. 



The bottom organisms of the offshore waters of Western Lake Erie 



Introduction 



Previous investigations in the Great Lakes 



Our knowledge of the bottom organisms of the Great Lakes is based 

 almost entirely on qualitative studies. The first to use a dredge for 

 this purpose was Stimpson (1870), who reported the kinds of animals taken 

 in fairly deep water in Lake Michigan. Hoy (1872), who worked with 

 Stimpson, also gave a brief account of the results. More extensive 

 studies of the same kind were made by Smith (I87I and l87U) in Lake 

 Superior, and by Nicholson (1872) in Lake Ontario, In addition to 

 tteasgeneral reports, there have been a number of reports on special 

 groups of organisms. Such are certain of the appendices to a paper by 

 Reighard (l89h) on Lake St. Clair, and to a paper by Ward (I896) on 



2U9 



