Diaptomus, Daphnia, Diaphanosoma, and Rotifera. For Cyclops and the 

 nauplii there was less agreement. The abundance of Crustacea in this 

 section as compared to that in the other sections vri.ll be considered 

 in later pages, 



Detroit River Section 



Station 126 is located five miles out from the mouth of 

 Detroit River, and the water here, except possibly under unusual 

 conditions, has come directly from the river. Samples were taken 

 at this station six times in 1929 and seven times in 1930 (Table 78). 

 It is obvious from the results given that the water of Detroit River 

 is extremely poor in plankton. None of the crustacean groups 

 appeared in greater abundance than 3 per liter, and Daphnia appeared 

 only in traces. The largest number of rotifers found was 5 per liter. 



A possible explanation of the small amount of plankton here 

 was suggested by the results obtained by Reighard in September, 1893. 

 He found that the volume of plankton per unit volume of water near 

 the islands of Lake Erie was three times the volume of plankton per 

 unit volume of water in Lake St, Clair (Reighard, I89U, p. 37). Also, 

 in the spring of the same year he found little plankton in upper 

 Detroit River as compared with Lake Michigan (Reighard, 1893) . Obviously 

 if there were little plankton in the water entering Detroit River, there 

 still would be little when it emptied into Lake Erie, for it is well 

 known that plankton organisms do not reproduce well in rivers. 



In order to get additional data on the plankton in Lake 

 St. Clair, a trip was made to the lake on September 23, 1930, and 

 samples were taken near Reighard 's Station VIII. The depth was 

 3.9 meters. Trap samples were taken at depths of 0, 2, and 3 meters. 

 The only form which had an average count of more than 1 per liter was 

 Bosmina, with h per liter. Diaptomus, Cyclops, nauplii, and rotifers 

 were each represented by 0,9 individual per liter, Daphnia by D,l per 

 liter, and Diaphanosoma by 0,03 per liter. In view of such scarcity 

 of plankton, we might expect the low counts recorded for Station 126 

 on the same date (Table 78), In addition to the forms shown in this 

 table, Bosmina was found to the extent of 2 per liter. At this time 

 there was still a considerable number of plankton organisms in the 

 Island Section. On September 2h the following counts (per liter) were 

 recorded for Station 8F: Diaptomus 0,5, Cyclops 10, nauplii 2, 

 Daphnia 3, Diaphanosoma 0,5, rotifers 0,6, The average of several 

 stations for the period September l6-30 was somewhat higher for most 



238 



