592 
bulletin of the bureau of fisheries. 
course will be obtained from a large population of chlorophyl-bearing organisms and a 
small number of consumers. With a given amount of excess food the relative abundance 
depends upon the volume of the hypolimnion; the larger the volume of the water the 
smaller the relative abundance of food, and vice versa. 
These two types of vertical distribution have been noted also in the Wisconsin 
lakes. Only a comparatively small number of these bodies of water show the first type 
of distribution. Among those showing the second type the scarcity or absence of rotifers 
and Crustacea in the lower strata is due in all cases to the lack of oxygen, with the excep- 
tion of Green Lake, in which an insufficient supply of food is the important factor. 
O T 
685 1 Z02 
lAO 
IBO 
8.40 
680 
190 
nz 
m 
8.3 
8.70 
52 
8.90 
46 
Fig. 23. — Vertical distribution of plankton organisms in Seneca Lake, Aug. 4, 1910. Scale, i vertical space=s meters; i horizontal 
space=5 Crustacea, nauplii, and rotifers per liter of water and 100 algae and diatoms. Predo min a n t forms: Cyclops, Poly 
arthra, Ceratium, and Asterionella. Below 90 meters the organisms were too few to indicate in the diagram. The column at 
the right marked O shows the quantity of dissolved oxygen at the various depths as indicated, and T represents the 
temperature. 
Taking into account the results obtained both on the Wisconsin lakes and on the 
Finger Lakes, it appears that when the hypolimnion is well populated the maximum 
depth of the lake does not exceed 40 to 50 meters. On the other hand, when the maxi- 
mum depth reaches 70 meters or more a certain portion of the hypolimnion has a sparse 
population. The upper part of this stratum may possess a fairly large population, since 
it lies near the source of the food, and the bottom stratum may also be fairly well popu- 
lated, but between these two regions lies a zone which is poor in zooplankton, owing to 
the scarcity of food. The thickness of this poorly populated zone depends upon the 
maximum depth of the lake and also upon the relative amount of food contributed to 
the hypolimnion by the upper water. 
