A UMNOI.OGICAI. STUDY OF THF FINGFR LAKES. 
593 
The Finger Lakes differ widely in area, depth, gas content, etc., but there was no 
corresponding qualitative difference in the plankton. For the most part the same 
forms were present in all of the lakes, but the relative abundance of the various forms 
varied greatly in the different lakes. The most prominent qualitative differences were 
the absence of Daphnia in Seneca Lake and the absence of Limnocalanus and Mysis in 
the smaller and shallower lakes. 
Phytoplankton.—Three different classes of algae were represented in the plankton 
of the Finger Lakes, viz, the Chlorophyceae by Staurastrum; the Bacillarieae or diatoms 
by Melosira, Cycloiella, Tabellaria, Fragilaria, Symdra, Asterionella, and Navicula; and 
the Myxophyceae, or blue-green algae by Anabaena, Aphanizomenon, Lyngbya, Oscil- 
latoria, CcdosphcErium, Clathrocystis , Gloeocapsa, and Aphanocapsa. These forms were 
confined chiefly to the epilimnion where light conditions were most favorable for the 
process of photosynthesis. In some of the lakes, however, relatively large numbers of 
phytoplanktonts were found in the thermocline and even in the upper portion of the 
hypolimnion. In Cayuga Lake, for example, there were more than a thousand Asterio- 
nellas per liter of water at a depth of 30 meters and in Skaneateles Lake this same form 
numbered i,i6i per liter in the 30-50 meter stratum, more than five times as many as 
were found in the o-io meter stratum. The presence of this form in such large numbers 
in the deeper water where light conditions were not so favorable for photosynthesis was 
most probably due to the fact that they were senile individuals. Both lakes had a fairly 
high degree of transparency, a Secchi’s disk disappearing from view at a depth of 5.1 
meters in Cayuga Lake and at 10.3 meters in Skaneateles Lake, but it is doubtful whether 
enough light reached these organisms to enable them to carry on the process of photo- 
synthesis to any considerable extent. 
The circulation of the water of the epilimnion tends to produce a uniform dis- 
tribution of the phytoplankton in this stratum, but the diagrams (fig. 18-22) indicate that 
such a result was not attained, since all of the curves representing algae show a point 
of maximum density of population. 
In Canandaigua and Otisco Lakes the blue-green algae predominated, with Clath- 
rocystis and Ccelosphcsrium as the most abundant forms. Clathrocystis was the pre- 
dominant alga in Owasco Lake. Diatoms were most abundant in the other seven 
lakes, with Asterionella, Fragilaria, and Tabellaria as the predominant forms. 
Zooplankton. — Ceratium was found in all of the Finger Lakes, and was most abun- 
dant in Cayuga, where 2,525 individuals per liter of water were found at the surface. 
Hemlock Lake ranked second, with a maximum number of 1,645 individuals per liter 
at a depth of 12 meters. The smallest number was found in Owasco Lake, and Seneca 
Lake came next in order. Owing to the fact that this is a chlorophyllous organism, 
it has been included in the curves showing the blue-green alg$ in the diagrams. 
Dinobryon appeared in the plankton of 7 of the 10 lakes, but it was scarce in 
all except Owasco, where it was much more abundant than any of the other small 
organisms. 
