Biological Survey — Oswego Watershed 147 



Genera of Plankton Organisms in Net Plankton and Nanno- 



plankton 

 Cayuga Lake. — The great bulk of the organisms occurred in the 

 upper 10 to 15 meters of water. Except for diatoms, the organisms 

 occurring below 15 meters were relatively scarce. There was a 

 striking similarity in the plankton life in the north and south sta- 

 tions. All of the dominant genera were about equally well repre- 

 sented in both localities. Most of the plankton organisms, except 

 diatoms, were found in greatest numbers during July and August. 



Net plankton. Cladocera. — Bosmina was the only common mem- 

 ber of this group. It occurred in greatest numbers between 0-10 

 meters during July and August. Polyphemus was found near the 

 surface in both stations during the middle of August. Cerodaphnia 

 was found only once, 0-5 meters, at the north station. Traces of 

 Daphnia and Leptodom were found in a few samples from each 

 station. 



Copepoda. — Diaptomus and Cyclops were observed each time 

 samples were taken but at no time did they become abundant 

 except in the upper samples taken in September. Nauplii were 

 fairly abundant in all samples taken between 0-30 meters. 



Rotifera. — Pleosoma was the most common rotifer. It was not 

 found in June. It became most abundant between 0-15 meters 

 during July and August. Conochilus especially during July and 

 Anura&a throughout the season were abundant at the north sta- 

 tion but much less common at the south station. Polyarthra, 

 Asplanchna, Notholca and Triarthra were frequently found at 

 various depths at both stations. Synchaeta was found (39 per 

 per liter, 5-10 meters, and fewer at greater depths) at the south 

 station on June 30, but not seen later. At the north station it 

 appeared in only one sample, July 9. 



Protozoa. — Ceratium was practically absent in June but showed 

 a steady increase until the latter part of August after which it 

 began to decrease. It was most common between 0-15 meters, 

 only traces being found below this depth. Ceratium was much 

 more common at the south station than at the north station. Only 

 traces of Dinobryon were found before July. It increased very 

 rapidly until the middle of August and two weeks later it had 

 disappeared entirely. Dinooryon was very much more abundant 

 at the south station than at the north station. Only small num- 

 bers of Vorticella, mostly attached to colonies of Anabaena, and 

 Difflugia were observed, mostly between 0-15 meters and in the 

 latter part of the season. Mallomonas was found only at the 

 north station, 0-10 meters, on August 17. 



Phytoplankton. Cyanophyceae. — Anabaena was found in both 

 station from the latter part of July to the end of August, between 

 the 7-10 meter depth. Traces of Microcystis were found at the' 

 south station in 0-5 meter depth. 



Chlorophyceae. — Small numbers of Pediastrum and Staurds- 

 trum occurred in two samples from near the surface at the north 

 station. Aside from a few undetermined unicellular green algae 

 these were the only Chlorophyceae found. 



