LIMNOLOGICAL STUDIES OF KARLUK LAKE 425 
Table 12. — Numerical analysis of the net -plankton catches of Karluk, Thumb, and O’Malley Lakes — 
Continued 
[The average number of organisms per liter of water from surface to bottom is indicated for the different series] 
O'MALLEY LAKE 
KARLUK LAKE 
Five series of catches were taken in the deepest part of Karluk Lake (station 1) 
in 1927 and two series in each of the other years, 1928 to 1930, respectively. Twelve 
series of catches were also taken at station 2 in the Thumb during this same period 
of time and two at station 3 in the Lower Basin. (See map, fig. 1.) 
Zooplankton . — The Cladocera were represented in Karluk Lake by specimens of 
Bosmina and Daphnia. Numerically these two forms were about equally abundant in 
the various catches. Both forms were most abundant in the upper 50 meters; in 
some series, in fact, they were not found in the catches taken below this depth. The 
smallest number of Cladocera was noted in the series of catches taken on July 12, 1930. 
The maximum number of Daphnia was obtained in the 5-10-meter stratum at station 
1 on September 8, 1929, namely, nine individuals per liter of water. The largest 
catch of Bosmina (13 per liter) was found in the 30-50-meter stratum on September 3, 
1928. (See Table 12.) 
The Copepoda were represented in the catches by species of Diaptomus and Cyclops ; 
individuals belonging to the latter genus were more abundant than those belonging 
to the former. Both forms were more abundant between the surface and 70 meters 
than they were below the latter depth. The maximum number of Diaptomus was 
found in the 0-5-meter catch taken at station 1 on September 8, 1929, namely, 22 
individuals per liter of water. In the same catch Cyclops reached the maximum 
number of 145 per liter. The average number of Copepoda from surface to bottom in 
the catches taken on September 8, 1929, was 35 per liter. This was the highest 
average obtained in any of the series at station 1. The copepod nauplii were more 
numerous than the adults; they were more abundant in the upper 10 to 20 meters than 
at greater depths. In 1927 the largest average number of nauplii for the entire depth 
of the lake was found on August 13 when 47 individuals per liter were found. A 
maximum average of 100 per liter was noted on September 3, 1928. The smallest 
average number was found on July 12, 1930, namely, 3.3 per liter. 
Numerically the Rotifera constituted the major part of the zooplankton in Karluk 
Lake. Asplanchna, Anuraea, and Polyarthra were the most abundant forms in this 
group and they were most numerous in the upper 10 meters. Notholca was obtained 
in considerable numbers below a depth of 15 meters in some of the series. In all of 
the series the rotifers were much more abundant in July than in September. The 
decrease in the number of rotifers during the summer is well illustrated in the five 
