LeBRASSEUR and KENNEDY: LAKE FERTILIZATION. II. 



females were in about equal numbers at both 

 stations. In Figure 5 the eggs per Cyclops were 

 about equally numerous at both stations. There 

 were three and possibly four periods of 

 maximum egg production for Cyclops females, 

 i.e. June, mid-July through to the third 

 week in August, and the last week of September 

 through to the first week of November; the lat- 

 ter time interval could possibly be interpreted 

 as consisting of two separate periods of egg pro- 

 duction (late September and late October). 

 Diaptomus females at Station 1 had two major 

 periods of egg production, mid-June through 

 mid-July and mid-August through the first week 

 of September, with a period of relatively low egg 

 production from mid-July to the end of August. 

 At Station 2 there was no clear cessation of 

 Diaptomiis egg production from mid-June 

 through to the first week of September. For a 

 major part of this period there were more than 

 10 eggs per female being produced. There was 

 also a brief period of Diaptomus egg production 

 in mid-May. 



The production of Bosmlna eggs ranged be- 

 tween and 0.5 per individual. From May 

 through mid-August more eggs were produced 

 at Station 2 than at Station 1 and thereafter 

 the egg production was nearly equal at both sta- 

 tions. The summer minimum which occurred 

 in the first 2 weeks of August was followed 

 by a rise in the number of eggs in the first week 

 of September continuing until the end of the 

 third week of September. The summer max- 

 imum of adult Bosmina shown in Figure 4 oc- 

 curred approximately 1 week after that of the 

 eggs while the maximum standing stock of Bos- 

 mina (which occurred in mid-October) was pre- 

 ceded by the production of eggs 3 to 5 weeks 

 earlier. Holopedium exhibited two clearly de- 

 fined peaks in the production of eggs, from 

 the first to the third week of June and again 

 from the first to the third week of September. 

 The corresponding maximum in the standing 

 stock of Holopedium shown in Figure 4 occurred 



Figure 5. — Ratio of the number of eggs to the number 

 of adult females. The data from 50-m vertical samples 

 at Stations 1 and 2 have been averaged to give a 4-day 

 running mean ratio. Note: scale changes for different 

 species. 



from the second week of July through to August 

 25 and from September 27 to about October 20; 

 the summer minimum occurred between the two 

 peaks. The production of Daphnia eggs took 

 place from June to mid-September with a second 

 brief rise in egg production during mid-October 

 at Station 2. The numbers of eggs produced 

 per female at Station 2 by all species of clado- 

 cera was generally greater or equal to that at 

 Station 1. It should be noted that the latter was 

 found for both the prefertilization period in May 

 as well as during the period of nutrient additions. 



ZOOPLANKTON BIOMASS 



The wet weights for 1970 50-m vertical hauls 

 at Stations 1 and 2 were combined and expressed 

 as a monthly mean wet weight (g/m-) together 

 with the range about the mean weight (Figure 

 6) . Included in Figure 6 (below) are individual 

 weights for the 1969 sampling. The maximum 

 wet weight in 1969 never exceeded 1 g/m- where- 

 as in 1970 the weights ranged as high as 15 g/m^. 

 The average wet weight of zooplankton during 

 the period May through October was approxi- 

 mately 0.5 g during 1969; for the same period 

 in 1970 the average weight was 10 times larger, 

 i.e. 5.3 g. The sample weights increased at a 

 rate of 3'^r per day May through July to a max- 

 imum average wet weight of 8.6 g/m-; there- 



JON FEB M4HCH IPBIL MAY JUNE JULY 4UG SEPT OCT NOV DEC 



Figure 6. — Zooplankton wet weight (g/m^) for 50-m 

 vertical hauls. In the lower part of the figure, the points 

 marked "x" indicate individual weights (g/m2) for 1969 

 samples. 



33 



