38 U. S. BUREAU OF FISHERIES 



maximum, which in 1922 appeared on June 15. did not arrive in 

 Great Harbor until August 9. 



A very noticeable factor in the investigation in Vineyard Sound 

 was the direct effect of temperature on the distribution of pelagic 

 imimals and on the breeding seasons of benthonic animals having 

 planktonic larvae. In the deeper waters offshore, temperatures 

 were found in August which compared with the late May and early 

 June temperatures at Woods Hole. The plankton found there also 

 proved to be identical with the May and June plankton of Great 

 Harbor. 



The annual distribution of the diatom maximum of the American 

 coast is very similar to that of the eastern Atlantic waters, in that 

 the seasons of the greatest swarms retreat farther and farther from 

 the wannest months as one approaches the Tropics. A similarity in 

 the seasonal variation in European and American waters of the 

 same latitude is particularly noticeable, conditions at Woods Hole 

 corresi3onding to those in the Adriatic Sea. The great effect of the 

 arm of Cape Cod on the local plankton is again evident, for within 

 20 miles of Massachusetts Bay, where the seasons of diatom pro- 

 duction are similar to those in the Norwegian Sea, conditions com- 

 parable to those of the Mediterranean and Adriatic Seas are found in 

 Buzzards Bay. 



A rejDort on the plankton of the Woods Hole region for 1922 and 



1923, compiled with complete records of plankton collections by the 

 late Vinal N. Edwards covering the years 1893-1907, was submitted 

 for publication during the past year. 



Through the courtesy of the Coast Guard, Doctor Fish was able 

 to make a three weeks' cruise off the east coast of Newfoundland on 

 the Coast Guard cutter Modoch^ leaving Halifax on June 2. Col- 

 lections, which often yielded large numbers of fish eggs and occa- 

 sionally larval fish, were made over the northern part of the Grand 

 Banks. 



ECOLOGY OF FRESH-WATER LAKES 



The quantitative studies of the flora and fauna of Green Lake, 

 Wis., which have been in progress since 1921, were completed in 



1924. This work has been conducted by Dr. Chancey Juday, of 

 the Department of Zoology of the University of Wisconsin. The 

 survey of the flora showed that the large aquatic plants usually 

 extend down to a depth of 8 meters, but in favorable localities they 

 reach a depth of 10 meters. The average crop of these plants in the 

 — 8 meter zone amounted to 13,540 pounds per acre, wet weight 

 (1,588 pounds per acre, diy weight). About 49 per cent of the dry 

 material consisted of Chara, and 20 per cent of various species of 

 Potamogeton. 



The standing crop of plankton in Green Lake yielded an average 

 of 244 pounds of dry organic matter per acre. The living plankton 

 organisms weigh approximately 10 times as much as the dry or- 

 ganic matter, so that the live weight of this standing crop was sub- 

 stantially 2,440 pounds, or a little more than 1 ton, per acre. The 

 upper 10 meters yielded more than any other 10-meter stratum. 

 The horizontal distribution of the plankton was fairly uniform 

 over the entire lake. 



