PLANKTON 



265 



case, and the Copepod maximum usually about a month 

 after that of the Dinoflagellates. 



The cause of all these seasonal changes is still very obscure, 

 and they may be due to the interaction of several factors. 

 In addition to the normal succession of stages in the life- 

 histories of the organisms throughout the year, and the 

 diminution or extermination of those (such as Diatoms) 



JC.C 



*oopoo 



2.000 D 



»,oooC 



■t^^-*^-"-T •III "^^ t — 1 1 — =*— 1 r 



Jan. Feb. Mar. Apr. May Jitxe July Aug. Sept. Oct. Nov. Dec. 



Fig. 17 — Curves fob Total Plankton and fob Chief Constituent 

 Groups in Port Erin Bay in 1912. 



which form the food of others (such as Copepoda and young 

 fishes), we naturally turn to the meteorological conditions 

 prevaihng at the various seasons as being a possible cause 

 of the increase or the diminution in numbers. Although 

 one may arrive at the general conclusion that variations in 

 the amount of the plankton from year to year must be due 

 ultimately to meteorological conditions, it is not easy to 



