278 POPULATIONS OF THE SEA 



Looking back upon these scattered observations of growth re- 

 sponse in marine phytoplankton to the salinity of the environ- 

 ment, it may be stated that, so far as these go, they justify confi- 

 dence that information from experimental results may be applied 

 successfully in interpreting records from surveys at sea. The con- 

 sistent results for different clones of dinoflagellates from the same 

 locality, or from widely separated localities, indicate that even 

 with the use of a clone from only one locality, the results may be 

 applied for populations of a large area. Howe\'er, when we turn to 

 the temperature experiments, we soon see that the picture is more 

 confused. 



Temperature 



Since the first biogeographical sur\-eys of marine phytoplankton, 

 temperature has been regarded as an essential ecological factor 

 for the geographical distribution of each species. Terms such as 

 arctic, boreal, temperate, and tropical species are generally used 

 with the implication of a decisive temperature effect upon growth 

 and sur\ival. In trying to explain the succession of diatom species 

 in north European coastal waters during the spring maximum 

 and the following decline, temperature has also been suggested 

 as an important factor. Attempts at verifying the validity of these 

 assumptions through experiments are, however, few. 



In Table I data have been gathered from field obser\'ations 

 and from experiments for the few planktonic diatoms which have 

 been studied as to the effect of temperature upon growth. Schreiber 



Table I. Temperature-Growth Relationship in Marine Plankton Diatoms" 



" According to Ostenfeld, 1913; Schreiber, 1927; Gran, 1929; Braarud, 1937; Gr0ntved; 

 1949. 



