MARINE ORGANISMS AND ENVIRONMENTAL INFLUENCES 279 



(1927) found that the winter species Biddulphia aiirita showed far 

 better growth at low temperature than at ordinary room tempera- 

 ture, whereas the summer species Biddulphia sinensis reproduced 

 slowly at 5° and 9°C, but showed good growth at 16°C. Schreiber 

 concluded that this difference in temperature response gives an 

 explanation of the different seasonal occurrence of the two Bid- 

 dulphia species in the North Sea. 



On the other hand, recent experiments on Asterionella japonica 

 by Kain and Fogg (1958) gave results which are at variance with 

 those obtained by some of the field observations. Gran (1929) 

 reviewed the available field observations and concluded that 

 Asterionella, judged from its distribution, has a temperature op- 

 timum at about 8°C, and that it is also abundant in waters of 

 lower temperature, a conclusion which was supported by subse- 

 quent records from the North Sea area by Braarud et al. (1953). 

 Kain and Fogg (1958) observed, however, a definite temperature 

 optimum at 20-25°C and no growth below 10°C in a nonbacteria- 

 free culture (Fig. 6). The picture is becoming still more compli- 

 cated by the observations from Danish inshore waters by Gr0ntved 

 (1949) demonstrating abundant occurrence of Asterionella at a 

 temperature of 20-25°C. It becomes evident that neither the con- 

 clusions drawn from field observations by Gran (1929) nor the 

 experimental results by Kain and Fogg (1958) provide an ade- 

 quate characterization of the temperature response of Asterionella. 



Another discordance between the sea temperature during 

 periods of abundant occurrence and its growth in culture was ob- 

 served by Braarud (1937) for Thalassiosira nordenskioeldi, a 

 boreal neritic diatom species which also occurs in polar waters. 

 Ostenfeld (1913) gives a mean temperature for its occurrence in 

 Danish waters of about 2°C, a temperature which is similar to 

 that found by Gran and Braarud (1935) for waters showing the 

 greatest abundance of this species in the Fundy region and like- 

 wise, by Ramsfjell (1954) and Paasche (1959) for the Norwegian 

 Sea. In culture, however, Braarud found that it showed excellent 

 growth also at a temperature as high as 10-12°C, with growth 

 rates which presumably are near to the maximal ones for the 

 species. 



