270 Marine Microbiology 



Schwachlichtform en Starklichtfarmen 

 Kalteformen : Winterplankter Friihjahrsplankter 



Warmeformen : Herbstplankter Sommerplankter 



A similar interaction determines the seasonal occurrence of many 

 marine species, as demonstrated in Conover's (7) experiments 

 with natural phytoplankton populations in Long Island Sound. 

 Experiments with light adapted cultures of the diatom Biddulphia 

 mobiliensis suggest that upon exposure to other intensities the 

 growth rate is also a function of temperature (18). 



Halldal (17) has observed that pigment formation in the 

 hmnetic phytoplankter Anacystis nidulans is also dependent on 

 the simultaneous action of temperature and light intensity. Fin- 

 ally, it is well known that photosynthesis is determined by the 

 combined action of temperature and light above certain light 

 intensities (20). 



Temperature — Nutrients 



Hutner et al. (21) have demonstrated that the thiamine and 

 vitamin Bi:: requirements of the clnysophycean Ochromanas 

 malhamensis are related to temperature; indeed, there appears to 

 be a general relationship between temperature tolerance of natural 

 communities and nutrient availability (48). The marine diatom 

 Tlialassiosira nordenskioldii attains a maximum at 2° to 3° C 

 in Nature and disappears at slightly higher temperatures (15, 7, 

 33). Yet this diatom has exhibited prolific growth in culture at 

 10° C ( 1 ) when nutrients presumably were more concentrated 

 than normally encountered in Nati-ue. Braarud (2) has observed 

 boreal diatoms in active growth at 20° C in polluted areas of the 

 Oslofjord (Norway) whereas growth was negligible in non-pol- 

 luted areas. 



McCombie (29) observed that upon doubling the nutrient 

 concentration ( Chu No. 10 medium ) the lower limit of tempera- 

 ture tolerance of Chlamydomoims reinhardi shifted from 6° to 

 12° C and the optimum dropped from 28° to 18° C. The magni- 

 tude of the decrease in photosynthesis and growth of natural 

 populations caused by phosphate depletion is determined by 

 temperature ( 39 ) . The limiting effects of low phosphate supplies 

 become less pronounced as the temperature increases. 



