MARINE ORGAXrSMS AXD ENVIRONMENTAL INFLUENCES 273 



100% 



EXUVIAELLA BALTICA 



- 50%- 



10 



20 



30 



UQX< 



20 



30 



A07=c 



Fig. 1. Growth at different salinities as percentage of maximal growth rate 

 (Kain and Fogg, 1958; Braarud, 1951). 



samples with AsterioneUa showed a mean of 31.5%o (Ostenfeld, 

 1913) and, likewise, its general occurrence in the i\tlantic and the 

 Mediterranean at salinities above 35 %o and its absence in brackish 

 waters accord well with the experimental findings. 



Cultures of dinoflagellates isolated from the Oslofjord show 

 somewhat different curves for the salinity effect upon growth. 

 Let us first consider ExiiviaeUa haltica (Fig. 1). The growth rate is 

 remarkably high within the whole range from 10 %o to 40 %o, with 

 a slight indication of an optimum around 10 %c. These results are 

 in agreement with field records of its abundant occurrence in 

 waters of widely different character. It occurs in the brackish 

 waters of the Baltic, in the waters of varied salinity around Den- 

 mark, in the North Sea and the coastal waters along Norway, in 

 the oceanic parts of the Norwegian Sea and the North Atlantic, 

 in the Barents Sea, and e\'en in polar waters along the east coast 

 of Greenland. Obviously salinity does not restrict its distribution, 

 except in marine waters of extremely low salinities. 



If we consider the other dinoflagellates from the Oslofjord area 

 (Fig. 2), we may first point out that, like Exuviaella baltica, these 

 also have optima at salinities below 30 %0' namely between 15 %o 

 and 2Q^/cc, values which coincide with those for the surface waters 

 in the Oslofjord in summer, when these species occur in greatest 

 abundance. The main difference between the species is found in 

 their response to low salinities. 



Peridinimn triqiietrum, is characterized by fairly good growth 



