MARINE ORGANISMS AND ENVIRONMENTAL INFLUENCES 



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For the dinoflagellate species Exuviaella baltica, Peridinium 

 triqiietnim, and Ceratium tripos, the salinity experiments have 

 thus given an explanation of characteristic features in their dis- 

 tribution in habitats of relatively low salinity. In the other species 

 investigated, there is an overall agreement between the results ob- 

 tained in the experiments and the known distribution of the spe- 

 cies. This fact indicates that experiments on clone cultures from 

 one locality may give results which are applicable to the popula- 

 tion of the species within a larger area. 



Beforehand one might have reason to doubt whether this would 

 be the case. In experimental work of this kind one may question 

 whether clones or strains are constant in their response to en- 

 vironmental conditions; whether a single clone is representative 

 of a local population, and one may even ask if there exist geo- 

 graphical races, especially in species with a v^ery wide distribu- 

 tion. Only a very few observations are available for elucidating 

 these points, which are of obvious importance when trying to apply 

 experimental results to the understanding of what happens in the 

 sea. 



In Fig. 3 are shown graphs from salinity experiments on the same 

 clone of Peridinium trochoideum at different temperature condi- 

 tions and with media made up of different batches of sea water. 

 It will be seen that the general features of these curves are similar: 

 an optimum appearing at about 20 %o, while reproduction at higher 

 salinities differs somewhat. Two clones of Prorocentrum micans, 

 both from the Oslofjord, but isolated at different times, also show 



Fig. 3. Growth at different salinities as percentage of maximal growth rate. 

 Left, experiments on the same strain from Oslofjord ;r/g/z/, experiments on Oslofjord 

 strains from different years (Braarud, 1951). 



