Chapter 58 



Phytoplankton Successions in the 

 Canadian Arctic 



Adam S. Bursa 



Xhe term "succession" is defined as the sequence of species in 

 time and space. Broadly, phytoplankton is rare in the sea when 

 metabolic activities decline, and increases when factors pennit. 

 The time sequence of growth from initial populations, cyst for 

 mation and germination is therefore significant for the delimita- 

 tion of the duration of individual cycles of plankton species build- 

 ing up to their collective maxima. 



Cleve (5) classified early spring diatoms as "Arctic" and 

 later spring species as "Boreal." Recent views include those of 

 Braarud et al. (4), who conclude that successions which de- 

 pend on the initial composition of the phytoplankton may vary 

 from year to year. Margalef (9), on the other hand, has sug- 

 gested that the annual regularity of successions probably cannot 

 be distorted by tide and wind. 



The vegetative or growth season in warm seas lasts twelve 

 months, and in the high arctic, only two or three months. This 

 latter short vegetative period induces development of the uni- 

 modal annual cycle characteristic for the high arctic, although 

 a bimodal cycle occurs in low arctic seas ( 2 ) . 



The study of successions in the environment should be car- 

 ried out with the microscopic sedimentation method to include 

 ultraplankton normally lost in net samples. Sampling sliould be 

 frequent; because of the rapid quantitative fluctuation of arctic 

 plankton, maxima could be missed in samples which are separated 

 by periods of a few days. However, regardless of technical pre- 

 paredness, selective grazing and sudden changes of conditions of 

 water and ice can obscure tlie picture of successions. 



Phytoplankton collected 100 miles offshore in the Arctic 



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