-24- 



4. Factors Affecting Primary Production 



Antarctic waters are rich in nutrients. Circumpolar 

 upwelling introduces nutrients into the euphotic zone 

 throughout the year (Gordon, 1971) . Water temperature is 

 uniformly cold. The available light varies seasonally with 

 the polar light regime and is closely correlated with 

 primary production (El-Sayed and Mandelli, 1965). 



Primary production is concentrated in the summer season, 

 along the ice edge and in coastal regions (Balech, et al, 1968; 

 El-Sayed, 1970) . Because the early scientific investigations 

 were concentrated in the most productive areas, a misleading 

 picture of very high productivity for Antarctic waters was 

 developed. Estimates have since been revised downward. On 

 a yearly average basis over all southern ocean waters, in- 

 cluding the less productive open ocean regions, total pro- 

 ductivity is similar to that in other oceans (Holm-Hansen 

 et al, 1977) . 



Food chains are shorter in the Antarctic than in other 

 oceanic regions. Plants are consumed by krill (the dominant 

 herbivores), which are in turn eaten by fish, birds, and 

 mammals. But because food chains are shorter, a greater 

 proportion of the productivity reaches the vertebrate 

 trophic levels, and there is an unusually high density of 

 birds and mammals in Antarctic waters. 



Variation in sea ice cover affects light available to the 

 water column because ice screens out light. Primary produc- 

 tion in the winter is extremely low. 



B. Species in the Antarctic Marine Ecosystem 



There is a distinct fauna south of the Antarctic Con- 

 vergence. Phytoplankton consist primarily of diatoms south 

 of the Convergence, but include a great many dinof lagellates 

 north of it. Zooplankton species are different north and 

 south of the Antarctic Convergence. Euphausia superba and 

 E. crystallorophias are only found south of the Convergence, 

 E. superba in oceanic regions and E_^ crystallorophias near 

 the continent (Marr, 1962) . 



The term krill refers to the group of euphausiid crusta- 

 ceans which are the food of large baleen whales. Species of 

 krill are listed in Table 1. By far the most abundant of 

 these species is E_^ superba . 



