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VI. ECOSYSTEM ASPECTS OF THE ANTARCTIC 

 MARINE SYSTEM 



In addition to the contributions made by various species 

 groups to the Antarctic marine ecosystem, there are several 

 other factors which must be considered in managing the 

 ecosystem as a whole. The following section discusses three 

 such aspects: primary productivity, nutrient cycling, and 

 energy flow. 



A. Primary Productivity 



Primary productivity is essential to all ecosystems, 

 including that of the Southern Ocean. Although other 

 factors affecting primary productivity doubtless exist, 

 nutrient levels, geographical areas, currents, seasonality, 

 light, and temperature have been examined south of the 

 Convergence. 



Hardy and Gunther (1935) concluded that the "simpler" 

 nutrients (nitrates, phosphates, and silicates) are found in 

 great enough concentrations that they do not limit primary 

 production. Other investigators (El-Sayed, 1968; Knox, 

 1970; Everson, 1977) also felt these nutrients were probably 

 not rate-limiting. However, not all scientists agree. 

 Holm-Hansen et al., (1977) state that in cold Antarctic 

 waters, nitrate, phosphate, and silicate concentrations are 

 high. On crossing the Convengence from north to south, 

 these researchers noted that nitrate and phosphate levels 

 increased but that silicic acid levels did not. They thus 

 concluded that silicic acid may limit phytoplankton growth. 

 Although nitrates, phosphates, and silicates are important 

 to primary production, other trace elements must be present 

 before maximum primary production can be realized. Volkovinsky 

 (1966) found a correlation between primary production and 

 levels of manganese and molybdenum. El-Sayed (1968) maintained 

 that cobalt, zinc, copper, and vanadium may also be important. 



Geographical factors also enter into primary production 

 determinations. By measuring carbon 14 uptake and chlorophyll- 

 a levels, scientists have calculated productivity values for 

 many Southern Ocean regions. Ichimura and Fukushima (1963) 

 reported "very low" productivity values for the Indian Ocean 

 sector. El-Sayed (1970) recorded low carbon 14 uptake 

 values and low chlorophyll-a values for the northern Drake 

 Passage, east and south Weddell Sea, Bellingshausen Sea, 

 and much of the Pacific sector. He reported high chlorophyll-a 

 levels and rapid carbon 14 uptake in the southern Drake 



