-97- 



(1965) believed that light and temperature were the most 

 important factors affecting primary production in the 

 Weddell Sea. Knox (1970) and El-Sayed (1970) felt that not 

 enough is known about light in Antarctic waters to reach 

 definite conclusions. Moiseev (1971) attributed low production 

 to low light levels. Holm-Hansen et al. (1977) maintained 

 that summer solar energy is higher in Antarctica than in the 

 tropics and solar radiation intensity is so great that 

 photo-inhibition occurs in surface phytoplankton. With 

 respect to winter month activity, Fogg (1977) speculated 

 that in winter algae may reassimilate extracellular organic 

 products formerly liberated when light intensities were 

 higher. 



Temperature may also affect productivity. Moiseev 

 (1971) believes that low temperatures could explain, at 

 least partially, depressed growth rates as one travelled 

 south from the Convergence. Knox (1970), on the other hand, 

 discounted temperature because the greatest annual surface 

 temperature range was less than 4-5° C. Holm-Hansen et al . 

 (1977) agreed that Antarctic algae are psychrophilic . 

 However, after comparing observed data and expected calculations 

 for algal growth rates, they decided that Antarctic phytoplankton 

 may not be physiologically adapted for high growth rates at 

 low temperature, and that temperature may limit primary 

 productivity. 



In summary, no single factor necessarily limits Antarctic 

 primary production. Growth may be controlled by combinations 

 of the factors discussed or by completely different phenomena. 



B. Energy Flow and Nutrient Cycling 



Energy flow in the Antarctic marine ecosystem is 

 poorly understood (El-sayed, 1971) . A crude way to view 

 energy flow is by examining trophic relationships within the 

 ecosystem (Figures 21 and 22) . Figure 22 quantitatively 

 delineates interactions between the various trophic levels. 



In contrast to those of other oceans, the Southern 

 Ocean's food chain involving phytoplankton-krill-vertebrates 

 can be short and relatively simple (Knox, 1970). Nevertheless, 

 there are serious gaps in our knowledge of energy flow 

 (e.g., consumption rates). For example, squid and fish are 

 potentially the ecosystem's greatest krill consumers, thereby 

 potentially accounting for a major portion of energy in the 

 system. Yet poor data on these key groups clouds the reliability 

 of energy flow estimates. 



