C-14 



short but intense growing season. Physiological and 

 behavioral mechanisms have evolved to spread the production 

 pulse and to make food available throughout the year, even 

 when the plants are not growing. 



(2) The southern ocean is productive, but not as much 

 so as initially supposed. Early observations were made in 

 coastal or ice edge areas during the summer. But on a per 

 square meter per year basis, Antarctic waters are not much 

 more productive than other oceans. 



(3) However, the short food chains in the southern 

 ocean allow a greater proportion of fixed carbon to be 

 transferred to carnivores such as fish, birds, and mammals. 

 Since no group is more than three steps away from phyto- 

 plankton in the food chain, the southern ocean supports an 

 unusually dense population of carnivores. 



(4) Perhaps the most significant aspect of the sou- 

 thern ocean ecosystem is the dependence of many predators 

 on one prey species, krill. At first glance, ecological 

 theory indicates that this situation should not occur; 

 different predators tend to specialize on different prey 

 species. However, the unusual dependence of several preda- 

 to;."b on one prey is possible in the Antarctic because each 

 pi'edator consumes a different segment or partition of the 

 ki'ill population. Predators feed in different geographic 

 locations, inside or outside the pack Ice zone, at different 

 times of year, and take different size classes of krill. 



(5) The life span of krill is very long, compared to 

 that of other marine zooplankton. In warmer waters, zoo- 

 plankton may produce several generations per year. Krill, 

 Ir contrast, require several years to reach sexual maturity. 



