C-13 



COMPARISON WITH OTHER MARINE ECOSYSTEMS 



There are several characteristics of the southern- 

 ocean which are shared with all other marine systems: 



( 1) Both organic and inorganic nutrients are dis- 

 solved in the water column. This nutrient reserve is 

 analogous to nutrients held in soil in a terrestrial 

 ecosystem. 



(2) In land ecosystems, plant biomass is much 

 greater than that of animals. This system exhibits an 

 inverted pyramid of biomass; i.e.,' plant plankton standing 

 stock at any given time is probably lower than animal 

 plankton standing stock. However, the rapid turnover or 

 replacement rate of the plant plankton allows the small 

 standing crop to support the larger zooplankton biomass. 

 As in other marine and terrestrial systems, the standing 

 stock of other animal groups decreases with distance from 

 plants in the food chain; i.e., standing stocks of primary 

 carnivores are lower than standing stock of herbivores, 

 etc . 



(3) Most of the primary production in the system is 

 carried on by single celled plants. 



(4) Nutrients are recycled within the ecosystem, but 

 energy is dissipated as it flows through the food chain. 



(5) Distributions of organisms are three dimensional 

 in marine environments. Overlapping mapped distributions 

 of two species does not necessarily indicate that they 

 interact, since one may be a surface and one a bottom- 

 dwelling organism. Krill are found at the surface in the 

 southern ocean. 



(6) The biology of a marine ecosystem is closely tied 

 to its physical environment. Light, ice cover, temperature 

 and current movement are the most significant physical fac- 

 tors in the southern ocean. 



(7) Productivity is higher in upwelling and coastal 

 regions in the southern ocean as in other oceans. 



There are some special characteristics of the southern 

 ocean which are not shared by other marine ecosystems and 

 which deserve emphasis for understanding the dynamics of 

 the Antarctic marine ecosystem. 



(1) Extreme seasonality in the light and ice regime, 

 particularly below the Antarctic circle, dictate a very 



