H-8 

 RESEARCH PROGRAMMES 



extension of our present knowledge. Additional biological data are necessary, both field data on 

 the biomass of ecologically important elements of the system and experimental data on transfer 

 rates. Such a model can serve to organize existing information and to point out areas where 

 additional research is needed. At the same time, it can be flexible enough to incorporate further 

 information in the course of its future development. 



A model has been constructed of the Ross Sea ecosystem (Green, 1975) which describes 

 the interactions of nutrients, light, ice, phytoplankton, zooplankton and larger animals. The 

 general flow structure of this model is shown in Figure 2. For a Southern Ocean model, the 

 main modifications needed include: (a) elements describing harvest by man, particularly of 

 whales, krill, fish and cephalopods; (b) sub-division of certain elements (eg, of zooplankton into 

 krill and other species); and possibly (c) division into various geographic zones, with some 

 interchange between zones {eg, migration of whales). The Ross Sea model has been quantified, 

 using available data and making estimates where necessary, to provide a descriptive simulation 

 of an annual ecological cycle. 



ICE 



COMMUNITY 



ALGAE 



ICE 



COMMUNITY 



INVERTEBRATES 



DETRITUS AND 

 DECOMPOSERS 



FIG 2. Conceptual model of the pelagic ecosystem of the Ross Sea; exchanges between the system 

 and its environment are shown. (After K. A. Green, 1975.) 



Construction of one model, however complex, does not offer a complete framework from 

 which to gain an understanding of an involved system. The development of a general model of 

 the entire system must be accompanied by other activities, such as the development of more 

 detailed sub-models of certain elements of the system. As an example, models which deal just 

 with the fishes and (in a simpUfied manner) other elements interacting directly with the fishes, 

 can simulate gross changes in fish populations. Size and age composition of the population, 

 individual growth rates, recruitment, and variable food consumption can be included in a fish 

 sub-model, but it would not be practicable to do this in a general ecosystem model. Similar 

 detailed sub-models can help explain the quantitative behaviour of single components of the 

 total system and can be used to check on the realism of the general overall model. 



The important sub-models on which work should start as soon as possible are: 



(a) the physical/chemical environment as a forcing function for phytoplankton growth, 

 with a built-in ability to allow for different sized phytoplankton to be produced under 

 different physical/chemical conditions; and 



