regions, where median conditions prevail, biotic development is manifold. Species 

 diversity increases, food webs become interminably intermingled, and elaborate 

 biotic interactions (biochemical, intraspecific, symbiotic and biocoenotic) become 

 controlling. It is in these latter circumstances that the network variable becomes 

 predominantly important. 



MARINE ECOSYSTEM MODEL 



In Figure 1, the whole ecosystem model consists of four submodels: Plankton, 

 Nekton, Benthos, and Organic Complex (Notes, e). Plankton and Benthos are 

 aggregated as compartments 8 and 9, and the environment (outside the broken 

 border) consists of pelagic and benthic detritus of the Organic Complex submodel 

 which flows across the boundary as inputs and outputs. The Nekton compartments 

 are guild-like, being based on the input and output carbon environments inhabited 

 by virtue of feeding and excretion habits which reflect migration, spawning and 

 development patterns of different basic life history ontogenies. 



FIRST ORDER (DIRECT) CAUSES AND EFFECTS 



The northern continental shelf of the Gulf of Mexico is biogeographically 

 subtropical in a moderate environment, so that rich biological development is 



Q" 



1 



Pelagic 

 Planktivores 



C^ 



I 



2 



Pelagic 

 Omnivores 



•9 



¥ 



Demersal 

 Carnivores 



<i^ 



Reef-Type 

 Schoolers 



6 



Benthic 

 Residents 



3 



Pelagic 

 Carnivores 



^ 



V 



■+-> 



J 



Figure 1. Northern Gulf of Mexico regional ecosystem Nekton submodel (compart- 

 ments 1 -7), with coupling to Plankton (8), Benthos (9) and Organic Complex 

 (environment) submodels. Arrows represent carbon flows. Inputs from 

 environment are due to detritivory, and outputs are by excretion. Intrasystem 

 flows represent feedings. 



94 



