APPLICATION OF STRUCTURAL DYNAMIC APPROACH TO ESTIMATE SPACE VARIABILITY OF PRIMARY PRODUCERS IN SHALLOW MARINE WATER

Structural dynamic models attempt to simulate ecosystem dynamic interm s of species composition by using flexible state variable parameters t hat are allowed to change in order to optimize a given ecological goal function. In the present paper, this modelling approach has been appl ied to the two main groups of primary producers in shallow water of th e Lagoon of Venice, namely free floating macroalgae and seagrass. Diff erences in macroalgae species considered (Ulva rigida, Chaetomorfa aer ea, Gracilaria confervoides) have been characterized by expressing the main physiological parameters as function of one morphological parame ter: surface/volume ratio. This latter parameter has been used as uniq ue flexible parameters of the state variable representing macroalgae a nd its actual value s found by optimizing exergy under a given scenari o. This corresponds to find the best adapted macroalgae species in a g iven environmental condition. The same concept is applied to seagrass by stressing different capacities of the three species observed (Zoste ra marina, Z. noltii and Cymodocea nodosa) to react to self shading an d erosion processes. The application was able to explain in a satisfac tory way the observed distributions of both macroalgae and seagrass in the Lagoon of Venice. (C) 1997 Elsevier Science B.V.