Application of structural dynamic approach to estimate space variability of primary producers in shallow marine water

Structural dynamic models attempt to simulate ecosystem dynamic interms of species composition by using flexible state variable parameters that are allowed to change in order to optimize a given ecological goal function. In the present paper, this modelling approach has been applied to the two main groups of primary producers in shallow water of the Lagoon of Venice, namely free floating macroalgae and seagrass. Differences in macroalgae species considered (Ulva rigida, Chaetomorfa aerea, Gracilaria confervoides) have been characterized by expressing the main physiological parameters as function of one morphological parameter: surface/volume ratio. This latter parameter has been used as unique flexible parameters of the state variable representing macroalgae and its actual value s found by optimizing exergy under a given scenario. This corresponds to find the best adapted macroalgae species in a given environmental condition. The same concept is applied to seagrass by stressing different capacities of the three species observed (Zostera marina, Z. noltii and Cymodocea nodosa) to react to self shading and erosion processes. The application was able to explain in a satisfactory way the observed distributions of both macroalgae and seagrass in the Lagoon of Venice. (C) 1997 Elsevier Science B.V.