The application of a model with dynamic structure to simulate the effect of mass fish mortality on zooplankton structure in Lago di Annone

A mass mortality of the most abundant zooplanktophagous fish due to an infectious gill disease eliminated almost the entire population of this species in the Eastern basin of the Lake Annone, Italy in'75-76, while no mortality occurred in the Western basin. This event offered the opportunity to study whether a recently developed structural dynamic modelling approach would be able to describe the changes in the properties of zooplankton observed in the Eastern basin as a result of an abnormal high fish mortality in August '75. As a change in size of zooplankton was observed (from 1000 µm to1600 µm) it would even be possible to see if the modeling approach could describe the actually observed changes in structure(properties of the organisms, in this case zooplankton). The modelling approach uses the thermodynamic concept exergy as a goal function which determines the current changes of the properties of the species included in the model description. From the study it can be concluded that this modelling approach was able to describe the focal state variables of the model (phytoplankton, zooplankton and fish) in accordance with the observations from '75 to '76 and also to assess the actually observed changes in zooplankton size.

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