Food web modelling on the structure and functioning of a Mediterranean lentic system

Τhe ecosystem structure of a Mediterranean lentic system (Lake Volvi, Northern Greece) was assessed and quantified for the first time, using the Ecopath with Ecosim model. Biological and fisheries-related data were collected during 2014–2015 from field surveys; moreover, operational and other data concerning fisheries exploitation were assessed by interviews. The model will (a) describe the ecological structure of the lake in terms of trophic flows (b) disaggregate the impacts imposed by fishing and other factors on the food web and (c) investigate the ecosystem’s functional changes by testing the introduction of a new fish species. Lake Volvi constitutes a mature system whose food web is characterized by “bottom-up” processes, exhibiting a “good” systemic resistance to unexpected perturbations and a rather low intensity of fisheries exploitation. Simulations from 2015 to 2025 revealed that an increase in fishing effort and/or stocking with the new species will have negligible impact on the food web and will not affect negatively the fisheries resources and top megafauna. The model presented provides key ecosystem information that is lacking for most European freshwaters systems, which can be useful in assessing their ecosystem structure and in simulating the pressure of fisheries exploitation on their food web.