Trophic network model of a shallow water area in the northern part of the Lagoon of Venice

Abstract

A network model of trophic interactions within Palude della Rosa, a shallow water area in the northern part of the Lagoon of Venice, was developed with the objective to coherently quantify state variables as well as matter and energy flows between system components. Structure of flows and their distribution within and between trophic levels were analysed by aggregating single flows into combined flows for discrete trophic levels. Ninty-eight percent of total throughput is confined to the 1st and 2nd trophic level with the overall system strongly depending on the consumption of detritus. The distribution of energy and the poor structure of the flows suggest that the network is able to reflect prominent features of the ecosystem as, for example, effects produced by eutrophication processes, validated by field observations. Direct and indirect effects and dependencies between system components such as nekton, zoobenthos and detritus are quantitatively described. Predation pressure amongst system components is discussed. Nektonic fauna emphasising commercially exploited species was included in the model to also show the potential use of the trophic network for purposes of fisheries and of sanitary management. The present model is considered to be a first step in mapping the entire Lagoon through trophic networks for different areas in the Lagoon of Venice, along a gradient of hydrodynamic characteristics and levels of pollution. A large amount of ecological and biological information on the lagoon ecosystem may thus be summarised in a coherent framework. Information on fish stocks and other nektonic fauna present in the lagoon are one of the main gaps in the database. Such lack of information should be covered by additional field investigations to obtain more reliable knowledge on the exchanges of matter and energy also within higher trophic levels.