Food-web changes in the Adriatic Sea over the last three decades

21 pages, 9 figures, 5 tables
We used a process-oriented model (Ecosim) to characterize changes in marine resources in the north-central (NC) Adriatic Sea (Mediterranean) from 1975 to 2002, and to explore the extent to which these changes were driven by trophic interactions, environment and fishing. Fishing efforts and fishing mortalities were used to drive the ecosystem model, and available biomass and catch data were compared to the model predictions. We calibrated and assessed the fit of the model using the sum of the squared deviations of the observed and predicted biomass values. Trophodynamic indicators were then calculated and used to analyse changes to the ecosystem. Trophic interactions, fishing, and environmental conditions were important driving factors of the ecosystem. Predictions from the model adequately matched observed biomass and catch data for each year. Observed trends and predicted data for biomasses decreased with time for several species, including Norway lobster, hake, red mullets, flatfish, and anchovy. The environmental functions resulting from the fitting procedure predicted that primary production and nutrients increased beyond the baseline from 1975 level, and then showed a decrease. They were negatively correlated with mean sea surface temperature and positively correlated with the Mediterranean Oscillation Index. Our results suggested that the NC Adriatic ecosystem became more degraded over time due to expanding fishing effort, bottom-up effects, and climatic anomalies. Possible mechanisms involved are discussed. Comparing our findings with descriptions of the south Catalan Sea ecosystem showed certain similarities between these 2 Mediterranean ecosystems and revealed unique features of the Adriatic Sea
This work was made possible by a bilateral co-operative-agreement between the Istituto di Scienze Marine (CNR), Italy, and the Consejo Superior de Investigaciones Científicas, Ciencia e Investigación (CSIC), Spain. The integrated project ’Site Effect Assessment Using Ambient Excitations’ (SESAME) contract no. 036949-2, supported by the European Commission’s Sixth Framework Programme, Sustainable Development, Global Change and Ecosystems, which allowed the continuation of this work, is greatly acknowledged. During part of the work, M.C. was supported financially by doctoral and postdoctoral fellowships from the Spanish Ministry of Science and Technology and the Ministry of Education and Science, and by Dalhousie University (Canada)