Definition of type-specific reference conditions in Mediterranean lagoons

Defining 'reference conditions' (sensu Water Framework Directive)in Mediterranean lagoons is a challenging issue since the Mediterranean societies have used lagoons for centuries, lagoons are naturally enriched ecosystems, physically stressed and characterised by strong and unstable internal gradients and lagoons show an high taxonomic redundancy and a low taxonomic similarity. Here, accounting for these peculiarities, we have compared a priori and a posteriori approaches to identify the main sources of uncertainty in the ecological status of Mediterranean lagoons. Mixed model analysis showed that the a posteriori approach emphasises metric-specific ecosystem types and reduces the uncertainty of the ecological status classification when compared with the a priori approach based on fixed ecosystem Typology.