IMPLEMENTATION OF THE HABITAT FISH BIO-INDICATOR IN TWO WATER BODIES OF THE VENICE LAGOON: THE ROLE OF SEASONAL AND ENVIRONMENTAL VARIABILITY IN THE ASSESSMENT OF ECOLOGICAL STATUS OF FISH FAUNA

Under the Water Framework Directive (WFD; Dir. 2000/60/EC), fish are one of the Biological Quality Elements that need to be taken into account when evaluating the Ecological Status of transitional water bodies. The Habitat Fish Bio-Indicator (HFBI), a multi-metric index composed of six descriptors based on functional traits of fish assemblages, was recently developed to assess Italian transitional waters. In this study, HFBI was applied, following the national application protocol, to two water bodies in the Venice lagoon featuring different water and sediment physco-chemical properties and habitat distribution. The analysis highlighted that, in addition to seasonality, environmental variability along confinement gradients and presence and extent of seagrass meadows strongly influence the six metrics, the HFBI score and the subsequent assessment outcome. The selection of number and location of sampling sites must then be based on environmental characteristic and variability found within each water body, and is therefore a crucial step in the evaluation of Ecological Status in transitional water ecosystems.