Benthic foraminifera to assess Ecological Quality Statuses in Italian transitional waters

Estuaries, lagoons and lakes, identified as transitional waters (TWs), are fragile ecotones at the interface between terrestrial and marine ecosystems. The assessment of their Ecological Quality status (EcoQ), required by marine legislations, is rather uncertain when based on traditional benthic macrofaunal indices. This study proposes to assess the EcoQ of marine waters using the diversity index Exp(H-bc') based on living benthic foraminifera. By testing this method on datasets from five Italian TWs, we showed that EcoQ's assessment based on foraminifera reflected changes in environmental conditions. Benthic foraminifera highlighted the degradation of most, if not all, study sites, ranking most of the TWs in "Moderate" to "Bad" EcoQs. Although the assessment of EcoQs estimated from diversity indices was similar when based on benthic foraminifera or macrofauna, discrepancies occurred if diversity index calculated on foraminifera and sensitivity-based indices applied on macrofauna were compared. Our results demonstrated that the Exp(H-bc') index based on living benthic foraminifera is a promising approach to assess EcoQs. Finally, we argue that benthic foraminifera, for their preservation potential as fossil within sediment, are a reliable option to define reference conditions and targets.