Structural and functional responses of macroinvertebrate communities in small wetlands of the Po delta with different and variable salinity levels

Coastal areas often host small water bodies described by high levels of biodiversity, which are threatened by environmental changes such as saltwater intrusion. This work evaluates the salinization effects on macroinvertebrate communities of 16 permanent small wetlands (ponds) located in a coastal Mediterranean forest in Northern Italy, characterized by different salinity levels. From a preliminary multivariate analysis (CCA), salinity was detected as the main driver affecting taxa distribution. Thus, diversity in terms of taxa, biological and functional traits of macroinvertebrate communities were analyzed considering three salinity classes (freshwater, oligo-mesohaline and polyhaline). The threshold indicator taxa analysis (TITAN) was used for detecting changes in taxa abundance and trait distributions within the salinity range and for assessing synchrony among their change points as evidence of community thresholds. Taxonomic and functional diversity indices and single functional/biological traits among the three salinity classes were also compared. The findings demonstrated that ponds’ macroinvertebrate communities are resilient to moderate increases of salinity, but salinization increase to polyhaline levels causes loss of biodiversity and a drastic community simplification in terms of functional evenness due to increased functional specialization. Since climate change and anthropogenic activities are expected to exacerbate salinization, management measures are required for the conservation of aquatic biodiversity in small coastal wetlands.