Functional diversity of free-living nematodes in river lagoons: can biological traits analysis (BTA) integrate traditional taxonomic-based approaches as a monitoring tool?

In four Po River lagoons, functional diversity of free-living nematodes was studied according to five biological traits (feeding type, life history, tail shape, body length and shape) considered singularly and combined in a Biological Traits Analysis (BTA). With the exception of ‘Body length’, similar distribution patterns were obtained for the other biological traits, considered singularly or in combination. From a functional point of view, the higher number of slender c-p3 selective deposit feeders with elongated tails rendered the assemblage in Marinetta-Vallona different from those in the other waterbodies where, by contrast, the nematodes were mainly represented by c-p2 non-selective deposit feeders with clavate tails and variable body lengths and shapes. On the contrary, the spatial patterns highlighted by genera data did not perfectly overlap with those identified by the biological traits. From a taxonomic point of view, the change ascribable to the higher abundance of Terschellingia in Marinetta-Vallona was comparable to those attributable to the other dominant genera (Sabatieria and Daptonema) in the other lagoons. Only the biological traits analysis was able to indicate that the dominance of Terschellingia in Marinetta-Vallona led also to a functional change within the assemblage. According to both functional and taxonomic approaches, the nematodes seemed influenced by polybrominated diphenyl ethers (ΣPBDEs), whose concentrations in the sediments clearly exceeded their toxicity thresholds in Marinetta-Vallona, suggesting, therefore, that this group of emerging pollutants might induce a nematodes response at both taxonomic and functional level. Our findings suggest that for scarcely biodiverse assemblages, such as those of river lagoons, the BTA may not provide further information than the analysis of single traits while both these functional approaches may add relevant ecological information to traditional taxonomic-based methods, representing therefore a potential integration in the use of nematodes in monitoring actions.