Giorgio Pace

Weak Concordance between Fish and Macroinvertebrates in Mediterranean Streams

Although anthropogenic degradation of riverine systems stimulated a multi-taxon bioassessment of their ecological integrity in EU countries, specific responses of different taxonomic groups to human pressure are poorly investigated in Mediterranean rivers. Here, we assess if richness and composition of macroinvertebrate and fish assemblages show concordant variation along a gradient of anthropogenic pressure in 31 reaches across 13 wadeable streams in central Italy. Fish and invertebrate taxonomic richness was not correlated across sites. However, Mantel test showed that the two groups were significantly, albeit weakly, correlated even after statistically controlling for the effect of environmental variables and site proximity. Variance partitioning with partial Canonical Correspondence Analysis showed that the assemblages of the two groups were influenced by different set of environmental drivers: invertebrates were influenced by water organic content, channel and substratum features, while fish were related to stream temperature (mirroring elevation) and local land-use. Variance partitioning revealed the importance of biotic interactions between the two groups as a possible mechanisms determining concordance. Although significant, the congruence between the groups was weak, indicating that they should not be used as surrogate of each other for environmental assessments in these Mediterranean catchments. Indeed, both richness and patterns in nestedness (i.e. where depauperate locations host only a subset of taxa found in richer locations) appeared influenced by different environmental drivers suggesting that the observed concordance did not result from a co-loss of taxa along similar environmental gradients. As fish and macroinvertebrates appeared sensitive to different environmental factors, we argue that monitoring programmes should consider a multi-assemblage assessment, as also required by the Water Framework Directive.

Benthic diatom assemblages and their response to human stress in small-sized volcanic-siliceous streams of central Italy (Mediterranean eco-region)

The river typology ‘volcanic rivers’ represents a unique typology in the Mediterranean eco-region in Europe but its type-specific diatom assemblages are still poorly investigated. The main aims of this study were (i) to analyse the diatom diversity of this river type, (ii) to investigate the relationships between diatom diversity and environmental variables and (iii) to identify the characterizing diatom community structure of different environmental groups. To this end, we selected 13 streams located in central Italy, belonging to a single river type and covering the whole quality range from human impacted sites to those in ‘reference conditions’. Most frequent and abundant diatom species found were Cocconeis placentula var. lineata, Planothidium lanceolatum, Rhoicosphenia abbreviata and Amphora pediculus. Species richness in reference and less impacted sites was not higher than in intermediate and heavily degraded ones, but non-metric multidimensional scaling (N-MDS) analysis revealed a substantial difference among their diatom community structure. The indicator species analysis defined the characteristic species of three environmental groups identified by N-MDS. The findings of this study represent a contribution to the knowledge on diatom communities of Mediterranean volcanic-siliceous rivers and provide information for a data-driven implementation of the Water Framework Directive in Italy for this specific river typology.