Macroinvertebrate assemblages at mesohabitat scale in small sized volcanic siliceous streams of Central Italy (Mediterranean Ecoregion)

According to the guidelines of the European Water Framework Directive, assessment of the ecological quality of streams and rivers should be based on type-specific reference conditions. Moreover to support biological indicators an hydromorphological analysis is also requested for each river type. The rationale for including an habitat assessment in biomonitoring study is that a biological community can be influenced by habitat quality just as water chemistry. In the present work benthic macroinvertebrates were analysed in a specific river type of Central Italy (small-sized streams, volcanic-siliceous), to identify taxa assemblages at the mesohabitat scale and to test how common measures of benthic community used in biomonitoring differ between riffles and pools in order to evaluate if differences may influence water quality classification. Macroinvertebrates were collected in 10 selected streams, covering the whole quality range present in the geographic area from 'reference sites' to human-impacted sites, along a pool-riffle sequence following a multihabitat sampling protocol. We compared assemblage of macroinvertebrates found in different mesohabitats using principal component analysis (PCA). Similar site grouping was obtained in riffle, pool and abiotic analysis. The measures of diversity and abundance were used as replicates in ANOVA analysis to test differences between pools and riffles within the groups of sites. There were no significant differences in terms of taxa richness and total abundance. When we compared the abundance of each taxon we found significant differences only in the group of reference sites with 18 taxa (about 25%) that showed a significant habitat preference. Our findings support that macroinvertebrates assemblages reflected primarily the environmental conditions and differences at mesohabitat scale are strongly correlated to hydromorphological condition and are maximized in reference sites. However such differences do not influence the ecological status assessment in this typology.