Using macroinvertebrate species assemblages to identify river channel habitat units: an application of the functional habitats concept to a large, unpolluted Italian river (River Ticino, northern Italy)

The functional habitat concept was applied to a large Italian river for the first time. The characteristically wide range of hydraulic conditions present in this river (compared to previously-studied small, lowland, English rivers) were expected to be of central importance to biota and, therefore, to habitat definition. TWINSPAN analysis of the invertebrate assemblages sampled in the Ticino river identified five distinct habitats: two habitats in lotic areas (run-riffle and macrophytes in current), two along the river margins (with and without macrophytes) and one in backwater areas. These correspond to five of the functional habitats identified in U.K. lowland rivers. Each of these five functional habitats could be defined either in terms of hydraulics, substratum and/or presence/absence of macrophytes. Representative taxa are presented for each habitat and community structure discussed. Macrophyte and run-riffle habitats supported the most heterogeneous and abundant benthic fauna. No match was found between replicates grouped by invertebrate assemblage (the five functional habitats identified by TWINSPAN) and the grouping of the same replicates by PCA, carried out on the physical data matrix. While obvious velocity differences were found between the functional habitats, of particular note was the fact that the Froude number did not show any clear association with habitat type. In the future, improved river management will follow improved understanding of river habitats.