Twenty years study of the zoobenthos associated with aquatic vegetation in the volcanic lakes of Central Italy: species composition, biodiversity and water quality assessment.

The role played by the system zoobenthos-macrophytes in the lacustrine metabolism and the great importance of this community as a source of biodiversity have encouraged the analysis of this biocoenosis, investigated in lakes of Central Italy during more than twenty years. Data refer at six volcanic lakes located in the Latium Region (lakes Nemi, Albano, Bracciano, Vico, Monterosi and Martignano). Eighteen taxa of aquatic plants (macroalgae and macrophytes) were identified; the size of the bottom area covered by vegetation in term of maximum depth of colonization, distribution along the lacustrine perimeter and presence and quantity of bioindicators (especially macroalgae Charales) have given a reliable indication about the trophic level, useful for comparisons with quality evaluation coming from fauna structure. The invertebrate community was well diversified, composed so far of 262 taxa, most of which (54%) identified at species level. Most part of the taxa were chironomid larvae, oligochaetes and nematodes (42% of the total), and secondarily microcrustaceans (20%) that constitute also quantitatively the dominant component. A series of community parameters, involving simple and more complex bioindices (species richness, Shannon diversity, ISC values) and several bioindicators (number of cladoceran species, percentages of Chydorus sphaericus, Hydrobioidea, Decapoda), have represented so far the most significant elements to reach a quality evaluation perfectly in agreement with other diagnoses, based both on composition of the aquatic vegetation and on physico-chemical data.