In the Orbetello lagoon basin there are some intensive land–based fish–farming facilities which contribute to cause a significant cyclic development of the opportunistic chorophycea Ulva laetevirens, and consequent serious decay events in spring and summer. To minimise the nutrients' impact, fish farming was supplied with phytotreatment system. The purpose of this study was to evaluate the composition of macrobenthos in the phytotreatment system. The results of this study showed variations of the quali–quantitative composition of the assemblages of the four ponds in accordance with U. laetevirens biomasses. In particular, amphipoda showed a composition connected with macroalga development. During the warm season, macroalgae underwent degradation processes and this caused the presence of high abundance of opportunistic species and species connected to perturbed sediment. The composition and the dynamic of macrobenthos of phytotreatment system can be useful to understand what happen, on a big scale, in some areas of Orbetello lagoon.
Keywords: macrobenthos assemblages, phyotreatment, environmental pollution, aquaculture, fish ponds, coastal lagoons, land–based fish farms, Italy, water pollution, chorophycea Ulva laetevirens, biomass, macroalgae degradation, opportunistic species, perturbed sediment