Untitled - CNR

Fishery and Sea Resourcesimmediately beneath the sea cages is a directresult of the sedimentation of particulatewaste products from the fish farmand a decreasing concentration with the increasingdistance from the point source istypically observed [6, 7]. The continuousflow of faeces and food pellets from fishcages alters the quantity and the biochemicalcomposition of sediment organic matter,and the progressive transformation ofthe substrate into an anoxic environment[8, 7]. These environmental changes maylead to a reduction in benthic species richness,abundance and biomass, mainly dueto oxygen depletion associated with biochemicaloxygen demand and the formationof toxic products in anoxic sediments[9].Monitoring of biological parameters ratherthan chemical ones is important as it givesthe bioavailability rather than the absoluteconcentration of pollutants. The closeassociation of meiofauna with the sedimentmatrix means that changes in interstitialwater chemistry will soon lead tochanges in meiofaunal abundance and diversity[10]. Since meiofauna organismsplay a crucial role in the decomposition ofdetritus, as well as in nutrient cycling andin energy flow, they proved to be one of thefauna among the benthic components thatare appropriate for detecting biodepositionimpact [11, 12, 13].Metazoan meiofauna, for their ecologicalimportance in the benthic ecosystemsand the lack of larval dispersion,are becoming a popular tool for investigatingstructural and functional changesof natural and anthropogenically-impactedecosystems [13, 14, 15].We hypothesized that the presence of fishfarms influences the meiofaunal assemblagesin terms of abundance, communitystructure and diversity (i.e. richness oftaxa).2 Materials and Methods2.1 Study Site and SamplingThis study was conducted from December2006 to October 2007 in an coastalarea along the South-West of Sicily(Sicily Channel, Mediterranean Sea, Lat.37°32’079” N; Long. 12°57’202” E). Thefish farm is composed by 6 floating cages(n=2, 6500 m 3 , n=4, 2100 m 3 ) that producesabout 500 t year −1 of European seabass (Dicentrarchus labrax).Salinity and bottom temperature rangedfrom 37.4‡ to 37.8‡ and from 14°Cto 25.3°C respectively, during the entiresampling period. The area has microtidalregime and dominant currents flow in SE-NW or WNW-ESE directions, followingthe main circulations of the Sicily channel.The study area is sheltered and has sandymuddysediments.Fish are fed using automatic distributorssupplying an amount of pellets equivalentto about 3% (daily) of the totalbiomass contained in the cage. Food suppliedis composed of proteins (46-51% ofdry weight, DW), carbohydrates (18-20%),lipids (14-17%) and the remaining fractionis accounted by ash, vitamins and pigments.A preliminary survey was carried out to determinethe spatial extent of the fish-farminfluence and to identify the control station.Sediment samples were collected on a seasonallybasis (December 2006, April, Mayand October 2007), manually by SCUBAdivers at four stations: the two Impactedstations under the net pens (in the farmsediments)and the two Control stations,about 1 km far from the fish farms, in a area2164