Impacts of a marine fish farm in Argolikos Gulf (Greece) on the water column and the sediment

The aim of this study was the qualitative and quantitative assessment of impacts on the physicochemical characteristics of the water column and the sediment caused by an intensive marine fish farm. The study area was the Plateia Island which is located in an open seawater area in the outer part of Argolikos Gulf (Northeastern Peloponnese, Greece). The particular plant has been in operation since 1988, producing about 350-400 tons per year of Gilthead seabream (Sparus auratus) and European seabass (Dicentrarchus labrax). The samples were taken on a three-season period started in August 2001 and ended in May 2002. During this study, the main physical and geochemical parameters on the water column and the sediment were investigated. Specifically, the parameters that were measured included: ammonium-nitrogen, phosphate and suspended solids in the water column and organic matter, organic carbon, and phosphorus (total and inorganic) in the sediment samples. The conclusions drawn from this work clearly verify that the most important impacts, mainly identified as increased nutrients and organics concentrations both in the water column and the sediment, were realized at the stations closest to the farm. These concentrations gradually decreased with increasing distance from the cages. The peak values in most of the parameters measured were obtained during summer or spring. However, it has to be mentioned that although the measured concentrations clearly depict the influence of the fish farm especially on the sediment, their values were, in general, considerably lower than those reported in relative studies in Greek fish farms.

The main conclusions drawn from this study can be summarized as follows: • The influence of the particular fish farm to the water column is limited to the stations closer to the farm. The higher nutrient concentrations (ammonium-nitrogen and phosphate) were observed right beneath the fish cages (P1 station). All the other stations presented ammonium-nitrogen concentrations about 1.5 times higher compared with the control station, during summer, and at the same level as the control during the winter and spring sampling. Besides P1 and P8 stations all other stations presented similar total P concentrations with the control station. • The measured parameters in the sediment samples presented maximum concentration values at the nearby to the farm stations. The peak values in most of the cases were identi- fied during summer or spring. The concentrations in most of the cases gradually decreased with increasing distance from the cages verifying the enrichment in mainly organic matter of the environment resulting from fish farming and its relatively localised character. It has to be mentioned that although the measured concentrations clearly depict the influence of the farm especially on the sediment, their values were in general considerably lower than those reported in relative studies in Greek fish farms [25]. A potential explanation of the low environmental burden identified in the specific case is that food losses are minimal as confirmed by the farm owners. An important role in the consumption of any food wastage (which is one of the main pollutants in this case) plays the approach of wild fish species (e.g. Pomatomus saltator, Diplodus annularis, Seriola dumerili and even Thunnidae) to the farm, which was also confirmed by scuba diving in the study area. This is a common case occurring in marine fish farms as also reported by Papoutsoglou et al. [41], who surveyed two fish farms in south-west Greece. Indeed, no accumulation of waste food or faeces below the cages were detected while at the same time thousands of wild fish, including mullet (Mugilidae), Spicara sp. and Diplodus spp., were present around the cages. Aquaculture has grown substantially not only in Greece but in most EC countries over recent years. The intensification of aquaculture and the overall competitive use of water resources have highlighted the extreme importance of adequate control measures to safeguard this growing industry and to protect the natural environment. In order to achieve the sustainable development of the aquaculture sector several countries have already introduced regulatory control and monitoring measures in their legislation. In this view, there is a recent EU Directive “Council Directive 97/11/EC of 3 March 1997” amending Directive 85/337/EEC on the assessment of the effects of certain public and private projects on the environment [42] which includes aquaculture in Annex II, reinforcing the need for certain projects to undergo compulsory Environmental Impact Assessment (EIA), mostly depending on scale, intensity and local conditions [43]. In this context, the installation and operation of every new facility or extension of operating farming activities (regarding either the number of cages and/or the biomass reared) should undergo compulsory EIA. In the overall framework of such an EIA the impacts identified in our and other relevant studies should be incorporated after being correlated with the cultivated area or the amount of reared biomass. It is realized, of course, that for the needs of an integral EIA, the identified impacts on the water column and the sediment should be supplemented and interpreted taking into account additional experimental data describing the annual variation of other physical parameters such as temperature, salinity and sea-currents etc. in order to draw sound conclusions on the impacts of marine fish farming to the wider ecosystem. Since all the impacts surveyed and described from aquacultures all around the globe are mainly of local character, in any case, careful siting of new farming activities must be the primary goal in order to avoid any undesirable local effects on the selected ecosystem.