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The spatial and seasonal impact of ¢sh farming on the water column of two ¢sh farms in the Eastern Mediterranean was investigated, between July 2004 and April 2005. In the area of each ¢sh farm, three stations were sampled. One was located at the centre of the ¢sh farm, the other at a distance of 50 m from the centre and the last one at a distance of 300 m from the ¢sh farm centre. At each sampling station, water samples were collected at the surface, at 5 m and at every further 10-m depth from the surface to the bottom, for nutrient analysis (ammonium, nitrite, nitrate, phosphate, silicate). Statistical analysis showed signi¢cant di¡erences between seasons for all nutrients, with the exception of nitrite in one of the farms. Furthermore, ammonium, nitrite, phosphate and silicate values showed signi¢cant di¡erences among sampling stations. The maximum concentrations of the above nutrients (1.64, 0.10, 2.57, 0.28 and 4.89 mM respectively) were recorded at the sampling stations located at the centre of each ¢sh farm and they were gradually reduced with increasing distance from the cages. The concentrations of nutrients did not appear to exceed permitted levels for the appearance of eutrophication. The maximum concentrations were considerably lower than those observed previously in the study area.

Spatial and temporal effects of fish farming on the benthic community structure at 2 fish farms in the Eastern Mediterranean were investigated between July 2004 and April 2005. In the area of each fish farm, 3 stations were sampled. At each station, sediment samples were collected for analysis of organic carbon, organic matter and benthic community parameters. There were statistically significant differences in organic matter and organic carbon among all stations. This impact seems to be only spatial, since 1-way ANOVA indicated no significant differences in organic matter and organic carbon between seasons for both farms. Furthermore, significant differences were found in species number, abundance and species richness among stations and seasons for one of the farms (2-way ANOVA). One-way ANOVA indicated that the significant differences, detected in the benthic community parameters of this farm, were spatio-temporal for species number, temporal for abundance and spatial for species richness. The spatial effect of fish farming on benthic community structure was present up to 50 m from the centre of cages on one farm and between 50 and 300 m from the other farm. Capitella capitata was the most dominant species at the farm sites, while Nephthys hystricis was the most dominant species at the control sites. In all cases, the benthic assemblages in the immediate vicinity showed symptoms of disturbance, but the spatial and temporal extent of this effect was less than one would expect considering the fact that the study area is located in a semi-enclosed gulf.

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