Abstract
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 analy- sis of organic carbon, organic matter and benthic community parameters. There were statistically sig- nificant 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 commu- nity 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 pre- sent 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.
Highlights
During the last 25 yr, aquaculture has proliferated in the coastal zone, becoming an increasingly important industry
The maximum values of organic matter and organic carbon were measured in spring at Stns AS1 and BS1, while the minimum values were measured in winter (Table 2)
Increases in sediment concentration of organic matter and organic carbon similar to those found at the farm stations in the present study have been reported for sandy seabed by Weston (1990), Karakassis et al (2000) and Yucel-Gier et al (2007)
Summary
During the last 25 yr, aquaculture has proliferated in the coastal zone, becoming an increasingly important industry. Increasing organic load in sediments might have a strong effect on the structure of benthic communities (Karakassis et al 2000, Hyland et al 2005, Klaoudatos et al 2006, Yucel-Gier et al 2007). Deposition of organic material under the cages may cause changes in the composition of basic benthic communities in terms of abundance, dominance and species richness (Pearson & Rosenberg 1978, Wu et al 1994). The effects described here tend to be localized around effluent discharge points and within 25 m of the perimeter of net-pen farms (Karakassis et al 2000, Pearson & Black 2001). In semi-enclosed marine areas with weak currents, the sediment characteristics beneath and around fish farm cages change with the accumulation of uneaten food, metabolic waste and faeces (Maldonado et al 2005)
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