The impact of fish farming on the water column and marine sediments in three coastal regions from eastern Aegean coast

The impacts of mariculture activities in the water and sediments were comprehensively evaluated for the first time in this study. Lower dissolved oxygen was detected near the cages during summer due to aquacultural activities and bacterial degradation of organic compounds. However, DO levels were not below the 5 mg L −1 limit recommended for aquatic growth, survival and metabolic processes. Different eutrophication assessment methods showed that Güllük Bay, where intensive aquaculture activities occurred, was characterized by poor status. Assessment of different eutrophication tools for Akköy and Ildır Bay indicated that water quality status was not similar to each other. The most noticeable effect of aquaculture activities is the sedimentation of faeces and uneaten food under the cages. Nutrients in the water indicated gradual decrease with distance from the cages. Comparison of total phosphorus in sediments showed that the most affected area is Güllük Bay owing to cumulative impact of aquaculture. The higher total organic carbon (TOC) in sediments was measured near and under the cages. TOC was a useful indicator to show benthic health, less than 10 mg g −1 corresponded to low risk deteriorations for all aquaculture sites. Sediment monitoring studies should be carried out to provide sustainable use of the aquaculture areas.