Can intensive fish farming for 20 years induce changes in benthic ecosystems on a scale of waterbody? An assessment from Cephalonia bay (Ionian Sea).

The environmental impacts of fish farming on benthic ecosystems beneath the fish cages have been widely addressed the past decades. However, the chronic release of nutrients can cause a shift in local primary productivity and a chronic increase in the sedimentation of organic material at a large spatial scale which could be reflected in benthic ecosystems. In this context, the indirect effects of aquaculture on the benthic ecosystem were studied in a semi-closed bay (Cephalonia, Ionian Sea) where a relatively large fish farm has been operating since 1982. Results from the present sampling were compared to historical data obtained in 1996 and 2001, in order to detect if nutrient release that could impact phytoplankton dynamics in the bay could indirectly alter benthic communities, as well. Macrofaunal communities have not shown deterioration but rather a small, yet statistically significant, improvement in diversity indices and ecological status indicators, and no significant change regarding bioturbation potential. This indicated that processes involved in nutrient consumption and transfer are highly effective in such an oligotrophic environment.