Modelling the impact of finfish aquaculture waste on the environmental status in an Eastern Mediterranean Allocated Ζone for Aquaculture

A modelling tool was implemented in an Eastern Mediterranean Allocated Zone for Aquaculture (AZA) (Vourlias Bay, Greece) to examine the fate of seabass/seabream aquaculture wastes from multiple farms and assess their potential impacts on the surrounding ecosystem in terms of good environmental status. The model was validated against available satellite (Chl-a) and in situ data (PO4, NO3, NH4, Chl-a, Mesozooplankton), showing a reasonable skill in reproducing the observed range and horizontal variability. Environmental status was assessed by means of two environmental indicators (TRIX, E.I.), calculated using the simulated outputs. The environmental conditions in the AZA were “good” during the well mixed period in winter and “moderate” to “poor” during more stratified periods, particularly summer, when effluents from the fish farms were higher. In the vicinity of different fish farms, environmental conditions were found to be correlated to the fish farm production, as well as to the predominant current speed/orientation. Fish farms, where stronger prevailing currents induced a more efficient off-shore dispersion of wastes, showed relatively better conditions, despite their high fish production. Changes in the food web structure from the input of fish farm wastes were mainly characterized by an increase in dinoflagellates, an indicator for eutrophication, and also nanophytoplankton and microzooplankton. A series of scenario simulations (fish farms production and position) were performed to investigate the ecological carrying capacity of the AZA and demonstrate the utility of the modelling system, as a management tool for AZA spatial planning and licensing of fish farms.