MERAMOD: predicting the deposition and benthic impact of aquaculture in the eastern Mediterranean Sea

A model composed of coupled particle tracking and benthic response modules was developed for predicting waste solids flux and benthic impacts of gilthead sea bream Sparus aurata L. and sea bass Dicentrarchus labrax L. aquaculture. The model was tested at 6 sites with different hydrodynamics, bathymetries and biomasses in the Aegean and Ionian seas, eastern Mediterranean Sea, and sediment trap flux and benthic impact indicators were observed. Seven sediment trap validation studies were conducted that varied in design with traps deployed either on the seabed, attached to nets or suspended in the water column. Model predictions of flux to traps spaced 5 m apart up to 50 m from the cages over a 13 d period were significant (R-2 = 0.61, n = 57, p <= 0.05). However, the model could not predict adequately the flux to traps spaced 2 m apart in the high-flux zone underneath cages where variability between trap observations was high. In this high-flux zone underneath cages, the averaged model flux predictions resulted in a performance of +/- 49%. Statistically significant relationships were established at 4 sites between modelled flux and either benthic fauna impact indicator species (S), abundance (A), A/S ratio, Shannon-Wiener index or biomass fractionation index (BFI), (R-2 = 0.82, 0.60, 0.57, 0.67 and 0.48, respectively; n = 24, p <= 0.05). Two other sites, which did not exhibit an abundance peak in enriched zones, did not fit these relationships. Using relative abundance of taxonomic groups, a modelled flux of 4.1 g m(-2) d(-1) was determined to be a useful boundary; on either side of this boundary, clear trends occurred in pollutant tolerant and intolerant species.