Dispersal and Variability of Chemical and Biological Indices of Aquaculture Pollution in Igoumenitsa Bay (NW Greece)

Abstract

The purpose of this work was to monitor nutrient enrichment around a fish farm site in Igoumenitsa Bay (NW Greece). Seasonal samples were collected from the waters and benthos surrounding fish farms in Igoumenitsa Bay, NW Greece. The study was carried out in Igoumenitsa bay between May 2011 and Dec 2012). Seawater samples were collected every month from different sampling sites which were: the open Ioanian sea, 60 meter south and North of the fish farms as well as in the water adjucent to the floating cages. The waters surrounding the fish farms exhibited profound increased mean annual content of phosphorus, which peaked during the summer months. This increase in phosphorus was also reflected in high primary productivity as indicated by increased chl-a content at the sites of the fish farms. A model of dispersion of wastes generated by the fish farms indicates that the major path of dispersion is towards the coast and over a range of more than 120 meters. The directions and velocity of water currents may result in the diffusion of nutrient from point sources such as the fish farms towards deepest part of the bay (South). The results indicate that benthic ecosystem around the fish farms is not significantly disturbed. Nevertheless, the levels of nutrients in the water body and the AZTI’s marine biotic index (AMBI) of the sampling points indicate a potential ecological risk during the summer period. Increased feeding and metabolism of the farmed fish during the growing season is combined with the natural seasonal hydrological conditions and result in a highly localized aquaculture induced eutrophication.