Nitrogen stable isotope composition as a tracer of fish farming in invertebrates Aplysina aerophoba, Balanus perforatus and Anemonia sulcata in central Adriatic

Information on aquaculture-related environmental impact along the eastern Adriatic coast is very scarce. In this paper, the area affected by fish farm and sewage derived particulate nitrogen in the Murter Sea and semi-enclosed Pirovac Bay (central Adriatic, Croatia) was assessed using the stable nitrogen isotopic composition (delta N-15) in particulate organic matter (POM) and benthic sessile invertebrates (Aplysina aerophoba, Balanus perforatus and Anemonia sulcata) in the exposed areas compared to an unpolluted reference site. The results suggest that increased delta N-15 values in the POM and biota in the impacted areas are predominantly due to nitrogen losses through feed wastage and fish excretion (faeces), but also due to the sewage discharge into the marine coastal ecosystems. The delta N-15 values of the selected organisms were significantly higher around fish cages, as well as at sites polluted by urban waste, compared to the reference site and some other pristine offshore locations. The N-15 enrichments of A. aerophoba, A. sulcata and B. perforatus collected around fish cages compared to the reference location were up to 6.8, 6.5 and 5.2 parts per thousand, respectively, which exceeds the natural variability. While the delta N-15 values of A. sulcata and B. perforatus showed an excellent linear correlation with those of the POM, a weaker correlation was found between delta N-15 of A. aerophoba and the POM, although its delta N-15 values consistently increased with the increased delta N-15 values of POM. This is attributed to the presence of different bacterial populations hosting in the sponge. A geochemical map of the delta N-15 values in the POM and organisms was created, which could be used for tracing the dispersion of N-15 loading generated by aquaculture and sewage in the receiving environment, and their transfer into biota in the adjacent coastal ecosystem. Sponges or other organisms, although known as non-selective suspension feeders, but hosting abundant bacterial populations, may have delta N-15 values lower than the POM, but still reflecting the overall enrichment of the environment in N-15 due to the presence of enriched effluents from aquaculture operation or municipal discharges. (c) 2006 Elsevier B.V. All rights reserved.