Application of Stable Isotopes of carbon (13δC) and nitrogen (15δN) in assessment of Gorgan Bay Fish dynamic in Golestan Province

Gorgan Bay and the southeastern coasts of the Caspian Sea in the Golestan Province are important biological and fisheries areas., while in recent years, they have been heavily contaminated. In present study, the dynamic of fishes, using stable nitrogen and carbon isotopes was evaluated to determine the diet and its trophic status, which can accurately chart the ecosystemchr('39')s biological conditions. Accordingly, in September-October 2015 at 5 ecological stations, sampling of prephytones, macrophytes, macro invertebrates and fish, were taken and dominant species were subjected to isotope analyzes using the EA-IRMS device. The results of the nitrogen-15 and carbon-13 isotopes indicate an imbalance in ecosystem conditions that alters the diet of the organisms and reduces the efficiency of the food web. The main factors of pressure on the ecosystem, the closure of the main channels of the sea to the bay, the entry of various pollutants into the ecosystem and weak physiography of Gorgan Bay, were determined.