Title: Classification of Gorgan Bay by using Ecological Indices

In this study, the ecological status of Gorgan Bay is classified by using the results of biological indicators and diversity index. For this aim, data on macrobenthose and  the sedimentation characteristics were recorded at 22 sampling points during 2011 to 2012. According to the changes in the depth of the bay in different parts, the stations were classified into four groups of depth less than 1 meter, 1-2 meters, 2-3 meters and more than 3 meters. The total Range of organic matter, gravel, silt and clay in the Bay was recorded in (1.3-4.7), (47.1-57.7), (37.6-51.7) and (6.2-8.4) percent. The positive relationship between the total organic matter and the texture of bed indicates the accumulation of organic matter in the depths of the bay. By using multivariate tests the classified and distinct high depth from low depth of the bay, based on environmental conditions and parameters. The amplitudes change of Shannon index, BO2A and M-AMBI in the Bay were, calculated in range of (0.1-96.69), (0.02- 0.06) and (0.6- 0.8). Overall, according to the average of the calculated indices, Shannon weakened the whole ecological status of the bay and BO2A and M-AMBI indices the desired results were obtained. On the other hand, evaluation of the indicators showed that the condition of the shallow western part is better than the deep eastern part. This is can because of the region's hydrodynamic conditions and the adverse conditions for different benthic species due to the proximity to the River and other entrance around the bay.