Assessment of aquatic ecosystem health in Gorgan Bay based on biotic indices

The relationship between spatial patterns of macrobenthic community characteristics and environmental conditions (dissolved oxygen, temperature, salinity, organic matter content and sediment particle size) was studied at 12 stations in Gorgan Bay (South Caspian Sea, Iran), seasonally in 2017. A total of 8803 individuals belonging to 11 families and 11 species were identified. Three species of polychaeta including Streblospio gynobranchiata, Tubificidae and Hediste diversicolor were the most dominant group in terms of abundance, making up 79.3% of all specimens. The highest density (4733 ind m^-2) was observed at St. 1 while the lowest (1166 ind m^-2) at St. 9. Biotic indices (i.e. AMBI, BOPA and BENTIX) were used to determine the quality of the bay. Gorgan bay is divided into two distinct zones (eastern and western regions) based on MDS analysis and ecological status. Generally, eastern part of the bay revealed the lowest abundance and biodiversity of macrobenthos. Our results suggest the effect of sediment particle size and TOM as significant parameters on distribution of macrobenthic community in Gorgan bay, South Caspian Sea.