Environment and Pollution; Vol. 8, No. 2; 2019 ISSN 1927-0909 E-ISSN 1927-0917 Published by Canadian Center of Science and Education 31 The Environmental Impact of Sturgeon Pen Culture on Diversity and Spatial Distribution Patterns of the Benthic Macro Fauna Communities in Gorgan Bay Farhangi Mohammad 1 , Hosseini Seyed Abbas 2 , Jafaryan Hojatollah 1 , Ghorbani Rasoul 2 , Harsij Mohammad 1 & Sudagar Mohammad 2 1 Department of Agricultural and Natural Resources, Gonbad Kavous University, Gonbad, Iran 2 Department of Fisheries and Environment, Gorgan University of Agricultural Science and Natural Resources, Gorgan, Iran Correspondence: Farhangi Mohammad, Department of Agricultural and Natural Resources, Gonbad Kavous University, P. O. Box: 163, Gonbad, Iran. E-mail: s.farhangi@yahoo.com Received: September 6, 2019 Accepted: September 26, 2019 Online Published: September 29, 2019 doi:10.5539/ep.v8n2p31 URL: https://doi.org/10.5539/ep.v8n2p31 Abstract Community structure and biodiversity of benthic macro fauna in around pen culture of Sturgeon fish in Gorgan Bay were studied for period of one year from August 2015 to July 2016. Seasonal samplings were carried out at 5 stations in 3 transects. In addition, depth (D), water temperature (T oc ), dissolved oxygen (DO); pH, total dissolved solid (TDS), biological oxygen demand (BOD 5 ), chemical oxygen demand (COD), phosphorus (PO 4 -3 ), nitrite (NO 2 - ) and total ammonia (NH 3 + ) were measured in each station. Results of season variations of Physico – chemical factors of water showed that, there were no significant differences between PO 4 -3 (p>0.05). However, there were significant differences between BOD 5 , COD, NO 2 - , NH 3 + and TDS (p<0.05). Totally, 11 genus's and 10 families belong to 3 phyla as Mollusks, Arthropods and Annelids were identified. The results showed, there were the maximum abundance percent belong to Hydrobiidae and Cochliopidae with 33.83% and 26.25% and the minimum abundance percent belong to Gammaridae with 0.05% respectively. However, the maximum abundance belongs to Pyrgohydrobia sp., from Hydrobiidae with 3410 n/m 2 . The results showed, there were the maximum and minimum abundance percent in autumn and spring with 1.07 and 0.88 % respectively. The results of distance-based redundancy analysis (db.-RDA) revealed that environmental factors such as depth, DO and TDS are all important in determining the distribution of macro benthic species in Gorgan Gulf. However, there were significant differences between abundance, species number (S), diversity (as Shannon–Wiener’s, H´), species richness (as Margalef’s, D), and evenness (as Pielou’s, J) (p<0.05). There were the most diversity species in 2 and 5 stations. Keywords: biodiversity, Macro fauna, environmental factors, Gorgan bay 1. Introduction Gorgan Bay is a unique ecosystem in the south-eastern part of the Caspian Sea. It is separated by Miankaleh peninsula from the sea. Sediment texture is different from west to east (Lahijani et al., 2002; Lahijani et al., 2010). Salinity regime is different throughout the bay and it is influenced by internal current (Sharbaty, 2012) and some small rivers from east and west which created some freshwater marshes especially at the western part (Taheri et al., 2012). Therefore, different types of habitats are found in the bay (e.g., salt marsh, mud flat, sand flat, fresh and brackish water area) and each type is inhabited by different species (com- munity structure). These variable conditions made it the most important natural ecosystem in the south part of the Caspian Sea that serves as a nursery area for a lot of juvenile fishes and very good place for breeding and wintering of the water birds The macro fauna play important roles in marine ecosystems, involving nutrient cycling, dispersion, sediment burial, and secondary production. Distribution patterns in general are related to environmental factors such as tidal currents, depth, food supply, salinity, sediment texture, organic matter content and current velocity (Gogina et al., 2010; Nicastro and Bishop, 2013). Hence, any changes in environmental conditions can be reflected in macro fauna community characteristics. Response of macro benthic species to these conditions is different and related to their adaptation strategies (Baldanzi et al., 2013; Conde et al., 2013). In fact, most of the species