Spatial and temporal patterns of benthic macrofauna in Gorgan Bay, south Caspian Sea, Iran

We quantified the distribution, abundance and assemblage structure of macrofauna at 22 stations in Gorgan Bay, seasonally in 2012-2013. Also, depth, temperature, salinity, DO, TOM and sediment particle size were measured in each station. The highest concentration of TOM was measured near the western littoral zone (10.22) while the mouth part and north-eastern area was characterized by the lowest values (2.65 % and 4.69). A total of 31658 individuals belonging to 12 families and 14 species were identified. Polychaeta with 3 species was the most dominant group in terms of abundance. The four most abundant taxa making up 85% of all specimens were Streblospio gynobranchiata, Tubificidae, Hediste diversicolor and Abra segmentum. The maximum density (7,893 ind/m^2) was obtained at station 1 while the minimum (1,777 ind/m^2) was observed at station 16. The western area was characterized by the highest species diversity (H', 1.94) and the stations 10, 8 and 7 were characterized by the lowest diversity indices (H', 0.72, 0.77 and 0.87, respectively). The PCA showed that water parameters with more temporary variations had a greater significance in explaining the system variability, and a not marked but evident difference between the two parts of Gorgan Bay was observed and supported by nmMDS test. So Gorgan Bay presents transitional macrobenthic assemblages that are spatially distributed along substrate gradients but it seems that the coastal ecosystem of the south Caspian Sea and mouth-eastern part of Gorgan Bay is very dynamic and some species are forming a metapopulation toward western sites

Distribution pattern of heavy metals in the surficial sediment of Gorgan Bay (South Caspian Sea, Iran)

The Gorgan Bay is an important ecosystem receiving discharge from their tributaries. In this study, concentration of Pb, Zn, Ni, Fe, Al, Cu and As was seasonally determined at 22 sampling points during 2012-2013. Sediment samples were collected using a Van Veen grab. The levels of heavy metals were determined by ICP-AES (Inductively Coupled Plasma Atomic Emission Spectrometry) and AAS (Atomic Absorption Spectrophotometer). The percentages of sand, silt, clay and TOM (Total Organic Matter) in the sediment samples were determined (44.4± 15, 53.4 ± 14, and 2.2± 2.2 and 7.2% ± 1.6, respectively). The results showed that range of Al, As, Cu, Fe, Ni, Pb and Zn in the sediment samples were 0.4-2%, 2.6-8.6 ppm, 8.1-12.4 ppm, 0.9-1.2%, 11.5-16.8 ppm, 5.9-13.6 ppm and 21.8-28.8 ppm, respectively. In spring, both Al and Ni were higher than the guideline level. In the event that arsenic was exceeds the guidelines in summer. In general, according to the results of EF (Enrichment Factor) and PLI (Pollution Load Index) can be concluded, Gorgan Bay is low risk and not contaminated. According to the results of the nmMDS (non-metric Multidimensional Scaling), PCA (Principal Components Analysis) and the map of distribution of heavy metals, it seems Gorgan Bay are divided into two separate zones (the eastern and the western parts)