Effects of sediment grain size and seasonal changes on macrobenthic community structure inhabiting the south and southeastern parts of the Caspian Sea shoreline

In this study, we investigated the effects of sediment grain size and seasonal change on the structure of macrobenthic communities in the south and southeastern shorelines of the Caspian Sea for one year using a hand corer. Sediment sampling was performed at four stations (Sari, Sisangan, Khajeh Nafs-Ashuradeh, and Bandar-e-Turkmen wharf) with different substrates. Results of PERMANOVA analysis showed a significant interaction effect between the season and the sampling station. The dominant species composition varied in each station at different seasons. Stenogammarus sp. and A. improvisus and P. eichwaldiana contributed to 100% dissimilarity between Bandar-e-Turkmen and Farahabad shorelines in summer, winter, and spring. In all seasons, Stenogammarus sp. was dominantly present in most sampling replications with a uniform frequency at the Sari shoreline. C. albidus and C. littoralis species were dominant in Khajeh Nafs-Ashuradeh and Sisangan stations during four seasons, respectively. Based on dbRDA plots, the sediment organic matter and electrical conductivity in summer; salinity, pH, and silt percentage in autumn; sediment organic matter and pH in winter; and organic matter and percentage of clay in spring had a substantial role in the distribution of macrobenthos and their frequency differences.