The effect of summer monsoon on macrobenthic's community structure in Jask creek (Gulf of Oman)

Gulf of Oman, in the summer, is influenced by the southwest monsoon winds of India, and Jask protected area, which is ecologically and economically very important, is located in the northwestern area of this gulf. In this study, sampling of sediments was done from 2009 to 2010, in three station (mouth, mid and end) of Markazi creek (located in Jask city), by 0.04 m2 Van Veen Grab. Water physicochemical parameters (including dissolved oxygen, salinity, temperature and pH) of the water near the seabed, as well as sediments grain size, and total organic matter (TOM), were measured at each station. The relationships between diversity and abundance of macrobenthos and biological and non-biological factors, were studied in sampling seasons (premonsoon, monsoon and postmonsoon). A total of 14425 pcs per m2, belonging to 64 species of macrobenthos were counted and identified. In total, Gastropoda with 22 species and Bivalves with a frequency of 9125 pcs per m2, had the highest diversity and density of macrobenthos, respectively. The results of this study showed that, the spatial and temporal variation of macrobenthos in this area affected by climatic fluctuations are due to the Indian Ocean monsoon. The maximum and minimum densities of macrobenthos were identified at postmonsoon season (8075 pcs per m2, equivalent to 58.24% of total species), and during monsoon season (2766 pcs per m2, equivalent to 17.21% of total species), respectively. Results of calculating the diversity index, Shannon-Wiener, showed that the maximum and minimum value of this index were observed at premonsoon, end station (1.03), and postmonsoon, mid station (0.41), respectively.