Study of biodiversity and frequency of polychaetes in the southwestern shores of the Caspian Sea

This study aimed to identify the effect of environmental conditions on the diversity and abundance of polychaetes in the southern shores of the Caspian Sea in Guilan, Iran. Sampling of seasonal sediments was done (June 2017 - May 2018) in 4 stations and three depths of 1, 5 and 10 m with the help of a Van Veen grab sampler with cross section of 225 cm2 and three replications. Temperature, salinity, pH, dissolved oxygen, suspended solids and organic matter were recorded at each station. A total of 2711 polychaetes belonging to 5 species, 5 genera from 3 families were identified. The highest abundance was related to H. kowalewskii (39%) and the lowest abundance was related to H. invalida species (3%). The mean density in the four seasons of spring, summer, fall and winter was 67.66, 81.25, 48.66, and 28.33 worms per m2, respectively. The highest species diversity was 2.16 species per square meter and the biomass of 62.75 mg/m2 in spring and the lowest was in winter. The highest density, diversity and biomass were 80.41 worms per square meter, 2.33 species per square meter and 70.83 mg/m2 on the shore of Chamkhaleh, respectively; and the lowest were 16.83 worms per square meter, 1.5 species per square meter, and 31.41 mg/m2 on the shore of Chaboksar, respectively. The highest density, diversity and biomass were 127.87 per square meter, 3.68 species per square meter and 107 mg/m2 at a depth of 10 meters, respectively. The correlation results showed that among environmental factors, only organic matter had a direct significant relationship with species diversity. Density had a significant direct relationship with temperature and organic matter. Other factors did not show a significant relationship. The results of stability level of different species in the southern shores of the Caspian Sea (Guilan province) showed that N. diversicolor and H. kowalewskii species exist temporarily and other species randomly.