Study on pollution indices based on biological characteristics of macrobenthos in the southern Caspian Sea (2018-2019)

The aims of the present study were to investigate the macrobenthos communities in the Caspian Sea and to investigate the pollution of this ecosystem based on the pollution indices ABC (Abundance Biomass Comparison), BC (Biotic Coefficient) and ABC curve in 2018 (autumn and winter) and 2019 (spring and summer). According to the results, polychaetes, crustaceans, and bivalvia formed the major groups of macrobenthos communities with 4, 11 and 1 species, respectively. The polychaetes (mainly Streblospio gynobranchiata) included about 70% of the total abundance and the group of bivalvia (Cerastoderma glucaum) included about 76-93% of the macrobenthos in all seasons except in spring. The mean values of the Shannon index and evenness indices were calculated as (1.56) and (0.55), respectively. The annual pollution (ABC) and BC indices were obtained as -3.1 and 2.7, respectively. These values along with characteristics of ABC curve indicate severe stress caused by pollution in the Caspian Sea ecosystem. In this study, the percentage abundance of the invasive species S. gynobranchiata in macrobenthos communities was 52%, which is about 10% decrease compared to 2009 and 2010. This decreasing trend can be considered as positive evidence in the improvement process of the ecosystem in this part of the food chain. However the continuity of recovery trend needs more time, no force by new stressors, proper management, and reduced pollutions into the ecosystem.