The Process of Species Replacement In The Southeastern Part of The Caspian Sea and its Relation To The Ecosystem's Trophic Conditions

Ongoing ecological study of the Caspian Sea, in particular distribution, identifying the species composition and regional variations, seems to be necessary before any study. In order to, in present study, the replacement of benthic groups in the Gorgan Bay and southeastern basin of the Caspian Sea (Golestan province) was studied and compared with the results obtained in previous studies. The results of the study of benthoses showed that the polychaete worms, oligochaete worms, nematodes, chironomidae worms, bivalvias and amphipoda crustaceans constitute the main benthic founa of the ecosystem. These results indicate a very inadequate quality status in the studied areas. The results of the comparison with other previous studies also showed that factors such as the input of organic and inorganic pollutants, inappropriate disposal of wastes, the closure of the main channels of the Caspian Sea and the lack of ventilation of the ecosystem, the construction of inappropriate fishing facilities and etc. caused the hypertrophy conditions and a significant reduction in density and diversity of benthoses in these areas.