The following study aimed to investigate the macrozoobenthos species composition, depth distribution, and seasonal variations in the South Caspian Sea sector of Azerbaijan. During the study period of 2018 to 2019, the identified macrobenthic organisms totaled 56, representing 10 systematic groups in the Azerbaijan sector of the South Caspian Sea. The most recorded species resulted in spring and summer (48–56 species), while the lowest appeared in autumn (28 to 32 species). The average annual biomass of macrozoobenthos ranged from 166.36 to 192.10 g/m², with a density of 1,281 to 1,994 specimens/m². These organisms with peak development occurred in summer (201.29 to 239.75 g/m²), while the lowest manifested in autumn (134.17 to 138.9 g/m²). Mollusks play a primary and vital role in the formation of the benthos biomass, comprising 63.8% to 64.9% of the total biomass. Species diversity and abundance were the highest at the sea depth of 25–50 m, with a total biomass and density range from 210.96 to 259.91 g/m² and 1,774 to 1,913 specimens/m², respectively.

Keywords: Macrozoobenthos, species composition and distribution, biomass, density, quantity, sea depth, seasons, South Caspian Sea, Azerbaijan

Key findings: By investigating the macrozoobenthos species composition, depth distribution, and seasonal variability, the identified macrobenthic organisms totaled 56, with an average annual biomass and density in the South Caspian Sea sector of Azerbaijan.