In order to investigate the density and composition of different macrozooplankton groups in the Persian Gulf and Sea of Oman, 55 sampling stations were selected in the waters of Sistan and Baluchistan, Hormozgan, Bushehr and Khuzestan provinces. Sampling of the selected stations was done in the fall and winter seasons of 2018, 2019 and 2020 using a plankton net with a spring size of 300 micrometers equipped with a HYDROBIOS model flowmeter. In this study, 152 species, 58 genera, 78 families, 23 orders, 13 categories and 10 branches of zooplankton were identified and counted. Among the identified groups of zooplanktons, pinnipeds were the most abundant group with 97% and among pinnipeds, calanoids were the most abundant group with 74.25%. The examination of other zooplankton groups, apart from the pinniped group, showed that the pikanian group and the rope-dwelling group had the highest frequency with 18.96% and 18.76%, respectively, and the comb-dwelling group had the lowest frequency with 0.027%. The abundance of zooplanktons in Sistan and Baluchistan province was 51.35% compared to Hormozgan 39.76%, Bushehr 5.26% and Khuzestan 3.61%. Acartia amboinensis species from the subcategory of pinnipeds as the most abundant species in 4 provinces were identified. In the investigation of zooplankton groups other than pinnipeds sp. Larvacea was identified as the most abundant species. In Hormozgan and Sistan and Baluchistan provinces, the most abundant species was Acartia amboinensis, and in Khuzestan and Bushehr provinces, the most abundant species was Temora turbinata. In Hormozgan and Bushehr provinces larvacea sp. From the Appendicularia category and in Sistan and Baluchistan province, sp. Ostracoda, in Khuzestan province, Penilia avirostris from Branchiopoda was reported as the most abundant species other than pinnipeds. The results showed that the amount of diversity indicators has decreased from Hormozgan provinces to Khuzestan province, and Hormozgan and Sistan-Baluchistan provinces have relatively good conditions due to the monsoon phenomenon, the mixing of water layers and the relative stability of the environment.
Keywords: Zooplankton, Biological indicators, Persian Gulf, Density