ساناز احمدی فالحی

Planktonic crustaceans are of specific importance in energy transfer due to their location in the middle links of the food chain of aquatic ecosystems. Therefore, they directly affect the abundance and diversity of the higher categories of the food pyramid, especially stocks and fishery resources. In this study, the impact of a tidal cycle on the zooplanktonic Crustacean ecosystem in the estuarine Bahmanshir River (Northwestern Persian Gulf) was studied. Our samples were collected during the spring of 2018 by plankton net with mesh sizes of 100 μm. Samples were taken at 5 stations to have a tidal effect on the abundance of zooplankton, approximately from 8:00 to 18:00 every two hours. In general, 72 species belonging to 28 families related to 3 groups of crustaceans named Cirripedia, Cladocera, and Copeoda were observed. The highest percentage of relative abundance was related to Cladocera with 35%, which was caused by the abundance of Daphnia mendotae. The highest diversity (Shannon index = 2.71 ± 0.04) of copepods was revealed to be caused by the large number of species at station 5 (near the mouth of the Bahmanshir River). Most species among the families belong to the Acartiidae family, which has 10 species of Acartia. The results of PCA analysis showed that among environmental factors, salinity has a direct effect on the total density, density of Harpacticoida and Calanoida, in the first component. The tides appear to significantly affect the density and types of planktonic crustaceans during the mentioned springtime periods. Our results showed relatively strong influence of the tidal cycle on the spatial pattern of Copepod assemblages in the study area. This study may be useful for future biological monitoring and seawater salinity intrusion into rivers in the northwest of the Persian Gulf.