Gelatinous zooplankton (GZ) populations are sensitive to climate change such as environmental perturbations, and spatial changes in their abundance and biomass may be associated with degraded environmental and biota conditions. Big data time series of GZ abundances and biomass were used to analyze the annual population dynamics of gelatinous zooplankton as well as mesozooplankton in the southern Caspian Sea, IRAN from 1996, 2001-06, 2008-13 to 2018-19. The ctenophore, M. leidyi population control by environmental factors was primarily a result of decreasing the concentration of zooplankton resulted to lower reproduction as well as temperature which was highest in August-September and lowest in winter time. On the other hand, the maximum catch of Kilka on the whole coast of Iran was equivalent to 95,000 tons in the year of 1996, and after that it was severely reduced to 15,000 tons in the year of 2003 and afterward.
Keywords: Gelatinous zooplankton, Abundance and biomass, temperature, Caspian Sea