Latest Diversity Trend and Seasonal Abundance of Population of Zooplankton (Holoplankton) Communities in the South Caspian Sea, Iran

Seasonal variations of zooplankton communities were studied in the southern Caspian Sea for ۴ successive seasons and ۸ transects with ۵ stations from ۵ to ۱۰۰ m depths which sampled during ۲۰۰۹. The zooplankton population constituted of ۷۳.۳۳% copepods, ۲۴.۲۱% rotifers, ۲.۲۳% cladocerans and ۰.۲۳% protozoans. Copepods were dominant at all stations with a density between ۱۴۵۶±۵۳۱ ind. m-۳ (Transect ۸) to ۴۵۲۴±۱۲۱۵ ind. m-۳ (transect ۲). The predominant species of copepods was Acartia tonsa constituting ۹۹.۵۰% of all copepod populations. They were most abundant during warm months of summer in the upper layers (surface to ۲۰ m depth) while rotifers replaced them during cold season. The maximum density of zooplankton was observed in the west decreasing towards the eastern parts of the sea.