List of Zooplankton Taxa in the Caspian Sea Waters of Iran

A total of 61 zooplankton taxa were found in the southwestern Caspian Sea between 1996 and 2010. Thirteen of them were meroplankton taxa and forty-eight were holoplankton taxa. The occurrence of 14 freshwater taxa indicated the influence of the Anzali wetland and river inflows. The decrease in zooplankton taxa was detected since 1996-1997 and continued till 2010. Pleopis polyphemoides, the only one out of the nine recorded Cladocera species in 1996-1997, was found after 2001. Similarly, of the five Copepoda species recorded in 1996-1997, only one, Acartia tonsa, was found abundant during the 2001–2010 sampling period. It was striking that many species which were abundant in the Caspian Sea in 1996-1997 were not found after 2000. Many reasons could have contributed to the changes in the zooplankton composition of the southern Caspian Sea, notably the serious environmental degradation since the early 1990s. It is also possible that invasive species might play a role in wiping out some sensitive endemic species. 1. Introduction The Caspian Sea is a large inland water body. It is called a sea even though not being directly connected to any marine system due to its large size [1]. Water is mainly sourced from the big river Volga in the north (almost 76.3% of the total), and other rivers like Kura, Ural, Terek, and Sefidrood [2]. In the Iranian coast, the Sefidrood river is the largest river pouring into the Caspian Sea with 67,000？km2 of catchment area and an average discharge of 4,037 million m3 per year [3, 4]. The Caspian Sea has undergone significant ecological alteration during the past 30 years. This could be linked to dramatic changes in the southern Caspian Sea due to increased pollution: sewage, industry effluent, and agricultural waste water discharges into the river as well as deforestation of the river’s watersheds [5, 6]. Zooplankton is recognized among the best indicators to be particularly useful to investigate and document environmental changes [7]. Main zooplankton taxa have short life cycle and the community structure is able to reflect real-time scenario as it is less enforced by the stability of individuals from previous years [8]. Besides this, zooplankton is also the food of choice for many fishes and as such plays a very significant role in pilaring the upper stages of the food chain [9]. Bagirov [10] reported that the number of zooplankton taxa was almost 200 in the northern Caspian Sea with 70 taxa of Protista, 50 taxa of Rotatoria, 30 taxa of Cladocera, and 20 taxa of Copepoda. Meroplankton, represented mainly by larvae of bivalves