Oligochaetes (Annelida, Clitellata) in the Anzali International Wetland, north-western Iran

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INTRODUCTION Transitional waters, for example lagoons, represent important but fragile ecosystems in the coastal landscape, providing key ecosystem services such as water quality improvement, fisheries resources, habitat and food for migratory and resident animals, and recreational areas for human populations. The Anzali International Wetland was registered in the Ramsar Convention in 1975 as Ramsar Site #40, Wetlands International Site Reference No. 2IR005 (JICA 2005). The Anzali Wetland complex comprises large, shallow, eutrophic freshwater lagoons, shallow impoundments, marshes, and seasonally flooded grasslands at the south-western coast of the Caspian Sea (Fig. 1). It consists of different aquatic and dry land ecosystems and is a good example of a natural habitat supporting an extremely diverse wetland flora and fauna (Ayati 2003). Oligochaete annelids have a worldwide distribution, being frequently the most abundant benthic organisms in freshwater ecosystems; many species are cosmopolitan (Brinkhurst and Jamieson 1971). They are used in biodiversity studies, pollution surveys, and environmental assessment and have also economic importance (Mason 1996; Wetzel et al. 2000; Rodriguez and Reynoldson 2011). Although many researchers have studied the Anzali Wetland from the pollution-related, faunistic, and ecological points of view (e.g. Ayati 2003; JICA 2005; Charkhabi and Sakizadeh 2006; Akbarzadeh et al. 2008; Jafari 2009; Tahershamsi et al. 2009; Mirzajani et al. 2010; Pourang et al. 2010; Jamshidi-Zanjani and Saeedi 2013), there are no data on the species diversity of the Oligochaeta of the region, except the single record of Tubifex tubifex by Pourang (1996). The aquatic Oligochaeta species of Iran are mentioned only in a few papers: Stephenson (1920), Egglishaw (1980), Aliyev and Ahmadi (2010), Ahmadi et al. (2011, 2012), Ardalan et al. (2011), Jablonska and Pesic (2014). Until now 19 species of aquatic oligochaetes occurring in inland waters of Iran have been recorded. The aim of this study was to evaluate the diversity and distribution of this group and to contribute to the Oligochaeta fauna of both the Anzali Wetland and Iran. MATERIAL AND METHODS Study area The Anzali International Wetland (37[degrees]28' N, 49[degrees]25' W), one of the largest freshwater coastal wetlands of Iran, is located in the Guilan Province at the south-western coast of the Caspian Sea and covers an area of 193 [km.sup.2] (Pourang et al. 2010) (Fig. 1). The main wetland covers about 11 000 ha; it comprises an open freshwater lagoon with a length of 26 km and a width of 2.0-3.5 km, surrounded by reed beds extending its eastern border for another 7 km. Eleven rivers and groundwater seeps feed the wetland. The wetland complex is separated from the Caspian Sea by a dune system; the passage to the sea has a width of 426 m. The wetland supports extensive reed beds and an abundant submerged and floating macrovegetation. Its permanently aquatic portion is surrounded by seasonally flooded marshes and water impoundments, which are also fringed by reed beds and damp grassland. The southern part of the wetland is mainly adjacent to rice fields and patches of woodland, while the northern part borders on sand dunes with grassland and a scrubby vegetation. The wetland consists of four main parts: the western, the central (Sorkhankol Wildlife Refuge), the south-western (Siahkeshim Protected Area), and the eastern; the last part has different physico-chemical, morphologic, phytoecological, and geographical characteristics, including a higher anthropogenic pressure (Ayati 2003). [FIGURE 1 OMITTED] Total precipitation in the Anzali Wetland is about 1500 to 2000 mm [y.sup.-1]. Maximum water depth is about 3 m but it is fluctuating (Jafari 2009). The water depth has decreased, owing to solid sedimentation, in some parts to less than 0.5 m (Ayati 2003). In the last ten years, salinity has slightly increased with the rise of the level of the Caspian Sea, which has caused more intensive mixing of water, as well as with the inflow of salt from increased upstream irrigation. …