Ecological Assessment Of Plankton Community And Affects Of Alien Species In The Southwestern Caspian Sea
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Date
2012-05
Authors
Khoughani, Siamak Bagheri
Journal Title
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Publisher
Universiti Sains Malaysia
Abstract
The Caspian Sea ecosystem, with its high level of endemic taxa has suffered from anthropogenic pollution, changes in the quantity of nutrients, and the effects of invasive species since the 1980s. To study the temporal changes in phytoplankton and zooplankton communities, seasonal surveys were undertaken at 12 stations in the southwestern Caspian Sea from 1996 to 2010. Among 158 phytoplankton species identified, the dominant species were the diatoms Thalassionema nitzschioides, Dactyliosolen fragilissimus, the dinoflagellate Prorocentrum cordatum, and the cyanophyte of genus Oscillatoria. An increase in phytoplankton abundance was observed after 2000, and has continued until 2010. Except in 2001 and 2002 diatoms predominated thoughout the study. During these two drought years (2001 and 2002), a decrease in river discharge and silicate levels, coupled with an increase in water temperature and salinity were the main factors causing a bloom of dinoflagellate P. cordotum and cyanophyte Oscillatoria sp. in the southwestern Caspian Sea.
A total of 61 zooplankton taxa were found in the study area. Thirteen of them were meroplankton and 48 holoplankton. A decline in zooplankton species was observed before 2000 and continued until 2010. Only one of nine Cladocera species recorded during 1996/1997 were again, found in 2010. Of the five Copepoda species recorded during 1996/1997, only one, Acartia tonsa, was recorded after 2000. Bivalvia larvae have also declined by one order of magnitude since 1996/1997. Bivalvia larvae formed more than 50% of the total abundance of zooplankton before 2000. The dominant zooplankton species was A. tonsa after 2000.
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Keywords
Ecological assessment of plankton community , alien species in the Southwestern Caspian Sea