| چکیده انگلیسی مقاله |
The diversity and abundance of planktonic primary producers play a critical role in aquatic ecosystems, serving as indicators of ecological health and vitality. The Anzali Wetland, located on the southwestern coast of the Caspian Sea, is currently experiencing severe ecosystem degradation, with notable impacts on its biological communities. This study examined the phytoplankton community structure in the Anzali Wetland from March to December 2023 and compared the findings with historical data. The number of genera in the dominant phytoplankton groups—Bacillariophyceae, Chlorophyta, and Cyanobacteria—declined by 59%, 63%, and 53%, respectively. Additionally, the Euglenozoa phylum experienced an 80% reduction in genera. Despite the overall decline, several genera remained dominant in both occurrence and abundance, including Cyclotella, Nitzschia, Synedra, and Navicula (Bacillariophyceae); Ankistrodesmus and Scenedesmus (Chlorophyta); Oscillatoria and Merismopedia (Cyanobacteria); and Euglena (Euglenozoa). The average annual abundance of phytoplankton in 2023 was 7.8 million cells/L, representing a nine-fold decrease compared to data from the past two decades. The highest abundances were recorded in Bacillariophyceae (1.5 million cells/L) and Cyanobacteria (1.3 million cells/L). Notably, the abundance of Euglenozoa (587,000 cells/L) showed a significant increase compared to levels observed in the 1990s. The decline in phytoplankton diversity and abundance over the past 30 years is largely attributed to anthropogenic pressures and major environmental changes, particularly the declining water level of the Caspian Sea. This has drastically transformed the Anzali Wetland’s landscape, with extensive drying of water bodies. To restore the ecological integrity of the Anzali Wetland, urgent rehabilitation measures are required. These should include hydrological restoration, pollution and sedimentation control, and management of invasive species such as Eichhornia crassipes (water hyacinth). Implementing these strategies is essential for improving the planktonic community structure and reviving the wetland’s ecological health.
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