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Volume 34, Issue 1 (4-2025) |
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Zooplankton biodiversity, distribution, and abundance in Anzali Wetland in 2023: A comparative study with previous decade
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Siamak Bagheri   , Alireza Mirzajani1 , Jalil Sabkara , Mehrdad Nasri Tajan |
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Abstract: (62 Views) |
Introduction
The Anzali Wetland is located along the southwestern coast of the Caspian Sea and was the first wetland in Iran to be registered on the Ramsar Convention's list. However, it was soon added to the Montreux Record due to ecological concerns (Mirzajani et al., 2020). Zooplankton is a crucial link in the wetland's food chain, play an important role as secondary producers and serve as a primary food source for aquatic animals. Planktonic communities are highly responsive to environmental changes, their population structure is strongly influenced by nutrient levels in the water in the water (Mulani et al., 2006; Boyd, 2007; Bagheri et al., 2017). Following the invasion of the water hyacinth plant, a decline in the Caspian Sea's water level, and reduced rainfall and river inflow due to climate change, this study represents the most recent investigation into the temporal and spatial distribution of zooplankton in the Anzali Wetland. The objective of this study was to assess the biodiversity, composition, and density of zooplankton in the Anzali Wetland in 2023, compare the findings with previous research, and evaluate the broader ecological changes over time.
Materials and methods
The Anzali Wetland is located at 37º 28' N latitude and 49º 25' E longitude, with a maximum depth rarely exceeding one meter. Zooplankton sampling was conducted in March, May, June, August, October, November, and December 2023 at 14 stations. Sampling took place over three days each month using boats with engine powers of 85 and 25 horsepower. A Ruttner Water Sampler was employed for zooplankton collection. The collected samples (30 liters) were passed through a 55-micron zooplankton net, and the water retained in the net was transferred to 300 cc polyethylene bottles. The samples were then fixed with 4% formalin and transported to the plankton laboratory for quantitative and qualitative analysis (APHA, 2005).
In the plankton laboratory, after homogenization, 5 ml of the sample was transferred using a pipette to 5 ml counting chambers (KIEL Hydro-Bios). After 24 hours of sedimentation, the samples were identified and counted under an inverted microscope (F-S Leitz-LABOVERT). Zooplankton density was calculated as the number of individuals per liter of water. The methods for sampling and determining zooplankton density were based on APHA (2005) and Ruttner-Kolisko (1974), while zooplankton identification followed the keys of Thorp and Covich (2001) and Pontin (1978).
Results
In this study, 58 genera from four zooplankton groups were identified in the Anzali Wetland. The highest number of genera belonged to the phylum Rotifera, with 28 genera. This was followed by Arthropoda and Protozoa, with 12 and 11 genera, respectively. In terms of abundance, Rotifera was the dominant group, accounting for 48% of the total zooplankton population (148 individuals per liter). Protozoa ranked second with 26% (81 ind.l⁻¹), followed by Arthropoda with 24% (72 ind.l⁻¹). Other zooplankton groups made up the remaining 2%. The average total zooplankton abundance in the Anzali Wetland was estimated at 305 individuals per liter.
The genera Cyclops and Cyclocypris (phylum Arthropoda) were observed across all areas of the Anzali Wetland. From the phylum Rotifera, the genera Brachionus, Cephalodella, Philodina, and Rotaria were consistently found throughout the wetland, showing a 100% observation frequency. The highest zooplankton abundance was recorded in June, with an average of 652±208 ind.l⁻¹, while the lowest values were observed in October (142±36 ind.l⁻¹) and November (155±37 ind.l⁻¹).
Among the zooplankton groups, Rotifera showed the highest abundance, reaching an average of 405 ± 188 ind.l⁻¹ in June, with the lowest abundance being 20±5 ind.l⁻¹ in other months. The abundance of Arthropoda ranged from 120±44 ind.l⁻¹ in June to 27±11 ind.l⁻¹ in November. Statistical analysis revealed a significant difference (P<0.05) in zooplankton abundance among different phyla and sampling months.
Spatial analysis showed that the western region of the Anzali Wetland had the highest average zooplankton abundance at 613±128 ind.l⁻¹, while the lowest abundance was recorded at the wetland outlet (116±31 ind.l⁻¹). The maximum abundance of Rotifera ranged between 206 and 335 ind.l⁻¹ in the western and eastern regions, respectively. The highest Arthropoda abundance (176 ind.l⁻¹) was also observed in the western region. The abundance of Protozoa varied between 41 ind.l⁻¹ in Siah Keshim and 106 ind.l⁻¹ in the central wetland.
Discussion and conclusion
Over the past 30 years, increased human activities and significant environmental and climatic changes have contributed to notable shifts in the zooplankton community of the Anzali Wetland. Biodiversity has drastically declined, with the number of zooplankton genera dropping from 87 genera in 1994 to 58 genera in 2023 (Mirzajani et al., 2009). This study reveals a more than 13-fold decrease in zooplankton density compared to the 2013-2014 period. Specifically, the abundance of Rotifera and Protozoa in 2023 was reduced by 17-fold and 19-fold, respectively (Fallahi et al., 2018).
The substantial decline in zooplankton density observed in this study suggests a disruption in the food chain within the Anzali Wetland ecosystem, which could lead to a further reduction in aquatic resources. The highest zooplankton abundance was recorded in the western wetland area, which remains the only intact section of the Anzali Wetland. However, this area has experienced significant changes, including a dramatic reduction in depth and near-total coverage by the invasive water hyacinth (Pontederia crassipes).
Several factors have contributed to the decline in zooplankton biodiversity and density in the Anzali Wetland. These include the spread of non-native water hyacinth, decreased water depth, increased sedimentation, higher rates of water evaporation, reduced flow from rivers entering the wetland, climate change, the decrease in the Caspian Sea water levels, and a lack of proper wetland management. These cumulative pressures have worsened over the past decades.
To address the issues affecting the Anzali Wetland and to restore the zooplankton community, which plays a critical role in the food chain and aquatic resources of this ecosystem, it is essential to prioritize the removal of non-native water hyacinth and accumulated sediments. Efforts should focus on the western, central, and southern areas of the wetland to help clean and increase its depth. These measures should be incorporated into the action plans of relevant executive organizations to revitalize the ecosystem.
Conflict of interest
According to the authors of this article, there is no conflict of interest.
Acknowledgment
This study was conducted in Anzali wetland with the approved code of 01051-011052-034-12-73-14. The colleagues of the ecology department, Javad Vesaghi, Yaqoub Ali Zahmtakesh, Omid Imani, and Reza Mohammadidoost, are grateful for their helps in sampling and laboratory works. |
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| Keywords: Zooplankton, Planktonic population, Biodiversity, Anzali Wetland |
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Full-Text [PDF 1559 kb]
(27 Downloads)
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Type of Study: Research |
Subject:
اكولوژي محيطهاي آبي
Received: 2024/12/11 | Accepted: 2025/04/30 | Published: 2025/06/29
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Bagheri S, Mirzajani A, Sabkara J, Nasri Tajan M. Zooplankton biodiversity, distribution, and abundance in Anzali Wetland in 2023: A comparative study with previous decade. isfj 2025; 34 (1) :97-113 URL: http://isfj.ir/article-1-2849-en.html
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