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In this study, investigation was conducted to determine the seasonal species composition and structure of zooplankton population of Caspian Sea at three commercial regions, Amirabad, Nowshar and Anzali harbors in 2010. According to the results a total of 24 species was found to build zooplankton populations. These zooplanktons were include of copepods (4 species), Cladocera (7 species), Rotatoria (9 species), protozoa (2 species) and 2 temporary plankton species (Meroplankton). Maximum species abundance of zooplankton species was recorded in autumn and Winter (21 species) and lowest in summer (15 species). The study showed that the average annual population density and biomass of zooplankton were 3848 ± 1114 /m3 and 35.1±9.6 mg/m3 respectively. Maximum average of annual zooplankton abundance and biomass were belonged to copepods with 3085±810/m3 and 23.9±5.7 mg/m3. Quarterly seasonal review (temporal distribution) of zooplankton abundance and biomass showed that was more in the summer with an average density of 4390 ± 1230 /m3 and 48.9±15.9 mg/m3 in winter, respectively. The aim of this study was to assess the zooplankton population in Anzali, Nowshar and Amirabad harbors which showed the highest density and biomass of zooplankton in Anzali region with 5789±1352 /m3 and 44.7 ± 11.1 mg/m3 respectively and the lowest was in Noshahr with 3142±658/m3 and 32.2±8.0 mg/m3 respectively.

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The study investigated the relationship between some of biological parameters (phytoplankton, zooplankton and Mnemiopsisleidyiabundance) and some environmental parameters (temperature, salinity and water clearness) in the southern Caspian Sea during 2009 to 2010. Sampling was performed in four seasons (spring, summer, autumn and winter) and at eight transects perpendicular to the coast. Phytoplankton and environmental parameters samples were collected using Niskin. Zooplankton and Mnemiopsisleidyi samples provided by net. Total of 384 phytoplankton and water samples and 160 zooplankton andMnemiopsisleidyi samples were collected at the euphotic zone from depths of 5, 10, 20, 50 and 100 m. According to results, minimum and maximum values of phytoplankton biomass were observed in summer and winter, respectively. During spring and winter, the abundance of zooplankton was in highest level and conversely the minimum values observed during summer and autumn with obvious increasing inM. leidyi abundance. Maximum temperature and salinity were observed in summer and autumn, respectively. Result on PCA analysis in summer showed that decreasing of salinity had positive effect on M. leidyiandzooplankton abundance especially coppepoda and cirripedia groups. In this season, phytoplankton biomass was affected by temperature and salinity. However, with considering PCA analysis in autumn, phytoplankton biomass was correlated with PC1 which had a principal rule as compared to zooplankton. In this season, M. leidyiabundance was correlated with temperature and salinity of water. M. leidyiabundance was negatively correlated with water transparency during the two periods of time. It can be due to mucus excretion of M. leidyiwhich may decrease transparency of the water. In this study for the first time the dynamic population of M. leidyi is used as key factor in the Caspian seaecosystem events, however the interaction of different factors such as biotic and environmental parameters may also have effect on changes of dynamic of zooplankton abundance and its groupscomposition.

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To study the diversity and structure of zooplankton, samples were collected at two commercial regions, Nowshar and Anzali harbors at the depths of 5, 10, 15 and 20 meters in the southern Caspian Sea in 2011. A total of 10 species formed zooplankton populations included of copepods (2 species), cladocera (1 species), balanidae (1 species), rotatoria (2 species), protozoa (1 species) and 3 temporary plankton species (meroplankton). The study showed that the average annual population density and biomass of zooplankton were 3120±552 ind/m3 and 22.5±5.0 mg/m3, respectively. Maximum average of annual zooplankton abundance and biomass were belonged to copepods with 998±60 ind/m3 and 4.1±0.3 mg/m3. Quarterly seasonal review (temporal distribution)of zooplankton abundance and biomass showed that most with the spring season of an average density of 3767±770 ind/m3 and 32.9±7.4 mg/m3, respectively. Seasonal distribution of zooplankton showed that crustacea (included copepods, cladocerans and balanidae) consisted 70.5% of population and 36.4% of biomass.

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This study carried out aimed to identify and evaluate density of zooplankton population. Sampling was conducted at six stations during the spring and fall on April 2013 and October 2014. Zooplanktons sampling was performed by a mesh (30µ) and water sampling done with Routner water sampler. Environmental factors, such as temperature, salinity, turbidity, conductivity, dissolved oxygen pH and TDS were measured at different time sampling. Mesh was pulled up from depth of 15 and its contents drained to plastic containers with 0.5 L capacity, and then fixed with formalin after transferring to laboratory. According to results, 7 families and 21 geniuses were identified during the investigations. The frequency of dominant groups identified was included Copepoda 76%, Zoobenthos 13%, Bivalve 5%, Cladocera 3%, Balanidae 2% and Ichthyoplankton 1%. Density of zooplankton at each station was calculated. The highest and lowest density in autumn was 146250000 nm^-3 for Halicyclops sp. and 50000 nm^-3 for Foraminifera, respectively. The highest and lowest density in spring was 12475000 nm^-3 for Halicyclops sp. and 2500 nm^-3 for Cyprisbalanus sp., respectively. Dominated genus was Halicyclops sp. which has been seen in both seasons. The highest density and lowest density in both seasons were recorded 21909321.43 and 3070678.57 nm^-3, respectively. There was a significant difference between two seasons in zooplankton density (P<0.05). Also there was a strong significant correlation between temperature, dissolved oxygen (among environmental factors) and zooplankton density in waters near the Assalouyeh harbor (P<0.01). 

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The present study aims to examine and identify zooplanktons species carried by ballast tanks of the ship and discharged into Bandar Imam Khomeini waters. The samples were taken during summer 2014 from 12 ships loaded with ironstone, condensate and ironware traveled from both South America and the Southeast Asia within two seasons. For this purpose, 50 liter-three specimens was filtered by a 100 micron plankton catching net and stabilized by formalin. The specimens were detected by microscope and by using the valid identification keys. Considering to the obtained results within two seasons of summer and winter, it is found that there were totally 9 families and 18 genera transported through South America route where the greatest frequency was related to Paracalanidae with 35%, whereas in the Southeast Asia route there were 18 families and 30 genera of zooplanktons in which the greatest frequency was found in Cyclonidae and Sididae families with 9 and 8%, respectively. By comparing both local and foreign reports related to this zone it was revealed that no species can be regarded as invasive species.

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In the past two decades, the effects of stressers’ factors such as biological and chemical pollution on biotic and abiotic components have increased in the Caspian Sea. The aim of the study is the survey on zooplankton structural pattern changes from 2008 to 2011 (nearly two decades after the introduction of biological stressor such as Mnemiopsis leidyi) and comparison with the data before the introduction of M. leidyi (1996-97) in the basin of Iranian coastal of Caspian Sea. Samples were collected from 5 to 100 m depths at eight transects (Astara, Sefidrud, Tonekabon, Nowshahr, Babolsar, Amirabad and Turkman) during four seaons (spring, summer, autumn and winter). The results showed that the total number of species in meroplankton and holoplankton groups were 67 which 62 species were belonged to holoplankton group. The number of species in 1996-97 which was considered as a stabale ecosystem was 3.9, 2.3 and 3.4 more than in years of 2008-09, 2009-2010 and 2010-2011, respectively. The number of species in Cladocera group in years of 2008-09, 2009-2010 and 2010-2011 were 9.6, 3.6 and 7.2 less than in years 1996-97, respectively, which showed the most declined of species between other different groups (copepoda, rotifera, protozoa and meroplankton) of zooplankton. Abundance of zooplankton in years of 2008-09, 2009-2010 and 2010-2011 were 1 to 1.5 folds less than in years of 1996-97. Finally, it seems that there is little reasons on improving the ecosystem toward stability, although the Shannon index in 2010-2011 was increased compare to 2009-2010.

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The purpose of this study was to compare the Biomass variations of zooplankton in the eastern coast of Chahbahar in the summer and autumn seasons. Sampling was done using a 100-micron zooplankton net to horizontally in two summer (Monsoon) and autumn (Post-Monsoon) in 2015 at 8 stations. According to the results, the mean of dry weight of zooplankton was 115.46±16.34 and 23.45±2.26 mg m³ in autumn. Independent T test showed a significant difference between the seasons of summer and autumn in terms of biomass (P<0.05). There were significant difference of biomass in the sampling stations (P<0.05) at each seasons. The Maximum and minimum values of biomass recorded at Station 3 (Shipbuilding) and Station 8 (Out of the Beris Port) respectively. According to the results of one-way ANOVA, there was no significant difference of salinity and temperature between different stations in the summer and autumn seasons (P>0.05). Also, the transparency at station 3 was significantly higher than other stations in summer. According to the results of Pearson correlation, inverse linear relationship were observed between biomass and temperature (r=-0.796) and salinity (r=-0.285). Bay are affected by the monsoon and the western winds of the Indian Ocean. Zooplankton density is due to environmental, nutritional and reproductive conditions in different seasons should be.

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