Phytoplankton identification, density and dispersal assessment were conducted from June to October 2005 in Lar Reservoir. Samples were taken by simple plankton net (30rm mesh size) and by Ruttner from different depths (0, 5, 10, 20, 30m) and then fixed with formalin 4%. We used inverted microscope in the laboratory to study the samples.We distinguished 34 genera of PHYTOPLANKTONS consisting of 7 Phyla. Number of genera for Bacillariophyta was 11, for Euglenophyta was 1, for Chlorophyta was 11, for Cyanophyta was 5, for Pyrrophyta was 3, for Cryptophyta 1 and for Chrysophyta was 2. Phylum Bacillariophyta was dominant comprising 82.83% of phytoplankton population annually.Cyclotella, Navicula and Nitzchia were the dominant genera. Phylum Chlorophyta was second in dominance and consisted of Oocystis, Pediastrum, Scenedesmus and Chlorella genera altogether sharing 12.89% of the total phytoplankton frequency. Chrysophyta with genera Dinobryon. and Malomonas had a frequency of 2.21%, Cyanophyta with Genera Anabaena, Oscillatoria and Gleocapsa comprised 1.32% of the total frequency, Pyrrophyta with genera Cyratium, and Peridinium had a frequency of 0.52%, Euglenophyta with genus Euglena had a frequency of 0.13% and Cryptophyta with genus Cryptomonas had a frequency of 0.08%.In all sampling months, the highest mean density belonged to Phylum Bacillariophyta with 10,770,666±21.571 individuals per liter of water. Also, in all seasons, the most dominant genus of the Phylum Bacillariophyta was Cyclotella. Phylum Chlorophyta came second in numbers, with a mean density of 2927000±39.573 individuals per liter of water. The dominant genera of this Phylum were Oocystis, Pediastrum, Scenedesmus and Chlorella.Non-parametric Kruskal-Wallis and Mann-Whitney analyses showed that Phytoplankton frequency in different stations and months were statistically different (P<0.05). No significant statistical difference was found between different depths (P>0.05).

During the period of 1979-1980 in Abkenar and Hendkhaleh in Anzali lagoon, 67 I genus of PHYTOPLANKTONS belong to 5 phylum were identified. The results showed that there is two peaks of phytoplankton blooms during a year (summer and, autumn) in which Cyanobacteria (blue-green algae) were the most abundant groups. 5 species of them were identified in which one species was recognized toxic. This toxicity was confirmed through bioassay studies on mouse.Also, This toxin was hepatotoxin belongs to microcystins. Microcystins are cyclic peptides and contain seven aminoacids.

In regard to study the distribution pattern of PHYTOPLANKTONS (with emphasize on chrysophyta and pyrrophyta), a series of 4 cruises were carried out seasonlly in 1996. A total of 93 species belong to 2 main phyllums of chrysophyta (mainly diatoms) and pyrrophyta were identified consist of73 and 20 species, respectively. The diatoms have an important role in the whole Caspian Sea from point of species diversity and on the other hand contain the most abundance and biomass in all seasons.There are two main species of Rhizosolenia calcaravis (belong to chrysophyta) and Exuviealla cordata (from Pyrrophyta) inhabit in the southern Caspian Sea. Comparing the density and biomass of different phyllums of PHYTOPLANKTONS showed that chrysophyta with 75% and pyrrophyta with 17% are the most abundant PHYTOPLANKTONS in the said region.

In this investigation, the quantity and quality changes of PHYTOPLANKTONS were seasonally studied in the littoral waters of Larak Island from October 2005 to September 2006. Nine stations were randomly selected in north-east, north and north – west of Larak Island. The samples were collected by phytoplankton net; fixed by formalin 4٪and then were transferred to the laboratory ashore. In the laboratory 1cc subsample of each 100cc sample were studied under microscope for further identification and counting with the Rafter lame. The results indicated that, 51 genera of phytoplankton were totally identified of which 17 genera belong to phylum CHromophyta, class Dinophyceae and 1 genera belongs to class Chrysophyceae and 33 genera belong to Bacillariophyceae.Oscillatoria sp. and Anabaena sp. from phylum Cyanophyta, class Cyanophyceae were found in autumn and summer. Density of phytoplankton in winter were measured more than other seasons, meanwhile this value was the least in summer.According to one-way ANOVA analysis, it was revealed that there is a significant difference between diatoms density and dinoflgellate density, and ANOVA results showed that diatoms and dinoflagellate density in seasons were significantly different too. But there was no significant difference between stations from point of density value.

Esteel wetland with 138 ha extent is one of the conserved regions in Guilan Province. This study was carried out from spring 2008 to winter 2009 in order to recognize phytoplankton species of Esteel wetland and their diversity, density, abundance, and seasonal changes. According to geographical situation of Esteel wetland, 13 stations were spotted. Sampling was done with tube (P.V.C. pipe) in the middle of each season by noticing the depth of wetland. Physicochemical properties of water such as temperature, dissolved oxygen, pH, nitrite, nitrate, ammonium, phosphate, and EC in 5 stations were measured in each sampling. In this study, totally 10 phyla and 42 genus of phytoplankton were identified. From these, 6 genus belong to Cyanophyta, 17 genus belong to Chlorophyta, 1 genus belongs to Chrysophyta, 8 genus belong to Bacillariophyta, 4 genus belong to Euglenaophyta, 1 genus belongs to Heterokontophyta, 1 genus belongs to Cryptophyta, 1 genus belongs to Phyrrophyta, 2 genus belong to Charophyta, and 1 genus belongs to Cyanobacteria phylum. The average annual density of phytoplankton in this lagoon was 12387 cell/ml1-. Cyanophyta with the density of 283274 cell/ml1- and the abundance of 93.34% and Cyanobacteria with the density of 3 cell/ml1- and the abundance of 0.001%, respectively had the most and the least annual phytoplanktonic density and abundance that had significant differences (P<0.05) with other phyla. Seasonal changes of these planktons also showed that summer with 10 phylum and 25 genus of phytoplankton and autumn with 5 phylum and 10 genus phytoplankton had the most and the least diversity, respectively. Also summer with the density of 46801 cell/ml1- and winter with the density of 14 cell/ml1- had the most and the least annual density of phytoplankton which had significant difference (P<0.05) with other seasons.

In this research 47 genus of different phylum of PHYTOPLANKTONS such as Cyanophyta, Chlorophyta, Pyrophyta, Chrysophyta and Euglenaphyta were surveyed that their numbers (ind. /m^3) and biomasses (mgr/m^3) were estimated. Frequncy of phytoplantons (ind. /m^3) was 131. 2, 1. 6, 65. 3, 18. 9 and 23. 8 million respectively. Furthermore, their biomasses was 08. 4, 1. 9, 1358. 9, 295. 1 and 124. 7 mgr/m^3, respectively. The maximum and minimum numbers were observed in Leptolingbaya belonged to Cyanophyta and diatoms of Chrysophyta 84. 3 and 0. 025 million ind. /m^3 respectively. The maximum and minimum biomass was observed in Gyrosigma (Chrysophyta) and Tetradron (Chlorophyta), 12317. 3 and 0. 014 mg/m^3 respectively.

Esteel wetland with 138 ha extent is one of the conserved regions in Guilan Province. This study was carried out from spring 2008 to winter 2009 in order to recognize phytoplankton species of Esteel wetland and their diversity, density, abundance and seasonal changes. According to geographical situation of Esteel wetland, 13 stations were determined. Sampling was done with tube (P.V.C. pipe) and plankton mesh in the middle of each season by noticing the depth of wetland. Physicochemical properties of water such as temperature, dissolved oxygen, pH, nitrite, nitrate, ammonium, phosphate and EC in 5 stations were measured in each sampling. In this study totally 10 phyla and 42 genus of phytoplankton were identified. From these, 6 genus belong to Cyanophyta, 17 genus belong to Chlorophyta, 1 genus belongs to Chrysophyta, 8 genus belong to Bacillariophyta, 4 genus belong to Euglenaophyta, 1 genus belongs to Heterokontophyta, 1 genus belongs to Cryptophyta, 1 genus belongs to Phyrrophyta, 2 genus belong to Charophyta and 1 genus belongs to Cyanobacteria phylum. Seasonal changes of these planktons also showed that summer with 10 phylum and 25 genus of phytoplankton and autumn with 5 phylum and 10 genus phytoplankton had the most and the least diversity, respectively.

A Comprehensive hydrobiological and hydrological investigation was conducted on Hevigh River, west of Guilan Province from 2001 to 2002. Totally, 4 Phyla of PHYTOPLANKTONS including 21 genera were observed. The maximum phytoplankton density belonged to the Phylum Chrysophyta with genera, Nitzchia, Diatoma, Cocconeis, Navicula and Cymbella comprising 95.7% of the phytoplankton population throughout the year. Chlorophyta ranked second with genera Scenedesmus, Cruciginia and Ankistrodesmus, comprising 2.20% of the population during the year. Cyanophyta with Oscillatoria and Euglenophyta with Euglena consisted the remaining few percents of the phytoplankton population.Zooplankton population in Hevigh River was found to be very poor, and mostly belonged to Protozoa and Rotatoria. However, 4 Phyla and 12 genera of zooplanktons were distinguished in the River the highest density of which belonged to Protozoa with genera Arcella, Difflugia, Cyphoderia and Euglypha, comprising 64% of the total population. Rotatoria with genera Keratella, Cephalodella, Lecane and Rotaria, consisted 14% of the zooplankton population during the year. Arthropoda, Nematoda, Tardigrada were very low in numbers.

An ongoing ecological study of the Caspian Sea, in a particular distribution, identifying the species composition and regional variations, seems to be necessary before any study. According to this, in the present study, the type of dominance of planktonic groups in southeastern basin of the Caspian Sea (Golestan Province) was studied. For this purpose, sampling of planktonic groups was done once in September 2015 with 3 repetitions. The results of phytoplankton study showed that there are 4 orders, 4 families and 4 genera in the study areas, which constitute Euglenophyta (Euglena sp. 99. 9% density), Dinoflagellata (Procentrum sp. 99. 5% density) and Bacillariophyta (Diatum group. 100% density), the main PHYTOPLANKTONS flora of the ecosystem, respectively. The Genus Euglena is the index of hypertrophic waters and is the first time that has been seen predominantly in the studied basins. The results of zooplankton study also indicate the destruction of this planktonic group (only 1 zooplankton of the species Keratella cochlearis from the genus Rotifera was observed), which is mainly due to the toxin produced by Euglena and the anaerobic conditions in the ecosystem. In general, the results indicate a critical quality status of the studied areas, the loss of high amounts of living fauna and flora and the dominance of toxic and inappropriate planktonic groups in the ecosystem.