en Ecology Ecology پژوهشي Orginal research papers <font face="Times New Roman" size="3"> </font><p class="MsoNormal" style="margin: 0cm 0cm 0pt text-align: justify line-height: 120% unicode-bidi: embed direction: ltr"><i><span style="color: black line-height: 120% font-family: "Times New Roman","serif" font-size: 12pt">Cochlodinium polykrikoides</span></i><span style="color: black line-height: 120% font-family: "Times New Roman","serif" font-size: 12pt"> was bloomed in the Persian Gulf for the first time in September 2008, started from the Strait of Hormuz and then spread out towards the northern parts covering most of the areas of the Gulf and lasted 8 months. In order to find out environmental conditions during the bloom, a monthly sampling program was carried out in seven surface stations in 2008-2009. At each station, three samples (triplicates) were collected for phytoplankton analysis and also one sample for environmental analyses, including salinity, chlorophyll a and </span><span style="line-height: 120% font-family: "Times New Roman","serif" font-size: 12pt">nutrients. </span><span style="line-height: 120% font-family: "Times New Roman","serif" font-size: 12pt mso-bidi-language: AR-SA">Blooms of <i>C. polykrikoides </i>were observed with a seawater<font size="3"><font face="Times New Roman"><span style="color: rgb(41, 37, 38)"> </span>temperature of 20.1 to 31.0 °C</font></font></span><span style="line-height: 120% font-family: "Times New Roman","serif" font-size: 12pt">, salinity 37.0-40.1 ppt and nutrient concentration ranges during the<font size="3"><font face="Times New Roman"><span style="color: black"> bloom and red tide were 0.064-0.707 mg/l nitrate + nitrite and 0.001-1.66 mg/l phosphate, </span>respectively. Maximum of </font></font></span><i><span style="line-height: 120% font-family: "Times New Roman","serif" font-size: 12pt mso-bidi-language: AR-SA">C. polykrikoides </span></i><span style="line-height: 120% font-family: "Times New Roman","serif" font-size: 12pt mso-bidi-language: AR-SA">abundance was measured 26 × 10⁶cells L^-1in October 2008. Kruscal wallis test demonstrated </span><span style="line-height: 120% font-family: "Times New Roman","serif" font-size: 12pt">a significant difference in densities and chlorophyll-a in different months and seasons not in different stations. This study showed increase of temperature (></span><span style="line-height: 120% font-family: "Times New Roman","serif" font-size: 12pt mso-bidi-language: AR-SA">31.0 °C) stopped bloom and red tide due to <i>C. polykrikoides </i>in both the eastern and middle sampling stations but in the western stations was determined decrease in nutrient amounts as the major factor therefore increased nutrient of coastal waters, and environmental conditions could have efficacy the occurrence of this dinoflagellate.</span><span style="color: black line-height: 120% font-family: "Times New Roman","serif" font-size: 12pt"><o:p /></span></p><font face="Times New Roman" size="3"> </font> Red tide, Cochlodinium polykrikoides, Environmental conditions, Nutrients, Persian Gulf 475 489 http://jifro.ir/browse.php?a_code=A-10-1-172&slc_lang=en&sid=1 S. M. R. Fatemi 10031947532846003965 10031947532846003965 No S. M. B. Nabavi 10031947532846003966 10031947532846003966 No G. Vosoghi 10031947532846003967 10031947532846003967 No M. Fallahi 10031947532846003968 10031947532846003968 No M. Mohammadi mojhde.bam52@yahoo.com 10031947532846003969 10031947532846003969 Yes