Scale characteristics of the bloom event: A case study in the Iranian coastal waters of the Southern Caspian Sea

Nutrient enrichment in water and sediments due to excessive anthropogenic activities in recent years has caused excessive algal growth in the Caspian Sea. The current study was conducted to survey the abundance of phytoplankton, its dominant species and chlorophyll-a [Chl-a] concentration in algal bloom aspect in the Iranian coastal water of Caspian Sea during four seasons from 2013 to 2014. The minimum and maximum phytoplankton abundance was recorded 73±31 and 505±55 million cells/m3 in summer and winter, respectively. The median concentration of Chl-a was increased to 5.81 mg/m3 in autumn, as compared to annual median value (2.43 mg/m3). The result indicated that bloom started in autumn and it continued falling with a low rate during winter (Chl-a :2.59 mg/m3). The three species Stephanodiscus socialis, Binuclearia lauterbornii and Thalassionema nitzschioides classified in medium bloom class (100-1000 cells/mL) in spring, summer and autumn seasons, respectively. While in winter Pseudonitzschia seriata and Dactyliosolen fragilissima was classified in medium bloom class with high relative frequency. Finally, the bloom at the regions with more than 100 cells/m3 of total phytoplankton abundance and dominant species was overlapped with the bloom regions based on Chl-a concentration.