Temporal and spatial variations of phytoplankton in the Caspian Sea

Abstract

Geographic information system (GIS) can be used to perform a number of fundamental spatial analysis operations. Its major advantage is that it allows the user to identify the spatial relationships between various map features. In this study, phytoplankton cell abundance, biomass and species composition were evaluated in the Iranian coasts of the Caspian Sea during 1996 to 1997 and 2005 to 2006. Totally 1562 water samples were collected in Southern part of Caspian Sea (SCS) for durations of 1996 to 1997 and 2005 to 2006. There were changes in the highest seasonal means of phytoplankton biomass. While maximum phytoplankton biomass were recorded in spring and summer during 1996 to 1997, after the invasion of Mnemiopsis leidyi shifted to a winter period and biomass shifted to winter-spring during 2005 to 2006. Maximum cell abundance was observed in 2005 to 2006, contributed mostly by small size of phytoplankton, although its population decreased in 1996 to 1997 while maximum biomass was observed in 1996 to 1997, belonged to big size of phytoplankton such as Rhizosolenia calcaravis. Its population aggregated at the depth of 0 to 20 m more than 87% of the total cell abundance, due to some favorable conditions such as higher water temperature, light, dissolved oxygen and nutrient concentration. Phytoplankton was vertically distributed until the depth of 20 m, and the population decreased at the lower depths. Key words: Phytoplankton, seasonal variation, biomass, geographic information system (GIS) and Caspian Sea, Iran.