Investigation of the Seasonal Variation in the Phytoplankton in the Surface Waters of the Gulf of Edremit

The aim of this study was to determine the phytoplankton species existing in the Gulf of Edremit and some environmental conditions affecting them. Samples were collected in July and October 2003 and in January and April 2004 from 3 stations through horizontal tows using a plankton net. After the analysis of plankton samples, 123 species that belong to 5 classes were identified. It was determined that one species (Phalacroma cuneus Schutt, 1895) was a new record for Turkish waters. The species composition mostly consisted of dinoflagellates (53.7%) which were followed by diatoms (43.9%). Most of the species which were identified in this study were similar to those phytoplanktonic algal species which were reported from the Eastern Mediterranean Sea in previous studies. These are neritic, oceanic, temperate and subtropical climate species. It was detected that 10 out of 19 potentially harmful algal species identified in this study were toxic species; however, they did not show an extreme increase. Dinophyceae had the highest cell number in July (1100 cell/L, St.1) and Bacillariophyceae in April (2280 cell/L, St.2). The environmental variables of the seawater such as temperature (13.0-26.5 oC), salinity (35.9-38.5‰) and dissolved oxygen (4.43-8.46 mg/L) were measured in every sampling period. Consequently, the phytoplankton species and their abundances in the Gulf of Edremit were firstly determined with this study, and phytoplankton composition representing oligotrophic sea water characteristic in the Aegean Sea was obtained.