1545-1559Seasonal changes of phytoplankton communities in the coastal waters of the Gulf of Erdek from November 2006 to August 2008 were examined in relation to some environmental variables and 95 species from 6 different algae groups were identified. In addition, two species were recorded for the first time in the Turkish coastal waters and one species for the Sea of Marmara. The maximum total phytoplankton abundance (1.99 × 105 cells L-1) were observed in May 2008, with Pseudo-nitzschia sp. being the most dominant species of that month (1.52 × 105 cells L-1). Both the Bray-Curtis diversity index and the Euclidean distance indicated that the upper and lower water layers were separated from each other at the stations, and the Spearman’s rank-correlation and CCA analyses also showed that environmental variables affected the abundance of species. Furthermore, according to the CCA diagram, especially the temperature and dissolved oxygen had a bigger impact on the distribution of species. The Shannon-Wiener diversity index (Hʹ) values were low when Pseudo-nitzschia sp., Prorocentrum micans, Gymnodinium sp. and Prorocentrum scutellum were dominant over other species in the sampling period
