Temporal variations in phytoplankton composition in the north-eastern Sea of Marmara: potentially toxic species and mucilage event

Temporal variations in phytoplankton composition in the northeastern Sea of Marmara were investigated in conjunction with physico-chemical variables, from January 2004 to December 2007. The occurrence of potentially toxic species and a mucilage event was also evaluated during the study period. The confined upper layer of the Sea of Marmara is mesotrophic to eutrophic and is characterised by higher productivity compared to the neighbouring Black Sea and Aegean Sea. 132 taxa were identified in the micro-phytoplankton community, 11 of which are blown to be potentially toxic. The most abundant species were the diatom Pseudo-nitzchia spp. and the dinollagellate Prorocentrum micans. Potentially toxic species were more common at the coastal stations. The onset of a mucilage formation was observed in October 2007, and well-known mucilage producers such as Gonyaulax hyalina (reported as G. fragilis) and Thalassiosira gravida (reported as T. rotula) dominated the phytoplankton community during this event. A marked decrease in the number of species and the diversity index after June 2007, and the reported shifts in the zooplankton community during the same period point to possible cascading effects in the pelagic ecosystem of the Sea of Marmara.