Investigation of phytoplankton composition of İzmit Bay and the Northeastern Marmara Sea with water quality variables

In this study, temporal and spatial changes of phytoplankton distribution, species composition and phytoplankton marker pigments and environmental parameters affecting them were investigated. Seasonal sampling was carried out at 6 stations and in two depths (surface water and fluorescence maximum depth) during 2015-2018 sampling period. The highest phytoplankton abundance was observed at the surface. 146 species belonging to 68 genera in 10 taxonomic classes were identified in the study area. Dinophyceae and Bacillariophyceae were found as the major phytoplankton groups in all stations. Skeletonema costatum, Leptocylindrus minimus, Prorocentrum micans, Prorocentrum scutellum and Tripos fusus were the dominant diatom and dinoflagellates species in the studied area, respectively. The low diatom/dinoflagellate ratio detected in the community indicated the dinoflagellate dominance in the marine ecosystem. Significant positive and negative correlations were observed between phytoplankton abundance and dissolved oxygen, chlorophyll-a, temperature, and secchi disc depth. The bloom of Leptocylindrus minimus, a diatom species, was detected in the winter of 2018. During this period of diatom bloom, a high N/Si ratio was detected in the environment due to the depletion of silicate. The data measured with the in-situ fluorescence sensor and the chlorophyll-a results measured with the spectrophotometer were found to be compatible with each other. The major marker pigments detected in the study area were fucoxanthin and peridinin, which are diagnostic pigments for diatoms and dinoflagellates. A highly significant relationship (p<0.001) was determined between phytoplankton abundance and their marker pigments, and it was evaluated that observed biomass of fucoxanthin and peridinin came from diatom and dinoflagellate species. It has been determined that the TRIX index is generally quite variable during the entire period of study. High risk of eutrophication was determined in winter and spring months. Eutrophic status was observed in three periods (2015 spring, 2016 winter, 2018 autumn) during the sampling time at the inner part of the bay.