Akademik Veri Yönetim Sistemi
Journal of the Black Sea / Mediterranean Environment, cilt.27, sa.2, ss.232-257, 2021 (Hakemli Dergi)
In the present study, phytoplankton composition in relation to mucilage and accompanied
physicochemical conditions were investigated in the sea water samples collected from four
stations in İzmit-Kocaeli, Fatih-İstanbul, Biga-Çanakkale (in the Marmara Sea), and Rivaİstanbul (in the Black Sea). Samplings were carried out before (i.e., during September
2020) and at the beginning stage of the mucilage formations (i.e., during April 2021) which
was observed in the Marmara Sea during spring and summer months of 2021. Seawater
temperature, salinity, pH, and dissolved oxygen levels were measured in situ. Inorganic
nitrogen, orthophosphate, and chlorophyll-a concentrations were analyzed
spectrophotometrically. In total 83 phytoplankton species (44 Bacillariophyceae-BAC, 36
Dinophyceae-DIN, 2 Dictyochophyceae-DIC, and 1 Chlorophyceae-CHL) were identified
during the study. BAC species were generally dominant. Among the 83 phytoplankton taxa
identified, Cerataulina pelagica, Cylindrotheca closterium, Pseudo-nitzschia sp.,
Skeletonema costatum, Thalassiosira rotula, Alexandrium tamarense, Dinophysis
acuminata, Dinophysis caudata, Dinophysis fortii, Gonyaulax fragilis, Gonyaulax
spinifera, Gymnodinium sp., Gyrodinium sp., and Prorocentrum micans are known as the
species associated with mucilage formation. The highest number of species was
determined at the Biga-Çanakkale station (MDG25) with 38 taxa in September 2020. Skeletonema costatum (11200 cells/L) was the most abundant species at 10 m depth in the
İzmit-Kocaeli station (MDG22) in April 2021. The mucilage formations in MDG22, and
MDG25 stations were observed at their beginning stage as a tule curtain form in April 2021
while the seawater temperature and salinity levels were below 15°C and around 30‰,
respectively. While the taxa dominance of the BAC in the total phytoplankton remained
similar from September to April (i.e., 56%), its number of species decreased dramatically
from 59 to 28 in the Marmara Sea. Despite the decreasing biodiversity, there was an
increase in total abundance in the sampling stations, particularly in MDG22 and MDG25.
In both stations, total abundance increased from 12000 to 42000, and 2000 to 50000
cells/L, respectively, compared to September 2020 and April 2021. Despite the decrease
in biodiversity, an increase in the number of cells suggests that eutrophication and, as a
result, mucilage formation occurred in the Marmara Sea. TRIX values showed that while
the eutrophic conditions increased, the ecological quality in the region generally decreased
from September 2020 to April 2021, and it was described as Bad for all stations in the
Marmara Sea. The data indicated that the limiting factor for phytoplankton was nitrogen
during April 2021 simultaneously with the mucilage formation in the Marmara Sea.