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

Temporal variations in phytoplankton composition in the northeastern Sea of Marmara was investigated associated with physico-chemical variables from January 2004 to December 2007. The occurrence of potentially toxic species and a mucilage event was also evaluated during this study period. The confined upper layer of the Sea of Marmara is mesotrophic to eutrophic and has higher productivity when compared to the neighbouring Black Sea and Aegean Sea. 132 taxa in the micro-phytoplankton community were identified, 11 of which are known to be potentially toxic. The most abundant species were Pseudo-nitzschia species from diatoms and Prorocentrum micans from dinoflagellates. 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 diversity index following June 2007 and reported shifts in the zooplankton community during the same period points to probable cascading effects in the pelagic ecosystem of the Sea of Marmara

Planktonic diatom composition and environmental conditions in the Golden Horn Estuary (Sea of Marmara, Turkey)

Planktonic diatom composition was investigated in association with environmental factors at bi-weekly and weekly intervals from October 2013 to September 2014 in the Golden Horn Estuary (Sea of Marmara). Sixtysix diatom taxa (50 centrics and 16 pennates) within 32 genera were identified in samples taken during the study period. Chaetoceros species were the most abundant species (30 % of the total number of diatom). The other most common species were Proboscis alata, Rhizosolenia hebetata and Skeletonema marinoi from centrics; Ceratoneis closterium, Nitzschia longissima, Pseudo-nitzschia calliantha and Thalassionema nitzschioides from pennates. The abundance of diatom increased towards the upper estuary, but its species richness decreased markedly. The contribution of diatoms to the total phytoplankton abundance decreased from 60 % to 26 % from the lower to the upper estuary. Some diatom taxa, P. calliantha, S marinoi, T minima and C closterium, formed blooms between May and July, reaching the highest abundances 1.6 x 106, 39 x 106, 13 x 106 and 2 x 106 cells L-1, respectively. Salinity, Sec chi depth, dissolved oxygen and pH values decreased gradually from the lower to the upper estuary, while inorganic nutrient concentrations increased. There was a significant positive correlation between temperature and diatom abundance (p<0.01), while there was a negative correlation between temperature and species richness (p < 0.01). However, salinity, Secchi depth and dissolved oxygen were positively correlated with species richness (p < 0.01). Inorganic nutrients were negatively correlated with diatom abundance (p < 0.01) and species richness (p<0.05). Therefore, the main environmental factors affected the distribution of diatoms along this study area. Thus, diatom assemblages may be considered as a good indicator of changing environmental conditions in such environments

Planktonic diatom composition and environmental conditions in the Golden Horn Estuary (Sea of Marmara, Turkey)

Planktonic diatom composition was investigated in association with environmental factors at bi-weekly and weekly intervals from October 2013 to September 2014 in the Golden Horn Estuary (Sea of Marmara). Sixtysix diatom taxa (50 centrics and 16 pennates) within 32 genera were identified in samples taken during the study period. Chaetoceros species were the most abundant species (30 % of the total number of diatom). The other most common species were Proboscis alata, Rhizosolenia hebetata and Skeletonema marinoi from centrics; Ceratoneis closterium, Nitzschia longissima, Pseudo-nitzschia calliantha and Thalassionema nitzschioides from pennates. The abundance of diatom increased towards the upper estuary, but its species richness decreased markedly. The contribution of diatoms to the total phytoplankton abundance decreased from 60 % to 26 % from the lower to the upper estuary. Some diatom taxa, P. calliantha, S marinoi, T minima and C closterium, formed blooms between May and July, reaching the highest abundances 1.6 x 106, 39 x 106, 13 x 106 and 2 x 106 cells L-1, respectively. Salinity, Sec chi depth, dissolved oxygen and pH values decreased gradually from the lower to the upper estuary, while inorganic nutrient concentrations increased. There was a significant positive correlation between temperature and diatom abundance (p<0.01), while there was a negative correlation between temperature and species richness (p < 0.01). However, salinity, Secchi depth and dissolved oxygen were positively correlated with species richness (p < 0.01). Inorganic nutrients were negatively correlated with diatom abundance (p < 0.01) and species richness (p<0.05). Therefore, the main environmental factors affected the distribution of diatoms along this study area. Thus, diatom assemblages may be considered as a good indicator of changing environmental conditions in such environments

Microalgal blooms in a eutrophic estuary (Golden Horn, Sea of Marmara) following a remediation effort

The present work describes microalgal blooms that occurred in a eutrophic estuary (Golden Horn, Sea of Marmara, Turkey) between October 2013 and September 2014 following a remediation effort. The relationships between bloom-forming microalgal species and environmental factors were investigated during the study period. The changing environmental conditions (e.g. increasing water transparency and salinity) after seawater transfer to the Golden Horn Estuary stimulated phytoplankton growth with dense algal blooms. Annual average values of Secchi depth, salinity and dissolved oxygen increased in comparison with those in an earlier study in 2009-2010. Nine microalgal species, which consisted of four diatoms, two dinoflagellates, one cryptophycean, one raphidophycean and one euglenophycean, formed the blooms with water discolorations during spring and summer. The species that reached the highest bloom density were Plagioselmis prolonga (62.4 x 10(6) cells l(-1)) among crytophyceans, Heterocapsa triquetra (21.8 x10(6) cells l(-)(1)) among dinoflagellates and Skeletonema marinoi (39 x10( )(6)cells l(-1)) among diatoms. The abundance of dinoflagellates and phytoflagellates increased particularly in the upper estuary when compared to diatoms and their rapid growth and bloom formation revealed that they have a wide range of tolerance to changing environmental conditions and a strong ability to compete with other species in this study area

Seasonal variations in the phytoplankton community in the north-eastern Sea of Marmara and a species list

This paper describes phytoplankton abundance data collected in the Sea of Marmara in 2000 and identifies new species to the region. The quantitative sampling was carried out monthly at 3 stations and seasonally at 6 stations at depths of 0.5, 5, 10 and 20 m. Additionally, vertical samplings by plankton net from 15 - 0 m were carried out in order to determine the species diversity. Simultaneously measured physical (salinity, temperature and Secchi disc) and chemical parameters (dissolved oxygen, nitrate + nitrite, chlorophyll-a, phosphate and silicate) were evaluated together with phytoplankton data. One hundred and fifteen species were recorded which are members Of 55 dinoflagellates, 42 diatoms, 11 silicoflagellates and 7 other groups. Those species include toxic species with high reproduction rates and species that are accepted as carrying risk. Blooms of Anabaena sp., Nitzschia longissima (Brebisson in Kutzing) Ralfs in Pritchard and Prorocentrum triestinum Schiller species were observed during the study. Dictyocha antarctica Lohmann 1919, Dictyocha crux Ehrenberg 1840 and Nitzschia rectilonga Takano 1983 species were recorded for the first time from the coastal waters of Turkey. The maximum phytoplankton abundance has been observed during the winter and autumn seasons in the 0.5 and 5 m depths; the concentration of the diatoms was higher during late winter and autumn, however, the concentration of the dinoflagellates was always high during the whole year and they did not show a seasonal variation. The phytoplankton density was lower at the 20 m depths because of the low light penetration property of the Sea of Marmara

Temporal and spatial variability of the potentially toxic Pseudo-nitzschia spp. in a eutrophic estuary (Sea of Marmara)

Spatial and temporal variability and bloom formation of the potentially toxic diatom Pseudo-nitzschia spp. was investigated weekly to monthly from October 2009 to October 2010 in a eutrophic estuary, the Golden Horn. Pseudo-nitzschia spp. were detected in 195 of 512 samples (38%) collected throughout the year. Two species, P. calliantha and P. pungens, were identified based on the SEM examination. Blooms of Pseudo-nitzschia occurred in the lower and middle estuary in January and May. The bloom in January mainly comprised P. calliantha. In the bloom in early May, P. calliantha made up 72% of the Pseudo-nitzschia cells and P. pungens 28%. However, the contribution of P. pungens increased to 83% in late May. The Pseudo-nitzschia blooms occurred at low temperature (9-15 degrees C) and moderate salinity (17-18), and for P. calliantha a significant negative correlation was found with temperature and a significant positive correlation with salinity. The percentage of Pseudo-nitzschia cells decreased gradually from lower to upper estuary (59-14%), correlating with a decrease in Secchi depth (5.5-0.5 m). Principal components analyses (PCA) were used to explore the spatial and temporal variability of environmental factors in relation to Pseudo-nitzschia abundances, and showed that NH4, pH, Secchi depth and DO values were the most important factors reflecting spatial differences, while temperature, salinity, Chl-a and Si:N were more important factors showing temporal differences. High abundances of P. pungens correlated mainly with pH, Secchi depth and DO values, whereas P. calliantha also correlated with NO3 + NO2. Low light availability due to high concentrations of suspended material and very variable environmental conditions (e.g. pH, DO and NH4) may have limited growth of Pseudo-nitzschia in the upper estuary. Regular monitoring of Pseudo-nitzschia is important for improving the understanding of the influence of environmental parameters on bloom dynamics in the study area

Temporal and spatial variability of the potentially toxic <i>Pseudo-nitzschia</i> spp. in a eutrophic estuary (Sea of Marmara)

Spatial and temporal variability and bloom formation of the potentially toxic diatom Pseudo-nitzschia spp. was investigated weekly to monthly from October 2009 to October 2010 in a eutrophic estuary, the Golden Horn. Pseudo-nitzschia spp. were detected in 195 of 512 samples (38%) collected throughout the year. Two species, P. calliantha and P. pungens, were identified based on the SEM examination. Blooms of Pseudo-nitzschia occurred in the lower and middle estuary in January and May. The bloom in January mainly comprised P. calliantha. In the bloom in early May, P. calliantha made up 72% of the Pseudo-nitzschia cells and P. pungens 28%. However, the contribution of P. pungens increased to 83% in late May. The Pseudo-nitzschia blooms occurred at low temperature (9-15 degrees C) and moderate salinity (17-18), and for P. calliantha a significant negative correlation was found with temperature and a significant positive correlation with salinity. The percentage of Pseudo-nitzschia cells decreased gradually from lower to upper estuary (59-14%), correlating with a decrease in Secchi depth (5.5-0.5 m). Principal components analyses (PCA) were used to explore the spatial and temporal variability of environmental factors in relation to Pseudo-nitzschia abundances, and showed that NH4, pH, Secchi depth and DO values were the most important factors reflecting spatial differences, while temperature, salinity, Chl-a and Si:N were more important factors showing temporal differences. High abundances of P. pungens correlated mainly with pH, Secchi depth and DO values, whereas P. calliantha also correlated with NO3 + NO2. Low light availability due to high concentrations of suspended material and very variable environmental conditions (e.g. pH, DO and NH4) may have limited growth of Pseudo-nitzschia in the upper estuary. Regular monitoring of Pseudo-nitzschia is important for improving the understanding of the influence of environmental parameters on bloom dynamics in the study area

Potentially harmful microalgae and algal blooms in a eutrophic estuary in the Sea of Marmara (Turkey)

Distribution of potentially harmful microalgae and algal blooms were investigated at monthly and weekly time scales between October 2009 and September 2010 in the Golden Horn, a eutrophic estuary in the Sea of Marmara (Turkey). Several physical and chemical parameters were analysed together with phytoplankton composition and abundance. A total number of 23 potentially harmful and/or bloom-forming microalgae (14 dinoflagellates, 4 diatoms and 5 phytoflagellates) were identified throughout this study period, of which nine taxa have been confirmed to be toxic elsewhere in the world. Most harmful species and algal blooms were observed in late spring and summer particularly in the middle and upper estuaries, and nine taxa formed dense and successive algal blooms causing water discoloration. Nutrient concentrations increased significantly from the lower to the upper estuary. Additionally, high organic matter loads in the upper estuary could also have benefited by mixotrophic species. The increasing number of potentially harmful and bloom-forming species and algal blooms indicated that the GHE is a potential risk area for future HABs