Seyfettin Taş

A study on phytoplankton following ‘Volgoneft-248’ oil spill on the north-eastern coast of the Sea of Marmara

Following the ‘Volgoneft-248’ oil spill, phytoplankton distribution within the affected area was investigated for two years. Simultaneously measured physical variables such as salinity, temperature, Secchi disc, current speed and direction, and total petroleum hydrocarbons (TPH) were evaluated together with phytoplankton data. At the time of the accident, the TPH concentration in surface water was measured as 2.17 mg l and decreased to 88.5 mg l after five days. In the first sampling period, no diatoms were detected in surface water, while dinoflagellates were dominant in the phytoplankton community. The species composition of phytoplankton changed rapidly in two months and the diatoms increased in terms of abundance and diversity. This indicated that the diatoms might be more sensitive to oil pollution than the dinoflagellates. In comparison with the historical datasets, the low phytoplankton abundance following the oil spill should be considered as the small effect of oil on the phytoplankton rather than natural variability of the ecosystem. High oil concentration in the water column caused stress on the phytoplankton and influenced the species composition negatively depending on the sensitivity of groups and the natural variability of the ecosystem.

Presence of the diatom genus Pseudo-nitzschia and particulate domoic acid in the Golden Horn Estuary (Sea of Marmara, Turkey)

The potentially toxic diatom genus Pseudo-nitzschia and particulate domoic acid (pDA) concentrations were investigated weekly to bi-weekly from October 2013 to September 2014 in the Golden Horn Estuary. Pseudo-nitzschia species were detected in 324 of the 666 samples (∼49%). Two species, Pseudo-nitzschia calliantha and Pseudo-nitzschia pungens, were identified based on the scanning electron microscopy examination. A bloom of P. calliantha occurred between May and June, average cell density, 1.1 × 106 cells L−1 in May. Pseudo-nitzschia calliantha was commoner than P. pungens almost throughout the study period. They occurred over a wide temperature range (7.4–26.3°C) and moderate salinity (5.9–19.9). The highest cell density occurred at 14.7–19.6°C and 18.5–19.0 salinity, in the lower and middle estuary in winter and late spring. Pseudo-nitzschia species were found in very low densities in the upper estuary, which has variable salinity and low light availability due to high concentrations of suspended material. The pDA concentration in seawater was 0.03–1.0 µg L−1. The distribution pattern of pDA coincided with the presence of Pseudo-nitzschia. Pseudo-nitzschia abundance was low in October, when pDA was highest. There was a highly positive correlation between Pseudo-nitzschia abundance and salinity/Secchi depth/pH (p ≤ .001), but a negative correlation with inorganic nutrients and Si:N (p < .001). pDA was positively correlated with temperature/salinity and Secchi depth, but negatively correlated with inorganic nutrients (p < .001). Low light availability and highly variable salinity may limit the growth of Pseudo-nitzschia in the upper estuary and the presence of pDA throughout the study area may be related to transport by particulate matter.

Diversity and distribution of the planktonic diatom genus Chaetoceros (Bacillariophyceae) in the Golden Horn Estuary (Sea of Marmara)

The diversity and distribution of the diatom genus Chaetoceros (Bacillariophyceae) was studied at monthly, bi-weekly and weekly intervals over two periods (2009–2010, 2013–2014) in the Golden Horn Estuary. Chaetoceros was the most diverse genus in the diatom assemblage of the study area. A total of 23 Chaetoceros species were identified based on light and scanning electron microscopy. Three taxa, Chaetoceros aequatorialis, C. contortus and C. lorenzianus f. forceps were recorded for the first time in Turkish seas. The most common species were C. affinis, C. curvisetus, C. decipiens and C. holsaticus. The contribution of Chaetoceros species to the number of total phytoplankton species was between 15% and 17%. The highest abundance of Chaetoceros species was 507 × 103 cells L−1, dominated by C. affinis, C. constrictus, C. holsaticus, C. lauderi in the middle estuary in spring. Chaetoceros species were more abundant in the middle and lower estuary in April and May. In the upper estuary (UE), Chaetoceros species were rarely observed due to low water transparency caused by suspended particulate materials. Light limitation may be considered one of the most important factors affecting the diversity and spatial distribution of these species in the UE. The present work is the first detailed study on the diversity and distribution of Chaetoceros species for Turkish seas.