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Temporal variations of phytoplankton community and their correlation with environmental factors in the coastal waters of the Çanakkale Strait in 2018

Demir Egemen ̇Inan, Turkoglu Muhammet

Oceanologia

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2022

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No. 64 (1)

176--197

EN

In order to investigate temporal variations in phytoplankton connected with hydrography, high-resolution (twice a week) samplings were carried out between January and December 2018 at a single, shallow water station in the Dardanelles. Diatoms dominated in early and mid-winter, late spring and early summer, and between August and October. Whereas dinoflagellates dominated in the period from mid-February to the end of the third week of May, mid-summer, and late autumn. Other groups were generally more abundant in the early summer and mid-autumn than any other period. Late spring and early summer, mid-autumn and middle winter were the important bloom periods. The average contribution of diatom abundance (5.00 × 105±7.80 × 105 cells L−1) to average total phytoplankton abundance (9.63 × 105±7.88 × 105 cells L−1) was above 50% (average: 51.88%) during the year except spring (34.32%). However, the average contribution of dinoflagellates (43.32±20.69%) and others (4.81±6.99%) to the total phytoplankton abundance were lower than the abundance of the diatoms (51.88±21.61%). The study revealed a decrease both in the total number of algal blooms which also included HABs and their densities in the region compared to the previous findings. These observations seem to evidence environmental status improvement of the investigated area, manifested in an average chlorophyll a concentration (0.71±0.52 µg L−1) and quantitative phytoplankton structure (103 to 105 cells L−1).

2

Variation in radical antioxidant capacity and the total amount of carotenoids in razor clams, Ensis marginatus (Pennant, 1777), from the Çanakkale Strait (Abidealtı), Turkey

Kizilkaya Bayram, Acarli Sefa, Ertuğrul Pervin Vural, Berber Selçuk, Çelik Pinar

Oceanological and Hydrobiological Studies

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2021

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Vol. 50, No. 1

16--23

EN

Metabolic activities such as breathing and digestion, resulting from natural functions of the body through oxidation, lead to the formation of free radicals that cause cancer, premature cardiac aging and some chronic diseases. Antioxidants are substances that remove free radicals and prevent cell damage. Seafood significantly contributes to the elimination of free radicals, especially owing to its high quality nutrient content. In this context, the objective of the study was to determine the radical antioxidant capacity and the total amount of carotenes in razor clams. The IC50 (mg g−1) value of the DPPH radical sweeping effect varied over the months (p < 0.05), showing the highest value in June, gradually decreasing from September and reaching the lowest level in February. The total amount of carotenoids also varied, with the highest value in September (p < 0.05). The total amount of chlorophyll ranged from 6.15 µg g−1 in August to 66.71 µg g−1 in December.

3

First record of straight-needle pteropod Creseis acicula Rang, 1828 bloom in the Çanakkale Strait (NE Aegean Sea, Turkey)

Tunçer Sezginer, Öğretmen Nazik, Çakır Fikret, Öztekin Alkan, Oral Ayhan, Suner Salih Can

Oceanological and Hydrobiological Studies

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2021

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Vol. 50, No. 3

310--324

EN

Pteropods are marine pelagic calcifier mollusks sensitive to chemical changes in seawater due to their highly soluble aragonite shells. Increased acidity (reduced pH) of seawater causes difficulties in precipitating their shells and/or results in their dissolution, which is related to increased atmospheric CO2 concentrations and warming of seawater. They are therefore indicators of environmental changes. In this paper, we present the first record of the straight-needle pteropod Creseis acicula Rang, 1828 bloom in the surface waters of the Ҫanakkale Strait, Turkey (NE Aegean Sea), encountered in July 2020, when the highest sea surface temperatures and pH levels since 2007 were recorded. In coastal zones, such as the Ҫanakkale Strait, anthropogenic activity contributes significantly to environmental changes. Consequently, the increase in pH at elevated temperatures indicates an auxiliary factor (i.e. anthropogenic activity) that triggered the C. acicula bloom, rather than global atmospheric CO2 levels.

4

Spatial distribution analysis of ship accidents in the Çanakkale Strait

Bayazit Ozan, Toz Ali C., Buber Muge

Zeszyty Naukowe Akademii Morskiej w Szczecinie

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2020

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nr 62 (134)

9--17

EN

This study used a spatial distribution analysis to identify the risky areas in the Çanakkale Strait – one of the narrowest waterways with high marine traffic – in terms of ship accidents. To accomplish this, a point density analysis, as part of the geographic information systems (GIS) methodology, was used to create accident density distributions and thematic maps. A total of 162 marine accidents in the Çanakkale Strait between 2007 and 2018 were taken into account. Detailed technical data of accidents were obtained from accident reports provided by the Turkish Maritime Search and Rescue Coordination Center (TMSRCC). The results showed that, among the 162 cases, bulk carriers have the highest accident rate, and most accidents at the Nara Turn were caused by engine failure. In addition, accidents due to navigational failure occurred in every region of the strait. Remarkably, factors directly and indirectly related to human error were still the determining factors in marine accidents. As a result, the risk of marine accidents was higher in the narrow portions of the waterway, and navigation was difficult, especially in areas such as the Nara Turn Point. In future research, it is recommended to consider a wider period of activities using different methods to provide more comprehensive results.

5

Trotline hook selectivity for the Atlantic Bonito (Sarda sarda Bloch, 1793) fishery in the Çanakkale Strait (northern Aegean Sea, Turkey)

Öztekin Alkan

Oceanological and Hydrobiological Studies

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2020

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Vol. 49, No. 3

281--290

EN

This study was conducted to determine the selectivity of hooks (galvanized, tin, carbon, nickel) used for Atlantic bonito (Sarda sarda Bloch, 1793) in the Gallipoli Peninsula and the Dardanelles during the 2015 and 2018 fishing seasons (spring and autumn). The Atlantic bonito was fished with hooks of size 1/0, 2/0, 3/0, and 4/0. A total of 604 bonitos were caught, including 201 individuals using a galvanized hook, 194 individuals using a tin hook, 158 individuals using a nickel hook and 51 individuals using a carbon hook. A lower catch was obtained with hooks of size 4/0 (42 in total). The highest catch (100 total) was obtained with hooks of size 1/0 and a lower catch (19 in total) was obtained with hooks of size 4/0 in the case of tin hooks. In the case of nickel hooks, the highest catch (63 in total) was obtained with hooks of size 1/0 and a lower catch (eight in total) was obtained with hooks of size 4/0. The optimum catch length and curve width were calculated in relation to the size of hooks. It was determined that all hooks used in the experiments catch below the length allowed for fishing. It was therefore concluded that the use of the largest hooks would be preferable, with size 4/0 being the most suitable for maintaining the continuity of the species.