Marmara Sea Research Articles

Determination of metals in different tissues of Trachurus trachurus from the Marmara Sea and evaluation of their health risks

The present study aimed to determine the differences in metal levels of Aluminum (Al), Cadmium (Cd), Chromium (Cr), Copper (Cu), İron (Fe), Manganese (Mn), Nickel (Ni), Lead (Pb) and Zinc (Zn) between muscle and liver tissues of Trachurus trachurus, the correlation of metal accumulation in tissues with fish length and weight was examined. Health risks and nutritional adequacy were evaluated based on metal levels accumulated in fish muscle. The results demonstrated that fish liver accumulated higher metal levels than muscle. The investigation revealed that the majority of metals present in the tissues of the fish did not exhibit a significant correlation with their size (p>0.05). It can be concluded that fish are not an adequate source of these nutrients because their nutrient levels are below reference values. The fish were found to be nutrient deficient, as the levels of nutrients were below reference values. The estimated daily intakes of all metals accumulated in muscle were below reference doses. The target hazard coefficient and target hazard index values were less than 1. Lifetime carcinogenic risk values were below 10-4, and total carcinogenic risk values were within the acceptable range. Pb and Cd concentrations in muscle exceeded the tolerable limit. The daily amount of fish that could be consumed without non-carcinogenic health risk was 181 grams for Cd and 295 grams for Pb. The daily amount of fish that could be consumed without carcinogenic health risk was 1.21 grams for Cd and 231 grams for Pb.

Geographic expansion of the blackbellied angler (Lophius budegassa) towards the east along the Turkish coast of the Black Sea

The natural range of Lophius budegassa, originating from the Atlanto-Mediterranean region, extends from the Mediterranean Sea basin to the Sea of Marmara. However, its occurrence along the Turkish coast of the Black Sea has previously been limited to the Sinop coast in the Western Black Sea. This study provides the first scientific evidence of L. budegassa extending to the easternmost part of the Black Sea, based on capturing two specimens under different circumstances. This observation underscores the dynamic nature of marine ecosystems and the interplay of ecological and anthropogenic factors. The congruence between species temperature preferences and actual water temperatures in the Black Sea suggests suitable environmental conditions for L. budegassa. However, the absence of an established stock and the discovery of only two large-sized adult individuals suggest a potential isolated event rather than a significant range expansion. Factors such as navigation errors, food availability, or reproductive behaviour may contribute to the presence of L. budegassa in this region.

Some Population Parameters of Picked Dogfish (Squalus acanthias L. 1758) Incidentally Captured in Commercial Fisheries in Southern Black Sea Shores and a First Record of Angular Roughshark (Oxynotus centrina, L. 1758) for Black Sea

The study, which aimed to determine some population parameters of picked dogfish (Squalus acanthias L. 1758) distributed in the Black Sea, was carried out in the five fishing seasons (between 2016 and 2023 years). The sharks draw attention as a bycatch for all fishing gear used in the Black Sea. In the study, total length (cm), weight (g) and sex (female/male) data were obtained from the sharks captured with all fishing gears (demersal trawl, midwater trawl, gillnets purse seine, turbot gillnets, trammel nets and bottom) used in commercial fishing activities in the Black Sea of Türkiye. A total of 576 specimens were collected all fishing gears during the sampling period. Length-weight relationship (LWR) was founded as W=0.0097L2.8521 (R2 =0.9854) for all the picked dogfish. Also, mean total length 48.9±0.707 cm respectively. In addition, the first record of the angular roughshark (Oxynotus centrina, L. 1758) species was given for the Black Sea coasts, which originated in the western Atlantic, was seen in the Mediterranean, Aegean Sea and the Marmara Sea of Türkiye. The shark, which was accidentally caught with a purse seine net, measured as 33.5 cm in total length and weighed 585 g.

Fees Received under the Montreux Convention: An Assessment on the Value of the Golden Frank

Montreux Convention signed in 1936 regulates the cruise and voyage passages through İstanbul Strait, Marmara Sea and Çanakkale Strait, known as the Turkish Straits. Within the framework of this convention, there are mutual rights and obligations concerning the navigation through the Turkish Straits and pertain to both the vessels utilizing the straits for passage and the Republic of Türkiye, which holds sovereignty over these straits. While the ships passing through the Turkish Straits benefit from the freedom of navigation, it is stipulated that they make payments to the Republic of Türkiye for the services (sanitary control, lighthouse, life-saving services) included in Annex-1 of the convention. Articles 1 and 4 of this annex refer to these fees. The article examines these issues. Annex-1 states that the amount to be paid will be determined in terms of net ton, service type, and Gold Francs. Taking into consideration the number of ships passing through the straits and their total tonnage, this study makes a mutual comparison between the Golden Francs application in the Montreux Convention and the current applications in determining the fees charged by Türkiye and discusses which of the methods would provide more gains to the Republic of Türkiye. The result of the study clearly shows that the new pricing policy to be applied can provide more income to Türkiye and can be in line with the spirit of the Montreux Convention.

Mollusc Diversity of Hard Substrate Habitats of Gökçeada Island

In the present study, molluscs diversity between 0-0.5 m depths of the hard substrate habitats of Gökçeada coasts was investigated qualitatively and quantitatively, seasonally, and monthly in 2010 and 2011. In addition, in summer months of 2021, samples were taken to investigate the mucilage impact on the mollusc fauna, which occurred in the Marmara Sea in 2021 and affected Gökçeada coasts due to the currents. A total of 76 mollusc species were identified and 27 of the determined species are new records for Gökçeada. Among the found species, while Cardita calyculata (Linnaeus, 1758) was the most dominant species at the Yıldız Koy station sampled monthly, Musculus costulatus (Risso, 1826) was the dominant one at all other sampling stations. The Tepeköy station was found to has the highest number of species and individuals. As the main reason for this can be indicate the limited human access to the region and the presence of various habitats. Mollusc species diversity, which was detected in 2010 due to the pouring of sand for tourists by the municipality at Yıldız Koy station, was found to be increased greatly in 2021 after this practice was abandoned. It was also detected that the mollusc species distributed on the coasts of Gökçeada were not acutely affected by the mucilage event occurred in 2021. However, more detailed studies need to be monitoring and report the negative effects that may occur the mucilage event on the species diversity of the region in the coming years.

Türk Balıkçı Gemileri Tarafından İşlenen Yasa Dışı, Kayıt Dışı, Kural Dışı (YKK) Trol İhlallerinin Değerlendirilmesi

This study analyses a highly damaging and prevalent fishing practice of trawl infringements, which is one of the crucial components of IUU fishing in Turkish waters. The raw data gathered from the Turkish Coast Guard Command (TURCG), covered 2012 – 2014 period. Data covered a total of 1040 trawl infringements, with considerable differences in trawling violations among the seas surrounding Türkiye; the Black Sea, the Sea of Marmara, the Aegean Sea, and the Mediterranean Sea. With respect to trawling infringements, the Sea of Marmara (37%) and Istanbul Strait (15%) were the hot points. The most common infringement type was trawling in a closed area (43%) and when combined with the rate of infringements on trawling during the closed season (10%), these violations accounted for 53% of spatio-temporal infringements. Regarding illegal trawling by vessel type, trawl vessels had a 44% share and non-trawlers had a share of 56%, of which included infringements by other type of fishing vessels (46%) and non-fishing vessels (10%). It was also found that infringement by vessels smaller than 12 meters in length had a share of 46%. These vessels (known as "şebeke" in Turkish), trawl illegally using small types of nets and gears in coastal waters without giving any obvious indication of fishing activity. The results of this study will be useful to policy-makers, practitioners and scientists to successfully combat trawling infringements by providing information on distribution, intensity and methods of trawl violations.

Coastal upwellings in the Sea of Marmara

Based on in situ measurements between 2017 and 2022 in the Sea of Marmara, three "warm and saline" upwelling events were observed during autumn and winter scientific expeditions. These observations were crucial and worth mentioning since the surface salinity value increased and even reached the lower layer value, which is ~38 psu, during the process. Other characteristics of the lower layer were also detected, either as they are or in between upper- and lower-layer values due to mixing. After analysing the effects of coastal upwellings on the upper layer, it was concluded that coastal upwelling, which has been underestimated for a long time, has to be well studied because it could be another reason or way of nutrient enrichment in the upper layer and salinity increase in winters. This phenomenon also has huge potential to differ the upper layer characteristics with a rise in frequency. Therefore, it is advised that coastal upwelling should always be considered with other well-known features during marine studies and for future engineering solutions in the basin.

Does Sea Level Change in The Strait of Istanbul, Türkiye?

Bosphorus is a narrow water passage connecting the Marmara Sea and the Black Sea through a sea level balance current flow. In this study, change points in mean and in variance and trend analysis are performed to reveal whether sea level is changing or not. Moreover, the simple linear regression is calculated to explain the relationships among sea level data in the three stations located in the Black Sea, the Marmara Sea and Bosphorus. The Turkish National Sea Level Monitoring System (TUDES) measures sea water level at each 15-minute periods in three stations in order to minimize the effect of turbulence. The sea level in the coastal area of Istanbul city is most populous region with its highly economic importance. The most important reason for this is the serious decrease in the amount of water discharged into the Black Sea due to dams and excessive water usage. The three sea level stations have no change points on the average of the whole data. The change points in variance are depicted especially in gap data years and especially around year 2018. While the difference in the sea level of the Istanbul and Sile stations contain seasonality, the difference between the other stations has a sinusoidal component. While this study lights on understanding the sea level characteristics of the Bosphorus, it also emphasizes the importance of accuracy, completeness and long-term measurement data requirement.

The September 26, 2019 Silivri Earthquake (Mw=5.6), NW Türkiye

The September 26, 2019 Silivri earthquake (MW=5.6-5.8) occurred along the North Anatolian Fault Zone segments extending beneath the Marmara Sea. In the present study the teleseismic P waveforms and 20-year long background seismicity of the earthquake (MW=5.6-5.8) have been analyzed. Point-source inversion of the teleseismic P waveforms revealed that the earthquake was due to oblique faulting and released a seismic moment of 3.2 x 1017 Nm (MW=5.6). The frequency-magnitude distributions (FMDs) for the background seismicity have been calculated for 5-year long time windows after the 1999 İzmit earthquake. The considerable decrease of b-value of the FMDs just before the 2019 Silivri earthquake has been interpreted as stress increase along the fault segments which provides a reasonable clue for the occurrence of the earthquake. The FMD distribution for the 5 year-long time windows before the 2019 Silivri earthquake suggests a recurrence time interval of 168 years and occurrence probability of %16 within the next 30 years for a Mw=7.5 earthquake.

Troglophonte Huys & Lee, 2000 (Copepoda, Harpacticoida, Laophontidae) Cinsinin Değiştirilmiş Diyagnozu ve Yeni Bir Türünün Deskripsiyonu

A new species of the monotypic genus Troglophonte Huys & Lee, 2000 (Harpacticoida, Laophontidae) was discovered among the interstitial samples collected from the Kumada Coast in the Sea of Marmara. The new species can be distinguished from the type species T. spelaea (Chappuis, 1938) by the following characters: (i) female 6-segmented antennule, (ii) P3 exp terminal segment with 7 setae, (iii) female P5 exopodal lobe with 5 setae, (iv) female P5 baseoendopod with 3 setae on endopodal lobe, (v) surface ornamentation of swimming legs, (vi) male P5 baseoendopod distal seta ornamentation, and (vii) male P5 exopod setal ornamentation. The type material of T. spelaea does no longer exist and its diagnosis is concise. Therefore, the generic diagnosis has been updated to include the characters displayed by the new species. Additionally, a phylogenetic analysis including other genera related to the Troglophonte was conducted using parsimony. The results obtained from the phylogenetic analysis were generally consistent with the previous studies.

Status, distribution, and threats of the last surviving fan mussel populations in Greece

Since the first confirmed records of mass mortality events (MME) in the Aegean Sea in 2018, Pinna nobilis populations in Greek seas have been decimated. To bolster recovery efforts, this study aimed to assess the status of fan mussel populations in the Aegean and Ionian seas and investigate potential recolonization through natural recruitment. From May 2022 to May 2023, 163 independent underwater visual surveys were conducted across various locations and depths along the Greek coastline. A total of 4348 P. nobilis individuals was recorded, of which 87.3% were found dead and 12.7% were alive. The sole surviving fan mussel populations were located in the semi-enclosed gulfs of Amvrakikos in the Ionian Sea and of Kalloni in the Aegean Sea, with estimated recent mortality rates (excluding potential poaching) of 7.7% and 6.3%, respectively. To track potential new recruitment, a network of larvae collectors was deployed in multiple locations. Additionally, an ocean circulation model (OCM) was developed to predict the export and fate of larvae from the surviving populations in the Marmara Sea towards the Aegean Sea. Beyond the MME, this study identified several other threats, which significantly endanger fan mussel survival. The findings of this study underscore the urgent need to implement protection measures and restoration actions to enhance the chances of P. nobilis survival and recovery in the Greek seas.

Genetic structure and demographic history of whiting Merlangius merlangus (Linnaeus, 1758) populations distributed in Turkey inferred from variation in mitochondrial DNA sequences

The genetic diversity, structure, and demographic history of the economically important and overfished Gadidae species Merlangius merlangus were investigated using the non-coding mitochondrial Control Region (CR) from five different sites in the Sea of Marmara and the Black Sea in Turkey. The populations of M. merlangus were found to be genetically diverse, with 14 haplotypes and 15 polymorphic regions. The overall haploid diversity was 0.910 ± 0.024, and the nucleotide diversity was 0.003± 0.0003. Genetic distances between populations varied between 0.13% and 8.02%, while genetic distances within M. merlangus populations varied between 0.09% and 0.42%. Principle Coordinates Analysis showed that Marmara, Black Sea, and Karadeniz Ereğli populations were clearly separated. Pairwise FST values varied from 0.12 to 0.69, highlighting high genetic variation among populations. The Black Sea and Marmara lineages of M. merlangus diverged from the North Sea lineage 1.65 (1.08-2.29) mya, whereas the separation between the Atlantic lineage occurred about 0.84 (0.51-1.2) mya. The recent expansion of the whiting population was identified through neutrality tests and mismatch distribution analyses. This study provides important insight into the genetic structure, conservation, and management of this species.

The last observation of the long-spined exotic Sea Urchin (Diadema setosum) in the Gulf of Antalya

Diadema setosum, a Red Sea migrant, was first identified on the shores of the Kaş Peninsula in the Mediterranean. Approximately a year after this observation, the same species was reported for the second time from Konyaaltı Beach in Antalya Bay. This sea urchin rapidly multiplied and expanded its distribution along the coasts of the Mediterranean and Aegean Seas, reaching as far as the Marmara Sea. Some individuals of this sea urchin, which expanded distribution to coastal areas posing a risk to swimmers, were observed to start dying in the summer months of 2022. Scuba diving surveys were conducted in five different areas with rocky and stony seabed structures in the Gulf of Antalya during the winter season (Cliffs, Konyaaltı Beach, Sıçan Island surroundings, Çaltıcak region, and Kemer Ağva Cape), and it was determined that 99% of the D. setosum population had died in February and March. No living individuals were encountered during scuba diving surveys conducted in the same stations in April and May. In conclusion; mass mortalities have occurred in the D. setosum population in the rocky areas of the Gulf of Antalya, including the cliffs, Konyaaltı beach, Sıçan island surroundings, Caltıcak region, and Kemer Ağva Cape. This study presents the first report on matter.Keywords: Diadema setosum; Gulf of Antalya; Sea urchin.

Microplastic pollution in wild and aquacultured Mediterranean mussels from the Sea of Marmara: Abundance, characteristics, and health risk estimations

Microplastic (MP) pollution raises urgent concerns about the environmental well-being and the safety of the food supply for humans. Mussels are essential filter-feeding organisms that may be highly susceptible to MPs uptake due to their global distribution and sedentary lifestyle. There is also a knowledge gap regarding MP levels in commercially-farmed and wild-sourced mussels for human consumption, creating gaps in risk identification for food safety. This study aims to fill this gap in understanding by (a) investigating the presence and abundance of MPs in both wild and aquacultured mussels collected from six different stations in the Sea of Marmara, (b) comparing the levels of MPs between aquacultured and wild mussels, and (c) evaluating the potential health risks associated with the consumption of these contaminated mussels. Polymer types were verified by ATR-FTIR (Attenuated Total Reflectance Fourier Transform- Infrared Spectroscopy), and 6 different polymers have been identified. Among the total 753 identified MPs, the majority (79.8%) were fibers, with the predominant size range (42.4%) falling between 0.1 and 0.5 mm. Consuming wild mussels was associated with a 187.6% higher risk of MP intake compared to aquaculture. A consumer can potentially be exposed to 133.11 to 844.86 MP particles when consuming a 100 g serving of mussels, with risks becoming more significant as portion sizes increase, as is the case in some countries where portions reach 225 g. In this study, detailed information is presented on MP pollution in both wild and aquacultured mussels from Sea of Marmara, providing valuable insights for ensuring food safety, effective management and control of MP pollution in this region.

Optimum site selection for oil spill response center in the Marmara Sea using the AHP-TOPSIS method

Optimum site selection for oil spill response center in the Marmara Sea using the AHP-TOPSIS method

The soil characterization of the region between the Maltepe-Beykoz Fault and the Marmara Sea in İstanbul (Türkiye) with the integrated HVSR (Nakamura technique) and MASW method

Completing the earthquake recurrence period of the Marmara segment, one of the two seismic gaps of the northern Anatolian fault zone, necessitates earthquake hazard studies for Istanbul, considering the population density. This study focuses on determining the soil properties of the study area in the Maltepe district of Istanbul. The Maltepe, with its large population density, stands very close to this fault zone and is vulnerable to earthquake damage. The soil properties such as Vs30, dominant period (T0), and amplification ratio (A0) were determined with the MASW from surface wave analysis methods at 48 points and the HVSR approach of microtremor analysis methods at 26 points. These point-based properties were mapped in the GIS environment, and spatial distribution maps were prepared. In addition, seismic vulnerability (Kg) and effective shear strain (γe) calculations for different acceleration values were carried out to detect deformation-failure on the surface. It was understood from the maps and the 2D cross-sections produced to examine the lateral and vertical changes that the soil conditions in the study area developed under the control of the Maltepe Beykoz fault (MBF). Accordingly, the two sides of the MBF lineament were determined with different geophysical outputs by their different geological origins. Namely, the alluvial part in the coastal part was defined by low Vs30, high period, and Kg values; on the contrary, the more rigid parts located at high elevations were described by relatively high Vs30, low period, and Kg values. In addition, it was understood that the deltaic sediments spread loosely and undulated in the alluvium at the SE part of the MBF lineament. These results obtained in the study are significant for predicting disaster damages and taking precautions before disasters. In addition, the scientific data potential of the outcomes of this study will make future studies, which are carried out to determine other parameters to be used during the taking of the precautions, more accessible.

Climate change impacts on river discharge to the Sea of Marmara

The Sea of Marmara, located in Northwestern Türkiye, is under multiple stressors, including climate change and industrial, agricultural, and domestic pollution, that cause deoxygenation in coastal waters, with multiregional consequences affecting the surface and deep-water masses transported to the Mediterranean and Black Seas, respectively, via its straits. With climate-change driven changes in the intensity of extreme precipitation events, the marine environment becomes more vulnerable to increasing terrestrial pollutants. Evaluating the spatial and temporal variation of river runoff is crucial to understanding the interaction between the geophysical and hydrogeochemical processes that affects the nutrient balance of the sea. This study aims to (i) explore the historical (for the period 1960-2021) and spatial changes of monthly-averaged coastal discharges along the coastline of the Sea of Marmara for the first time, based on observations from the national hydrological service; (ii) analyze the change in long-term and seasonal trends of runoff and net-precipitation rate and derive a regional relation between the two parameters. Single Spectrum Analysis (SSA) is used to obtain the trends. Gaps in the time series are filled in using a non-parametric spectral estimation method. Discharges from the northern, eastern, and southern basins are, respectively, 3%, 17%, and 80% of the total discharge, which has varied between 1.5 and 15 km3 per year in the last decade, with short-lived extremes occurring in early spring. Total runoff rate shows a declining long-term trend that is accelerating with increasing evaporation. The intensity of the terrestrial precipitation extremes shows a temporal increase; there is a quadratic relation between the long-term trends of net precipitation and total runoff. Quantification of nutrient load distribution along the coastline associated with the spatial-temporal changes in coastal fluxes is urgent because the cumulative stressors (warming, nutrient overenrichment, pollutants) pose a threat of triggering extreme events and eutrophication in the Sea of Marmara with multiregional impact.

Mechanical, UV protection, and antibacterial properties of poly(vinyl alcohol)/marine mucilage biocomposite films

AbstractThe mucilage that accumulated in the Sea of Marmara in 2021 turned into an environmental disaster that threatened not only marine life but also the shipping and tourism industries. However, because of the partially organic structure of marine mucilage, it has the potential to be used as an additive for polymer films. In this study, bioplastic films were prepared from PVA with a series of mucilage content from 0% to 50% by mass, and their properties were investigated. The FT‐IR spectra revealed a shift in hydroxyl peaks, suggesting an interaction between the mucilage and PVA. SEM images showed the formation of crystal forms at the higher mucilage content of 20%, indicating ionic saturation of the PVA matrix. EDX and XRD analyses revealed that the crystal was NaCl coming from the mucilage composition. The tensile strength of the neat PVA film was measured as 9.86 MPa and improved to 14.56 MPa with 5% mucilage content, which is attributed to the ionic cross‐linking. The tensile properties were preserved up to 20% of the mucilage content, and then sudden decrements were observed. The transmittance percentage (T%) of the neat PVA film in UV–Vis spectra (800–200 nm) was detected as 75% at 500 nm and decreased down to 39% with increased mucilage content up to 50%. Furthermore, a rising limit of linearity (LOL) of the spectrums was observed from 350 to 580 nm, with increasing mucilage content from 5% to 50%. The biofilms showed antibacterial activity against Escherichia coli and Staphylococcus aureus bacteria. Hence, a robust and biodegradable film having UV protection and antibacterial activity was developed from the marine mucilage bio‐waste.Highlights Poly(vinyl alcohol)/marine mucilage biocomposite films were prepared. Biocomposite films showed increased UV‐A, UV‐B, and UV‐C protection with increased mucilage content. Enhanced tensile strength of biocomposite films up to 20 wt% mucilage content was determined due to ionic crosslink formed by NaCl salt ions. Biocomposite exhibited antibacterial activity against Escherichia coli and Staphylococcus aureus.

The Predation of Pinna nobilis (Mollusca) Juveniles by the Spiny Sea Star Marthasterias glacialis (Echinodermata) in the Sea of Marmara

The critically endangered bivalve species, the pen shell Pinna nobilis, has been suffering from an epidemic disease in the Mediterranean Sea, and its populations have totally disappeared in many areas across the basin. The Sea of Marmara’s populations of the pen shell, which were previously assumed to have remained unaffected by the epidemic disease because of the special hydrographical condition of the sea (brackish water), have been devastated after the catastrophic mucilage event suddenly outburst in November 2020 in the region. The settlement of healthy juvenile specimens of the species was frequently observed in the area after the mucilage event. However, an unexpected predator of juvenile specimens of the pen shell, the spiny sea star Marthasterias glacialis, was encountered in the area in January 2023. Two cases were observed and the spiny sea star has a capability of crashing one valve of the sea-pen through which it consumes its flesh. This predation might have the potential to affect populations of P. nobilis, which has been struggling to survive in the region after its mass mortality due to the mucilage event. Such data are of utmost importance to imply effective conservation planning for the sustainability of the remaining populations of the pen shell in the region.

Morphometric Analyses of the Angular Roughshark, Oxynotus centrina (Oxynotidae), with Biological Notes on Specimens from the Sea of Marmara

Morphometric measurements as percentages of total length of 6 specimens of Oxynotus centrina (Linnaeus, 1758), captured in the Sea of Marmara were reported. All of the analyzed proportions of landmark measurements as percentage of total length show allometry. Although, slight differences were seen between the morphometrics of Marmara specimens of O. centrina and those reported for the angular roughsharks captured in several geographical subregions of the Mediterranean Sea, these variations can be considered admissible based on allopatry. Regarding the mouth morphology in particular, the proportion of head length/mouth width to total length showed negative allometry, indicating O. centrina is a small-mouthed shark compared to increasing body size. A partly digested shark embryon and vitellus like slurry were found in the stomach content of one specimen captured in the Sea of Marmara, which provided supporting evidence for the predation on elasmobranch eggs by O. centrina in the wild.