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1

Reproductive biology of the European anchovy Engraulis encrasicolus (Linnaeus, 1758) in the Turkish Aegean Sea

Taylan Burcu, Bayhan Bahar

Oceanological and Hydrobiological Studies

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2024

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Vol. 53, No. 1

7--15

EN

The present study investigated the reproductive biology of European anchovies obtained seasonally from fishermen in İzmir Bay (Aegean Sea). The total length range of the investigated individuals was 9.0 – 15.7 cm. Of the 750 samples in which sex was determined, 34% were males, and 66% were females, resulting in a female-to-male ratio of 1.91:1. The first maturation length was determined to be 10.47 cm for females and 9.95 cm for males. Based on the total values of the gonadosomatic index, it was concluded that the reproductive period of the species falls in the summer season. The batch fecundity of the species ranged from 2.123 to 6.951 oocytes, and the fecundity–length relationship was expressed as F = 1134.4TL – 10034 (R2 = 0.84). Histological examination of the female ovaries revealed the presence of oocytes at different stages of development, indicating multiple spawning during the reproductive season.

2

Determination of genetic diversity between natural and cultured populations of Common Dentex (Dentex dentex) fish in the East Aegean Sea

Kayaci Ali, Can Mehmet Fatih, Güner Yusuf, Güleç Fartih

Oceanological and Hydrobiological Studies

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2023

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Vol. 52, No. 1

52--67

EN

Common dentex (Dentex dentex) is a commercial species of fish that is a highly valuable food source living naturally near Mediterranean and Atlantic Coasts. Therefore, monitoring and maintaining common dentex habitats are of high importance. A total of 53 specimens were collected from 6 natural habitats (from the Eastern Aegean and from the Antalya coast, which is the closest coast to the Western Mediterranean), and one aquaculture facility in the Eastern Aegean Sea. The mitochondrial Cytochrome Oxidase I (COI) gene was used to detect a total of 26 haplotypes. Along with the COI gene sequence, real-time PCR and high-resolution melting analyses were performed as rapid and inexpensive alternatives. Sequence analysis showed that the highest haplotype diversity was obtained from the aquaculture facility in Karaburun and Antalya Locations, Turkey. Analysis of Molecular Variance (AMOVA)based on the haplotype frequencies resulted in 92.54% genetic variation within localities and 7.46% genetic variation between/among localities. The mean fixation index (Fst) was calculated as 0.0746 (p < 0.001). Genetic distances were primarily in collaboration with geographical distances and were efficiently confirmed by high resolution melting (HRM) analysis. The results will be valuable in monitoring and maintaining natural habitats as well as aquaculture facilities where common dentex are grown.

3

Spat efficiency of the smooth scallop Flexopecten glaber in the Aegean Sea, Türkiye

Yigitkurt Selcuk, Kirtik Ali, Kurtay Evrim, Ugur Sinem, Durmaz Yaşar

Oceanological and Hydrobiological Studies

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2022

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Vol. 51, No. 3

298--307

EN

This study was carried out to determine the spat efficiency of the smooth scallop Flexopecten glaber (Linnaeus) in surface and bottom water at the Ozbek coast (Türkiye) of the Aegean Sea from September 2017 to August 2018. The environmental parameters (temperature, salinity, chlorophyll-a, and total particulate matter) were also monitored at two depths. The average water temperature at the surface and bottom were 19.79 ± 5.62°C and 19.73 ± 5.24°C, respectively. The lowest chlorophyll-a values were recorded in February (1.12 g l-1) and June (1.23 μg l-1) at the surface and bottom, respectively. The highest chlorophyll-a value was recorded in August at both depths. Throughout the study, the number of F. glaber on the collectors was 270.33 ± 43.54 spat m-2 and 145.66 ± 18.03 spat m-2 were detected on the bottom collectors. A statistically significant difference was found between the growth of the spat attached to the surface and bottom collectors (p < 0.05).

4

Effects of anthropogenic activities on nutrient parameters in the North Eastern Mediterranean Sea (Bay of Sığacık/Aegean Sea)

Çulha Saniye Türk, Karaduman Fatma Rabia, Gündoğdu Ayşe, Barış Kamil Emre

Oceanological and Hydrobiological Studies

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2022

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Vol. 51, No. 2

189--202

EN

This study aims to examine the physicochemical parameters of seawater (temperature, pH, salinity, dissolved oxygen, suspended particulate matter, ammonium-nitrogen, nitrite-nitrogen, nitrate-nitrogen, and phosphate-phosphorus, burnable organic matter in the sediment), and possible effects of pollution in Sığacık Bay where different anthropogenic activities are carried out. Samples of surface seawater (0 m), bottom seawater (2 m), and sediment were collected monthly from four sampling sites between September 2013 and September 2014. Annual mean nutrient values were determined as 1.6 ± 0.14 μg.at.NH4+-N l-1, 0.1 ± 0.01 μg.at.NO2--N l-1, 0.8 ± 0.08 μg.at.NO3--N l-1, 0.7 ± 0.08 μg.at.PO43--P l-1, SPM 21.4 ± 0.33 mg l-1. The BOM content in the sediment was 5.6 ± 0.39%. As a result of the study, it was determined that Sığacık Bay was polluted by anthropogenic point and non-point source pollution. According to the water quality criteria, the bay was found to be in the group of polluted seawater in terms of phosphate phosphorus.

5

Effects of seasonal changes and depth on growth parameters of the Mediterranean mussel (Mytilus galloprovincialis) on a shipwreck in the Eastern Mediterranean Sea

Şensurat-Genç Tuğçe, Karadal Onur, Oruç Adnan Çağlar, Özgül Aytaç, Aytaç Altan

Oceanological and Hydrobiological Studies

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2021

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Vol. 50, No. 4

441--454

EN

The study was conducted between July 2018 and May 2020 to compare seasonal changes in growth parameters of the Mediterranean mussel (Mytilus galloprovincialis) at different depths in two different areas of the Northeastern Mediterranean Sea (Aegean Sea). In a preliminary study, mussels were placed in cages at different depths of an artificial reef (AR – shipwreck) and natural reef (NR). Temperature, salinity, pH, and dissolved oxygen were determined seasonally at both sites at a depth of 37 m (deepwater) and 25 m (midwater). Linear increases in length and width of mussels at the AR site were recorded, while no consistent changes were observed for mussels at the NR. There was negative correlation between the specific growth rate (SGR) and salinity (r2 = 0.5098) and temperature (r2 = 0.1470) at the AR site. Negative correlations were also recorded between pH and the commercial condition index (CCI) at both the AR (r2= 0.3869) and NR (r2 = 0.3600) sites. Our findings show that depth had a significant effect (p < 0.05) on the CCI of mussels at the NR site, while its effect was insignificant for this index at the AR site (p > 0.05). This study indicates that natural reefs provide more suitable conditions for the growth of Mediterranean mussels than shipwrecks used as artificial reefs.

6

Biodiversity of freshwater macroinvertebrates on Gökçeada Island (North Aegean Sea, Turkey)

Odabaşı Serpil

Oceanological and Hydrobiological Studies

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2021

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Vol. 50, No. 4

421--429

EN

Island ecosystems have attracted the attention of scientists since the early days of science because of their formation and biodiversity. Despite their abundant freshwater resources, data on freshwater diversity of Gökçeada are incomplete, especially for macroinvertebrates. This study was conducted in a wide range of freshwater ecosystems on Gökçeada between May 2016 and September 2018. Sampling of macroinvertebrates was performed using a hand net from 34 pre-selected sampling sites on the island. A total of 78 aquatic macroinvertebrate taxa were found, 46 of which are new records for the island. The most common species during the study were Gammarus komareki and Bythinella gokceadaensis with a frequency of 25.93%, followed by Tubifex tubifex, Gammarus sp. and Caenis sp. with a frequency of 22.22%. Endemic and invasive species on the island were assessed according to their presence and frequency values. Based on the results of the current study and previous data, it can be concluded that Gökçeada is characterized by a remarkable species diversity compared to aquatic macroinvertebrates on other Aegean islands.

7

Co-seismic and post-seismic deformation, field observations and fault model of the 30 October 2020 Mw = 7.0 Samos earthquake, Aegean Sea

Ganas Athanassios, Elias Panagiotis, Briole Pierre, Valkaniotis Sotiris, Escartin Javier, Tsironi Varvara, Karasante Ilektra, Kosma Chrysanthi

Acta Geophysica

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2021

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Vol. 69, no. 3

999--1024

EN

On 30 October 2020, a large Mw = 7.0 earthquake occurred north of the island of Samos, Greece. Here we present the characteristics of the seismic fault (location, geometry, geodetic moment) as inferred from the processing of geodetic data (InSAR and GNSS). We use the InSAR displacement data from Sentinel-1 interferograms (ascending orbit 29 and descending 36) and the GNSS offsets from fourteen (14) stations in Greece and Turkey to invert for the fault parameters. Our inversion modelling indicates the activation of a normal fault offshore Samos with a length of 40 km, width of 15 km, average slip of 1.7 m, a moderate dip-angle (37°) and with a dip-direction towards North. The inferred fault is located immediately north of, and adjacent to Samos with the top of the slip ~ 0.6 km below surface, and ~ 1 km offshore at its closest to the island. Near the fault, the earthquake caused the permanent uplift of the island up to 10 cm with the exception of a coastal strip along part of the northern shore that subsided 2–6 cm. The co-seismic horizontal motion of GNSS station SAMO was 35.6 cm towards south and 3 cm towards west. A post-seismic signal (22–33% of the co-seismic on the vertical component) was observed at GNSS stations SAMO and SAMU, with a time constant of 30 days. The effects of the earthquake included liquefaction, rock falls, rock slides, road cracks and deep-seated landslides, all due to the strong ground motion and associated down-slope mobilization of soil cover and loose sediments.

8

Spat efficiency in the pearl oyster Pinctada radiata (Leach, 1814) in the surface and bottom water at Karantina Island

Yigitkurt Selcuk, Lök Aynur, Kirtik Ali, Acarli Sefa, Kurtay Evrim, Küçükdermenci Aysun, Durmaz Yaşar

Oceanological and Hydrobiological Studies

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2020

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Vol. 49, No. 2

184--192

EN

The present study was carried out to determine the spat efficiency in the pearl oyster (Pinctada radiata, Leach, 1814) in surface and bottom water at Karantina Island (Izmir/Turkey). Polyethylene mesh bags were used as collectors. An annual average of 175.16 ± 11.32 spat m-2 was obtained from PSC (placed surface collectors) and 82.65 ±3.89 spat m-2 was obtained from PBC (placed bottom collectors). The largest number of new spat attachments occurred in August, both on PSC and PBC: 44 ± 3.46 and 26 ± 2.88 spats were found respectively in the outer and inner mesh bags of PSC, and 33 ±5.77 and 48 ± 6.92 spats were found respectively in the outer and inner mesh bags of PBC. New spat attachments (≥ 10 mm) continued throughout the study period, except April and May. Adult pearl oysters (≥ 50 mm) were found in May. There was a significant difference between PSC and PBC in the total number of spat attachments, the monthly spat attachments and the first spat attachments (p < 0.05). The total number of new spat attachments was positively correlated with temperature and chlorophyll a for both depths (p<0.05).

9

Subdividing the tectonic elements of Aegean and Eastern Mediterranean with gravity and GPS data

Kahveci Muzaffer, Çırmık Ayça, Doğru Fikret, Pamukçu Oya, Gönenç Tolga

Acta Geophysica

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2019

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Vol. 67, no. 2

491--500

EN

Western Anatolia has been formed by the motions of the African plate, Arabian plate and Hellenic Subduction zone. The Hellenic Subduction zone, which has high seismicity, is the main tectonic feature of the eastern Mediterranean Sea related to the subduction of the African Plate beneath the Aegean Sea Plate. The Hellenic Subduction zone has a complex lithospheric structure and shows complex differences in the Aegean Sea in terms of continental crust thickness and mantle velocity. In the study area, the directions of Global Positioning System (GPS) velocity vectors which are towards SE change towards S from North of Western Anatolia to Hellenic Subduction zone. It is thought that the factor which controls this mechanism is the shear force or subduction zone located in Aegean Sea. Western Anatolia region, which is located in Western Anatolia Extensional province, includes several morphologically significant N–S trending active normal faults. Besides, the NE–SW and NW–SE trending faults, which their kinematic features change from north to south, are very effective on the tectonic regime of the region. Additionally, for determining the boundaries of these tectonic elements, the Complete Spherical Bouguer (CSB) gravity anomaly of study area was calculated by using World Gravity Map (WGM2012) model. Moreover, in historical and instrumental studies, the high seismicity of the study area is remarkable. It is thought that this case is also related with the mechanism which oriented the GPS velocity vectors to southward. Consequently, the dominant kinematic structure of the region was classified by combining the GPS velocity vectors computed for Izmir and its surroundings bounded by Western Anatolia, Aegean Sea and Eastern Mediterranean and the CSB gravity anomaly. Finally, the results were interpreted together with focal depth distributions of earthquakes and Bouguer gravity data.

10

Reproductive biology of the black-striped pipefish Syngnathus abaster Risso, 1827 (Pisces: Syngnathidae) in the Aegean Sea of Turkey

Taylan B., Tatarhan G. E., Aksoy O., Culha M.

Oceanological and Hydrobiological Studies

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2018

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Vol. 47, No. 1

67--74

EN

The paper presents the results of research on the reproductive biology of Syngnathus abaster – a species distributed in Çandarli Bay. For this purpose, seine nets were collected from a depth of 0.5–2 m in 15 minute periods between April 2013 and March 2014, and a total of 185 individuals were sampled. It has been determined that 94 individuals (50.81%) were females, 79 were males (42.70%) and 12 were immature (6.49%). The sex ratio was 1:0.84. The average length values in female, male and immature individuals were 111.5 ± 7.35, 109.9 ± 11.08 and 79.8 ± 5.30 mm, respectively. The maximum mean surface water temperature is in spring and summer seasons. When Gonadosomatic Index (GSI%) values were examined, the spawning period of the species was indicated as spring and summer. Three groups of species were identified as maturing (diameter: 0.61–1.20 mm), mature (diameter: 1.21–1.70 mm) and hydrated oocytes (diameter: 1.71–2.10 mm) in ovaries of female individuals. The number of eggs in the brood pouch of pregnant male fishes was on average 48 (mean ± SD = 48 ± 14.09 eggs, range: 23–78 eggs). The hydrated oocyte/total length relationship was: y = 0.8651x – 84.332 (n = 14, r2 = 0.64) and the number of eggs/total length relationship in the brood pouch of pregnant males was: y = 1.0168x – 67.715 (n = 33, r2=0.58).

11

Diet composition of the Morocco dentex : Dentex maroccanus Valenciennes, 1830 (Teleostei: Sparidae) in the central Turkish Aegean Sea

Bayhan B., Sever T. M., Heral O.

Oceanological and Hydrobiological Studies

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2017

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Vol. 46, No. 2

133--139

EN

This study examined the stomach contents of 230 individuals out of 439 samples obtained from commercial fishermen between January 2013 and March 2014 from a trawler using trawl bags with a full cod-end mesh size of 44 mm. It was found that 216 samples were full and the stomach fullness index was estimated at 93.9%. The varying diet composition of the species was determined by estimating the percentage numerical composition (N%), frequency of occurrence (F%), gravimetric composition (W%) and the index of relative importance (IRI%). Diversity (Shannon index), richness (Margalef index) and similarity (Bray-Curtis index) of the catches in different seasons were calculated using the Biodiversity Professional (Version 2) software. Three major groups were identified in the catches: Crustacea, Mollusca and Teleostei. At least 17 different prey groups were identified. With regard to the diversity of consumed prey, the winter (1.204), autumn (1.079) and spring (1.000) seasons were characterized by a medium level of diversity, summer (0.699) – by a low level of diversity. However, the richness of prey does not show seasonal differences. As indicated by the Bray-Curtis index, the highest similarity between the prey groups was observed between the autumn and winter seasons, at 81.61%.

12

Avoiding collisions, enhancing marine safety – a simplified model for the Aegean Sea

Ventikos N. P., Rakas D. K.

Zeszyty Naukowe Akademii Morskiej w Szczecinie

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2015

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nr 42 (114)

78--85

EN

Ship collision is a hazardous event within the chain of maritime transport. Collisions may result in human losses, adverse economic consequences, and environmental damages causing significant impact to local societies and related activities. A major factor in any risk analysis concerning ship collisions is the probability of these collisions occurring. The purpose of this study is to assess the probability of ship-to-ship collision in the Aegean Sea. The basic concept of the developed model is to (statistically) simulate traffic flow in the area of interest and determine the collision candidates; this will be implemented in a pilot study in a segment of the Aegean Sea. The input of this effort is based on values that are extracted from statistical analysis of the international fleet in combination with the study of maps depicting traffic flow in the studied area. Hence, it does not employ detailed AIS data. The obtained results are presented and their agreement with actual incidents is discussed in depth. The paper concludes with interesting insights of the aforementioned tasks.

13

Reproductive Biology of the Mediterranean Green Crab Carcinus aestuarii Nardo, 1847 (Crustacea, Brachyura, Portunidae) in Homa Lagoon, Aegean Sea, Turkey

Özbek M., Koçak C., Acarli D.

Oceanological and Hydrobiological Studies

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2012

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Vol. 41, No. 4

77-80

EN

The Mediterranean green crab Carcinus aestuarii Nardo, 1847 (Crustacea, Brachyura, Portunidae) is a common inhabitant of the shallow waters of Homa Lagoon in Izmir Bay, Turkey, in the eastern Mediterranean. Monthly samples were collected in Homa Lagoon from June 2006 to May 2007 using trammel nets, fyke nets, beach seines and fence traps. In total, 608 males and 559 females of C. aestuarii were collected. The highest sex ratio (81-86% females) was recorded between October and December, and in August (58% females). Ovigerous females were obtained only from November to February with the highest ratio of ovigerous females (55%) observed in January 2007. The maturation curve presenting the carapace width showed that 50% of female crabs with the carapace width of 26.84 š1.58 mm (r= 0.72) were physiologically mature. Regression analyses indicated that the number of eggs was positively correlated with carapace width and wet weight (P < 0.05, in both cases).

14

Decapod crustaceans of soft-sediments on the Aegean Sea coast of Turkey (the eastern Aegean Sea) Beijerinck

Ateş A.S., Katagan T.

Oceanological and Hydrobiological Studies

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2008

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Vol. 37, No.1

17-30

EN

58 species of decapod crustacean were identified (1 Dendobranchiata, 14 Caridea, 5 Thalassinidea, 14 Anomura, 24 Brachyura) on soft substrates of the Aegean Sea coast of Turkey. Samples were collected from 60 sampling sites along the Turkish Aegean shore (eastern Aegean Sea) between July 2000 and September 2000 with dredge and a van Veen grab at bottom depths of 7 to 150 m. Different species dominated in each ecological zone with the anomuran squat lobster, Galathea intermedia Lilljeborg, 1851, being the most dominant species across the whole sampling area, comprising 11.71% of the individuals collected. This report represents the first published investigations into soft-sediment decapod communities in the coastal waters of the Turkish Aegean Sea.

15

Preseismic Earth's electric field anomalies recorded at Lesvos station, northeastern Aegean

Hadjicontis V., Mavromatou C., Eftaxias K.

Acta Geophysica Polonica

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2002

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Vol. 50, nr 2

151-158

EN

Significant electromagnetic preseismic activity has been recently recorded at the telemetric VAN station of Lesvos Island, northeast Aegean, Greece. This was followed, after a few weeks, by intense seismic activity with Ms 5.8, close to Psara island (38.5°N, 25.6°E). These field results are strongly correlated with laboratory experiments aiming at detection of electromagnetic signals before the fracture of rock samples.