Crimean Shelf Research Articles

Recent Variations in the Size and Age Structure of the Population of Horse Mackerel <i>Trachurus mediterraneus</i> (Steindachner, 1868) on the South-Western Shelf of Crimea

The influence of the average annual sea surface temperature (SST) on the development of horse mackerel Trachurus mediterraneus on the south-western Crimean shelf has been shown. The changes in the main indicators of the population and their relationship with the change in the average annual SST (0.055°C/year) in 2000–2020 have been identified. Against the background of the observed increase in SST in recent years, the state of the horse mackerel population has improved: there has been an increase in the average age and, accordingly, the proportion of larger, well-fed individuals, and, in general, the average size and weight of fish. It has been shown that according to the nature of the change in the average annual SST, three periods can be distinguished: 2000−2007, 2008−2013 and 2014−2020.

Results of Seismostratigraphic Investigations of the Crimean Shelf by Continuous Seismoacoustic Profiling

Results of Seismostratigraphic Investigations of the Crimean Shelf by Continuous Seismoacoustic Profiling

Multiyear changes in oceanographic factors of the autumn migration of the Black Sea anchovy to the shores of Crimea from satellite data in 2000–2021

The purpose of this work is to analyze long-term changes in oceanographic indicators in the southeastern area of the northwestern Black Sea in November-December 2000–2021, which determine the migration activity and fishery performance of the Black Sea hammerhead off the coast of Crimea. Materials and methods used: The fishery statistics, data of information system Copernicus Marine Service of satellite altimetry and surface temperature of waters near the western coast of the Crimean Peninsula in November-December 2000–2021, graphic and statistical methods of the analysis of these data were used in work. Novelty: The element of novelty in the work is the use of oceanographic satellite data in the study of the behaviour of the Black Sea anchovy and long-term changes in its catch off the coast of Crimea. Result: During the period under consideration, the tendency of catch increase of the Black Sea anchovy of the Crimean coast is obvious. The main reasons for the activation of the autumn migration of the Black Sea anchovy to the shores of Crimea is a multi-year increase in sea surface temperature and the strengthening of south-eastern currents to the west of the Crimean Peninsula. Practical significance: The revealed causes of the mass autumn approaches of the Black Sea anchovy to the Crimean coast allow hoping for possibilities of their use in forecasting the results of the Black Sea anchovy fishing in the Crimean fishing area, and also give grounds for continuing research with special attention to monitoring of the Black Sea anchovy occurrence on the Crimean shelf.

The pelagic ecosystem of the Black Sea goes gelatinous

ABSTRACT Following up on the issue of worldwide growing gelatinous plankton dominance, we analysed historical records on zooplankton biomass from the 1970s to the present, in order to assess the ratio of gelatinous- to-non-gelatinous zooplankton (GN). The latter is poorly analysed in current publications featuring the Black Sea pelagic ecosystem. The GN characterizes the quality of zooplankton as a food source for small pelagic fishes which dominate Black Sea fishery. The retrospective analysis of zooplankton biomass constituents in coastal and open sea waters retrieved from published papers was complemented by an 11-year sampling (up until 2021), across the Crimean shelf. The comparison over regions (represented by the north-eastern, the northern, the north-western, the southern and the open sea) showed that the jellyfish Aurelia aurita, the ctenophore Mnemiopsis leidyi, and the dinoflagellate Noctiluca scintillans act as major contributors to the total gelatinous biomass of the 2000s, on a basin scale. On average, the wet gelatinous biomass is about one hundred times that of the non-gelatinous one. High values of the GN ratio (in wet mass and in carbon units) in coastal waters indirectly imply a leading role of a detritus pathway of organic matter in a pelagic ecosystem.

Changes in the Reproductive Period of Mediterranean Horse Mackerel and Blunt-Snouted Mullet Living in the South-Western Crimean Shelf in 2016–2021

Changes in the Reproductive Period of Mediterranean Horse Mackerel and Blunt-Snouted Mullet Living in the South-Western Crimean Shelf in 2016–2021

Characteristics of Bottom Sediments in the Coastal Areas of the Crimean Peninsula

The aim of this work was to assess the influence of physical, chemical, and hydrochemical factors on the characteristics of bottom sediments in various areas of the shelf of the Crimean Peninsula. The data obtained during the cruises of the RV “Professor Vodianitsky” in the fall of 2018 and summer of 2019 were analyzed. Hydrochemical analyses of the bottom waters were carried out using standard hydrochemical methods. Profiles of dissolved oxygen, hydrogen sulfide, and oxidized and reduced forms of iron in pore waters were obtained, and the geochemical characteristics of bottom sediments were determined. The features of their spatial and vertical distributions were considered. Pelite-aleuritic sediments with inclusions of sandy material and shell detritus prevailed in the coastal zone of the Crimean shelf. The organic carbon content varied from 0.5–0.6% in the gravel–sand sediments of the Kerch pre-strait area to 2.5–2.7% in the northwestern part. The prevalence of suboxic conditions was noted, and the main processes in the sediment upper layer were controlled mainly by reactions involving iron. In some areas of the southern coast of Crimea and the Kerch pre-strait area from the Sea of Azov, the development of anoxic conditions in the surface layer of bottom sediments was recorded.

Dissolved Methane in Coastal Waters of the Northeastern Black Sea

As the largest methane reservoir in the world, the Black Sea is characterized by significant variability in its dissolved methane distribution patterns. Aerobic waters in the coastal regions are influenced by various factors governing the biogeochemical processes in the water column; however, their impact on the distribution pattern of dissolved methane is not always well studied, especially in the shallow areas of the northeastern Black Sea, which have hitherto not been thoroughly covered by observations. Here, we consider the measurements of methane content in several regions of the northeastern Black Sea carried out from 2013–2017 with large and detailed spatial coverage in order to identify the key factors determining the dissolved methane pattern in each region of the study area. The CH4 pattern in the region of Sochi is dominated by the impact of river flow. The increased methane saturation in surface waters of the southeastern Crimean shelf (up to 40 nM) is caused by the influence of the Azov Sea outflow. The waters of the Feodosia Bay and to the south of it are mainly characterized by an increase in methane content towards the bottom (up to 100 nM), which is associated with water–sediment interactions and gas emission from the bottom.

Seasonal and interannual variations of the abundance of the dinoflagellate Noctiluca scintillans in the northern Black Sea

ABSTRACT Noctiluca scintillans (Macartney) Kofoid and Swezy, 1921 contributes ∼ 85% of the total biomass of heterotrophic plankton in Crimean coastal waters. Data for the retrospective analysis come from a 20-year sampling (in 2000s) across the Crimean shelf and in adjacent open sea waters. Samples were collected onboard research vessels, in the upper 150 m layer, by Juday nets (vertical hauls) fitted with 145 µm mesh. These data were compared to field surveys of the 1960s. Seasonal blooms of Noctiluca were pronounced during summer time, with the peak of abundance in June. The mesoscale spatial distribution of Noctiluca abundance was most heterogeneous in June as well. The annual concentration of cells in coastal waters exceeded that of the open sea by four times. The coefficient of Noctiluca seasonal abundance variation in coastal waters was 1.5 times higher than that of the open sea. The Principal Component Analysis implied that the seasonal variation of the Noctiluca abundance offshore was modulated by coupling of the atmospheric precipitation, sea surface temperature, photosynthetically active radiation, euphotic depth, chlorophyll-a concentration, Noctiluca abundance in coastal waters, mesoscale eddies and wind stress. A general decline of Noctiluca abundance and biomass was observed in coastal waters, from the 1960s to the present.

ТЕХНОЛОГИЯ ГЕОЛОГО-ГЕОМОРФОЛОГИЧЕСКИХ ИНСТРУМЕНТАЛЬНЫХ ИССЛЕДОВАНИЙ НА ЗАПАДНОМ ШЕЛЬФЕ ПОЛУОСТРОВА КРЫМ

ТЕХНОЛОГИЯ ГЕОЛОГО-ГЕОМОРФОЛОГИЧЕСКИХ ИНСТРУМЕНТАЛЬНЫХ ИССЛЕДОВАНИЙ НА ЗАПАДНОМ ШЕЛЬФЕ ПОЛУОСТРОВА КРЫМ

Современное состояние репродуктивного потенциала черноморского шпрота Sprattus sprattus phalericus (Risso, 1826) (Pisces: Clupeidae) в Крымском регионе и условия его формирования

Черноморский шпрот Sprattus sprattus phalericus (Risso, 1826) — один из наиболее массовых видов рыб в Азово-Черноморском бассейне. Благодаря своей многочисленности играет исключительно важную роль в экосистеме моря, являясь промежуточным звеном между зоопланктоном и представителями высшего трофического уровня ― крупными хищными рыбами, дельфинами и птицами. В то же время шпрот относится к числу важных промысловых объектов всех причерноморских стран, устойчиво занимая в последние десятилетия второе место по объёму вылова (после хамсы). Общий вылов достигает 100 тыс. тонн. Основные добывающие государства — Турция и Украина. Мониторинг и прогноз состояния популяции шпрота в условиях роста интенсивности промысла и изменения климата являются актуальными задачами. Предмет исследования данной статьи — многолетняя (2000–2016) динамика биологических (качественных) параметров, определяющих популяционную плодовитость черноморского шпрота в Крымском регионе, современное состояние репродуктивного потенциала и условия его формирования. В основу работы положены результаты собственных исследований. В числе параметров, определяющих популяционную плодовитость, изучены размерно-возрастная структура нерестового (родительского) стада, абсолютная индивидуальная плодовитость и половая структура нерестового стада (численное соотношение самок и самцов). В 2011–2016 гг. по сравнению с 2000–2004 гг. средняя длина нерестовых самок сократилась в 1,22 раза (с 7,36 до 6,03 см), что сопровождалось снижением абсолютной индивидуальной плодовитости в 2,39 раза (с 13 625 до 5690 икринок). Численное соотношение между самками и самцами уменьшилось в 1,23 раза (с 1,95 до 1,59). Одновременно величина запаса шпрота в северной половине Чёрного моря сократилась более чем в 2,5 раза (с > 500 тыс. т до < 200 тыс. т). В результате популяционная плодовитость шпрота в Крымском регионе уменьшилась более чем в 7 раз (2,39 × 1,23 × 2,5). Изучены условия промысла шпрота в северной половине Чёрного моря (от устья р. Дунай до Керченского пролива), которые показали 2-кратное снижение (с 251,9 тыс. тонн в 2000–2004 гг. до 129,1 тыс. тонн в 2011–2016 гг.) общего вылова и более чем 2,3-кратное (с 50,4 до 21,4 тыс. т) — среднегодового. На крымском шельфе, напротив, общий вылов в это время увеличился в 1,2 раза (с 76,9 до 92,2 тыс. т), а его среднегодовая величина осталась без изменения (15,4 тыс. тонн). Запас сократился в 2,5 раза, а значит, величина промысловой нагрузки на крымскую популяцию увеличилась в 2,5 раза, что даёт основание рассматривать фактор промысла в качестве главной причины её деградации. Справедливость данной версии подтверждает установленный ранее факт сопряжённости межгодовых колебаний между выловом и размерно-возрастными показателями шпрота в Крымском регионе в 2003–2013 гг.: выловы свыше 15–16 тыс. т сопровождались уменьшением средней длины шпрота в следующем году. Необходимым условием для предотвращения дальнейшей деградации, а также для восстановления и поддержания стабильного состояния популяции шпрота в Крымском регионе и её репродуктивного потенциала является регулирование промысла. Негативное воздействие природных (климатического и трофического) факторов на состояние популяции следует признать второстепенным. Локальный перелов косвенно указывает на структурированность промыслового запаса черноморского шпрота, его подразделённость на ряд пространственно-обособленных образований (единиц запаса), то есть на наличие внутривидовой дифференциации.

Internal waves of mode 2 in the Black Sea

The results of the first observations of mode 2 internal waves in the Black Sea are presented. The measurements were carried out on the Crimean shelf from the MGI platform in July 2011. In the period after the sweep, when measurements were taken, firstly mode 1 inertial internal waves were observed, and then mode 2 one. The oscillations of mode 2 were most pronounced in the vertical displacements of the water column, reaching amplitudes of 10 m. The features of mode 2 were also noted in fluctuations of the horizontal component of the currents. Along with the registration of mode 2 inertial internal waves, the appearance of short-period internal waves of mode 2 was also noted.

Internal Waves of Mode 2 in the Black Sea

The results of the first observations of mode 2 internal waves in the Black Sea are presented. The measurements were carried out on the Crimean shelf from the MGI platform in July 2011. In the period after the sweep when the measurements were performed, mode 1 inertial internal waves were observed first and then mode 2. The oscillations of mode 2 were most pronounced in the vertical displacements of the water column, reaching the amplitudes of 10 m. The features of mode 2 were also noted in fluctuations of the horizontal component of the currents. Along with the registration of mode 2 inertial internal waves, the appearance of short-period internal waves of mode 2 was also noted.

Soft-walled monothalamids (Rhizaria: foraminifera) of the Crimean shelf (Black Sea): taxonomic composition and inter-regional patterns of species diversity and distribution

ABSTRACTWe present new data on monothalamous (single-chambered) foraminifera from the Black Sea Crimean shelf zone between Karkinitsky Gulf in the west to the area near Kerch in the east. Within this region we recognized a total of 40 morphospecies; 8 are assigned, in some cases tentatively, to known species and another 9 to known genera, again sometimes tentatively. Twelve species (all undescribed) are reported here for the first time. The most abundant species are Psammophaga sp. (sensu Gooday et al. 2011), Goodayia rostellata Sergeeva & Anikeeva 2008 and Vellaria pellucida Gooday & Fernando 1992, each of which is evenly distributed in all studied areas. The highest species richness of monothalamous foraminifera was observed in the Yalta region. Based on a multivariate analysis of monothalamid assemblage structure and diversity indices [Shannon (H’), Margalef (D’), eveness Pielou (J’), Simpson (1-λ’) and rarefaction ES(n)], we recognized three groups of stations, corresponding to the Western, Southern and Eastern coasts of the Crimean peninsula. The monothalamid assemblages found in each of these coastal regions exhibit different structural features and are distinguished by certain characteristic species.

Non-native zoobenthic species at the Crimean Black Sea Coast

More than 40 non-native species have been registered in the zoobenthos of the Black Sea. Only, five alien species, the Crustacea, Rhithropanopeus harrisii (Gould, 1841) and Rhithropanopeus harrisii (Gould, 1841), and the Mollusca, Rapana venosa (Valenciennes, 1846), Mya arenaria (Linne, 1758) and Anadara kagoshimensis (Tokunaga, 1906), were recorded in the benthos on the Crimean shelf between 1999-2014. The blood-cockle A. kagoshimensis had settled on many sites of the Black Sea shelf in the past forty years. The first detection (1999) at the Crimean coast and the temporal variability of this mollusc’s population coincided with the tendency in variability of the water temperature in the area.The five alien species had spatial aggregation and their occurrence did not exceed 23 % in the boundaries of the distribution sites. An increasing trend for their abundance in the last five - seven years was observed. These years were characterized by temperature rise in the surface layer of coastal waters. Similar patterns have been observed in the interannual variability of the biomass and abundance ratio of aliens to native for all zoobenthic taxonomic groups, i.e. of dominance index of alien species.The low level of the dominance index of the introduced species is indicative of low impact on the diversity of the benthic communities of the Crimea coast, i.e. on the scale of the metacommunity. With the exception of the R. venosa, they exhibited lower biomass and abundance along the Crimean coast shelf as opposed to other areas of the Black Sea shelf. Occasionally, the dominance index for the barnacle Amphibalanus improvisus (Darwin, 1854) could be high, a fact attributed to the low biomass and abundance of other benthic species.

Hydrophysical state of the Gulf of Feodosia in May 2015

Distribution of Sea of Azov water on the Crimean shelf and its penetration into the Gulf of Feodosia result in significant changes in the hydrophysical and hydrochemical structure of the water area. This inflow is also estimated as a major source of anthropogenic pollution in the region. At the same time, the Gulf of Feodosia is one of the least investigated areas of Russian Black Sea coast. The paper focuses on the hydrophysical structure of the Gulf of Feodosia and southeastern part of the Crimean shelf. The results of a field survey in May 2015 made it possible to reveal the presence of Sea of Azov water in the gulf and describe its thermohaline properties, along with the character of distribution. It is shown that contamination of Sea of Azov water in the gulf could mostly be determined by the synoptic dynamic processes in the area rather than by the seasonal variability of discharge in the Kerch Strait. The possible influence of the distribution of Sea of Azov water on the formation of cyclonic gyres in the coastal area of the region is indirectly confirmed by in situ measurements.

Distribution and Composition of Thiotrophic Mats in the Hypoxic Zone of the Black Sea (150-170 m Water Depth, Crimea Margin).

At the Black Sea chemocline, oxygen- and sulfide-rich waters meet and form a niche for thiotrophic pelagic bacteria. Here we investigated an area of the Northwestern Black Sea off Crimea close to the shelf break, where the chemocline reaches the seafloor at around 150–170 m water depth, to assess whether thiotrophic bacteria are favored in this zone. Seafloor video transects were carried out with the submersible JAGO covering 20 km2 on the region between 110 and 200 m depth. Around the chemocline we observed irregular seafloor depressions, covered with whitish mats of large filamentous bacteria. These comprised 25–55% of the seafloor, forming a belt of 3 km width around the chemocline. Cores from the mats obtained with JAGO showed higher accumulations of organic matter under the mats compared to mat-free sediments. The mat-forming bacteria were related to Beggiatoa-like large filamentous sulfur bacteria based on 16S rRNA sequences from the mat, and visual characteristics. The microbial community under the mats was significantly different from the surrounding sediments and enriched with taxa affiliated with polymer degrading, fermenting and sulfate reducing microorganisms. Under the mats, higher organic matter accumulation, as well as higher remineralization and radiotracer-based sulfate reduction rates were measured compared to outside the mat. Mat-covered and mat-free sediments showed similar degradability of the bulk organic matter pool, suggesting that the higher sulfide fluxes and subsequent development of the thiotrophic mats in the patches are consequences of the accumulation of organic matter rather than its qualitative composition. Our observations suggest that the key factors for the distribution of thiotrophic mat-forming communities near to the Crimean shelf break are hypoxic conditions that (i) repress grazers, (ii) enhance the accumulation and degradation of labile organic matter by sulfate-reducers, and (iii) favor thiotrophic filamentous bacteria which are adapted to exploit steep gradients in oxygen and sulfide availability; in addition to a specific seafloor topography which may relate to internal waves at the shelf break.

Statistical Analysis and Numerical Modeling of Hydrodynamical Sea Oscillation Parameters in Subinertial Range on the Crimean Shelf

Statistical Analysis and Numerical Modeling of Hydrodynamical Sea Oscillation Parameters in Subinertial Range on the Crimean Shelf

Statisticheskiy analiz i chislennoe modelirovanie ostsillyatsiy gidrodinamicheskikh parametrov morya v subinertsionnom diapazone na shel'fe Kryma

Statisticheskiy analiz i chislennoe modelirovanie ostsillyatsiy gidrodinamicheskikh parametrov morya v subinertsionnom diapazone na shel'fe Kryma

Mesozoic to recent geological history of southern Crimea and the Eastern Black Sea region

Abstract We provide a synthesis of stratigraphic data to unravel the history of the geological evolution of South Crimea in the Mesozoic and Cenozoic. The South Crimea Orogen consists of three major mega-sequences: (1) the Triassic–Early Jurassic; (2) the Aalenian–Bathonian; and (3) the Callovian–Eocene. The Late Triassic–Early Jurassic deposits formed in the environment of a forearc basin and a remnant basin. The Aalenian–Bathonian deposits formed above subduction extension and a volcanic belt. Three main Callovian–Eocene tectonic units can be identified in South Crimea: (1) the South Crimean Shelf Basin; (2) the Sudak Deepwater Trough; and (3) the Alchak–Kaya Shelf Basin at the northern margin of the Shatsky Ridge. The Oligocene–Quaternary deposits are considered to be syn-orogenic. A description of the anticipated stratigraphic units on the Shatsky Ridge is suggested for the Middle Jurassic, Callovian–Late Jurassic, Neocomian, Aptian–Albian, Late Cretaceous–Paleocene, Eocene and Maykopian. We propose a model for the geological history of the Eastern Black Sea Basin. Graben formed during the Late Barremian–Albian at the location of the future Eastern Black Sea Basin and a phase of volcanism occurred in the Albian. The main phase of rifting and spreading of oceanic crust took place during Cenomanian–Santonian time. Supplementary material: A Google Earth kmz file of the location of the outcrops and sections is available at http://www.geolsoc.org.uk/SUP18850

Effects of fluctuating hypoxia on benthic oxygen consumption in the Black Sea (Crimean shelf)

Abstract. The outer western Crimean shelf of the Black Sea is a natural laboratory to investigate effects of stable oxic versus varying hypoxic conditions on seafloor biogeochemical processes and benthic community structure. Bottom-water oxygen concentrations ranged from normoxic (175 μmol O2 L−1) and hypoxic (< 63 μmol O2 L−1) or even anoxic/sulfidic conditions within a few kilometers' distance. Variations in oxygen concentrations between 160 and 10 μmol L−1 even occurred within hours close to the chemocline at 134 m water depth. Total oxygen uptake, including diffusive as well as fauna-mediated oxygen consumption, decreased from 15 mmol m−2 d−1 on average in the oxic zone, to 7 mmol m−2 d−1 on average in the hypoxic zone, correlating with changes in macrobenthos composition. Benthic diffusive oxygen uptake rates, comprising respiration of microorganisms and small meiofauna, were similar in oxic and hypoxic zones (on average 4.5 mmol m−2 d−1), but declined to 1.3 mmol m−2 d−1 in bottom waters with oxygen concentrations below 20 μmol L−1. Measurements and modeling of porewater profiles indicated that reoxidation of reduced compounds played only a minor role in diffusive oxygen uptake under the different oxygen conditions, leaving the major fraction to aerobic degradation of organic carbon. Remineralization efficiency decreased from nearly 100 % in the oxic zone, to 50 % in the oxic–hypoxic zone, to 10 % in the hypoxic–anoxic zone. Overall, the faunal remineralization rate was more important, but also more influenced by fluctuating oxygen concentrations, than microbial and geochemical oxidation processes.