Coastal Shallow Areas Research Articles

Characteristics of Black Sea dispersion of freshened and polluted transitional waters from the Dnipro-Bug estuary after destruction of the Kakhovka Reservoir dam

This study examines the characteristics of distribution of large volumes of freshened and polluted transitional waters from the Dnipro-Bug estuary across the northwestern part of the Black Sea (NWBS) that was caused by destruction of the Kakhovka HPP dam in June 2023. From June 6, 2023 to June 12, 2023 14.4 km³ of water were discharged from the Kakhovka Reservoir into the Dnipro-Bug estuary and subsequently into the sea. This volume constitutes 27% of the total annual average natural runoff of the Dnipro River (53.5 km³). During the initial days following the dam destruction water flow through the breach amounted to 40-50 thousand m³/s. The water carried a variety of pollutants into the sea that were present in the water of the Kakhovka Reservoir, in its bottom sediments, and also washed off from the flooded territories of the lower Dnipro area (more than 2000 hectares).
 The analysis of the distribution characteristics was conducted using satellite images of the sea surface color and chlorophyll a concentrations, as well as the results of hydrodynamic modeling with application of the 3-D variant of a numerical hydrodynamic model Delft3D-Flow Flexible Mesh. It was established that the plume of freshened and polluted water initially spread across the Dnipro-Bug estuarine region of the NWBS and then moved towards the sea coast of Odesa reaching it on June 9-10, 2023. Subsequently, the plume began to spread along the western sea coast and reached the Tuzlivski Limans area on June 14, 2023. After this the narrow plume of dispersed water along the sea coast began to dilute when moving towards the open sea in the form of "tongues" that had formed over the sea bottom elevations. The modeling of dispersion of a conservative neutral buoyancy admixture serving as a marker of pollution spread with the transitional waters from the Dnipro-Bug estuary showed that reduction in pollution levels took place solely due to hydrodynamic dilution (up to 60% in Odesa District of the NWBS and up to 30% in the Danube-Dniester interfluve area of the river water pollution level observed in Kherson).
 The identified characteristics were determined based on the water circulation process that formed in the Dnipro-Bug estuarine area under the influence of significant sea level gradients resulting from the inflow of large volumes of freshened transitional waters through the estuary and the Kinburn Strait during the first days, and then followed by the density currents formed at the hydrofront between the transformed river water and surrounding sea. The influence of wind conditions manifested itself in the form of spread across the NWBS of the plume of dispersed transitional water from the Dnipro-Bug estuary and the hydrofront's position and configuration. Though wind-induced currents were not dominant, they still influenced the water dynamics and distribution of concentrations of admixtures, for instance, chlorophyll a, within the freshened plume that was outlined by the hydrofront. They also promoted penetration along the coastal shallow area of transformed river water towards Odesa.

Impact of the brine discharge on the bottom ecosystem of the Sambia Peninsula coast (South-Eastern Baltic Sea)

The first underground gas storage facility in Russia, built in rock salt deposits, was developed in the coastal zone of the Kaliningrad Region. Since 2018, seawater for erosion of rock salt is taken from the Baltic Sea, and after appropriate treatment, brine is discharged back to the sea. The aim of the work was to assess the impact of the brine discharge on the bottom ecosystem of the coastal shallow area. A comprehensive study was carried out on the possible path of salt brine propagation, including a bathymetric survey, CTD sounding of the water, sampling of bottom sediments and zoobenthos, determination of heavy metals in sediments. The main pathways for the spread of brine along the bottom were determined, and the additional supply of salt to the coastal zone naturally led to local changes in the existing bottom ecosystem of the coastal shallow water, including changed in the structure of zoobenthos.

Биогеохимические характеристики мелководных струйных метановых газовыделений в прибрежных районах Крыма в сравнении с глубоководными сипами Чёрного моря

Струйные метановые газовыделения (сипы) — широко распространённый феномен в Мировом океане, в том числе в бассейне Чёрного моря. Актуальность исследований метановых сипов обусловлена их важной ролью в качестве источника метана как парникового и средообразующего газа для водной толщи и атмосферы. В работе представлен сравнительный анализ данных собственных биогеохимических исследований мелководных сипов Крымского полуострова, охватывающих последние десять лет, и материалов, посвящённых глубоководным газовыделениям Чёрного моря. В этот период были проведены поисковые гидроакустические исследования, выявлен компонентный состав пузырькового газа, измерен изотопный состав углерода метана, а также молекулярно-биологическими методами определена структура микробного сообщества бактериальных матов, покрывающих площадки газовыделений, и выполнена оценка газовых потоков от отдельных сипов. В течение многолетнего мониторинга обнаружено и описано 14 отдельных газовыделяющих площадок в прибрежных районах Крыма, которые располагались от мыса Тарханкут на западе полуострова до бухты Двуякорная на юго-востоке. Превалирующая часть прибрежных сипов Крыма имела биогенную природу и сезонный характер газовыделений. К глубинному газу термокаталитического генезиса отнесены сипы в бухте Ласпи. Наблюдался значительный разброс величин изотопного состава углерода метана δ13C-CH4 пузырькового газа прибрежных мелководных районов (−94…−34 ‰), что указывает на разные условия его генерации и созревания в донных отложениях. Так же, как и глубоководным сипам, прибрежным струйным газовыделениям сопутствовали бактериальные маты разной структуры с различными доминирующими видами. Показано, что для формирования устойчивой бактериальной биомассы, основу которой составляли, как правило, сульфид- и сероокисляющие бактерии, необходим флюидный поток восстановленных растворённых газов, тогда как точечная разгрузка пузырькового газа не обеспечивает достаточных градиентов концентрации и может механически разрушать структуру образующегося сообщества. Различными методами сделаны оценки размерных спектров пузырьков и потоков от отдельных струй. Диапазон значений газового потока варьировал от 1,8 л·сут−1 (бухта Мартынова) до 40 л·сут−1 (бухта Ласпи). Проанализированы средообразующие эффекты, связанные с выделением пузырькового газа в прибрежных районах: влияние сипов на кислородный режим в донных осадках и в толще воды́ над точками газовыделений; вертикальное перемешивание вод за счёт газлифтового эффекта; флюидная разгрузка на площадках струйных газовыделений.

Diversity and space-time dynamics of fish assemblages in a coastal lagoon, western Atlantic

The knowledge of the temporal and spatial dynamics in the composition of fish fauna makes it possible to identify patterns of occupation of ecosystems, providing a basis for evaluation and preservation of the local biodiversity. Monthly samplings were carried out at seven sites in a coastal lagoon, using a casting net, dip net and beach seine. A total of 4,110 individuals were collected, distributed in 23 families and 49 taxa of fish, with a predominance of Mugilliza, M.curema, Atherinellabrasiliensis, Micropogoniasfurnieri and Eucinostomusargenteus, corresponding to more than 80% total weight of all individuals caught. Regarding seasonality, greater abundances were recorded in fall, influenced by the high abundance of A.brasiliensis in this period. In addition to fall, this species was also abundant in summer. However, this pattern of dominance was different for the families Mugilidae and Gerreidae, with higher abundances in spring and summer, respectively. The highest abundances were found in the southern section of the lagoon, which are related to the high abundance of A.brasiliensis, M.liza and M.curema. In relation to the indices of average taxonomic distinctness and variation in the taxonomic distinctness, no significant differences were detected between the seasons of the year. Thus, the patterns of distribution and occurrence of fish in the lagoon were consistent with the patterns observed in Brazilian coastal lagoons and estuaries, as well as to the coastal shallow areas of the southeastern and southern regions.

Differences in planktonic ciliate spatial distribution in spring and autumn in the southern Yellow Sea

Seasonal variation of marine plankton spatial distribution is important in understanding the biological processes in the ocean. In this study, we studied spatial distribution of planktonic ciliate abundance and biomass in the central deep area (station depth greater than 60 m) and the coastal shallow area (station depth less than 60 m) of the southern Yellow Sea (32°–36.5°N, 121°–125°E) in spring (April) and autumn (October–November) of 2006. Our results showed that both ciliate abundance and biomass in the surface waters were higher in spring ((1 490±2 336) ind./L; (4.11±7.81) μg/L) than in autumn ((972±823) ind./L; (1.11±1.18) μg/L, calculated by carbon). Ciliate abundance and biomass in the surface waters of the coastal shallow area were similar in spring and autumn. However, in the central deep area, those values were much higher in spring ((1 878±2 893) ind./L; (5.99±10.10) μg/L) than in autumn ((738±373) ind./L; (0.74±0.76) μg/L). High values of ciliate abundance and biomass occurred in the central deep area in spring and in the coastal shallow area in autumn. Mixotrophic ciliate Laboea strobila was abundant in the central deep area in spring, when a phytoplankton bloom occurred. However, in autumn, L. strobila was abundant in the coastal shallow area. Boreal tintinnid Ptychocyli obtusa was found in spring. Both L. strobila and P. obtusa were concentrated in the surface waters when their abundance was more than 1 000 ind./L. Peaks of these species were in the subsurface waters when their abundance was less than 400 ind./L. This study showed that both high abundance and biomass of ciliates occurred in different areas in southern Yellow Sea seasonally.

Reproductive biology of the stingrays, Myliobatis goodei and Myliobatis ridens (Chondrichthyes: Myliobatidae), in southern Brazil.

This study, carried out between spring 2012 and winter 2014, characterized the sexual development and reproductive cycle of Myliobatis goodei and Myliobatis ridens in the extreme south of Brazil to support future management and conservation plans. Ninety-five specimens of M. goodei (24 males and 71 females) and 175 M. ridens (24 males and 151 females) were sampled. Female M. goodei attained disc-width-at-50% maturity (WD50 ) at 683 mm. Uterine fecundity was four to five embryos. The largest male recorded, a mature individual, had a disc width of 650 mm. In M. ridens, WD50 was 662 mm. Uterine fecundity varied from one to eight embryos. The largest male on record was a maturing 590 mm WD individual. The hepato-somatic index was higher in autumn in females of M. goodei, and in the summer in M. ridens. The gonado-somatic index and the largest vitellogenic follicle diameter were higher in spring in both species. Pregnant females of both species were recorded during spring, although for M. ridens, these females also occurred in summer. Embryos had WD of 61-218 and 40-236 mm for M. goodei and M. ridens, respectively. The incidence of pregnant females in southern Brazil in spring-summer coincides with the small-scale beach artisanal fisheries season peak, when M. goodei and M. ridens suffer fishing mortality, while using the coastal shallow areas in the warmer periods (spring-summer) to give birth.

Effects of the Yellow Sea Warm Current on the winter temperature distribution in a numerical model

The temperature distribution and circulation patterns in the Yellow Sea (YS) are examined by using a wave‐tide‐circulation coupled numerical model. This model sufficiently reproduces the variation of the warm tongue structure of the Yellow Sea Warm Current (YSWC) from the double branches flowing along the YS Trough and the western 60 m isobath in January to the single stream along the western temperature front in March. This is observed in both the long‐term monthly climatology and the satellite‐based sea surface temperature images in recent years. Examining the local heat balance in the numerical model during the entire cooling period, it is found that the YSWC has a very important influence on the YS warm tongue structure. Compared with the surface cooling, the influence of the advection is small in the coastal shallow area but large in the deep warm tongue area (up to 50% of the magnitude of heat flux). Although bathymetry is the essential factor which causes the temperature front, the YSWC is the key factor which positions, shapes, and maintains the warm tongue structure. This helps to affirm the existence of the YSWC, at least as a monthly mean flow. However, more high‐resolution current observations in deeper layers west of Cheju Island and the western fork of the YS Trough are needed to confirm the existence of the YSWC and its characteristic timescale in the real YS.

Morphology and ecology of bivalve molluscs from Admiralty Bay, King George Island, Antarctica

Bivalve species were collected from shallow coastal areas of King George Island (Martel, Mackellar and Ezcurra Inlets of Admiralty Bay). Twenty one species belonging to 16 genera and 12 families were identified and their morphometric and morphological shell characteristics were described. Three main characteristics were found to be common to the majority of the bivalve species sampled: 1) thin fragile shells; 2) small size of individuals (76%), and 3) the lack of true cardinal teeth (72%). Comparison of calcium data from a tropical estuary and a subantarctic coastal shallow area suggested that the calcium in the sea water was not a constraint to shell building but shell thickness could be an adaptation to the efficiency of energy partitioning. Small individual size and the lack of true cardinal teeth are discussed in relation to a high deposition environment and widespread mud bottoms.

The Reproductive Ground of the Common Jelly-fish, Aurelia aurita, in Urazoko Bay, Fukui Prefecture

In spite of the world-wide distribution and common occurrence of Aurelia aurita, the details of its reproductive ground have little been given. A series of work to make the reproductive ground of this medusa clear was carried out in Urazoko Bay, a small inlet, situated in the eastern part of Wakasa Bay on the Japan Sea coast, in the period from November 1970 through April 1973.The occurrence patterns of early liberated ephyrae, metephyrae and young medusae at their maximum season were respectively checked by examining the samples collected by means of vertical hauls of a plankton-net (45cm in mouth diameter and 0.33mm in mesh szie) at each of the stations settled in the bay (Fig. 1). The settlements of planulae and early polyps were examined by monthly observations throughout the breeding season from late November 1970 through July 1971, using the collectors made of five upper shells of Pecten albicans and hung at the depth of 0, 2, 5 and 10 meters (Fig. 3) from the rafts which were set at each of the stations in the bay (Fig. 2). The results obtained are summarized as follows:1) Early ephyrae were mainly distributed in the inner part of the inlet or the coastal shallow areas of the waters (Figs. 4 and 5).2) Planulae and early polyps were found on the collectors in the inner part of the bay from January to June, most abundantly between the surface and 5 meter layer (Fig. 6).3) According to these results and the distribution patterns of marine plants in the bay, it will be concluded that the reproductive ground of this medusa in the bay is the areas that are covered with marine plants such as Sargassum and Zostera (Figs. 8 and 9).