Zooplankton constitute a key trophic link between primary producers and higher trophic levels in marine food webs, making them important indicators of environmental and climatic change. However, in many marine systems, long-term data are still limited, and major interannual fluctuations in zooplankton biomass and composition remain poorly understood. The article presents data assessing the impact of climate and warming in the Black Sea region on the interannual dynamics of macro- and mesozooplankton biomass in the outer shelf of Sevastopol Bay from 2002 to 2021. Over this period, the biomass of organic matter accumulated by gelatinous species has decreased, while that of mesozooplankton has increased by 15-20 %. Winter warming, which minimises convective mixing and nutrient transport into the zone of active photosynthesis, may have negatively affected the populations of the jellyfish Aurelia aurita, the dinoflagellate Noctiluca scintillans, and the chaetognath Parasagitta setosa. The increase in sea surface temperature (SST) during January-March appears to have a positive effect on microphages such as the copepod Paracalanus parvus and the appendicularian Oikopleura dioica. Early increases in SST during April-May, along with a synchronous improvement in the biogenic regime of the upper pelagic zone, suggest an increase in the biomass of large copepods (Calanus euxinus, Paracalanus elongatus, Acartia clausi and Centropages ponticus), regardless of their temperature tolerances. The extreme increase in SST during July-August was accompanied by the early development of ctenophores Beroe ovata and Mnemiopsis leidyi, as well as small crustaceans like Penilia avirostris and Oithona davisae. Overall, outer shelf macro- and mesozooplankton communities have remained relatively stable in species composition and total biomass of organic carbon. This study highlights the complex response of Black Sea macro- and mesozooplankton communities to regional warming, with species-specific seasonal sensitivities to changing environmental conditions.

The study of the seasonal and interannual dynamics of populations of ctenophore invaders Mnemiopsis leidyi A. Agassiz, 1875 and Beroe ovata Bruguière, 1789 on the shelf of Sevastopol Bay in 2013–2021 established that gradual warming accompanied by a change in the hydrologic regime of the Black Sea has led to a significant transformation of the phenology, structure, and intensity of development of their populations in recent years. The early seasonal emergence of the warm-water ctenophore B. ovata in the pelagic zone expanded the time span of its presence in plankton from two or three months in the first years of introduction (1999–2000) to eight months in 2019–2020. At the same time, the maximum size of individuals decreased from 50 (2000–2001) to 35 mm (2019–2020). Significant decrease in the abundance of M. leidyi and weakening of its trophic pressure on the forage zooplankton in the coastal areas of the Black Sea were the consequence of the longer and active predation, as well as structural changes in the population of B. ovata expressed in the reduction of body weight. Increased warming of the upper mixed layer of the sea in the summer months resulted in a decrease in the size of M. leidyi, the intensity of its reproduction, and the proportion of reproductive individuals in the population.

The abundance, biomass, distribution and feeding patterns of the ctenophoreMnemiopsisleidyiA. Agassiz 1865 were studied in the deep-water Black Sea in October 2019. The biomass of the ctenophore in the open areas of the sea was 100–200 g m–2, the abundance was 16–38 ind. m–2. With the dominance of large individuals (≥30 mm) in the population, the activity of their reproduction remained extremely weak. The specific daily ration varied from ~4% to 13% of body carbon in adults and juveniles, respectively, and exceeded the minimum food requirements of the ctenophore. The daily consumption of three species of copepods (Acartiaspp.,Calanus euxinus,Oithona davisae) byM. leidyireached 4.5–11% of their biomass, while that of appendiculariansOikopleura(Vexillaria)dioica– 1.6%. The predatory pressure ofM. leidyion the entire prey zooplankton attained 2–4% of the biomass of organisms per day.

The field data on the abundance, biomass, age structure, and lipid reserves of the copepod Сalanus euxinus population in deep pelagial and Crimean shelf regions of the Black Sea in November 2017 were analyzed. The abundance and biomass of this species in deep areas (10.2 ± 0.5 × 103 ind./m2 and 7.3 ± 0.5 g/m2, respectively) were similar to the average annual values for seasons with moderate development of planktivorous jellyfish populations. The average abundance and biomass of the copepods were similar to analogous 2016 values when the jellyfish abundance was twice as low. However, in 2017, the denser aggregations of C. euxinus (12.8 ± 1.0 × 103 ind./m2 and 9.8 ± 0.5 g/m2) were found in the central parts of cyclonic circulations, while in 2016, they were recorded more frequently at the peripheries of cyclonic gyres. A structure of the C. euxinus population also changed. In November 2017, the percentage of copepodites I–IV, females and males, increased, whereas the proportion of copepodites V reduced. These changes likely resulted from a later sampling period in 2017, when the C. euxinus population was ready for active reproduction. Sufficient amounts of lipids in copepodites V, decreased oil sac volumes in females, and increased abundance of males in anticyclonic regions are indicative of more favorable trophic conditions for this part of the C. euxinus population and its higher maturity.

On the basis of the results of cruises and long-term monitoring at the outer shelf of Sevastopol Bay, the interannual dynamics of the state of the population of the alien ctenophore Beroe ovata in the Black Sea for 2000–2021 was analyzed. It was established that, in recent years, the ctenophore was found in plankton earlier than usual, the period of its active pelagic life increased to 7–8 months, and the body length in juveniles decreased from 40 to 20–25 mm. Three seasonal periods are distinguished, which, owing to their temperature conditions, were especially significant for the species: January–February, April–May, and July–August. The high temperature of seawater in July–August usually contributes to an increase in abundance and biomass of the ctenophore, as well as a decrease in the average size. The period of active life of B. ovata depends on the warming of the sea in May, as well as on the biomass of Pleurobrachia pileus. The early appearance of B. ovata leads to faster suppression of Mnemiopsis leidyi, preventing it from reaching a high abundance and biomass in summer.

Климатические изменения в гидрологическом режиме Чёрного моря, отмечаемые с 1990-х гг., отразились на состоянии эпипелагических комплексов морских организмов, прежде всего на сезонной изменчивости их биологических циклов. Это оказало существенное влияние на фенологию нереста природных популяций рыб, видовое разнообразие и пространственное распределение ихтиопланктона, а также на устоявшиеся трофические взаимоотношения в планктонном сообществе. В конечном итоге характер взаимодействия между различными звеньями трофической цепи в эпипелагических комплексах, их сезонная и межгодовая изменчивость влияют на эффективность нереста рыб, прежде всего массовых промысловых видов, и в значительной степени определяют успех пополнения их будущих поколений. С целью изучения видового состава, численности и пространственного распределения ихтиопланктона в октябре 2016 г. (89-й рейс НИС «Профессор Водяницкий», 30 сентября — 19 октября) были проведены исследования в шельфовых и открытых водах Чёрного моря у Крымского полуострова, проанализированы не только икра и личинки рыб, но и биомасса мезо- и макропланктона. Пробы ихтио- и макропланктона отбирали сетью Богорова — Расса (площадь входного отверстия — 0,5 м²; ячея — 300 мкм) методом тотальных вертикальных ловов от дна до поверхности моря в области шельфа и от нижней границы кислородной зоны до поверхности моря в глубоководной части. Ихтиопланктон фиксировали 4%-ным раствором формалина и анализировали позже под микроскопом, определяя таксономический состав организмов и по возможности — наличие и состав пищи в кишечниках личинок рыб. Проанализированы данные о видовом составе и пространственном распределении ихтио-, мезо- и макропланктона, а также о питании личинок рыб Чёрного моря у Крымского полуострова в октябре 2016 г. Период съёмки соответствовал начальной фазе осеннего гидрологического сезона. Ихтиопланктон был представлен икрой и личинками 9 видов тепловодных и 6 видов умеренноводных рыб. Средняя численность икры рыб составляла 2,92, а личинок — 3,56 экз.·м−2. Низкая доля (30 %) мёртвой икры тепловодной хамсы Engraulis encrasicolus, а также наличие её разноразмерных личинок в море свидетельствовали о продолжении результативного нереста. Биомасса зоопланктона возрастала в направлении от шельфа к глубоководным районам. Мелкоразмерные фракции планктонных организмов преобладали на шельфе, обеспечивая здесь лучшие кормовые условия для выживания личинок рыб. Несмотря на значительную биомассу желетелых-планктофагов в октябре 2016 г., их влияние на ихтиопланктонные комплексы Чёрного моря, по-видимому, оставалось несущественным.

Ctenophores are invertebrate, gelatinous predators that perform complex movements due to their numerous ciliary comb plates. We investigated the behavioral responses of the ctenophore Mnemiopsis leidyi A. Agassiz, 1865 to red, green, and blue lights of different powers and fluxes emitted by LEDs or lasers. White LEDs were used to mimic natural sunlight. When laser light was directed to the aboral organ, the animals tended to leave the illumination zone. The blue-light reaction was six times faster than the red-light reaction. The behavioral strategy of the animals changed significantly when their freedom of maneuvering was restricted. Typical locomotions were ranked according to the laser beam avoidance time from the beginning of exposure to going into darkness. The minimum reaction time was required for turning and moving the ctenophore, while moving along the laser beam and turning around required more time. Typical patterns of behavior of M. leidyi in the light flux were established using cluster analysis. Three preferential behavioral strategies were identified for avoiding laser irradiation: 1) body rotation; 2) shifting sideways; and 3) movement with deviation from the beam. The elementary ability of ctenophores to make decisions in situative conditions has been demonstrated.

The state of the population of the invader Mnemiopsis leidyi (A. Agassiz, 1865), the concentration and composition of mesozooplankton, and the trophic relationships and predatory impact of M. leidyi on the prey populations in the western and eastern sectors of the open Black Sea were studied in July–August 2017. The average biomass of M. leidyi at the peak of its seasonal development in these areas was 92–258 g m–2. The food spectrum of M. leidyi was dominated by copepods Acartia spp. and Calanus euxinus (Hulsemann, 1984). Spatial differences in the quantitative development of M. leidyi and zooplankton, the intensity of food consumption, and prey grazing were found. A high rate of food consumption (specific daily ration of 45.50 ± 8.31% C of body) and intensive grazing of M. leidyi (up to ~50% of the biomass of Acartia spp. per day) in the western offshore part of the sea should be accompanied by a decrease in mesoplankton biomass. On the contrary, predation by M. leidyi did not significantly affect the plankton community in the east, where M. leidyi consumed about 6% of the biomass of Acartia spp.

The seasonal and spatial dynamics of the key trophic characteristics were studied (food spectrum, feeding rate, and predatory impact on mesozooplankton) for populations of the jellyfish Aurelia aurita (Linnaeus, 1758) and ctenophore Mnemiopsis leidyi A. Agassiz, 1865. The investigation was carried out during four cruises of the RV “Professor Vodyanitsky” in the shelf areas of Crimean Peninsula in January to October 2016. The area was divided into inner (depth of < 50 m) and outer (51–150 m) shelves. To study the food spectrum and feeding rate of gelatinous predators, the composition of food items in the gastric cavity was analyzed under a binocular microscope. Daily ration (R, mg C·ind.−1·day−1) was calculated by the formula: R = Bz × DT−1 × 24, where Bz is zooplankton biomass in the predator gastric cavity (mg), and DT is zooplankton digestion time (h). Predatory impact of gelatinous zooplankton was estimated by the values of daily ration and mesozooplankton biomass. Zooplankton was sampled with a Juday plankton net with mouth diameter of 38 cm and mesh size of 140 µm. Vertical net hauls were performed: at the inner shelf stations, from the sea surface down to the bottom; at the outer shelf stations, down to the boundary of the hydrogen sulfide zone (δt = 16.2 conventional units according to a Sea-Bird probe). In the samples fixed with 4 % formalin solution, zooplankton abundance, its taxonomic composition, and size–age structure were quantified by standard method. In the food spectrum of the jellyfish, seasonal differences were revealed: predominance of Bivalvia veligers in winter and spring and wide species composition of Crustacea and other groups of prey in summer. The feeding rates of the studied species were similar: specific daily rations in winter, spring, and autumn did not exceed tenth of a percent of the carbon content in the body. Both species fed at a maximum rate in summer on the outer shelf: the specific rations reached 12.9 and 5.1 % C of the body for the jellyfish and ctenophore, respectively. A. aurita and M. leidyi populations consumed 0.2 to 5 % of the fodder zooplankton biomass per day; it did not result in a drastic reduction in zooplankton abundance and provided favorable feeding conditions for small planktivorous pelagic fish.

Species composition, abundance, and distribution of gelatinous macroplankton in coastal and deep-sea areas of the Black Sea in November 2017 are discussed. Despite the fact that species composition of gelatinous macroplankton (medusa Aurelia aurita, ctenophores Mnemiopsis leidyi, Pleurobrachia pileus, and Beroe ovata) in 2017 did not differ from that in 2016, structural changes occured. In autumn 2017 A. aurita and B. ovata biomass was higher than in 2016 whereas the inverse difference was observed in their abundance values. Namely, A. aurita biomass was on average 514 g m(-2) and 634 g m(-2) in the outer shelf and deep-sea areas, respectively. Both parameters of M. leidyi and P. pileus declined in 2017 compared to the previous year. In addition, the share of large-sized individuals increased in 2017, while that of small-sized animals decreased, in comparison with 2016. The number of small individuals increased in P. pileus and decreased in M. leidyi, although their biomass before the seasonal appearance of B. ovata in plankton was close to that in 2016. The unprecedented increase in the medusae biomass in November 2017 could not be explained only by the competition with planktivorous ctenophores and may indicate alternative drivers controlling population dynamics of A. aurita in the Black Sea. A negative correlation was depicted between the Danube discharge in February-March and the rate of somatic growth of A. aurita.

A copepod Calanus euxinus Hulsemann, 1991 is one of the most abundant mesozooplankton species constituting up to 60–80 % of planktonic crustacean biomass in the deeper Black Sea and being the main food component for small pelagic fish. Data on abundance, biomass, age structure, and lipid reserves of C. euxinus are required to estimate the state of its population in the open pelagial and on the shelf of the Black Sea. The data were obtained during the 89th cruise of the RV “Professor Vodyanitsky” (30.09.2016–09.10.2016) in the northwestern, central, and northeastern sea (62 stations). Zooplankton was sampled with a Bogorov–Rass net (mouth area of 0.5 m²; mesh size of 300 μm) by vertical net hauls from the seabed to the surface on the shelf and from the lower border of the oxygen zone to the surface in the deep-sea area. The samples were fixed with 4 % formaldehyde; in the laboratory, the abundance and biomass of all copepodite stages of C. euxinus were determined. Wax ester content in the bodies of late copepodite stages and adult specimens was estimated based on the specific oil sac volume (% of the body volume). The relationship between the quantitative species distribution and the habitat depth and macroscale hydrological circulation was revealed. In the deep-sea area, the mean abundance and biomass of C. euxinus amounted to (8.3 ± 0.8) thousand ind.·m−2 and (7.1 ± 0.7) g·m−2, respectively. On the outer shelf, the abundance and biomass of this species decreased twofold – down to (4.2 ± 1.4) thousand ind.·m−2 and (3.3 ± 1.2) g·m−2, respectively. In the deep-sea area, copepodites V, females, and males constituted 91 % of the total abundance and 96 % of the total biomass of the population. On the outer shelf, the ratio of these developmental stages reduced to 67 % and 86 % of the total abundance and biomass, respectively. In the deeper pelagial, the specific oil sac volumes in copepodites V, females, and males [(17.1 ± 0.6), (11.2 ± 0.8), and (11.9 ± 0.5) %, respectively] were twice as high as in the same developmental stages from the outer shelf [(8.1 ± 0.8), (4.7 ± 0.8), and (6.0 ± 0.5) %, respectively] indicating a relation between lipid accumulation in this species and hypoxic conditions of the biotope. Relatively high values of the abundance, biomass, and wax ester content in C. euxinus indicate that the population returned to its previous state – the one observed prior to expansion of alien ctenophores in the late 1980s and recent climatic changes resulting in a warming of the Black Sea basin.

Копепода Calanus euxinus Hulsemann, 1991 — один из наиболее массовых видов мезозоопланктона Чёрного моря, образующий в глубоководных районах 60–80 % биомассы планктонных ракообразных и составляющий здесь основу рациона мелких пелагических рыб. Данные о численности, биомассе, возрастной структуре и жировых запасах C. euxinus необходимы для оценки состояния его популяции в открытой пелагиали и шельфовой зоне Чёрного моря. С этой целью в 89-м рейсе НИС «Профессор Водяницкий» (30 сентября — 9 октября 2016 г.) проведены исследования в северо-западных, центральных и северо-восточных районах моря (62 станции). Пробы мезозоопланктона отбирали сетью Богорова — Расса (площадь входного отверстия — 0,5 м²; ячея — 300 мкм) методом тотальных вертикальных ловов от дна до поверхности моря в области мелководного шельфа и от нижней границы кислородной зоны до поверхности моря в глубоководной части. Пробы фиксировали 4%-ным раствором формалина, численность и биомассу всех копеподитных стадий C. euxinus определяли в лабораторных условиях. Содержание восков в теле старших копеподитов и половозрелых особей C. euxinus оценивали по удельному объёму жирового мешка (относительно объёма тела). Выявлена зависимость количественного распределения вида от глубины биотопа и макромасштабной циркуляции водных масс в море. В глубоководной части моря средняя численность C. euxinus составляла (8,3 ± 0,8) тыс. экз.·м−2, биомасса — (7,1 ± 0,7) г·м−2. На внешнем шельфе численность и биомасса вида снижались вдвое — до (4,2 ± 1,4) тыс. экз.·м−2 и (3,3 ± 1,2) г·м−2 соответственно. В глубоководных районах копеподиты V стадии вместе с самками и самцами составляли 91 % численности и 96 % биомассы популяции. На внешнем шельфе доля этих возрастных стадий сокращалась до 67 % численности и 86 % биомассы. В районах глубоководной пелагиали удельный объём жирового мешка у V копеподитов, самок и самцов [(17,1 ± 0,6), (11,2 ± 0,8) и (11,9 ± 0,5) % соответственно] был вдвое выше, чем у этих же возрастных стадий на внешнем шельфе [(8,1 ± 0,8), (4,7 ± 0,8) и (6,0 ± 0,5) % соответственно], что указывает на зависимость между накоплением липидных резервов у данного вида и гипоксическими условиями в биотопе. Сравнительно высокие величи́ны численности, биомассы и содержания восков у C. euxinus свидетельствуют о том, что его популяция практически вернулась к прежнему состоянию (наблюдавшемуся до экспансии гребневиков-вселенцев в конце 1980-х гг. и последних климатических изменений, которые привели к потеплению в бассейне Чёрного моря).

The study examines changes in the abundance (density) and distribution of European Sprattus sprattus (Linnaeus, 1758) eggs and larvae, as well as the phenology of its spawning depending on hydrologic factors and abundance of gelatinous macroplankton in the Black Sea in November 2016–2017. An increase in temperature of the sea surface layer observed since the beginning of the century and the enhanced heat content of the cold intermediate layer contributed to the preservation of warm-water mesozooplankton at the end of the fall hydrologic season, which provided favorable trophic conditions for all planktophages. The biomass of scyphomedusa Aurelia aurita was the third largest in the gelatinous macroplankton in 2016 and the largest in 2017 for the long-term annual research in fall months. Gelatinous macroplankton, however, did not have a significant impact on the survival of sprat in the early stages of its development. The average number of sprat eggs and larvae in November 2016 (184 and 11 ind/m2, respectively) and November 2017 (268 and 21 ind/m2, respectively) exceeded their maximum values recorded in the 1950s. The larvae did not differ in length composition in the beginning of the spawning season in 2016 and 2017.

Experiments on the feeding of the Moon jellyfish Aurelia aurita have shown that digestion time of zooplankton typically varies between 2.2 and 5.1 h depending on the body weight of the predator, diet composition, amount of food, and seawater temperature. The daily ration of a Moon jellyfish with a wet body mass of 1 g reached 0.025-2.845 mg zooplankton.ind-1.day-1 corresponding to a carbon-specific food uptake of 0.2-9.1% C day-1 with a mean value around 0.5% C day-1. Such mesozooplankton consumption rates are consistent with the ration values (around 0.9% C day-1) calculated from the feeding rate experiments of jellyfish at natural food concentrations. However, in both cases the amount of mesozooplankton was insufficient to compensate for the minimum food requirements, calculated from oxygen consumption (6.7 ± 0.6% C day-1) of the jellyfish. On average, the metabolic expenses of A. aurita were about one order of magnitude greater than its ration supplied by mesozooplankton, indicating the important role of visually overlooked food components in the jellyfish diet. Résumé : Écologie trophique et estimation de l’impact lié à la prédation par la méduse commune Aurelia aurita (Linnaeus, 1758) sur le zooplancton de la Mer Noire. Des expériences de nutrition menées sur la méduse Aurelia aurita ont montré que la durée de digestion du zooplancton varie entre 2,2 et 5,1 h, selon la masse du prédateur, la nature et la quantité de la nourriture, et la température de l’eau de mer. La ration journalière d’une méduse de masse 1 g est de 0,025-2,845 mg zooplancton.ind-1.jour-1, ce qui correspond à une absorption de carbone de 0,2-9,1% C jour-1, avec une valeur moyenne de 0,5% C jour-1. Ces taux de consommation du mésozooplancton sont en adéquation avec ceux (environ 0,9% C jour-1) calculés à partir d’expériences de nutrition de méduses menées à des concentrations naturelles de nourriture. Néanmoins, dans ces deux cas, la quantité de mésozooplancton est insuffisante pour compenser les besoins nutritionnels calculés à partir de la consommation d’oxygène (6,7 ± 0,6 % C jour-1) de la méduse. En moyenne, les dépenses métaboliques d’A. aurita sont supérieures d’environ un ordre de grandeur à la ration fournie par le mésozooplancton, ce qui suggère que d’autres sources de nourriture, négligées car moins visibles, pourraient jouer un rôle important dans le régime alimentaire de cette méduse.

Aim. The aim of the study is to find out what external factors may be the driving force behind the growth and population dynamics of two ecologically similar species of gelatinous macroplankton (scyphomedusa Aurelia aurita and ctenophore Pleurobrachia pileus), which play an important role in the functioning of the pelagic ecosystem of the Black Sea.Material and Methods. The state of zooplankton populations was estimated by data obtained in 2000‐2014 in the outer shelf of Sevastopol Bay, where monthly quantitative samples of meso‐ and macroplankton were taken 2 miles of the coast (depth 50‐70 m). Weather and hydrology related changes were assessed using open databases.Results. It was been established that size‐specific growth rate of these species depends on weather and hydrological conditions in the winter‐spring months and varies from 0.85 to 1.02% day‐1 and from 0.27 to 0.47% day‐1 for A. aurita and P. pileus, respectively.Conclusions. External factors unequally affect the growth of these species. Sub‐ latitudinal transit of warm air masses, accompanied by increased river flow and seawater circulation, activates the growth of the ctenophore, while sub‐meridional propagation of cold and dry air increases the growth rate of the jellyfish. In both cases, somatic growth is influenced by trophic relations, differing depending on the weather in February‐May. The changes in growth of ctenophore occur in parallel with synchronous variations in biomass of crustacea, while that in jellyfish may relate to an abundance of microplankton and its mesoplanktonic consumers.

The existence of two alternative points of view on the long-term dynamics of gelatinous macroplankton populations in the World Ocean determines the need for long-term monitoring as a basis for assessing their condition. The accumulation of long-term series of data on the development of gelatinous predators in the Black Sea makes it possible to assess their role in the functioning of the pelagic ecosystem in connection with climatic variability. The abundance, biomass, the size structure of the gelatinous predators (jellyfish Aurelia aurita; ctenophores Mnemiopsis leidyi and Pleurobrachia pileus) and the feeding intensity of the two species (A. aurita and M. leidyi) were investigated in the early summer period (June) of 2016 at 45 stations covering the shelf zone off the coast of Crimea from Cape Tarkhankut to Kerch, as well as at 3 stations of the deepwater area with the coordinates 44°23′N–45°5′N and 32°22′E–36°36′E. The material was collected from the bottom (10–100 m) up to the surface at the inshore stations and from the depth with σt = 16.2 to the surface – in deepwater by vertical trawls with modified Bogorov – Russ net with an inlet diameter of 80 cm, a mesh of 300 μm. The nutritional spectrum and its quantitative composition were determined under a microscope in the laboratory immediately after the catch of animals, followed by the calculation of diurnal rations and the rate of ingestion of zooplankton. Spatial differences in abundance of gelatinous species were observed: the maximum biomass of A. aurita, prevailing in all regions, was observed in the Yevpatoriya – Sevastopol region and was due to large accumulations of middle-sized specimens of new generation. Ctenophora P. pileus dominated in the abundance in the halistatic zone. The food spectrum of jellyfish was very diverse and included various stages of Copepoda, Tunicata, Cladocera, and also the meroplankton – the Bivalvia and Gastropoda veligers. The halistatic zone with great depths was characterized by the widest species composition of planktonic Copepoda in A. aurita food. The average daily rations of jellyfish varied from one region to another, being the lowest in the Karkinitsky Bay [(0.113 ± 0.10) mg C−1·day−1, or (1.6 ± 2.18) % of C body] with most of the food being algae C. granii. The most intensive feeding was in the halistatic zone [(56.2 ± 23.7) % of C body] with a predominance of Calanus euxinus and Pseudocalanus elongatus in the diet. In no region A. aurita can compensate the respiration requirements by the consumption of mesozooplankton. The highest impact on zooplankton was provided by jellyfish population in the Karkinitsky Bay and in the Yevpatoriya – Sevastopol region, although along all the shelf its impact was very low and did not lead to a dramatic reduction in the zooplankton community abundance.

The gelatinous macroplankton community of the Black Sea renews annually and functionates differently depending on the complicated system of trophic relations and interannual fluctuations of biotic and abiotic factors. Its monitoring is necessary for the evaluation of the current state and possible vectors of evolution of the whole pelagic ecosystem. For this purpose the data on the composition and distribution of gelatinous organisms were collected on the 89th cruise of the RV “Professor Vodyanitsky” (September – October of 2016) at 62 stations located in coastal areas and in the open sea to the south and southwest of Crimea. Samples were taken with the Bogorov – Rass net (inlet area of 0.5 m², mesh of 300 µm) using vertical net hauls from the bottom to the sea surface in the shallow shelf and from the lower boundary of the oxygen zone [according to the dissolved oxygen sensor CTD SBE plus (Sea Bird)] to the sea surface – in deepwater areas. Aurelia aurita and 3 ctenophore species (Mnemiopsis leidyi, Pleurobrachia pileus, and Beroe ovata) were present together in the 90 % of the samples (on 56 stations). In spite of some increase in average biomass of every species in deep sea areas, and, particularly, of A. aurita up to 260 g per m², there was no difference between the data of 2016 and 2010 (p > 0.05). The abundance of A. aurita increased by about one order of magnitude (p < 0.001); the abundance of P. pileus increased 2–5 times (p < 0.001); of B. ovata – 3–15 times (p < 0.01). M. leidyi abundance increased only at the outer Black Sea shelf; in other regions it could have been restricted by B. ovata predation. A. aurita linear specific growth rate in 2016 was one of the lowest for the last 15 years. Slow somatic growth of the jellyfish indicates unfavorable conditions for this species in 2016. However, the jellyfish biomass was higher than that of previous years because of the huge abundance of the spring generation. The weakening competition with planktivorous ctenophores may lead to even greater increase in the ecological valence of A. aurita among other gelatinous predators in the nearest future.

Abundances, biomasses, size structures, and reproduction rates of the comb jellies Mnemiopsis leidyi and Beroe ovata were studied in the shelf area of the Black Sea near Sevastopol in 2013–2014. Longterm data on the population development were analyzed. The peculiar feature of M. leidyi development in recent years is a shift of its development to an earlier time of the season and a significant decrease in its reproduction rate: in the summer months in 2014, the average reproduction rate of adult ctenophores (30–70 mm) constituted only 20% of that in 2004. Such shift was related to the increase in temperature in the upper homogeneous layer, which, in turn, resulted in a decrease in its feeding rate.

— The quantitative development of Mnemiopsis leidyi , the species structure of mesoplankton, and the food spectrum of ctenophores were studied in the shelf zone off the Crimean coast of the Black Sea during the summer seasons of 2013 and 2014. The feeding rate of the M. leidyi population and its predation pressure on the entire zooplankton community and certain species populations have been estimated from data on the diet composition, digestion time, and abundance of ctenophores. The volume of water cleared by M. leidyi varies by more than an order of magnitude depending on the systematic affiliation of the organisms consumed: it is maximum in the case of preying on Cladocera and Bivalvia veligers (up to 12 L ind. –1 h –1 ) and significantly lower for Copepoda (0.4–2.0 L ind. –1 h –1 ). The relationship between the value of the specific daily ration and carbon content in a M. leidyi body in the summer months of 2013 and 2014 is described by a parabolic equation with an exponent of –0.346 to –0.852. In 2014, the highest predation pressure, compared to other groups, was exerted on Copepoda and veligers of Bivalvia (on average 2.9 ± 1.5 and 2.2 ± 0.7% of biomass per day). The mean daily rate of predation on zooplankton in the Black Sea coastal zone was lower in 2014 (1.54 ± 0.58%) than in 2013 (3.94 ± 1.2% of zooplankton biomass) due to the low abundance of ctenophores. A comparative analysis of long-term data on the trophic role of the ctenophore in the plankton community has shown that the food spectrum, as well as the rate of predation on certain groups, varies from year to year. The low rate of predation on forage zooplankton by the M. leidyi population in recent years (2–5% of biomass per day) does not influence the interannual zooplankton dynamics in Black Sea coastal waters.