Zooplankton Structure Research Articles

Structure of Zooplanktocenoses of Water Bodies of Zoogenic Origin of Different Types in a Specially Protected Natural Territory

The features of the structure of zooplankton in beaver ponds and the course of successions in zooplanktocenoses have been studied in the territory of State Natural Reserve “Kologrivsky Les” named after M.G. Sinitsyn. Ponds are divided into groups according to the nature of the watercourse on which they are formed, the height of the floodplain, and the duration of existence. The seasonal succession of zooplankton for all types of ponds begins with the predominance of juvenile stages of Copepoda. In the summer, in newly formed ponds and ponds on rivers with high floodplains, a typical zoogenic transformation of communities is observed occurs with the development of large Cladocera. In long-term ponds on streams and rivers with low floodplains, the dominance of Rotifera and small Cladocera, characteristic of anthropogenic eutrophication, and the highest average values of abundance and biomass, indices of species diversity and evenness were noted.

Composition and structure of under-ice zooplankton of diverse lakes in Kenozersky National Park (Arkhangelsk Region)

Composition and structure of under-ice zooplankton of diverse lakes in Kenozersky National Park (Arkhangelsk Region)

Methylparaben changes the community composition, structure, and assembly processes of free-living bacteria, phytoplankton, and zooplankton

Parabens are common contaminants in river and lake environments. However, few studies have been conducted to determine the effects of parabens on bacteria, phytoplankton, and zooplankton communities in aquatic environments. In this study, the effect of methylparaben (MP) on the diversity and community structure of the aquatic plankton microbiome was investigated by incubating a microcosm with MP at 0.1, 1, 10, and 100 μg/L for 7 days. The results of the Simpson index showed that MP treatment altered the α-diversity of free-living bacteria (FL), phytoplankton, and zooplankton but had no significant effect on the α-diversity of particle-attached bacteria (PA). Further, the relative abundances of the sensitive bacteria Chitinophaga and Vibrionimonas declined after MP addition. Moreover, the relative abundances of Desmodesmus sp. HSJ717 and Scenedesmus armatus, of the phylum Chlorophyta, were significantly lower in the MP treatment group than in the control group. In addition, the relative abundance of Stoeckeria sp. SSMS0806, of the Dinophyta phylum, was higher than that in the control group. MP addition also increased the relative abundance of Arthropoda but decreased the relative abundance of Rotifera and Ciliophora. The β-diversity analysis showed that FL and phytoplankton communities were clustered separately after treatment with different MP concentrations. MP addition changed community assembly mechanisms in the microcosm, including increasing the stochastic processes for FL and the deterministic processes for PA and phytoplankton. Structural equation modeling analysis showed a significant negative relationship between bacteria richness and phytoplankton richness, and a significant positive relationship between phytoplankton (richness and community composition) and zooplankton. Overall, this study emphasizes that MP, at environmental concentrations, can change the diversity and structure of plankton microbial communities, which might have a negative effect on ecological systems.

Effects of Yellow Sea Warm Current on zooplankton community composition and functional groups in winter

The Yellow Sea Warm Current (YSWC) constitutes a significant hydrological feature in the Yellow Sea, particularly prominent during winter, facilitating the transport of warm, saline waters and warm-water species from the open sea to the Bohai and Yellow Seas. The YSWC induces alterations in the community structure and function of zooplankton. However, the effects of the YSWC on the functional trait compositions and functional groups of zooplankton remain unclear. This study aimed to elucidate the influence of the YSWC on the community structure, functional trait composition, and functional groups of zooplankton during winter of 2016. The YSWC significantly impacted the zooplankton assemblage in the central Yellow Sea (CYSA), resulting in notable distinctions from the Shandong coastal assemblage (SCA) and Jiangsu coastal assemblage (JCA). Compared to the SCA and JCA (comprising 45 and 34 taxa, with abundances of 119.4 ± 114.6 ind·m-3 and 82.8 ± 62.1 ind·m-3, respectively), the CYSA exhibited higher species richness and abundance (with 51 taxa and 144.4 ± 103.4 ind·m-3, respectively). This study documented a total of 11 warm-water species, showing a decreasing trend in both species richness and abundance from south to north. The CYSA was characterized by the predominance of medium‒sized, current‒feeding, omnivorous‒herbivorous broadcast spawners, whereas the SCA and the JCA were predominantly dominated by giant‒sized, ambush‒feeding carnivores. The Qingdao-Shidao anticyclonic eddy in the southern of Shandong Province led to a significant increase in the abundance of zooplankton, potentially impacting Yellow Sea fishery resource. This research contributed to a deeper understanding of how YSWC influence the zooplankton community and offered fresh insights into the effects of YSWC on zooplankton function traits and functional groups.

Silver nanoparticles alter planktonic community structure and promote ecosystem respiration in freshwater mesocosms

The widespread use of silver nanoparticles (AgNPs) has resulted in their release into the aquatic environment, which threatens the health of aquatic ecosystems. Although the ecotoxicological effects of AgNPs have been widely reported at individual and population levels, the impact of long-term exposure to AgNPs on community structure and ecosystem function in aquatic ecosystems remains poorly understood. Herein, the present study investigated the effects of long-term exposure (28 d) to environmentally relevant concentrations (1 μg/L and 10 μg/L) of AgNPs on the community structure and function of freshwater ecosystems by artificially constructed 28 mesocosms freshwater ecosystem in experimental greenhouses, using plastic water tanks and food web manipulation. The results showed that long-term exposure to AgNPs significantly altered the community structure of zooplankton, phytoplankton, and bacterioplankton in the aquatic ecosystem. Exposure to 10 μg/L AgNPs significantly reduced the zooplankton density (70.3%, p < 0.05) and increased the phytoplankton biomass and bacterial richness and diversity via a “top-down effect.” With regards to ecosystem function, AgNPs exposure significantly increased the respiration in freshwater ecosystems but did not have a significant effect on decomposition. The partial least squares path modeling (PLS-PM) further revealed that AgNPs may have a negative impact on ecosystem functions by reducing zooplankton community density and thus increasing phytoplankton biomass. This study is the first to show that long-term exposure to environmentally relevant concentrations of AgNPs leads to alterations in plankton community structure and promotes respiration in freshwater ecosystems. It emphasizes the need for assessing the environmental risk of long-term exposure to AgNPs at the ecosystem level.

At the base of deep-sea food webs: Assemblage and trophic structure of suprabenthos and zooplankton in submarine canyons

Submarine canyons act as hotspots of biodiversity, hosting vulnerable marine ecosystems, and playing a fundamental role in bridging coastal zones with deeper areas. Here, we investigated the suprabenthic and Deep Scattering Layer (DSL) zooplankton fauna, that play a key role in deep-sea food webs, as main resources for both mobile and sessile megafauna, in two submarine canyons (Squillace and Amendolara) of the Ionian Sea (Central Mediterranean Sea). Our results highlighted different taxonomic and functional diversity between the two adjacent canyons: (i) biomass and abundance of suprabenthos followed an opposite trend in the two canyons, increasing both with depth in Amendolara (higher abundance and biomass in the lower part of the canyon), and decreasing with depth in Squillace (greater in the head of the canyon); (ii) DSL zooplankton abundance and biomass followed a spatial distribution, decreasing with increasing distance from the coast for both canyons (i.e. lower offshore than at the head of the canyon). Food-web structure investigated by means of stable isotope analysis of δ13C and δ15N showed a more diverse trophic niche for suprabenthos than for zooplankton. Furthermore, possible feeding modes of species with unknown feeding behaviour have been proposed. The results of the current article highlight the different ecological processes occurring within each canyon. Understanding the spatial variations of communities inhabiting submarine canyons, especially those at the base of deep-sea food webs which can act as driver of megafaunal communities (both sessile and mobile-commercial species), is essential to focalise future conservation efforts.

Characteristics of plankton community structure and applicability of biomanipulation in midstream of the Jialing River—the biggest tributary of the Yangtze River

Plankton, as an important part of the food chain in the river ecosystem, is sensitive to changes in the environment. To investigate the influence of plankton community structure on the aquatic ecosystem and further verify the applicability of biomanipulation, the midstream of the Jialing River was selected as the study area. A total of 149 species (varieties) from 7 phyla, 18 orders, 34 families, and 72 genera were identified for phytoplankton. A total of 48 species were found for zooplankton. The mean density of phytoplankton was 2.09 × 106 cells/L, and the mean density of zooplankton was 27.1 ind./L. Moreover, the mean values of the Shannon–Wiener diversity index (H′), Pielou homogeneity index (J′), and Margalef abundance index (D) for phytoplankton were 3.17, 0.76, and 4.47, respectively. The mean values of the Shannon–Wiener diversity index (H′), Pielou homogeneity index (J′), and Margalef abundance index (D) for zooplankton were 2.64, 0.92, and 5.07, respectively. Based on the diversity indices, the water quality was evaluated as oligo pollution to β-medium pollution level. Redundancy analysis (RDA) was used to explore the relationship between dominant plankton species and environmental factors. The RDA results show that the main environmental factors affecting the community structure of phytoplankton and zooplankton were water temperature (WT), electrical conductivity (EC), pH, total phosphorus (TP), and transparency (Secchi depth; SD). There were 17 functional groups in phytoplankton, which are X1, S1, Y, Y2, and so on. In zooplankton, there were six functional groups, which are Pmsl, Prsu, Pfif, Pmip, Lrsf and Lmic. Many articles have demonstrated the feasibility of using biological manipulation to control algae. The number of piscivorous fish in the midstream of the Jialing River had increased, and phytoplankton density in this survey was significantly decreased. The results show that traditional biomanipulation can be applied to this region, which can provide better scientific support for the future management of the aquatic environment in the Jialing River basin.

Zooplankton and macrozoobenthos of small reservoirs of the State Natural Reserve «Kologrivsky Les» named after M.G. Sinitsyn

The article presents the results of studies of zooplankton and macrozoobenthos of small reservoirs on the territory of the State Natural Reserve «Kologrivsky Les» named after M.G. Sinitsyn. The hydrochemical and hydrophysical parameters of small reservoirs are given. In summer, the highest biomass and abundance of zooplankton were observed for long-existing beaver ponds on streams. In autumn, among the studied small reservoirs, the highest biomass and abundance of zooplankton are characteristic of oxbow lakes. The highest biomass of benthos was noted in oxbow lakes, and its abundance was found in beaver ponds. An analysis of the ecological groups of zooplankton and benthos by type of nutrition was carried out. In autumn, the composition of zooplankton was marked by a predominance of vertical feeders and primary filter feeders in beaver ponds, primary filter feeders and predatory forms in ditches, primary filter feeders and vertical feeders in oxbow lakes, and secondary filter feeders, scrapers, detritivores and stand feeders in hollows in wetlands. The benthos of beaver ponds and oxbow lakes contains all six ecological groups of benthos based on feeding type. There are no collectors, obligate filter feeders or active predators in the ditches. Only soil ingesters were noted in the hollows. A number of indices have been calculated to characterize the structure of zooplankton.

Inter-annual changes in zooplankton in the Volga delta kultuk zone in summer (low-water period)

The paper presents the results of our studies of inter-annual changes in the structure of summer zooplankton in the kultuk zone of the Volga delta depending on hydrological and meteorological conditions. The study shows the main trends in zooplankton differences in a series of low-water years. It was found that in low-water years in the kultuk zone with low runoff, short floods and weak watering of floodplain territories, zooplankton was characterized by low species richness, reduced average individual mass of crustaceans and the number of Rotifera, but a high proportion of the number of juvenile Copepoda. In the year when the water level decreased before the flood during the period of temperature increase, and then a rapid rise with the inflow of cold waters and the removal of fish larvae, zooplankton was characterized by a minimum species richness and quantitative values of Rotifera, but increased biomass of Cladocera and the Shannon index. In every low-water year, with a stable and relatively high water level before the flood, fish spawning in the kultuk zone, biomass of zooplankton reduced due to Cladocera, and the number of species in the sample. In every mid-water year, the flood had the largest runoff and prolonged, increased flooding of the floodplain, zooplankton was characterized by the maximum total and specific species richness, abundance of Rotifera, total biomass on account of Cladocera, and the individual mass of crustaceans, the Shannon index, but the minimum proportion of juvenile Copepoda.

Variation pattern of crustacean zooplankton in a bigheaded carps-dominated reservoir

The relationship between crustacean zooplankton and (planktivorous) fish has not been well clarified in bigheaded-carps-dominated reservoirs, for most of the past studies to explore that kind of knowledge above are often obtained from the studies in temperate lakes and/or shallow lakes. The limitation of these studies is that crustacean zooplankton lack of either large grazers such as the bigheaded carps or the vertical migrating space for zooplankton to avoid predation by planktivorous fish. Reservoirs are more and more important drinking water source for human consumption, so a better environmental management of reservoirs will rely on a better understanding on the relationship between zooplankton and fish in bigheaded carp dominated reservoirs. To help reach that goal, we investigated the structure and variation of zooplankton and studied the relationship between zooplankton and fish in Tangpu reservoir, Zhejiang province, China. Our results showed that the species of crustacean zooplankton were richer. A total of 59 species of crustacean zooplankton were detected, including 33 species of copepods and 26 species of cladoceran, and dominated by larger species. The density of crustacean zooplankton varied between 15.5–68.5 ind./L with an annual average density of 24.9 ± 14.4 ind./L, it is higher in this planktivorous carps dominated deep reservoir than in many carp-less-dominated reservoirs or in shallow lakes. We also found that zooplankton and fish had a differential vertical distribution, i.e., zooplankton occurred 5 m–10 m but fish occurred 0.5 m–10 m in many months of the year. This could well explain why zooplankton were not reduced and not dominated by small species in bigheaded carps dominated reservoir, so we concluded that in planktivorous carp dominated deep reservoir ecosystems, zooplankton might not compete directly with planktivorous carps for phytoplankton, instead by distributing or migrating to deeper water column, they may survive and thrive on the phytoplankton in deeper column and the detritus resulted from the feces of planktivorous fish, thus might be able to coordinately improve water quality with planktivorous fish.

Spatio-temporal variations in the mesozooplankton assemblages off Clarence Island, Magellan Strait, Chile

The seasonality in the light regime from subpolar regions impinges on limitations in the zooplankton dynamics. However, knowledge about seasonal variations in the mesozooplankton assemblages is limited in the southern tip of South America and around the Magellan Strait. Here, we studied the seasonal variation (summer vs. winter) and the spatial distribution (dozens of kilometers) of the mesozooplankton on the occidental shore of Clarence Island, Magellan Strait, Chilean Patagonia. A total of 69 taxonomic groups were identified in the samples, varying from 65 in summer (early March 2020) to 50 in winter (June 2020). Copepods numerically dominated the plankton, particularly Drepanopus forcipatus and Clausocalanus brevipes, although chaetognaths were also abundant in winter. The similarity in the composition was higher for samples collected in summer, whereas in winter there was larger variability in the zooplankton structure. At spatial scale, a large sound at the eastern coast of the island, Dyneley sound showed different composition of copepods compared to other channels both in summer and winter. Seasonal variation was five times larger than the spatial variation in the similarity of the mesozooplankton composition. Finally, higher richness and lower evenness were detected in austral summer, while the opposite was noticed in winter, with differences in alpha-diversity indices between seasons but not among locations. Understanding the drivers of seasonal variability in the zooplankton composition of this extreme ecosystem is essential for predictions of the impacts of salmon farming and climate change in southern Patagonia.

Structure and functioning of plankton communities оf the Rybinsky Reservoir under the conditions of climate change

Based on the data of complex environmental studies, which have been regularly carried out at six standard stations of the Rybinsk Reservoir since the middle of the 20th century, the orientation of changes in the elements of the reservoir ecosystem associated with global climatic events has been analyzed. During the period of climate warming, which began in 1977 and continues into the 21st century, the air temperature in the warm season increased by 0.9°C, the water temperature by 1.4°C, the average annual inflow by 7.5%, and the duration of the ice-free period by two weeks. An increase in electrical conductivity and color of water, a decrease in transparency were noted. With significant interannual variations in biological characteristics, in the XXI century, the number of bacterioplankton increased by 1.7 times, and bacterial production doubled. Chlorophyll content increased by 1.4 times and values 15 µg/L reflecting the eutrophic state of the reservoir began to be observed more often. In the biomass of phytoplankton, the proportion of small cell forms increased. The total abundance of phytoplankton increased due to the development of cyanobacteria, which form a long summer maximum in the seasonal dynamics of the community. The increase in water mineralization promoted the progressive spread of alien brackish-water algae. Biomass of zooplankton increased by 2.5 times. An increase in the abundance of crustaceans (Cladocerans, by 1.6 times; Copepods, by 1.9 times) caused a change in the structure of zooplankton and the formation of a strong late summer peak of biomass. The intensification of hydrobiological processes was clearly manifested after the abnormally hot 2010, the conditions of which not only stimulated the development of plankton communities, but also but also caused the formation of oxygen deficiency in the bottom layers. Warming has significantly transformed the ecosystem of the Rybinsk Reservoir, intensified eutrophication processes and worsened water quality. Changes in hydrometeorological characteristics have gone beyond the mild scenario of climate warming.

Zooplankton of Volga River reservoirs: structure, abundance and dynamics

The taxonomic structure and spatial distribution of the late-summer zooplankton in the Volga River from the upper Ivankovo reservoir to Volga Delta near Astrakhan during the period 2020–2021 were studied. Zooplankton biomass in the most of the Volga reservoirs was dominated by cladoceran Daphnia galeata and copepod Mesocyclops leuckarti (up to 45–84%). However different dominant species were observed in the Volgograd reservoir. Cladocerans Chydorus sphaericus and Bosmina cf. longispina formed there up to 43% of the total zooplankton biomass. Rotifers and Ponto-Caspian copepod Heteroscope caspian are dominated in the Volga River below the dam of the Volzhskaya hydropower plant (56% and 18% of the total zooplankton biomass respectively). Among the invasive species, most abundant are East Asian copepod Thermocyclops taihokuensis (up to 230 thsd. ind./m3 and locally 90% of the total biomass) and North American copepod Acanthocyclops americanus (up to 86 thsd. ind./m3 and 35% of the total biomass). The maximum abundance of the zooplankton (0.8–1.6 g/m3) was observed in the Upper Volga reservoirs while the minimum abundance (0.1–0.2 g/m3) – in the Lower Volga. The maximum abundance of zooplankton (0.8–3.3 g/m3) was recorded in the mouth areas of the reservoir tributaries, while the minimum abundance (0.1–1.4 g/m3) – in the pelagic zone of the reservoirs. A decrease in the zooplankton community biomass from Upper to Lower Volga was observed in all biotopes. A negative correlation between the community abundance and daily water inflow into the reservoirs and a positive correlation between the community abundance and water temperature were revealed. Long-term variations in zooplankton biomass and their relationship with water body trophic state, thermal and oxygen regimes were discussed.

Distribution pattern of zooplankton assemblages in the eutrophic Hangzhou Bay, China

To reveal the distribution pattern of the zooplankton community in the typical eutrophic Hangzhou Bay in the northern East China Sea, we investigated the zooplankton community. The study was conducted in 2019 during the summer. A total of 57 species of zooplankton belonging to 6 phyla and 52 genera were identified. During the sampling period, the abundance of zooplankton in Hangzhou Bay was 26.7–497.2 ind/m3, with an average of 179.58 ind/m3. The abundance of zooplankton increased from west to east, and the abundance of zooplankton in most waters of the offshore area was higher than that in the coastal waters of Hangzhou Bay. The top dominant species, Tortanus vermiculus, was distributed in Hangzhou Bay, whereas Paracalanus aculeatus was mainly distributed in the mouth of Hangzhou Bay, and Acartia (Odontacartia) spinicauda and Centropages dorsispinatus were distributed between Zhoushan Island and Hangzhou Bay. The spatial distribution of the ShannonWiener index and evenness index of the zooplankton in Hangzhou Bay and its adjacent waters showed that the community structure of zooplankton was stable in the estuary of Hangzhou Bay and eastern part of the Zhoushan Islands. In addition to salinity and water temperature, eutrophication-related water quality parameters were also crucial to zooplankton species number, Margalef species richness and the abundance of the dominant species Tortanus vermiculus. The zooplankton dominant species and community composition were affected or restructured by eutrophication-related factors, especially for phosphate (PO4), nitrate nitrogen (NO3), dissolved inorganic nitrogen (DIN) and the eutrophic index (EI).

Evaluation of Floating Net Cage (FNC) in Penerusan Bay, Bali Based on Their Plankton Community

Floating net cages (FNC) are one of the common methods to cultivate fish, in Indonesia, affecting the physicochemical and biological parameters. This study evaluated the water quality conditions in two different FNCs based on the physiochemical and biological parameters. There were four locations to be sampled: two FNC (snappers (KP) and groupers (KR)) and two control sites that were placed outside of FNC (Non-KP and Non-KR). Several water physicochemical parameters were measured, and the plankton community was identified. The observation showed the total suspended solid (TSS) (2.57–2.64 mg/L), pH (8.26–8.3), biochemical oxygen demand (BOD) (0.75–1.52 mg/L) and orthophosphate (P) (0.008–0.044 mg/L). Furthermore, in certain sites, some parameters did not meet the Indonesian Government Standard No. 22 in 2021, including nitrate concentration (KP, Non-KP, and KR), dissolved oxygen (KR and Non-KR), and P (KR and Non-KR). Meanwhile, the phytoand zooplankton diversity index (H') was 3.61-4.69 and 1.27-2.54, which confirmed that the level of diversity of phytoand zooplankton was high and moderate status. Four sites showed low phyto- and zooplankton dominance levels and were distributed evenly (E ≥ 0.81). This study concludes that based on water quality parameters, KP and KR did not meet the Indonesian Government Regulation in some parameters, but they had a stable ecosystem based on the phytoand zooplankton structure community.

Annual, seasonal and spatial differences in the growth rate of Baltic cod larvae and early juveniles in relation to zooplankton biomass fluctuations in 2006-2014

It is an acknowledged theory that a faster growth rate, determined by various environmental drivers, may boost the survival of larval and juvenile fish. In this study we examined the differences in the growth rate of larval and juvenile cod (age 2 – 136 d; SL: 4.1 – 39.2 mm) between the years 2006 and 2014, sub-areas of the Baltic Sea (Bornholm Basin, BB; Słupsk Furrow, SF; Gdańsk Basin, GB), and seasons (spring and summer). The average growth rate for all specimens was 0.25 mm/d, with significantly lower values between 2012 and 2014 than between 2006 and 2011. A reduction in zooplankton biomass, especially the large zooplankton fraction, was observed after the 2006–2008 period, which was related to the prevailing temperature conditions in the surface layers. The reduction in zooplankton biomass was accompanied by changes in the structure of zooplankton: less T. longicornis, C. hamatus, and Pseudocalanus spp., and more Acartia spp. The results suggest that the inter-annual differences observed in zooplankton biomass and structure are likely responsible for the observed reduction in the growth rate of cod larvae between 2012 and 2014 compared to the years between 2006 and 2011. The growth rate reduction could be one of the reasons for the decline in the recruitment of eastern Baltic cod between the years 2013 and 2015, after the high recruitment years of the period 2011-2012.

The Structure of the Zooplankton Communities in Sukhoe More Bay, Southeastern White Sea

This paper presents the results of our investigation of the zooplankton communities from Sukhoe More Bay, located in the southeastern part of Dvina Bay of the White Sea, in July−August, 2018. The species composition, quantitative characteristics and spatial distribution of zooplankton were studied. The zooplankton communities are composed of 34 species of hydrobionts. Copepods were the dominant group in the entire study area. The zooplankton communities were characterized by high quantitative indicators. Juvenile stages of copepods were a significant contribution to the formation of the total number of zoocenoses. During high water level, the abundance of zooplankton was 37 000 ind./m3, biomass, 0.6 g/m3 (wet weight). During low water level these parameters were 210 000 ind./m3 and 1.7 g/m3 (wet weight), respectively. The structure, abundance and spatial distribution of zooplankton in the bay are determined by the morphometric features of the reservoir (shallow water), the influence of a complex of environmental factors (temperature and salinity), as well as tidal phenomena.

COI metabarcoding better reveals the seasonal variations in the zooplankton community in the western Pacific Warm Pool

The environment of the western Pacific Warm Pool is considered to be pronouncedly uniform and stable compared with other tropical ocean environments. Knowledge of the seasonal variations in the zooplankton community structure in this region with a high plankton species diversity remains limited. In this study, three methods, including identification using microscopy, ZooScan digital imaging, and DNA metabarcoding, were used to analyze zooplankton samples collected in three seasons, and to detect the seasonal variations in the community. The results show that the metabarcoding method based on the mitochondrial cytochrome c oxidase I (COI) marker detected up to 2.3 times more zooplankton taxa than identification using microscopy. In contrast, the small subunit ribosomal RNA (18S) marker revealed fewer taxa than microscopy. Significantly positive correlations were observed between the sequence counts and three types of quantitative data, including the biovolume, dry weight biomass, and carbon biomass in all three seasons. The COI sequence counts exhibited a stronger correlation with the dry weight biomass than the biovolume and carbon biomass. Although both the microscopic and molecular methods detected seasonal variability of the zooplankton community, the COI metabarcoding method was more sensitive in detecting seasonal variations in the community, which was positively correlated with the taxonomic resolution of the different methods. In summary, the results of this study suggest that COI metabarcoding is an ideal tool for monitoring the seasonal variations in the diversity and community structure of zooplankton in the tropical open ocean regions with a stable environment all year round.

Structure and functional characteristics of zooplankton and food supply for nekton in the western Bering Sea

Structure and functional characteristics of zooplankton and feeding of the most abundant nekton species (pollock, herring and salmons) are analyzed using the data of ecosystem survey in the western Bering Sea in 2020 and compared with the structural indices for 2015−2019. The main patterns of composition and distribution of zooplankton and production of organic matter by zooplankton are determined. High values and turnover rate of production are noted for the non-predatory zooplankton (mainly copepods and euphausiids) in the eastern Anadyr Bay, the area at Cape Navarin, the shelf of Koryak coast, and the continental slope of Olyutorsky Bay. High production of predatory zooplankton (mainly hyperiids) is found on the slope of Karaginsky Bay, presumably because of these species transport from the southern areas with later stage of the seasonal succession. In autumn 2020, walleye pollock and pacific herring consumed from 15 to 55 % of the copepod, euphausiid and hyperiid production. This level of consumption did not affect their food supply because of very high turnover rate of these taxonomic groups of plankton. In the deep-water areas, salmons did not use more than 3 % of their food resource. Thus, the survey data indicate a good food supply for the most abundant nekton species in the western Bering Sea in the fall season.

Inter-annual changes of zooplankton in the kultuk zone of the Volga River delta in the spring period

The studies conducted in spring have shown the main trends in changes in the structure of zooplankton in the kultuk zone of the Volga River delta in years that differ in hydrological and temperature regimes. It was revealed that in low-water years (2012, 2014), with a decrease in the volume of runoff, water level, and a reduction in the duration of floods, zooplankton was characterized by relatively low species richness, high biomass of Copepoda and Cladocera. At the same time, the highest rates of specific species richness, biomass and abundance of all zooplankton groups were observed at spring of a low-water year (2014), which was characterized by a runoff volume during the flood of 101 km3, a high pre-flood water levels, the absence of a sharp and significant dilution, as well as an early warm spring and gradual warming of the waters. In the year (2012), characterized by a volume of runoff during the flood period of 114 km3, a decrease in water level and a sharp increase in temperature before the flood, and then its rapid rise with dilution by cold waters, zooplankton was distinguished by the minimum species richness, a low number of ecological groups and low abundance of Cladocera, but a high proportion of juvenile copepods (fine filter feeders) and in terms of biomass of active euryphagous predators and euryphagous collectors. In a medium-water year (2013) with a large volume of runoff during the flood of 140 km3, with early and high and long floods, zooplankton was distinguished by a high total number of species encountered, but a minimum abundance and biomass, which is associated with the “dilution effect” and an increase in the areas of flooded rich in higher aquatic vegetation.