Zooplankton Structure Research Articles

Zooplankton community structure of a tropical lake in a Northcentral State, Nigeria

One of the biological components that play a vital role in the ecological integrity of an aquatic ecosystem is zooplankton. These organisms are good indicators of stressors, especially anthropogenic stressors in their environment. Thus, there is a need to study the diversity in a diversified freshwater lake (Dangana Lake) in order to provide baseline information and knowledge on the status of the lake for proper and adequate water preservation and conservation. In addition to the zooplankton structure determination, the study also examined the physicochemical parameters of the Lake. Three sampling sites were identified with distinct characteristics where water and zooplankton samples were collected for physicochemical analyses and biotic identification using standard protocols. Sampling was conducted for a duration of eight months. The monitored physicochemical parameters, i.e., temperature, dissolved oxygen (DO), biochemical oxygen demand (BOD5) and pH revealed no significant difference (p>0.05) among sampling sites. However, significance (p<0.05) amongst sampling sites was recorded in electrical conductivity, nitrate and phosphate. Seasonally, there was a significant difference (p<0.05) among sampling months in all the monitored parameters. A total of ten species of zooplankton were recorded with four species each of rotifera and copepoda and two species of cladocera. The order of abundance of zooplankton population was rotifera (56.39%), copepoda (29.18%) and cladocera (14.42%). Zooplankton population was significantly (p<0.05) higher during the dry season than in the rainy season. The Canonical correspondence analysis (CCA) revealed a strong correlation between the zooplankton and physicochemical parameters. Ipso-facto, the lake exhibited spatiotemporal changes in zooplankton composition and physicochemical parameters during the sampling period.

Struktur Komunitas Zooplankton dan Fitoplankton di Isi Lambung Ikan Tongkol Komo (Euthynnus affinis)

Zooplankton and phytoplankton have an ecological function as primary producers in the food chain, so they are often used as a scale for measuring water fertility. The aim of the study was to determine the community structure of zooplankton and phytoplankton in terms of the level of diversity, level of uniformity, and level of dominance in the gastric contents of the Komo Tuna (Euthynnus affinis) caught by fishermen in Lamongan Waters. Sampling of the Komo Tuna fish was carried out from the catches of fishermen in Lamongan Waters. The experimental method was through direct observation of the types of zooplankton and phytoplankton in the gastric contents of the Komo Tuna fish. Analysis of zooplankton and phytoplankton community structure data in the stomach contents of the Tuna Tuna using the diversity index, uniformity index, and dominance index approaches. The results showed that the community structure of zooplankton and phytoplankton that had been identified in the gastric contents of the Tuna Tuna was in accordance with life in Lamongan waters indicated by the diversity index value belonging to the medium and low categories, the uniformity index value belonging to the high category, and the dominance index value belonging to the unstable and stable category.

Biochemical Composition of Zooplankton of Khour Al-Zubair Port, Southern Iraq

The study of the biochemical composition of zooplankton, which constitutes an important part of the food chain, is an accurate criterion for the nutritional importance of these organisms, as they constitute the basic food for fish in their various stages of growth and other aquatic organisms of economic value. The present study aims to describe the significance of biochemical composition of marine zooplankton from Khour Al-Zubair. This study investigates the biochemical structure of zooplankton by studying their contents of proteins, lipids, ash, moisture and carbohydrates in the Iraqi marine waters (Khour Al-Zubair Port) during the period from August to December 2016. This has been accompanied by studying the water temperature and salinity. The results showed that the protein content of the zooplankton were 19.23 – 22.31 %, ash amounted to 3.86 – 4.45 %, while the lipids were 6.27 – 7.18 %, moisture were 65.82 –70.12 % and the carbohydrates 0.25 – 0.47 % wet weight

Precision of mesoplankton sampling: A case study based on three net series in the South Atlantic and in the Black Sea

Mesoplankton is a key element of pelagic communities representing the largest biome on the planet. Many concepts in marine and freshwater biology are based on quantitative estimates of mesoplankton abundance, whereas precision of mesoplankton sampling remains underexplored and may depend on various factors. We analyzed ten contiguous daytime epipelagic samples in the Black Sea and 13 nighttime mesopelagic samples in the South Atlantic. We used a relative error as a measure of the sampling precision and ran a set of Generalized Linear Mixed Models (GLMMs) to estimate effects of six possible factors: abundance, size, diel migration, movement speed, taxonomic group, and net type. Abundance of taxa was the most powerful factor affecting sampling precision (positive effect) followed by the net type (BR provided better precision than Judey net) and taxonomic group. Conversely, size, movement speed, and diel migrations did not significantly influence sampling precision in all sample sets. We conclude that abundance and biomass of dominant species may be estimated with a satisfactory accuracy (relative error <20% of assessed values), which suggests that recent conceptions based on total mesoplankton abundance and biomass (contributed mainly by dominant taxa) are not greatly biased. Quantitative zooplankton structure and biodiversity assessed on the basis of non-transformed matrices are likely more relevant than those based on the root-transformed or presence/absence data.

The Composition, Structure, and Biomass of Zooplankton in the Chukchi Sea in August and September 2019

The Composition, Structure, and Biomass of Zooplankton in the Chukchi Sea in August and September 2019

Vertical Structure of Zooplankton in Stratified Lakes of Belarus with Varying Degrees of Trophy

Vertical Structure of Zooplankton in Stratified Lakes of Belarus with Varying Degrees of Trophy

Environmental flows stimulate estuarine plankton communities by altered salinity structure and enhanced nutrient recycling

Sustainable management of estuaries depends on understanding the synergistic effects of nutrients and hydrological factors on estuarine food webs. We examined how phytoplankton, zooplankton and selected fish larval counts (Acanthopagrus butcheri, black bream) vary in relation to groundwater inputs and environmental flow releases (EFRs) in a small, highly flow-regulated estuary (Werribee, Victoria, Australia). We found that groundwater-derived nutrients and an EFR were associated with the community structure of phytoplankton and zooplankton and abundance of fish larvae. Elevated phytoplankton concentration was associated with increased flagellate abundance (genus Euglena), followed by increased abundance of diatoms (Cyclotella sp). The latter increase was primarily associated with groundwater-derived nitrate entering the estuary. Cyclotella sp. abundance collapsed following an EFR and the subsequent increase in ammonium (NH4+) concentrations in the estuary. In addition, the strong halocline and increased bottom water NH4+ concentrations resulting from the EFR appeared to stimulate population growth of flagellate taxa and calanoid copepods. The abundance of calanoid copepodites and nauplii, which are the preferred food for larval A. butcheri, greatly increased due to the EFR, and was associated with an increase in larval A. butcheri abundance at this time. This effect of the EFR on the cascading trophic interactions in the estuarine food web has rarely been shown. Our study reinforces the ecological linkages between freshwater inputs, including groundwater and riverine discharge, and estuarine biotic community structure and function. Importantly, this study underscores the potential food web consequences of freshwater flow manipulation into estuaries and provides evidence for using environmental flows to enhance and/or manage the recruitment of estuarine fishes.

Considering zooplankton as a black box in determining PAH concentrations could result in misjudging their bioaccumulation

Zooplankton play an important role in energy transfer in the marine food web and form the dietary basis for the size of important fish stocks and the maintenance of their resources. Although zooplankton include numerous taxa with significantly different ecological characteristics and the interspecific differences in optimum body size and taxonomic specificity in fish feeding on zooplankton are remarkable, they are always considered as a whole (like a “black box”) in current studies about the transport of persistent organic pollutants through the food chain. This approach might result in misjudgment of their bioaccumulation. In this study, the distribution properties of each taxa of zooplankton community were discerned using data from two cruise surveys conducted in the northern South China Sea. Twelve groups of zooplankton were identified, all of which had distinct ecological and functional characteristics. The carbon-based community structure of zooplankton could explain their variability with respect to polycyclic aromatic hydrocarbons (PAHs). Smaller-sized zooplankton (smaller calanoids and cyclopoids) were more likely to accumulate low molecular weight PAHs (LMW-PAHs), while larger-sized zooplankton (larger calanoids) were more likely to accumulate high molecular weight PAHs (HMW-PAHs). The bioaccumulation capacity of the zooplankton community for LMW-PAHs was negatively correlated with the proportion of omnivores and carnivores, while the opposite was true for HMW-PAHs. These results suggested that the effects of complex community structure within plankton communities should be taken into account when assessing the transfer and bioaccumulation effects of PAHs in the marine food chain.

Spatio-Temporal Variations of Zooplankton and Correlations with Environmental Parameters around Tiaowei Island, Fujian, China.

The present study illustrates zooplankton dynamics in relation to environmental factors from the surrounding area of Tiaowei Island based on ten seasonal sampling cruises over three years. A total of 116 species of zooplankton were collected with a predominance of Copepoda (mainly consisting of Centropagidae, Oithonidae, Acartia, Labidocera and Paracalanus), accounting for 31.6 % of the total number of species. The diversity indices indicated a relatively high richness, abundance and evenness of zooplankton ranging from 2.794 to 4.012 on the Shannon–Wiener index for each cruise. More than 20 species of Cnidaria medusae are found as gelatinous organisms, which not only compete with fish but also potentially cause disasters. Significant seasonal variations were detected in both the zooplankton structure and environmental variables. NMDS illustrated a highly overlapping community structure in spring, autumn and winter, while the zooplankton composition in the summer was different from that of the other three seasons with a higher diversity index. Meanwhile, out of thirteen environmental parameters, eight varied significantly among seasons but there were no significant variations among stations. The biota–environmental relationship following a redundancy analysis revealed that water temperature, pH, salinity, dissolved oxygen and suspended particulate composition were the main environmental parameters, seasonally impacting the zooplankton communities. Planktonic larvae (such as nauplius larvae and branchyura zoea) and some zooplankton (including Corophium sinensis and Oithona similis) were significantly vulnerable to the dynamics of suspended particulate composition and water temperature.

Diversity and Community Structure of Zooplankton in Homestead Ponds of a Tropical Coastal Area

As an intermediary connection between primary producers and higher trophic levels, zooplankton are an important component of the aquatic food chain, contributing significantly to aquatic biological productivity. This study describes the zooplankton diversity and community structure, as well as their relationships with ecological factors, in homestead ponds of a coastal district along the northern Bay of Bengal region. Significant differences (p &lt; 0.05) were detected in the mean values of temperature, pH, DO, TDS, transparency, and phosphates from the ponds during December 2020, but no significant differences were found in the nitrate levels. However, no significant variances in the ecological parameters between months were found due to the study taking place in the same season. Sixteen zooplankton species, representing four groups, were found in the study area, with the highest mean abundance of 301.19 ± 40.55 ind./L recorded in February 2021 and the lowest of 293.02 ± 21.13 ind./L recorded in December 2020. The diversity (H’), evenness (e), richness (J), and dominance (D) ranged from 2.49 to 2.12, from 0.93 to 0.84, from 2.05 to 1.56, and from 0.13 to 0.09, respectively. Based on the SIMPER analysis, Diaptomus gracilis and Brachionus calyciflorus were found to be significant contributors (&gt;10%) to the zooplankton community structure in different months. The ANOSIM results revealed that 10 species of zooplankton were significant contributors based on their average dissimilarity. The canonical correspondence analysis (CCA) identified that pH, transparency, nitrates, and phosphates have a significant impact on the abundance of zooplankton species in the homestead ponds in the study area.

SEASONAL DYNAMICS OF ENVIRONMENTAL VARIABLES AND ZOOPLANKTON STRUCTURE IN WASTEWATER RESERVOIRS OF THE RIGHT-BANK SORBULAK CANAL SYSTEM

The annual increase in wastewater volumes necessitates comprehensive studies of water bodies subsidized by anthropogenic activities. An example of such reservoirs is Sorbulak and a system of shallow ponds into which pre-treated wastewater from Almaty and its environs is discharged. The published works provide fragmentary data on the hydrochemical and hydrobiological regimes of Sorbulak and ponds. There is no information on the seasonal dynamics of these variables. Our paper, aimed at studying the seasonal dynamics of pollutants and the zooplankton structure, partially fills this gap. Environmental and biological samples were taken in Sorbulak and two ponds by standard methods once a month, from April to September of 2021. The content of nutrients was high, and the heavy metals concentrations, except for copper, were low. The seasonal dynamics of pollutants in reservoirs were determined mainly by their entry from wastewater, with a more negligible contribution of natural factors. Zooplankton was represented by 80 species with an average abundance of 177.3-834.4 thousand ind./m3 and average biomass of 9.6-10.4 g/m3. The values ​​of the Shannon index were 1.98-2.12 bit/ind and 0.88-1.76 bit/mg, the average mass of an individual was 0.0140-0.0853 mg. The seasonal dynamics of zooplankton in the surveyed water bodies were different. The obtained results and comparison with the data of previous studies testified to the instability of the species composition of zooplankton communities both during one year and in individual years. Contradictions between the structure of zooplankton communities and the chemical variables of the studied reservoirs were identified. The results obtained to make a theoretical and practical contribution to understanding the formation of water quality in reservoirs with mixed pollution emphasize the need for further comprehensive studies of reservoirs of this type, and show specific differences between anthropogenic and natural successions of aquatic ecosystems.

Seasonality shapes community structure and functional group dynamics of zooplankton in Changjiang River estuary and its adjacent waters

AbstractAimFunctional trait‐based approach links the zooplankton community to the marine ecosystem functioning. It provides a comprehensive insight into the diversity of zooplankton ecological strategies but has rarely been used to characterize the zooplankton community in estuarine ecosystem. Here, we investigated the seasonality of mesozooplankton functional structure with respect to environmental changes in Changjiang River estuary (CRE) and its adjacent waters.LocationChangjiang River estuary and its adjacent waters.MethodsSamples were collected in three seasons of 2019. Morphologically identified species were assigned functional traits including body length, feeding strategy, trophic group, reproduction mode and habitat type, and clustered into functional groups. Taxonomic and functional diversity indices were calculated. The relative importance of the environmental variables in explaining the seasonality of functional structures was assessed.ResultsTen functional groups were identified, and functional structure showed strong seasonal dynamics. Current‐ and mixed‐feeding omnivore–herbivores were the predominant group over seasons. The contribution of carnivorous, detritivorous and omnivorous groups increased from winter–spring to autumn. The seasonality of zooplankton functional structure was mainly explained by the effect of temperature, fluvial discharge and warm current. Low temperature and riverine input of nutrient in winter–spring favoured the small‐sized herbivores. Subsequently, the rising temperature and run‐off in summer shifted the zooplankton community to larger herbivores and carnivores. Moderate temperature and relatively enhanced effect of warm current promoted the proliferation of carnivores and detritivores in autumn. Functional diversity also varied over seasons.Main conclusionsThe functional dynamics of mesozooplankton in CRE across estuarine gradient and seasonality is shaped by the seasonal variation of temperature, fluvial pulse and warm current intrusion. Our findings pave the way for further understanding estuarine biodiversity and have implications in conservation strategies.

Community structure of zooplankton during the southwest-northeast monsoon transition period in the southeastern East China Sea

Abstract The assessment of zooplankton spatial structure is critical to quantifying plankton production and biochemical cycling. Here, we show the effect of monsoon-driven hydrographic changes on the spatial patterns of zooplankton at regional scales. Based on a field survey conducted during the monsoon transition, we assess the community structure and ash-free dry weight above 100 m depth in the Kuroshio edge area, southeastern East China Sea. The zooplankton community was dominated by copepods, with calanoids as the most abundant taxon followed by poecilostomatoids. Copepod assemblages comprised 81 species belonging to 41 families, and 23 genera, with Undinula vulgaris as the most abundant species. The richness of zooplankton taxa showed a mounting trend from the coast to offshore, which was opposite to the spatial variation of total zooplankton biomass. Our results suggest a leading influence of the Kuroshio Current during the southwest-northeast monsoon transition period in the southeastern East China Sea.

Impact of Colonizer Copepods on Zooplankton Structure and Diversity in Contrasting Estuaries

The impact of the occurrence of the non-indigenous species (NIS) Acartia tonsa, Oithona davisae, and Pseudodiaptomus marinus and of the range-expanding copepods Acartia bifilosa and Calanipeda aquaedulcis on the structure and diversity of zooplankton communities was analyzed using 18 years (1998–2015) time series from the contrasting estuaries of Bilbao and Urdaibai (Basque coast, Bay of Biscay). Changes in the structure of communities were assessed by using multivariate analyses of taxa abundances and changes in diversity by using descriptors of alpha, beta, and gamma diversity. The most evident changes occurred at the upper reaches of the estuary of Bilbao, where an abundant and less diverse brackish community, dominated by the NIS, A. tonsa and O. davisae, succeeded a low abundance and more diverse community of neritic origin. The later establishment of C. aquaedulcis was linked to further changes in the structure of the community and a progressive increase in diversity. The seasonal pattern of diversity at the inner estuary and the beta diversity in the estuary were also significantly affected by the arrival of the NIS and C. aquaedulcis. In contrast, the original low diversity brackish community of the estuary of Urdaibai, clearly dominated by A. bifilosa, was far less affected by the arrival of the same copepod NIS, and A. bifilosa remained as the species best related to the changes in zooplankton structure and diversity in the brackish habitats of the estuary.

Relationship Between Community Structure of Zooplankton and Water Quality in Bojonegara Coastal Area, Banten Bay, Indonesia

Relationship Between Community Structure of Zooplankton and Water Quality in Bojonegara Coastal Area, Banten Bay, Indonesia

Invasive and toxic cyanobacteria regulate allochthonous resource use and community niche width of reservoir zooplankton

Abstract Cyanobacterial dominance or blooms can influence ecosystem structure in reservoirs, yet there are only few studies of its effect on the resource use and trophic structure of zooplankton. We hypothesised that zooplankton traits would exhibit a strong response to the increase of invasive and toxic cyanobacteria. We investigated the effect of an invasive bloom‐forming cyanobacterium Raphidiopsis raciborskii (formerly Cylindrospermopsis raciborskii) on zooplankton functional traits (e.g., growth, reproduction, allochthonous resource use and realised niche) through laboratory experiments and 3‐year field investigations in two subtropical reservoirs. The realised niche (i.e., resource and habitat use) was quantified using stable isotopes (termed isotopic niches). We fed the cladoceran zooplankton Moina sp. with Scenedesmus obliquus (chlorophyte), R. raciborskii, and a mixture of S. obliquus and R. raciborskii in laboratory experiments. A diet of R. raciborskii alone depressed the growth and reproduction of Moina sp. compared to a diet of S. obliquus alone, but a mixture of S. obliquus and R. raciborskii greatly alleviated the inhibition effects caused by cyanobacteria. Under natural field conditions, we did not find a strong inhibition effect of R. raciborskii dominance on the zooplankton, but a high biomass of R. raciborskii was associated with an increase (17%) in the relative allochthonous resource (terrestrially derived organic matter) use by cladocerans (but not for copepods), even though the chlorophyll‐a concentration increased from 17 μg/L in the non‐bloom period to 28 μg/L during periods of R. raciborskii dominance or blooms. Furthermore, a high biomass of R. raciborskii increased the contribution of inter‐taxa variation (taxa sorting) to the expanded isotopic niches of the zooplankton community. Our study helps to clarify cyanobacteria‐zooplankton interactions and highlights the importance of cyanobacterial dominance or blooms in regulating cross‐ecosystem resource use and biogeochemical cycling mediated by zooplankton in aquatic ecosystems.

Factors Affecting Water Quality and the Structure of Zooplankton Communities in Wastewater Reservoirs of the Right-Bank Sorbulak Canal System (South-Eastern Kazakhstan)

This work aims to assess the main factors that determined the variability of environmental and biological variables in wastewater reservoirs of the Right-Bank Sorbulak Canal system (South-Eastern Kazakhstan). We used standard methods for the collection and analysis of data, as well as the principal components analysis (PCA) to assess the relationship between environmental and biological indicators. The average depth of the surveyed reservoirs was 4.1–10.0 m, temperature—21.7–25.7 °C, pH—9.41–10.00, permanganate index—16.22–19.07 mgO/dm3, N-NO2—0.03–0.13, N-NO3—1.28–3.00, N-NH4—0.30–0.53, PO4—0.14–0.39, Si—3.69–8.26, Mn—0.03–0.07, Fe—0.34–0.38 mg/dm3. The content of Cd, Co, Pb, Zn, and Cr was low, Cu—0.012–0.036 mg/dm3. The water quality is influenced by the wastewater composition, chemical interactions, morphometric and physical-chemical conditions of the reservoir, pollution of the coastal area, and secondary water pollution. Changes in the species composition and zooplankton abundance reflected the instability of external conditions. PCA showed the priority influence of carbonates, bicarbonates, magnesium, temperature, nutrients, and heavy metals on zooplankton structure. The results obtained demonstrate the indicator significance of zooplankton, and the methodological approaches can be used to assess water bodies with the complex pollution located in other regions.

Seasonal and spatial variability of zooplankton diversity in the Poyang Lake Basin using DNA metabarcoding.

Freshwater ecosystems face multiple threats to their stability globally. Poyang Lake is the largest lake in China, but its habitat has been seriously degraded because of human activities and natural factors (e.g. climate change), resulting in a decline in freshwater biodiversity. Zooplankton are useful indicators of environmental stressors because they are sensitive to external perturbations. DNA metabarcoding is an approach that has gained significant traction by aiding ecosystem conservation and management. Here, the seasonal and spatial variability in the zooplankton diversity were analyzed in the Poyang Lake Basin using DNA metabarcoding. The results showed that the community structure of zooplankton exhibited significant seasonal and spatial variability using DNA metabarcoding, where the community structure was correlated with turbidity, water temperature, pH, total phosphorus, and chlorophyll‐a. These results indicated habitat variations affected by human activities and seasonal change could be the main driving factors for the variations of zooplankton community. This study also provides an important reference for the management of aquatic ecosystem health and conservation of aquatic biodiversity.

СЕЗОННАЯ ДИНАМИКА ЗООПЛАНКТОНА ШЕКСНИНСКОГО ВОДОХРАНИЛИЩА (ВОЛОГОДСКАЯ ОБЛАСТЬ)

The paper analyzes the seasonal dynamics of the composition, structure, and abundance of zooplankton in different parts of the Sheksna Reservoir in 2016–2020. The zooplankton in the reservoir includes 107 species (Rotifera – 41, Cladocera – 41, Copepoda – 25). The authors have found 88 species in Lake Beloye and 90 species in the river part of the reservoir. 7 species in the lake and 17 in the river part of the reservoir have been found for the first time. The communities of different parts of the reservoir are similar in terms of zooplankton composition (76%). The highest level of dominance (0.32–0.38) of zooplankton is observed during the ice period. In Lake Beloye, this figure is higher than in the river part of the reservoir. A small set of species (Kellicottia longispina, Keratella cochlearis, Eudiaptomus gracilis) is characterized by high density in all seasons of the year. Some species are dominant only in certain periods. In summer, rotifers of the genus Polyarthra and Mesocyclops leuckarti dominate the entire water area of the reservoir. Lake Beloye is dominated by Daphnia galeata and Chydorus sphaericus in summer. The composition of the dominant zooplankton complex in different parts of the reservoir is similar in certain seasons. Only in May, the structure of the dominant complex of the lake and river sections of the reservoir differs. The ratio of dominants in Lake Beloye in May is similar to the ice period. The maximum abundance of zooplankton in the reservoir is recorded in summer. From May to November the largest number of copepods is observed. In March, rotifers dominate. Cladocera were noted as dominants only in the lake part of the reservoir. The seasonal dynamics of the structure and abundance of zooplankton generally corresponds to those in the 1970s and early 2000s.

Species composition, structure and biomass of zooplankton in the Chukchi Sea in August-September 2019

Plankton survey was conducted in the Chukchi Sea in August-September 2019 by two research vessels: RV Professor Levanidov in the western part of the sea and RV Ocean Starr in its eastern part. Parasagitta elegans dominated everywhere in zooplankton. Beside these arrowworms, species of the arctic and arctic-boreal complex were abundant in the northwestern Chukchi Sea, as Calanus glacialis and other species typical for the adjacent East-Siberian Sea. C. glacialis was numerous in the northeastern Chukchi Sea, too, together with species of the Arctic waters and the Beaufort Sea. The southern Chukchi Sea was occupied by the waters invaded from the Bering Sea, so species of the Bering Sea complex were abundant there, as Eucalanus bungii and Neocalanus plumchrus/flemingeri, at Alaska coast together with neritic species typical for the Alaska coastal water mass. The zooplankton community structure corresponded to the spring phase of seasonal succession in the northern area, whereas to the summer phase in the southern area. Total density of zooplankton was estimated as 65 t/km2 for the northwestern part of the sea, presented mostly by large-sized fraction (56 t/km2) including arrowworms (35 t/km2) and copepods (13 t/km2), and as 48 t/km2 for the southwestern part of the sea, also mostly large-sized fraction (40 t/km2). So high zooplankton density in the western Chukchi Sea is considered as result of the Bering Sea waters advection (previously such abundance was observed in 2008 — 40 and 36 t/km2, when the advection was also active). In the eastern Chukchi Sea, the total density of zooplankton was 44 t/km2 in the northeastern area (including 29 t/km2 of large-sized fraction) and 43 t/km2 in the southeastern area, that was higher than in 2017 (15 t/km2) but lower than in 2007 (49 t/km2). However, different phases of seasonal succession should be noted: summer season in 2019, spring season in 2017, and late-summer season in 2007.