Zooplankton Biomass Research Articles

Assessing the Fishing Impact on the Marine Ecosystem of Guishan Island in the Northeastern Waters of Taiwan Using Ecopath and Ecosim

The northeastern waters of Guishan Island constitute one of the crucial fishing grounds for coastal trawl fishery in Taiwan and have been exploited for many decades. To construct the marine ecosystem and to examine the interactions among trophic levels of fisheries resources in the waters of Guishan Island, historical catch, catch composition, biological information, fishing effort, environmental data such as sea surface temperature, salinity, and nutrients were analyzed using Ecopath with Ecosim. The results indicated that the longline and drift net fisheries have a very minor incidental catch of cetaceans, with a fishing mortality (F) of 0.01 year−1 and an exploitation rate (E) of 0.03. The F and E were 0.308 year−1 and 0.617 for small skates and rays, and were 0.261 year−1 and 0.580, respectively, for small sharks. The F and E of the dolphinfish, Coryphaena hippurus, an important pelagic species, were 0.411 year−1 and 0.245, respectively. Fisheries had negative impact on major commercial species except the dolphinfish and the oil fish, Lepidocybium spp., which benefited from the reduction of their predators or competitors. The keystone species of the Guishan Island marine ecosystem is phytoplankton, which has the lowest trophic level and great biomass, and is an important energy source of the ecosystem. The influences of zooplankton and anchovy rank as second and third, respectively, with regard to the keystone species in the ecosystem due to their great biomass. Regarding the biomass of less abundant species, carangids had the highest influence followed by hairtail due to their feeding habits. The results of simulations using Ecosim indicated that the hairtail, small sharks, skates and rays, mackerels, and marine eels will benefit if fishing efforts are reduced by 30%. On the other hand, the biomass of phytoplankton, zooplankton, demersal benthivores, and shrimps will decrease due to the increase in the biomass of their predators.

The influence of locks on zooplankton in canals (the Bydgoszcz Canal and the Noteć Canal, Poland)

Artificial waterways are characterized by dams and locks that slow water flow. Such conditions can influence the environment of freshwater organisms, including the zooplankton community. Our research aimed to assess the impact of environmental and hydrological conditions on the zooplankton of sites upstream and downstream of canal locks. The study was carried out in 2021 and 2022. Water samples were collected monthly from two canals during the growing season. We evaluated how water flow velocity and selected environmental parameters (i.e., water temperature, Secchi disk visibility, conductivity, oxygen concentration, saturation, pH and chl-a concentrations) influence the zooplankton diversity (T) density (N) and biomass (B). Our study showed that the zooplankton of the canals was highly diverse. Rotifers dominated over crustaceans in diversity and density at all sites of canals. The statistical analysis revealed differences in environmental and biological conditions between habitats located upstream and downstream of locks. Rotifers density and biomass changed approximately proportionally to changes in chlorophyll at sites upstream of locks. It supports the hypothesis that rotifer communities are defined by the bottom-up effect linked to food supply (phytoplankton). The growth of crustaceans (density and biomass), as well as total zooplankton biomass, was affected by water temperature at sites downstream of the lock.

Long-term oscillations in the normalized biomass-size spectrum reveal the impact of oligotrophication on zooplankton trophic structure in the North Atlantic Subtropical Gyre

Ocean warming of the North Atlantic Subtropical Gyre (NASG) induced oligotrophication and a decrease in integrated net primary production during the 2010s, potentially affecting higher trophic levels. We analyzed long-term records (1994–2019) of daytime and nighttime zooplankton biomass in five size classes from the NASG. Daytime biomass decreased in the three largest size classes during the 2010s, while decrease in nighttime biomass was less evident due to the relative stability in diel vertical migrator biomass. We used the normalized biomass size spectrum (NBSS) to estimate the relative transfer efficiency between trophic levels. The steepness of the NBSS slope at the end of the time series increased by 14% (daytime) and 24% (nighttime) from the maximum observed annual average values (2011 and 2009, respectively). This suggests oligotrophication during the 2010s led to a significant reduction in the transfer of biomass across trophic levels, with negative impacts on the NASG planktonic food web.

Zooplankton of the Eastern Kara Sea: Response to a Short Ice-Free Period

—A characteristic feature of the eastern Kara Sea, which is separated from its central part by the shallow Central Kara Rise, is a later ice breakup, a shorter ice-free period, and lower water temperature. Zooplankton in this part of the sea is virtually unstudied. The first data on the composition, spatial distribution of zooplankton, age structure and feeding of the dominant species, and their grazing impact on phytoplankton were obtained in the cruise 125 of the R/V Professor Shtokman (September 2013) and cruise 63 of the R/V Akademik Mstislav Keldysh (September 2015) to the eastern Kara Sea. 2015 was a typical year in terms of the ice regime for this region, while in 2013, seasonal ice coverage lasted longer than usual. Zooplankton biomass (17–112 mg dry weight m–3), to which copepods Calanus glacialis contributed the main portion, were close to the values in the central Kara Sea in September. The seasonal development of the C. glacialis population began much later than in the central Kara Sea, but development of Metridia longa was not influenced by the specifics of the ice regime and hydrophysical conditions in the eastern Kara Sea. The interannual differences in the timing of ice retreat had almost no effect on the zooplankton abundance, seasonal development of the dominant copepod populations, feeding activity, and grazing impact on phytoplankton.

Zooplankton in brackish water bodies of the plain territory of the Altai territory in the vegetation season of 2022

The zooplankton of three small brackish lakes (Bulatovo, Korostelevskoye and Markovskoye) located in the plain territory of Altai Krai was studied in 2022. Data on the main characteristics of the zooplankton habitat are presented. An assessment of the ecological state of lakes is given based on qualitative and quantitative indicators of zooplankton. The taxonomic composition and main quantitative characteristics of zooplankton in the spring, summer and autumn periods are characterized. Seasonal dynamics of quantitative indicators and changes in the taxonomic composition of zooplankton were noted. The lowest quantitative indicators of zooplankton development were noted in the spring season (April). All identified representatives of zooplankton were cosmopolitans. Common to all lakes are 5 taxa of crustaceans and rotifers (Keratella quadrata, Filinia longiseta, Daphnia magna, Cyclopidae ind., Diaptomidae ind.). In the spring and autumn seasons, copepods dominated in abundance and biomass, reaching 99.9% of the zooplankton population. Differences in the composition of the dominant taxa in the summer season were noted between the lakes. In the lake Bulatovo was dominated in numbers by rotifers due to Brachionus quadridentatus, and in biomass by cladocerans due to Daphnia magna. In the lake Korostelevskoe, the dominant taxonomic group in terms of numbers was copepods, the basis of which were Diaptomidae ind., in terms of biomass — cladocerans due to Diaphanosoma brachiurum. Only in the lake In Markovskoe, copepods — Diaptomidae ind. — dominated in numbers and biomass. The zooplankton of the studied lakes was characterized by a poor species composition, but high summer numbers and biomass (from 342 thou. eq./m3 and 7.13 g/m3 in Lake Markovskoe to 1895 th. eq./m3 and 33.7 g/m3 in Lake Bulatovo). In the summer season, the zooplankton biomass of the lake. Markovskoye belonged to reservoirs of the α-eutrophic type, lakes Bulatovo and Korostelevskoye were of the polytrophic type. The majority of noted species (60%) were indicators of β-mesosaprobic conditions.

Contemporary community composition, spatial distribution patterns, and biodiversity characteristics of zooplankton in large alpine Lake Sevan, Armenia

We studied the quantitative composition, spatial distribution, and temporal dynamics of the zooplankton community of the alpine Lake Sevan, Armenia, the largest surface water in the Caucasus region. This article is providing a long-term information and fills the research gap of multiyear data on zooplankton, as the previous research on zooplankton provided only snapshots of the community, and a consistent assessment over multiple years was missing. However, an initial mini-review of historical studies indicated that zooplankton biomass and fish abundance were undergoing large fluctuations, indicating the importance of top-down control. We analysed 239 samples from the period 2016-2019 from 32 sampling sites in Lake Sevan and recorded 37 species of meso- and macrozooplankton (Rotifers, Copepods, Cladocera). Biomass fluctuations were high with peaking biomasses in 2016 and lowest biomasses in 2018, yearly averaged biomass varied about one order of magnitude. Variability over time was hence much higher than spatial variability. The pelagic habitat at the deepest part of the lake showed the highest diversity and biomasses but contrasts between sampling sites remained smaller than changes from year to year or seasonally. Many samples were dominated by a single species, and these key species explain observed biomass dynamics to a wide extent. We applied hierarchical clustering in order to identify phenological groups that appear to show similar patterns of occurrence. This clustering resulted in 6 groups where of 5 groups just consisting of one single species and these 5 key species were the Cladocerans Daphnia magna, Daphnia hyalina, Diaphanosoma sp. as well as the calanoids Arctodiaptomus bacillifer and Acanthodiaptomus denticornis. The most important species in Lake Sevan’s zooplankton during the observation period was D. magna, which reached high biomasses in 2016 and 2017 but then suddenly almost disappeared in 2018 and 2019. When there were more D. magna present, the water became clearer, which was measured using Secchi depth. This shows that these large water fleas effectively controlled the amount of phytoplankton in the water. Daphnia magna, in turn, managed to dominate zooplankton community only during times of extremely low fish biomass indicating strong top-down control of this large Cladoceran by fish. Both observations together imply a strong trophic linkage between fish, zooplankton, and phytoplankton and provide evidence for trophic cascades in Lake Sevan. Besides the novel insights into zooplankton community dynamics of this unique lake of high socio-economical, cultural, and ecological importance, our study also points to potential management opportunities for eutrophication control by biomanipulation, as well as our investigation allows us to conclude that probably biotic factors were more important than abiotic factors in explaining the observed changes and dynamics within the plankton community.

Structural characteristics of zooplankton communities in Hongze Lake driven by water environmental factors from 2016 to 2020.

This study investigated zooplankton species, density, biomass, and water physicochemical factors in Hongze Lake between 2016 and 2020. The correlation between zooplankton community changes and physicochemical factors was explored using canonical correspondence analysis and Spearman correlation analysis. The investigation found 48 species of protozoa, 52 species of rotifers, 36 species of cladocera, and 32 species of copepoda. The yearly mean density fluctuated between 529.01 and 2234.51 individuals per liter. The yearly mean zooplankton biomass was 950.14 mg/L, ranging from 271.92 to 1365.835 mg/L. A high diversity of zooplankton was found in the Overwater Area, with a large proportion of protozoa and copepoda. Correlation analysis revealed that nitrogen content, pH, water temperature, chemical oxygen demand, biochemical oxygen demand, water transparency, and chlorophyll a were important factors influencing the distribution of zooplankton in Hongze Lake. These factors collectively contributed to the evolution of the zooplankton community structure in Hongze Lake.

Seasonal and regional variability of model-based zooplankton biomass in the Salish Sea and evaluation against observations

We used a three-dimensional coupled biophysical model to examine zooplankton dynamics in the Salish Sea, NE Pacific. First, we evaluated the two zooplankton classes of the SalishSeaCast model using a transboundary zooplankton dataset comprised of observation data from the Canadian and United States waters of the Salish Sea from 2015 to 2019. Model zooplankton classes correspond to micro- and meso-zooplankton whose biomass is tightly coupled to phytoplankton through modelled food web dynamics (Z1) and mesozooplankton with life cycle-based seasonal grazing impacts (Z2). Overall, the model effectively captured seasonal patterns in observed biomass, although with slightly higher biomass estimates for both Z1 and Z2 (Bias = 0.10 and 0.08 g C m−2, respectively). Model fit varied regionally, with a weaker model fit being observed in nearshore regions. In addition, an autumn peak in Z2 was observed in the model, but not in the observations, suggesting some seasonal variations in model fit. Following the model evaluation, we used the model to determine seasonal and regional patterns of zooplankton grazing. Seasonally, the main peak in modelled zooplankton biomass increased in April or May in most of the regions defined within the Salish Sea and was driven by grazing on diatoms. Regionally, depth-integrated zooplankton biomass was consistently highest in areas adjacent to regions of strong tidal mixing. In addition, model-based zooplankton grazing was highest in the tidally mixed regions where phytoplankton biomass was high due to advection into the region despite low primary productivity. Our model-based results provide an opportunity to examine bottom-up food web processes at spatio-temporal scales not achievable with in situ sampling and help to elucidate key drivers of lower trophic level dynamics within the Salish Sea.

Zooplankton-phytoplankton biomass and diversity relationships in the Great Lakes.

Quantifying the relationship between phytoplankton and zooplankton may offer insight into zooplankton sensitivity to shifting phytoplankton assemblages and the potential impacts of producer-consumer decoupling on the rest of the food web. We analyzed 18 years (2001-2018) of paired phytoplankton and zooplankton samples collected as part of the United States Environmental Protection Agency (U.S. EPA) Great Lakes Biology Monitoring Program to examine both the long-term and seasonal relationships between zooplankton and phytoplankton across all five Laurentian Great Lakes. We also analyzed effects of phytoplankton diversity on zooplankton biomass, diversity, and predator-prey (zooplanktivore/grazer) ratios. Across the Great Lakes, there was a weak positive correlation between total algal biovolume and zooplankton biomass in both spring and summer. The relationship was weaker and not consistently positive within individual lakes. These trends were consistent over time, providing no evidence of increasing decoupling over the study period. Zooplankton biomass was weakly negatively correlated with algal diversity across lakes, whereas zooplankton diversity was unaffected. These relationships did not change when we considered only the edible phytoplankton fraction, possibly due to the high correlation between total and edible phytoplankton biovolume in most of these lakes. Lack of strong coupling between these producer and consumer assemblages may be related to lagging responses by the consumers, top-down effects from higher-level consumers, or other confounding factors. These results underscore the difficulty in predicting higher trophic level responses, including zooplankton, from changes in phytoplankton assemblages.

Brief floodplain inundation provides growth and survival benefits to a young-of-year fish in an intermittent river threatened by water development

Riverine floodplains are highly productive habitats that often act as nurseries for fish but are threatened by flow regulation. The Fitzroy River in northern Australia is facing development, but uncertainty exists regarding the extent to which floodplain habitats deliver benefits to fish, particularly given the brevity of seasonal floodplain inundation. We investigated the growth rate of young-of-year bony bream (Nematalosa erebi) in main channel and ephemeral floodplain habitats using age derived from otolith daily increments. We also investigated potential mechanisms influencing growth and modelled the consequences of differential growth rate on survival. Our results revealed higher growth occurred exclusively on the floodplain and that zooplankton biomass was the best predictor of growth rate. Modelling indicated that elevated growth rate in high-growth floodplain pools (top 25th percentile) could translate into substantial increases in survivorship. The positive effect of zooplankton biomass on growth was moderated under highly turbid conditions. Temperature had a minor influence on growth, and only in floodplain habitats. Our results indicate ephemeral floodplain habitats can deliver substantial growth and survival benefits to young-of-year fish even when floodplain inundation is brief. This study highlights the need to ensure that water policy safeguards floodplain habitats due to their important ecological role.

Abundance and biomass of copepods and cladocerans in Atlantic and Arctic domains of the Barents Sea ecosystem

Abstract Zooplankton in the Barents Sea have been monitored annually with a standard procedure with determination of size-fractioned biomass since the mid-1980s. Biomass of copepods and cladocerans was estimated based on measured abundance and individual weights taken from literature. Calanus species were dominant, making up ~85% of the estimated biomass of copepods. The second most important taxon was Oithona spp. (~0.5 g dry weight (dw) m−2, ~10%), followed by Metridia spp. (~0.15 g dw m−2, 2–3%) and Pseudocalanus spp. (0.10–0.15 g dw m−2, 1–5%). Estimated biomass of cladoceran taxa (Evadne and Podon) was low (0.01 g dw m−2). Calanus spp. contributed most of the biomass of the medium size fraction (1–2 mm), whereas small copepod species (Oithona, Pseudocalanus and others) contributed to the small size fraction (<1 mm). Estimated biomass of Calanus spp. and of the sum of small copepod species were both positively correlated with measured total zooplankton biomass (R2 = 0.72 and 0.34, respectively). The biomass ratio of small copepod species to Calanus was similar in Atlantic and Arctic water masses (~0.15–0.2) but tended to increase with decreasing total biomass. This suggests a shift to relatively larger roles of small copepods as Calanus and total biomass decrease.

Impact of critical eddy diffusivity on seasonal bloom dynamics of Phytoplankton in a global set of aquatic environments

The intensity of eddy diffusivity and the spatial average of water velocity at the depths of the water column in oceans and lakes play a fundamental role in phytoplankton production and phytoplankton and zooplankton biomass, and community composition. The critical depth and intensity of turbulent mixing within the water column profoundly affect phytoplankton biomass, which depends on the sinking characteristic of planktonic algal species. We propose an Nutrient-Phytoplankton-Zooplankton (NPZ) model in 3D space with light and nutrient-limited growth in a micro-scale ecological study. To incorporate micro-scale observation of phytoplankton intermittency in bloom mechanism in stationary as well as oceanic turbulent flows, a moment closure method has been applied in this study. Experimental observations imply that an increase in turbulence is sometimes ecologically advantageous for non-motile planktonic algae. How do we ensure whether there will be a bloom cycle or whether there can be any bloom at all when the existing phytoplankton group is buoyant, heavier, motile, or non-motile? To address these questions, we have explored the effects of critical depth, the intensity of eddy diffusivity, spatial average of water velocity, on the concentration as well as horizontal and vertical distribution of phytoplankton and zooplankton biomass using a mathematical model and moment closure technique. We quantify a critical threshold value of eddy diffusivity and the spatial average of water velocity and observe the corresponding changes in the phytoplankton bloom dynamics. Our results highlight the importance of eddy diffusivity and the spatial average of water velocity on seasonal bloom dynamics and also mimic different real-life bloom scenarios in Mikawa Bay (Japan), Tokyo Bay (Japan), Arakawa River (Japan), the Baltic Sea, the North Atlantic Ocean, Gulf Alaska, the North Arabian Sea, the Cantabrian Sea, Lake Nieuwe Meer (Netherlands) and several shallower lakes.

2022 ЖЫЛҒЫ КІШІ АРАЛ ТЕҢІЗІ ЗООПЛАНКТОНЫНЫҢ ТҮРЛІК ҚҰРАМЫ ЖӘНЕ САНДЫҚ СИПАТТАМАСЫ

Abstract. This article presents data on the state of zooplankton of the Small Aral Sea in May-June-September in 2022. During the periods of research, 32 taxa of true plankters were identified in the zooplankton of the Small Aral Sea: rotifers – 19, cladoceras– 7 and copepods – 6 species. Temporary plankters – larvae of bivalve mollusks, ostracoda, hadistediversicolorand chironomids were also noted. Zooplankton was created to varying degrees by four groups of invertebrates, but in both periods of research, copepods were in the lead. This is closely related to the development of the acclimatizant – Calanipeda quaedulcis. The leadership of this group of copepods was maintained throughout the PR (fishing area) of the sea. In general, the average values of zooplankton biomass corresponded to a very low trophic level. This may be due to the timing of material collection, the depth of sampling and the lack of a significant level of development of the group of cladoceras.

Water column distribution of zooplanktonic size classes derived from in-situ plankton profilers: Potential use to contextualize contaminant loads in plankton

Pollution is one of the main anthropogenic threats to marine ecosystems. Studies analysing the accumulation and transfer of contaminants in planktonic food webs tend to rely on samples collected in discrete water bodies. Here, we assessed the representativeness of measurements at the chlorophyll-a maximum layer during the MERITE-HIPPOCAMPE cruise for the entire water column by investigating the vertical distribution of particles and plankton obtained by in-situ optical profilers at nine stations across the Mediterranean Sea. We identified specific conditions where the interpretation of results from contaminant analyses can be improved by detailing plankton size structure and vertical distributions. First, the presence of higher than usual plankton concentrations can result in sampling issues that will affect biomass estimation within each size class and therefore bias our understanding of the contaminant dynamics. Secondly, the presence of an unsampled water layer with high zooplankton biomass might imply non-resolved contaminant pathways along the trophic structure. This study lays the basis for optimizing sampling strategy in contaminant studies.

Phytoplankton control by stocking of filter-feeding fish in a subtropical plateau reservoir, southwest China

Stocking of filter-feeding fish (mainly Hypophthalmichthys molitrix and Aristichthys nobilis) is a common method used in lakes and reservoirs in (sub)tropical China to control phytoplankton, but the results are ambiguous and lack long-term data to support. We analysed a decade (2010-2020) of monitoring data from a subtropical plateau reservoir, southwest China, to which filter-feeding fish were stocked annually. We found that the total phytoplankton biomass, cyanobacteria biomass and average individual mass of phytoplankton decreased significantly during the study period despite absence of nutrient concentration reduction. However, the grazing pressure of zooplankton on phytoplankton also decreased markedly as judged from changes in the ratio of zooplankton biomass to phytoplankton biomass and Daphnia proportion of total zooplankton biomass. This is likely a response to increasing predation on zooplankton by the stocked fish. Our results also indicated that water temperature, total phosphorus and water level promoted phytoplankton growth. Our results revealed that filter-feeding fish contributed to the decline in the biomass of phytoplankton but that it also had a strong negative effect on the grazing pressure of zooplankton on phytoplankton, even in this deep reservoir where zooplankton may have a better chance of survival through vertical migration. The particular strong effect on zooplankton is most likely due to imbalance of stocking and harvesting of fish. In the management of eutrophic reservoirs, the reduction of external nutrient loading should have highest priority. In highland (low temperature) deep-water eutrophic reservoirs, stocking of filter-feeding fish may help to control filamentous phytoplankton provided that the fish stocking is properly managed. The optimal stocking intensity of filter-feeding fish that can help control phytoplankton in such reservoirs without excessive impact on large-bodied zooplankton is a topic for further elucidation, however.

Integrating hydrological connectivity and zooplankton composition in Arctic ponds and lakes

Abstract Arctic landscapes are characterised by their numerous ponds and lakes. With increased climate warming and consequent changes in hydrological connectivity, the ecology of many of these waterbodies is expected to change. We sampled 13 ponds and 22 lakes for zooplankton and various limnological and physical environmental variables in the vicinity of Cambridge Bay, Nunavut (69.1169° N, 105.0597° W), with the aim of testing how well the degree of hydrological connectivity explained patterns in species composition and abundance and contributed to crustacean production. Ponds were hydrologically isolated while the lakes were arranged in four lake chains and ranged from the headwaters to highly inter‐connected lakes receiving water from one to 768 upstream lakes. In all sites combined, 77 zooplankton species were found, including 56 rotifers, six copepods, 11 cladocerans, two fairy shrimp species, a mysid, and a tadpole shrimp. We show that the zooplankton communities differed between hydrologically isolated (ponds) and connected (lakes) systems, with 17 species unique to ponds and 20 to lakes. Furthermore, the communities were more similar within lake chains and hence in lakes closer to each other. In ponds, distances between waterbodies had no impact on community similarity. Zooplankton abundance was higher in lakes (255 ind/L) than in ponds (65 ind/L) due to the higher number of rotifers that accounted for nearly 80% of the zooplankton abundance in lakes. In ponds, rotifers, cladocerans, and copepods were equally abundant. In terms of biomass, cladocerans represented 65% of total biomass in all waterbodies except for a chain of deep lakes that had abundant fish communities. In these lakes, cladoceran abundance and biomass were low and probably limited by fish predation. Zooplankton production was higher in ponds (4.6 mgC m−3 day−1) than in lakes (1.7 mgC m−3 day−1), and within lakes was lowest in the chain composed of large lakes (1.3 mgC m−3 day−1). The high production in ponds was closely linked to high zooplankton biomass and further explained by high gross primary production supported by relatively high nutrient concentrations in these shallow systems. Our study emphasises that hydrological connectivity is key to shaping zooplankton communities, although fish presence also appears to affect them. It shows that isolated ponds (that currently account for c83% of all waterbodies on southern Victoria Island) are hotspots of aquatic biological productivity that probably play an essential role in Arctic freshwater landscapes. Finally, our study provides critical baseline information on the current composition of Arctic zooplankton communities important for estimating climate change impacts.

Hydrobiological characteristic of small lakes in northern Karelia during the ice-covered period

The life of lakes in winter is still insufficiently studied. The purpose of this article is a comparative analysis of the quantitative development of planktonic and benthic communities and the abiotic conditions of their existence during the ice-covered period in two small (<1 km2) northern lakes that differ greatly in morphometry and the degree of water humification. A significant difference was revealed in the seasonal dynamics of plankton communities in the studied lakes. In a deeper lake with water uncolored by humus, the quantitative development of phytoplankton at the end of the ice-covered period was almost as significant as during the open-water period. It is necessary to note the rapidity of changes in under-ice phytoplankton in early spring: in April 2020, the content of chlorophyll a in water changed more than six times during a week. There was no mass development of phytoplankton under the ice in a shallow highly humified lake. The zooplankton of the studied lakes was characterized by the opposite trend. In the deep-water lake, the winter zooplankton was noticeably inferior to the summer one in terms of the level of quantitative development; in the shallow lake, a high biomass (~1 g/m2) of zooplankton was noted throughout the entire study period. The macrozoobenthos of lakes in winter, on the whole, retained the same high level of quantitative development as in the open-water period. Seasonal differences were local and were caused by the redistribution of bottom animals due to changes in the oxygen and, possibly, temperature regime of bottom waters. In particular, due to hypoxic-anoxic conditions at the end of the ice-covered period, benthic animals migrated from the profundal zone of the deep-water lake. After the ice melted and the near-bottom waters were saturated with oxygen, the profundal community quickly recovered. Thus, the quantitative development of biological communities in winter can vary greatly even in closely located lakes, in particular, it depends on the degree of humification of the water body. Given the high dynamism of phytoplankton in early spring, the assessment of the role of the under-ice period in the life of lakes, apparently, requires long-term research, including detailed observations at the end of ice-covered period.

Plankton communities of the “Pregolya River – Vistula Lagoon – Kaliningrad Sea Channel (KSC) – Baltic Sea system”

The species composition, abundance and biomass, trophic relationships of phytoplankton and zooplankton, as well as the proportion of dead individuals in zooplankton were studied in the water system "Pregolya River – Kaliningrad Sea Channel (KSC) – Vistula Lagoon – Baltic Sea" in July, August and October 2021. In total 173 taxa of phytoplankton and 73 taxa of zooplankton were found during period of investigation. The maximal species diversity was observed in the summer period, in autumn it was decreasing. The maximum number of taxa for both phyto- and zooplankton was found in the Vistula Lagoon and in the KSC, the minimum – in the Baltic Sea. In summer the 3 communities in phytoplankton, 4 in zooplankton, in autumn – 3 communities in both phyto- and zooplankton were found. The plankton communities were confined to water areas with different salinity: The Pregolya River, the KSC and the Vistula Lagoon, the Baltic Sea. The dominant complex of species at the stations differed; species of a predominantly freshwater complex were noted in the Pregolya River, brackish-water species were found in the Vistula Lagoon, and a marine complex of species was identified at the stations of the sea strait and in the Baltic Sea. More abundant plankton communities both in summer and autumn were in the KSC and the Vistula Lagoon (phytoplankton biomass varied from 1.19 g/m3 to 11.89 g/m3; zooplankton biomass varied from 305 mg/m3 to 1801 mg/m3). In this area the most optimal conditions for the development of plankton were formed such as an increased nutrient content and maximum water heating. Plankton communities both in the Pregolya River and in the Baltic Sea in summer and autumn were less abundant (phytoplankton biomass varied from 0.16 g/m3 to 2.50 g/m3; zooplankton biomass varied from 34 mg/m3 to 468 mg/m3). The most intense trophic relationships in the plankton community in the summer in the Baltic Sea, optimal – in the KSC and in the Vistula Lagoon were formed. The proportion of dead individuals in the zooplankton of the studied system in both seasons was maximal in the areas, which had the critical salinity for hydrobionts and high turbulence conditions such as KSC, the Sea strait and at the exit from Sea strait.

Distribution of siphonophores in the Northwest Pacific Ocean and links to environmental conditions

Despite their abundance in marine ecosystems, studies on siphonophores are limited. In this study, 26 species of siphonophores in the Northwest Pacific Ocean were identified during multiple cruises of the R/V ISABU from 2018–2020, and various factors that may affect the occurrence of siphonophores, including water temperature, salinity, zooplankton biomass, and trophic niche were investigated. Statistical analysis revealed that the distribution of siphonophores and their biomass could be divided into two water mass groups, affected by the Kuroshio and Oyashio Currents. The species with high contributions to distinguishing the water mass groups (including Chelophyes contorta, Dimophyes arctica, Bassia bassensis, and Eudoxoides spiralis—mainly belonging to the Diphyidae) showed species-specific correlations with water temperature and salinity. This suggests that diphyids can be used as indicator species for currents and hydrological factors that influence water mass. The biomass of siphonophores exhibited a trend opposite to that of non-gelatinous zooplankton and showed no association with other gelatinous zooplankton. These results can be interpreted from an ecological niche perspective. Through nitrogen and carbon stable isotope analyses, the dietary sources of siphonophores could potentially overlap with those of chaetognaths or non-gelatinous zooplankton. Because the trophic position of siphonophores (2.4–3.2) also falls in the range of those of chaetognaths (2.8–3.4) and non-gelatinous zooplankton including copepods, euphausiids, and amphipods (2.4–3.5), diet competition with carnivorous mesozooplankton could be predicted. Considering that the diversity and biomass of most siphonophores are strongly positively correlated with water temperature and salinity, expansion of the Kuroshio Current is expected to lead to an increase in siphonophores in the Northwest Pacific in the future. The findings of this study are anticipated to provide novel insights into climate change prediction and response and enhance our understanding of siphonophore communities.

Impact of selective grazing on the dynamics of a diffusive plankton model with component Allee effect and additional food

In order to explore the pattern formation of non-toxic phytoplankton, toxin-producing phytoplankton, and zooplankton, a spatiotemporal plankton model is formulated by incorporating the component Allee effect, additional food, and selective grazing. For the non-spatial scenario, the qualitative analyses and numerical simulations show that the system admits rich dynamics such as Hopf bifurcation and alternative stable states. For the spatial model, the stability analyses demonstrate that the moderate component Allee effect and adequate additional food promote stable coexistence. Furthermore, our findings illustrate that selective grazing facilitates toxin-producing phytoplankton biomass. Low grazing selectivity decreases zooplankton biomass. Moderate grazing selectivity contributes to coexistence. Excessive grazing selectivity promotes the rapid reproduction of toxin-producing phytoplankton and leads to spatiotemporal chaos. In addition, the variations in the component Allee effect, additional food, and grazing selectivity give rise to the transitions of spatial patterns, which shed valuable insights into controlling plankton distribution.