The Sambia Peninsula (Kaliningrad region) is historically well known for its amber mining. The 2019 year was the last year of direct overburden disposal into the Baltic Sea as a part of technological amber mining process. The extremely high-suspended particulate matter concentrations during that disposal were recorded immediately after the discharge of significant volumes of pulp and reached 200 mg/L. The impact of pulp discharge had sequentially suppressed plankton communities development due to the high content of suspended solids and afterwards stimulated plankton development due to the glauconite infusion. Cladocera were the most sensitive group to the effects of suspended matter. According to the preliminary forecast, when the pulp discharge stops, the restoration of plankton communities may take from 1 to 2 seasons to 1 year for different groups. This is due to the timing of the removal of fine suspended particulate matter from sediments and the possibility of secondary entry during resuspension.

The mass development of diatoms Dactyliosolen fragilissimus and Cerataulina pelagica, atypical algae for the southeastern Baltic Sea (SEB) water area, were registered along the Sambia peninsula coastline in the middle of October 2020. Both species were found in the coastal zone off the western and northern coast of the Sambia peninsula from the Baltic Strait to port Pionerskiy at depths reaching 32 m. In early November 2021, C. pelagica bloomed both in the shallow coastal zone of the northern coast of the Sambia peninsula and in the deepwater zone of the SEB. The biomass of this species reached 2.8 g/m3. Both diatom species were abundant within the entire Russian exclusive economic zone (EEZ). The prevailing hydrological situation during the study period probably facilitated the penetration of the species into the study area by surface transport from the Arkona Basin.

The article presents a comparative analysis of the use of direct search algorithms to perform automatic tuning and assessment of parameter values for two models of nonstratified aquatic ecosystems: the Neva Bay (NB) and the Vistula Lagoon (VL) of the Baltic Sea. Both models are built on the same methodological principles, but they have different structures, different numbers of model variables and empirical parameters. For the VL ecosystem, the biohydrochemical block consists of two parts: the «Plankton block» and the «Benthos» block. Modeling of the nutrients transformation processes in the lagoon was carried out jointly for the aquatic environment and the upper (active) layer of bottom sediments. The NB ecosystem model uses the «Plankton block», and all processes are described only for the aquatic environment. Modeling enables to quantitatively investigate the mechanisms of biohydrochemical transformation processes: compounds of C, N, P and Si in the ecosystem of the VL; N and P compounds in the NB ecosystem. Both models provide the means to study the features of spatiotemporal dynamics of oxygen dissolved in water. The NB ecosystem model contains 58 empirical parameters, while the VL ecosystem model contains 330 ones. The Theil criterion was used as a criterion for the models adequacy. The optimization problem is solved due to the two-stage computer-aided direct search algorithm. A random search algorithm was used at the first stage. At the second stage, a local search is performed using the modified Nelder-Mead simplex method. The used algorithms proved to be effective. They ensure reliability and computational convergence of the obtained calculation results. The article shows that interannual differences in parameter values are statistically significant for a number of parameters of the models under consideration. The models sensitivity to changes in parameters values was assessed.

The structure and dynamics of plankton communities in the coastal zone of the Curonian Lagoon of the Baltic Sea from January to December 2017–2021 has been studied. It was found that, at the coastal shallow littoral station surrounded by macrophytes, the species diversity was higher and the quantitative characteristics of phytoplankton and zooplankton were lower in all seasons and years of the study than at the deeper coastal station located behind the macrophyte belt. The exception was the period when, as a result of surge events, the phytoplankton biomass in the coastal littoral in October–November 2018 increased to 326–627 g/m3. Every year, Cyanobacteria “blooms” with different intensities and durations were observed at the Lagoon. The abundance of cells of potentially toxic Сyanobacteria exceeded the World Health Organization standard, as a rule, in summer months at a deepwater coastal station, especially in 2017–2018. This had a negative impact on the state of the entire ecosystem, primarily on zooplankton organisms, in which communities the proportion of dead individuals increased. Water during the period of Cyanobacterial blooms in summer and autumn 2017–2018 also had an acute toxic effect on planktonic test organisms.

A systematic study of the interaction of hydrobiological, hydrochemical, hydrological, and hydrophysical processes that occur in the ecosystem of the Vistula Lagoon (VL) of the Baltic Sea has been carried out using mathematical modeling and taking into account the processes in the active layer of bottom sediments (BSs). The features of the dynamics of nitrogen and phosphorus compounds, the turnover time, and the components of the balance of compounds of biogenic elements in the VL ecosystem, as well as the degree of their temporal variability, have been analyzed. It is shown that the variability of nitrogen and phosphorus compounds in the aquatic environment increases in spring and autumn periods. This is due to an increase in river flow into the lagoon and an increase in the level of external biogenic load on the water area of the VL. Model calculations of matter fluxes allow us to state that the inputs of dissolved organic and suspended matter into the lagoon from external sources and the removal to the Baltic Sea are important processes that significantly affect their content in the VL ecosystem. It has been established that under strong winds the process of sedimentation of suspensions can be largely blocked, and the intensity of BS resuspension can increase significantly. An analysis of the main qualitative and quantitative features of the nature of the temporal dynamics of the DON and DOP turnover times, as well as the mineral compounds of nitrogen and phosphorus, indicates a close conjugation of the processes of transformation of dissolved organic and inorganic substances in the water of the VL. A quantitative assessment of the processes of consumption and excretion of compounds of biogenic elements by different groups of aquatic organisms has been performed, and the important role of heterotrophic bacterioplankton and protozoa in the processes of transformation of compounds of nutrients in the VL ecosystem has been shown. The model can be used for scenario modeling and analyzing possible changes in the VL ecosystem under changing climatic and anthropogenic conditions.

In this work, potential (by the fluorescence method) and realized (by the radiocarbon method) phytoplankton primary production and the production of heterotrophic bacteria were determined in the euphotic zone of the seaward part of the Gdansk Bay of the Baltic Sea in summer and autumn. The maximum quantum efficiency of photosystem II of phytoplankton (Fv/Fm) varied significantly in depth in June (0.33–0.59), but was uniformly very high in October (0.68–0.71), which indicates a potentially more active state of early autumn phytoplankton. Integral primary production in October was almost two times higher than in June (633 and 375 mg C/m2 per day, respectively), while bacterial production was one-and-a-half times lower (239 and 371 mg C/m2 per day, respectively). In the upper tenth layer of the water column, autotrophic production (phytoplankton) only slightly exceeded heterotrophic (bacterial) production in June (63

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.

The article describes the general structure of the simulation model, the most important principles for describing the processes of bio-hydrochemical transformation of nutrient (C, N, P, Si) compounds, and the dynamics of dissolved oxygen in the ecosystem of the Vistula Lagoon (VL), Baltic Sea. Based on the results of long-term observations, tuning of the model parameters was performed, its adequacy and sensitivity to changes in parameter values were checked, within-year variations of nutrient compounds, components of the planktic and benthic parts of the VL ecosystem, turnover periods, as well as fluxes (balances) of dissolved and suspended solids between the selected components of the model were calculated and analyzed. Model calculations showed fairly good qualitative and quantitative correspondence of the simulated results to observed data for all variables of the simulation model. Practical implementation of computational procedures for model tuning proves that with the proposed algorithms for finding the parameters for the bio-hydrochemical block of the simulation model the optimization problem can be solved effectively even where the amount of observed data is insufficient and their variance is rather high. Attention should be given to statistically significant among-year variations in the values of the empirical parameters of the model. One should be cautious using the same values of model parameters in running computational experiments for different years of observations and in predicting VL ecosystem development in response to changes in external conditions. We quantified turnover times for the model components of the VL ecosystem. In a vast majority of cases there existed significant among-year variations in the turnover times for the model variables. Calculations of the balances of dissolved organic substances, as well as detrital nitrogen, phosphorus, and silicon have led us to an important conclusion that heterotrophic bacterioplankton and protozoa play a significant role in the processes of nutrient compound transformation in the lagoon ecosystem.

The seasonal dynamics of production processes in the Baltic Sea are poorly studied. The aim of our research was to study the seasonal features of primary productivity (including the balance with bacterial production) and its redistribution in plankton in the southeastern part of the Baltic Sea in different seasons. More than 70% of primary production is formed in the 0–10 m layer (74–97% of the PP in the euphotic layer). In the same layer, PP accounted for almost 100% of the sum of primary and bacterial production in April and October, and almost 60% in June. Photosynthetic efficiency (PP/rETR) increased in June and October, demonstrating an increase in phytoplankton utilization of absorbed light energy. The depth-integrated values of PP, Chl a, bacterial, and phytoplankton biomasses were maximal in October. The maximum values of zooplankton biomass were determined in June, and they were significantly (5–14 times) higher than in other seasons. The maximum values of bacterial production were also in June.

Ideas and methods of catastrophe theory are widely used to analyze “regime shifts” in ecosystems. In this work, the analysis of the seasonal dynamics of phytoplankton in the Russian part of the Vistula Lagoon of the Baltic Sea is carried out on the basis of using the simplest possible model of the catastrophe theory − cusp catastrophe. The total phytoplankton biomass is considered as a state variable. The use of one of the methods of multivariate analysis − principal components method − made it possible to carry out the entire analysis depending on a small number of parameters. A calculation of the control parameters values is carried out using the factor loadings of the main components for the data that characterize the hydro-physical and hydro-chemical regimes as well as the level of biogenic loading on the aquatic ecosystem of the lagoon. It was found that, depending on the specific situation, the same factor or different combinations of factors can play both a stabilizing role and be the cause of destabilization.

Our study examines the features of photosynthetic processes that occurred in the coastal area of the south-eastern Baltic Sea during the advanced phase of intensive summer bloom of 2018. We aim for a better understanding of short-time variability in primary production coupled with planktonic composition and phytoplankton functional activity in relation to location of nutrients sources on the coast and sub-mesoscale eddies, which appear over the coastal slope of Cape Taran and move alongside the Sambia Peninsula coast. These two-day studies, conducted on board of research vessels, represent a snapshot of a highly variable ecosystem alongside the Sambia Peninsula and Curonian Spit at the end of summer. Satellite images of sea surface temperatures and chlorophyll «a» concentration were also used for identification of spatial variations and eddies; the circulation conditions were derived from the operational system SatBaltyk. Across the coastal area, the effects of physico-chemical conditions influenced the phytoplankton composition and photosynthetic activity. In the south, the hot weather as well as the impacts of the Vistula Lagoon and the Amber combine affected the increase of nutrients and caused the strongest cyanobacterial bloom. In the Cape Taran area, the plankton community was transformed as a result of sub-mesoscale eddies development. Substantial gradients of nutrients, composition, biomasses and functional activity of phytoplankton along transects through eddies field was shown. Collecting of samples was done with a support of the state assignment of Shirshov Institute of Oceanology, Russian Academy of Sciences (topic no. 0149-2019-0013). Data processing was supported by the state assignment of Shirshov Institute of Oceanology, Russian Academy of Sciences (topic no. 0149-2019-0006) and RFBR grant ( no.19-05-50090).

Seasonal variations in marine primary production (PP) in the coastal zone of the south-eastern part of the Baltic Sea were studied between April 2008 and April 2009. The spring PP maximum was observed to be limited by the concentration of nitrates. Following a decrease in photosynthetic consumption of nutrients, an increase in ammoniacal nitrogen due to the decomposition of organic matter and concomitant increase in the biomass of diazotrophic cyanobacterial species, the growth of phytoplankton was limited by phosphates. By the middle of summer, concentrations of nitrate and phosphates had reached the analytical minimum (0.07 mmol m(-3) and 0.06 mmol m(-3), respectively). Terrestrial runoff, whose maximum occurred during the spring-summer decline of phytoplankton growth, had a moderately positive influence on PP, with the annual rate reaching the eutrophic level (290 g C m(-2) yr(-1)); however, the seasonal cycle was typical for mesotrophic waters of temperate latitudes of the Northern Hemisphere. The most significant producers of phytoplankton biomass (PB) were representatives of the Dinophyta, Chlorophyta and Cyanophyta systematic divisions at the study site. 77% of carbon-to-chlorophyll a ratio variability was determined by the seasonal variations in green algae biomass. During the spring bloom, dinoflagellates provided the highest contribution in the total biomass in comparison with diatoms. (c) 2019 Elsevier B.V. All rights reserved.

In the paper the statistical relationships between the size and production characteristics of phytoplankton and zooplankton of the Vistula and Curonian lagoons, the Baltic Sea, were investigated. Research phytoplankton and zooplankton within the Russian part of the area of the Vistula and the Curonian lagoon was carried out on the monthly basis (from April to November) within the framework of long-term monitoring program on evaluating of ecological status of the lagoons. The size structure of plankton is the basis for understanding of the development of production processes, mechanisms of formation of the plankton species diversity and functioning of the lagoon ecosystems. As results of the work it was found that the maximum rate of photosynthesis and the integral value of the primary production with a change in cell volume of phytoplankton are changed according to a power law. The result shows that the smaller the size of algal cells in phytoplankton communities the more actively occur metabolism and the more effective they assimilate the solar energy. It is shown that the formation of plankton species diversity in ecosystems of lagoons is closely linked with the size structure of plankton communities and with features of development of the production processes. It is proposed the structure of a spatially homogenous mathematical model of the plankton food chain for the lagoon ecosystems taking into account the size spectrum and the characteristics of phytoplankton and zooplankton. The model parameters are the sizedependent indicators allometrically linked with average volumes of cells and organisms in different ranges of their sizes. In the model the algorithm for changes over time the coefficients of food preferences in the diet of zooplankton was proposed. Developed the size-dependent mathematical model of aquatic ecosystems allows to consider the impact of turbulent exchange on the size structure and temporal dynamics of the plankton food chain of the Vistula and Curonian lagoons. The model can be used to study the different regimes of dynamic behavior of plankton systems depending on the changes in the values of its parameters and external influences, as well as to quantify the redistribution of matter flows in ecosystems of the lagoons.

The results of laboratory experiments on studying the characteristics of feeding of natural populations of Daphnia galeata from the freshwater Curonian Lagoon on cyanobacteria using the counting and radioisotope methods are discussed. The consumption and assimilation of the cyanobacterium Aphanizomenon flos-aquae by Daphnia have been revealed, as has the inhibition of feeding in Daphnia by species of the genus Microcystis. The results of PCR analysis of the total DNA of plankton from the Curonian Lagoon and enzyme-linked immunosorbent assay have proved the ability of Microcystis populations to produce microcystins, while no genes involved in the synthesis of cyanotoxins have been found in A. flos-aquae.

In 2002–2008, seasonal (April–November) monitoring of the phytoplankton in the Russian part of the Curonian Lagoon at five fixed sites was performed. A total of 91 Cyanobacteria, 100 Bacillariophyta, 280 Chlorophyta, 21 Cryptophyta, and 24 Dinophyta species were found. Six potentially toxic species of cyanobacteria: Aphanizomenon flos-aquae , Anabaena sp., Microcystis aeruginosa , M. viridis , M. wesenbergii , and Planktothrix agardhii dominated the phytoplankton biomass and caused water blooms. The seasonal average phytoplankton biomass ranged from 30 to 137 g/m 3 . The cyanobacteria’s biomass varied from 10 to 113 g/m 3 forming 30–82% of the total with a mean of 50%. With the aid of genetic markers (microcystin ( mcy ) and nodularin synthetases), six variants of the microcystin-producing gene mcy E from the genus Microcystis were identified. Due to the intensive and lengthy blooms of potentially toxic and toxigenic cyanobacteria, the environmental conditions in the Curonian Lagoon appear unfavorable. The water should be monitored for cyanotoxins with analytical methods in order to determine if the area is safe for recreational use.

Мониторинг фитопланктона проводили с апреля по ноябрь 2002–2008 гг. в российской части Куршского залива на 5 постоянных станциях. Был выявлен 91 вид цианобактерий, 100 видов диатомовых, 280 видов зеленых, 21 вид криптофитовых, 24 вида динофитовых, однако доминировали по биомассе и вызывали “цветение” воды 6 видов, являющихся потенциально токсичными: Aphanizomenon flos-aquae, Anabaena sp., Microcystis aeruginosa, M. viridis, M. wesenbergii, Planktothrix agardhii. Средняя за вегетационный период биомасса фитопланктона в исследуемые годы варьировала от 30 г/м3 до 137 г/м3, цианобактерий – от 10 г/м3 до 113 г/м3. Доля синезеленых от суммарной биомассы составляла от 33% до 82%, при среднем значении 50% в исследованные сезоны. С помощью генетических маркеров к микроцистин- и нодулярин-синтетазе выявлено 6 различных генотипов, принадлежащих цианобактериям рода Microcystis. Из-за интенсивных и продолжительных “цветений” воды потенциально токсичными и токсиногенными цианобактериями экологическую ситуацию в Куршском заливе можно оценить как неблагополучную. Для выяснения возможности рекреационного использования данного водоема без риска для здоровья людей необходим мониторинг цианотоксинов в воде с помощью аналитических методов.

The trophic relationships of the phytoplankton and zooplankton in the Vistula Lagoon in 2008–2010 were investigated. In the current period, the lagoon is an eutrophic water body with summer blooms of blue-green algae. The trophic level of the Vistula Lagoon influences both the composition and quantitative characteristics of the communities of phytoplankton and zooplankton and the trophic relationships between them. In the analyzed period, the consumption of phytoplankton by the zooplankton on the average in the growing season was 28%, which is 1.5 times higher than in the late 1970s. The high grazing pressure of the zooplankton on the phytoplankton reduces its biomass, production, and the intensity of the blooming by the blue-green algae in the Vistula Lagoon.

The abundance and distribution of predatory cladoceran Leptodora kindtii was investigated in the estuarine lagoon (Curonian Lagoon, SE Baltic Sea). Three hydrodynamically different parts of the lagoon were selected, representing transitory oligohaline, intermediate freshwater and stagnant freshwater sites. L. kindtii was least abundant at the oligohaline site, never occurring at salinities greater than 4 psu. At the two freshwater sites, the abundance of L. kindtii varied from a low of <0.1 up to 2.2 indv. L−1 during peak abundance. Two peaks of L. kindtii abundance were observed with timing differences between stations: at the stagnant site the population of L. kindtii peaked two weeks earlier relative to the more hydrodynamically active sites, likely due to a 2°C higher May temperature. The small body size of L. kindtii in the lagoon (seasonal mean 2.68±0.6 mm) shows high fish predation pressure and predicts small cladocerans, juvenile copepods and rotifers being in the preferred prey size range. The calculated L. kindtii daily consumption during the population peak was as high as 100% of the daily zooplankton production, which implies high potential of this predator to shape the grazing zooplankton community in the lagoon.