Baltic Sea Water Research Articles

Migratory pathways and winter destinations of Northern Gannets breeding at Helgoland (North Sea): known patterns and increasing importance of the Baltic Sea

We analysed the migratory behaviour of adult Northern Gannets (Morus bassanus) breeding at Helgoland in the North Sea, based on data obtained from geolocation devices in the non-breeding season 2016–2017. Birds moved east and south-west to a broad range of wintering sites, ranging from the western Baltic Sea to North-West Africa. Three out of 12 birds spent the winter in Africa, while 9 birds wintered in Europe, with the primary wintering sites in the North Sea. All but one tagged bird spent some time in the Baltic Sea or in the transitional waters between the North Sea and Baltic Sea. We also analysed data from online databases (dofbasen.dk, ornitho.de) and the German Seabirds at Sea database to explore the extent to which Northern Gannets used the western Baltic Sea, as well as the Kattegat and Skagerrak, during the winter months. Records of Northern Gannets in Danish waters have increased substantially over the last 18 winters, with particular increases in the Baltic Sea. There was also a notable increase in sightings of Northern Gannets in German Baltic Sea waters, but this occurred later than in the more northerly Danish waters. Both analyses demonstrated that Northern Gannets explored the western part of the Baltic Sea, as well as the Kattegat and Skagerrak, increasingly intensively. This recent increase in sightings is in accord with the establishment and exponential increase in the nearest breeding colony of Northern Gannets at Helgoland.

Estimation of net accumulation and removal of fluorescent dissolved organic matter in different Baltic Sea water masses

This study aimed to detect non-conservative processes that affect the distribution of fluorescent dissolved organic matter (FDOM) in the Baltic Sea. An extensive data set comprised of 408 FDOM data, optical and physical profiles, and the development of a water masses balance model allowed us to ascertain the sources of mixing anomalies. These were seen as second-order deviations in the FDOM distribution as a function of salinity in three layers: surface water, Baltic Sea Winter Water, and deep water. The difference between modeled and measured FDOM values at three different excitation/emission wavelengths allowed to show the strength of non-conservative processes, such as photochemical and microbial decomposition (negative residual values) or extracellular release of dissolved organic matter from phytoplankton, heterotrophic uptake and release from anoxic sediments (positive residual values). Humic-like FDOM fractions displayed positive residuals in all seasons for intermediate and deep layers and negative residuals in surface waters. Largest accumulation rates of humic-like fractions were reached in the Gulf of Gdańsk during summer in intermediate and deep layers, while the greatest removal in surface waters was observed during spring in the Bornholm and Gotland Basins and during summer in the Gulf of Gdańsk, probably due to photodegradation. Positive residuals of the protein-like fraction were observed at the surface in summer and autumn in the Gulf of Gdańsk, probably linked to the abundance of phytoplankton and also due to the low molecular weight by-products of photodegradation of humic-like components. Spatial transects revealed an increase in humic-like residuals with depth and a strong correlation with apparent oxygen utilization, increasing with higher fluorescence and exhibiting an asymptotic trend. A relationship was found between the protein-like fractions and phytoplankton biomass proxies. A generalized concept for FDOM cycling in the Baltic Sea was proposed, highlighting photobleaching as the dominant non-linear process determining the efficiency of humic-like FDOM removal. The protein-like component was found to be more efficiently taken up by aerobic prokaryotes at the surface. Microbial utilization and reworking of organic matter, release from sediments, and a decade-long stagnation of bottom water masses, all contribute to the observed accumulation of FDOM in mesohaline deep waters below the permanent pycnocline in the Baltic Sea.

Simulating sea level extremes from synthetic low-pressure systems

Abstract. In this article we present a method for numerical simulations of extreme sea levels using synthetic low-pressure systems as atmospheric forcing. Our simulations can be considered to be estimates of the high sea levels that may be reached when a low-pressure system of high intensity and optimal track passes the studied region. We test the method using sites located along the Baltic Sea coast and simulate synthetic cyclones with various tracks. To model the effects of the cyclone properties on sea level, we simulate internal Baltic Sea water level variations with a numerical two-dimensional hydrodynamic model, forced by an ensemble of time-dependent wind and air-pressure fields from synthetic cyclones. The storm surges caused by the synthetic cyclones come on top of the mean water level of the Baltic Sea, for which we used a fixed upper estimate of 100 cm. We find high extremes in the northern Bothnian Bay and in the eastern Gulf of Finland, where the sea level extreme due to the synthetic cyclone reaches up to 3.5 m. In the event that the mean water level of the Baltic Sea has a maximal value (1 m) during the cyclone, the highest sea levels of 4.5 m could thus be reached. We find our method to be suitable for use in further studies of sea level extremes.

Anthropogenic Forcing of the Baltic Sea Thallium Cycle.

Anthropogenic activities have fundamentally changed the chemistry of the Baltic Sea. According to results reported in this study, not even the thallium (Tl) isotope cycle is immune to these activities. In the anoxic and sulfidic ("euxinic") East Gotland Basin today, Tl and its two stable isotopes are cycled between waters and sediments as predicted based on studies of other redox-stratified basins (e.g., the Black Sea and Cariaco Trench). The Baltic seawater Tl isotope composition (ε205Tl) is, however, higher than predicted based on the results of conservative mixing calculations. Data from a short sediment core from East Gotland Basin demonstrates that this high seawater ε205Tl value originated sometime between about 1940 and 1947 CE, around the same time other prominent anthropogenic signatures begin to appear in the same core. This juxtaposition is unlikely to be coincidental and suggests that human activities in the surrounding area have altered the seawater Tl isotope mass-balance of the Baltic Sea.

Diphyllobothrium sp. and Other Parasites of Migrating and Rare Fish Species in the Southern Baltic Sea and Coastal Waters, Poland.

The present study is the first to analyse the parasite fauna of sole Solea solea, dab Limanda limanda, hake Merluccius merluccius, whiting Merlangius merlangus, and plaice Pleuronectes platessa in the Pomeranian Bay, as well as saithe Pollachius virens from the Szczecin Lagoon (Poland). The aim of this study was to determine the occurrence of parasites in migrating and rare fish in the Pomeranian Bay and the Szczecin Lagoon and to determine the composition of the diet of these fish. The fish for analysis were obtained in the years 2010-2019. The typical marine nematode Capillaria (Procapillaria) gracilis, rarely recorded in Poland, was found, in addition to the following parasites: Ichthyophonus hoferi, Trichodina jadranica, Diphyllobothrium sp., Dichelyne (Cucullanellus) minutus, Raphidascaris acus, Anisakis simplex, Contracaecum osculatum, Hysterothylacium aduncum, Pseudoterranova decipiens, and Echinorhynchus gadi. Because the fish species analysed in the study are not typically present in the Baltic (with the exception of plaice), and because we do not know how long they feed while they are in the Baltic, we cannot be certain which parasites they acquired in the water bodies analysed in the study and which were introduced during the migration of fish. Although these fish are outside of their normal geographic range (except for plaice), in the new environment, there were enough suitable intermediate hosts for the parasites of these fish to complete their life cycle and survive.

Variability of chlorophyll a concentration in surface waters of the open Baltic Sea

In situ, satellite and reanalysis data from numerical models were used to study the characteristic features of Chl variability in the Baltic Sea. The analysis is focused on the years 2003–2020 when regular observations of ocean color with the MODIS AQUA are available. In the Baltic Sea, there is a pronounced annual cycle in physical conditions in the water column, driven by seasonal cycles in atmospheric forcing. The seasonal cycle of Chl concentration does not conform to the picture known from classical models, with low phytoplankton concentration when nutrients are low. In contrast, in the Baltic Sea, the concentration of Chl is high even during the summer months when nutrients are depleted. This can be explained by a continuous supply of nutrients by runoff from land, as well as by a significant contribution to primary production by phytoplankton able to survive in environment poor in dissolved nutrients. There is also a considerable interannual variability in Chl. There are many possible cause/effect interactions involved, but the data series are still too short to make clear which of them are the most important. The most striking event was a spring bloom in 2008.

Spatial distribution of the diatoms <i>Dactyliosolen fragilissimus</i> and <i>Cerataulina pelagica</i> in the autumn phytoplankton of the South-Eastern Baltic in 2020–2021

The mass development of diatom Dactyliosolen fragilissimus and Cerataulina pelagica, which are atypical of the South-East Baltic Sea water area, were registered along the Sambia peninsula coastline in the mid of October 2020. Both species were found in the coastal zone of the western and northern coast of the Sambia peninsula to a depth of 32 m, from the Baltic Strait to port Pionerskiy. In early November 2021 a mass vegetation of C. pelagica was recorded –both in the shallow coastal zone of the northern coast of the Sambia peninsula and in the deep water zone of the South-Eastern Baltic Sea. The biomass of this species reached 2.8 g/m3. Both diatom species were abundant within the entire Russian Exclusive Economic Zone. The prevailing hydrological situation during the study period probably facilitated penetration of the species into the study area by surface transport from the Arkona Basin.

Hybrid desalination system for Baltic Sea water: A preliminary study

The world's water resources predominantly comprise salt water. In the face of forecasts of increasing demand for hydrogen obtained by electrolysis, it is becoming important to investigate the feasibility of seawater desalination. As part of a research project, the possibility of using a hybrid zero liquid discharge (ZLD) desalination system to desalinate seawater from the Baltic Sea was examined. In addition to analysing the operating parameters of the system, a detailed physico-chemical examination of the process water was carried out at each stage of treatment. It was found that the reverse osmosis (RO) and multiple-effect desalination (MED) systems allow sufficient water parameters to be obtained to feed the ion exchange (IX) system, and after deionisation it is possible to achieve the water parameters required by proton exchange membrane (PEM), anion exchange membrane (AEM) and alkaline water (AWE) electrolysers. Furthermore, the possibilities of concentrating brine in the multiple-effect desalination system and extracting salt in solid form in the ZLD system were verified.

Case report: first data on the foraging behaviour of velvet scoters (Melanitta fusca) in soft-bottom coastal waters of the southeast Baltic Sea

BackgroundThe foraging behaviour of sea ducks has always been difficult to study due to their exclusive occupancy of coastal waters during the wintering season. In this study we investigated the foraging behaviour of seven wintering velvet scoters (Melanitta fusca) in Lithuanian soft-bottom coastal waters by attaching a solar-powered external GPS‐GSM transmitter to each individual bird. This transmitter data allowed us to analyse the dive phase parameters and feeding depths during December 2021 and March 2022.ResultsThe results showed that velvet scoters dived deeper than a 30-m depth, with the dive duration lasting up to 90 s on average. The bottom duration increased rapidly in the first 5 m and then levelled off at around 40 s for deeper waters. The underwater duration varied between 2 and 7.5 h a day. The dive effort (as total underwater time) and the bottom duration of velvet scoters were related to the depth and prey biomass, although both factors were demonstrated to be interdependent. Moreover, the results showed that velvet scoters were less active in December than in March in terms of both average diving duration and diving frequency. The results also confirmed the high diurnal activity of the velvet scoter, although the birds demonstrated night activity in December and not in March.ConclusionThis information on the velvet scoter’s foraging behaviour may have important implications for the conservation of the species, and provides new insights into the improvement of conservation measures for the species in the Baltic Sea.

Population structure and density of a new invasive species Rangia cuneata in the Szczecin Lagoon (Odra/Oder estuary, Poland)

The native North American bivalve species Rangia cuneata was unintentionally introduced into European waters during the first decade of the 21st century. In the Baltic Sea, it is mostly found along the southeastern coast, but in 2018 researchers also discovered the species in the Bay of Pomerania, which indicated that it could eventually inhabit the adjacent Szczecin Lagoon and Odra River. In 2021, the species was discovered for the first time in the Szczecin Lagoon during a sampling campaign, at 5 out of the 12 dispersed study sites with diverse bottom substrates. The goal of this study was to ascertain R. cuneata population density, morphometric parameters, individual growth, and the potential for further expansion in the southern Baltic Sea waters. For the study, 201 individuals of this species were collected. Compared to other sites in the southeast Baltic, the Szczecin Lagoon had a much lower average R. cuneata population density, at 13.2 ± 7.11 individuals m-2 of the bottom area. The highest population density was found at sites with more silt (4–63 µm) and less sand (>63 µm). R. cuneata shells had an average length of 30.9 ± 4.6 mm and an average weight of 6.6 ± 2.8 g. The collected specimens were greater in size than other populations of the species in the Baltic Sea and were comparable in size to populations from the nearby Bay of Pomerania. There were no specimens that were under 10 mm in length, and the population was dominated by specimens in the 25–30 mm and 30–35 mm ranges, as well as the 3+ and 4+ age groups. Given the R. cuneata’s invasive potential and its fast rate of colonization of new areas, it would be prudent to monitor this population and the species migration patterns across the estuary waters of the western Baltic.

Anomalous NO[formula omitted] emitting ship detection with TROPOMI satellite data and machine learning

Starting from 2021, more demanding NOx emission restrictions were introduced for ships operating in the North and Baltic Sea waters. Since all methods currently used for ship compliance monitoring are financially and time demanding, it is important to prioritize the inspection of ships that have high chances of being non-compliant. The current state-of-the-art approach for a large-scale ship NO2 estimation is a supervised machine learning-based segmentation of ship plumes on TROPOMI/S5P images. However, challenging data annotation and insufficiently complex ship emission proxy used for the validation limit the applicability of the model for ship compliance monitoring. In this study, we present a methodology towards the automated and scalable selection of potentially non-compliant ships using a combination of machine learning models on TROPOMI satellite data. It is based on a proposed regression model predicting the amount of NO2 that is expected to be produced by a ship with certain properties operating in the given atmospheric conditions. The model does not require manual labeling and is validated with TROPOMI data directly. The differences between the predicted and actual amount of produced NO2 are integrated over observations of the ship in time and are used as a measure of the inspection worthiness of a ship. To add further evidence, we compare the obtained results with the results of the previously developed segmentation-based method. Ships that are also highly deviating in accordance with the segmentation method require further attention. If no other explanations can be found by checking the TROPOMI data, the respective ships are advised to be the candidates for inspection.

Changes of Hydrological Extremes in the Center of Eastern Europe and Their Plausible Causes

Regional studies of precipitation changes over Europe show that its eastern part is characterized by small changes in annual precipitation and insignificant aridity trends compared to central and southern Europe. However, a frequency analysis over the past 30 years showed statistically significant increasing dryness trends in eastern Europe and an increase in the occurrence of extremely high rainfall as well as prolonged no-rain intervals during the warm season. The largest increase in aridity was observed in the western and central parts of Belarus. During 1990–2020, the frequency of dry periods doubled in all river basins along the Black, Caspian, and Baltic Sea water divide areas of eastern Europe. From 1970 to 1990, there were high streamflow rates during the winter low-flow season. Consequently, over the past 50 years, in spring, we observed here a continued decrease in maximal discharges across all river basins. In summer, we detected a statistically significant increase in the number of days with anticyclonic weather over eastern Europe, a decrease in rainfall duration by 15–20%, an increase in daily precipitation maxima by 20–30%, and an increase in the number of days with a low relative humidity by 1–4 days per decade.

Stratigraphic records and inventories of anthropogenic 233U and 236U in Baltic Sea sediments

This work reports the first comprehensive observation for the distribution of 233U and 236U in sediment cores collected from the major basins across the Baltic Sea. In addition to 233U and 236U, this study encompassed the analysis of 137Cs, 239Pu and 240Pu in the same sediment core samples. Depth profiles of 233U and 236U in Baltic Sea sediments indicate that 233U or global fallout (GF)-derived 236U is a useful time marker, in addition to 239+240Pu, to identify the onset of the Anthropocene epoch. Based on the cumulative areal inventories reported previously for water columns and investigated herein for sediment cores, our estimated overall inventories of 233U and 236U in the present Baltic Sea water and sediment are about 18 ± 6 g and 2010 ± 547 g, respectively, with >80 % accumulated in the Baltic seabed (i.e., 16 ± 6 g of 233U and 1694 ± 522 g of 236U, respectively). The total budget for nuclear reactor (NR)-derived 236U in the Baltic seabed is estimated to be 683 ± 223 g. Despite covering only 13 % of the total area, the hypoxic regions (325 ± 64 g) reserve a nearly equivalent amount of NR-derived 236U as the oxygenated regions (358 ± 159 g), highlighting the significance of the hypoxic regions in retaining NR-derived 236U. With a multi-radionuclide approach, this work contributes to a more thorough understanding on distribution and accumulation of anthropogenic uranium in the Baltic Sea.

The influence of microtopography on soil carbon accumulation and nutrient release from a rewetted coastal peatland

Coastal peatlands have been frequently blocked from the sea and artificially drained for agriculture. With an increasing awareness of ecosystem functions, several of these coastal peatlands have been rewetted through dike removal, allowing seawater flooding. In this study, we investigated a recently rewetted peatland on the Baltic Sea coast with the aim to characterize the prevailing soils/sediments with respect to organic matter accumulation and the potential release of nutrients upon seawater flooding. Eighty disturbed soil samples were collected from two depths at different elevations (–0.90 to 0.97 m compared to sea level) and analyzed for soil organic matter (SOM) content and carbon:nitrogen (C:N) ratio. Additionally, nine undisturbed soil cores were collected from three distinct elevation groups and used in leaching experiments with alternating freshwater and Baltic Sea water. The results demonstrated a moderate to strong spatial dependence of surface elevation, SOM content, and C:N ratio. SOM content and C:N ratio were strongly negatively correlated with elevation, indicating that organic matter mineralization was restricted in low-lying areas. The results also showed that the soils at low elevations release more dissolved organic carbon (DOC) and ammonium (NH4+) than soils at high elevations. For soils at low elevations, higher DOC concentrations were observed when flushing with freshwater, whereas higher NH4+ concentrations were found when flushing with brackish water. Recorded NH4+ concentrations in organic-rich peat reached 14.82 ± 9.25 mg L–1, exceeding Baltic seawater (e.g., 0.03 mg L–1) by two orders of magnitude. A potential sea level rise may increase the export of NH4+ from low-lying and rewetted peat soils to the sea, impacting adjacent marine ecosystems. Overall, in coastal peatlands, geochemical processes (e.g., C and N cycling and release) are closely linked to microtopography and related patterns of organic matter content of the soil and sediments.

Four Novel Caudoviricetes Bacteriophages Isolated from Baltic Sea Water Infect Colonizers of Aurelia aurita.

The moon jellyfish Aurelia aurita is associated with a highly diverse microbiota changing with provenance, tissue, and life stage. While the crucial relevance of bacteria to host fitness is well known, bacteriophages have often been neglected. Here, we aimed to isolate virulent phages targeting bacteria that are part of the A. aurita-associated microbiota. Four phages (Pseudomonas phage BSwM KMM1, Citrobacter phages BSwM KMM2-BSwM KMM4) were isolated from the Baltic Sea water column and characterized. Phages KMM2/3/4 infected representatives of Citrobacter, Shigella, and Escherichia (Enterobacteriaceae), whereas KMM1 showed a remarkably broad host range, infecting Gram-negative Pseudomonas as well as Gram-positive Staphylococcus. All phages showed an up to 99% adsorption to host cells within 5 min, short latent periods (around 30 min), large burst sizes (mean of 128 pfu/cell), and high efficiency of plating (EOP > 0.5), demonstrating decent virulence, efficiency, and infectivity. Transmission electron microscopy and viral genome analysis revealed that all phages are novel species and belong to the class of Caudoviricetes harboring a tail and linear double-stranded DNA (formerly known as Siphovirus-like (KMM3) and Myovirus-like (KMM1/2/4) bacteriophages) with genome sizes between 50 and 138 kbp. In the future, these isolates will allow manipulation of the A. aurita-associated microbiota and provide new insights into phage impact on the multicellular host.

Variability of light absorption coefficients by different size fractions of suspensions in the southern Baltic Sea

Abstract. Measurements of light absorption coefficients by particles suspended in seawater (ap(λ)), by phytoplankton (aph(λ)) and detritus (ad(λ)) were carried out in the southern Baltic Sea for the original seawater samples and four size fractions: pico-particles (0.2–2 µm), ultra-particles (2–5 µm), nano-particles (5–20 µm) and micro-particles (20–200 µm). Chlorophyll a (Chl a) and suspended particulate matter (SPM) concentrations were determined. The proportions of particles from the size classes in the ap(443), aph(443) and ad(443) were determined. Pico- and ultra-particles had the largest contribution to the total particle absorption – an average of 38 % and 31 %. Particles of 5–20 µm accounted for approximately 20 % of ap(443) and aph(443) and 29 % of ad(443). The contribution of particles > 20 µm averaged 5 %–10 %. In total SPM contribution of micro-particles averaged 17 %; nano-, ultra- and pico-particles averaged 29 %, 26 % and 27 %, respectively. In total Chl a, the proportions of pico- and ultra-particles averaged 35 % each, nano-particles 16 % and micro-particles 15 %. Temporal and spatial variability of particles contributions in size classes were observed. The average chlorophyll-specific and mass-specific light absorption coefficients, i.e., light absorption coefficients normalized to Chl a or SPM, were determined for all size fractions. The chlorophyll-specific coefficients ap(Chla)(λ), ad(Chla)(λ) and aph(Chla)(λ), ± standard deviations, do not allow clear separation of the individual fractions. For mass-specific coefficients, ap(SPM)(λ), ad(SPM)(λ) and aph(SPM)(λ), it is possible to distinguish between large particles (20–200 µm) and small and medium particles (0.2–20 µm). These results will allow monitoring of suspended matter in size classes in optically complex waters of southern Baltic Sea.

Hydrogeochemical characterisation of the groundwater in the crystalline basement of Forsmark, the selected area for the geological nuclear repositories in Sweden

Numerous groundwater analyses from the crystalline bedrock in the Forsmark area have been performed between 2002 and 2019, together with thorough geological, geophysical, and hydrogeological studies, within the site investigations carried out by the Swedish Nuclear Fuel and Waste Management Company. The groundwater samples have been taken from boreholes down to ≈ 1000 m and the analysis include major- and trace-elements, stable and radiogenic isotopes, gases and microbes. The chemical and isotopic composition of these groundwaters evidences the presence of non-marine brackish to saline groundwaters with very long residence times (many hundreds of thousands of years) and a series of complex mixing events resulting from the recharge of different waters over time: glacial meltwaters, probably from different glaciations of which the latest culminated some 20,000 years ago, and marine waters from the Baltic starting some 7000 years ago. Later, meteoric water and present Baltic Sea water have recharged in different parts of the upper 100 m. These mixing events have also triggered chemical and microbial reactions that have conditioned some of the important groundwater parameters and, together with the structural complexity of the area, they have promoted a heterogeneous distribution of groundwater compositions in the bedrock. Due to these evident differences in chemistry, residence time and origin of the groundwater, several groundwater types were defined in order to facilitate the visualisation and communication. The differentiation (linked to the paleohydrological history of the area) was based on Cl concentration, Cl/Mg ratio (marine component), and δ18O value (glacial component).The work presented in this paper increases the understanding of the groundwater evolution in fractured and compartmentalised aquifers where mixing processes are the most important mechanisms. The model proposed to characterise the present groundwater system of the Forsmark area will also help to predict the future hydrogeochemical behaviour of the groundwater system after the construction of the repositories for the nuclear wastes.

Multidecadal climate variability dominated past trends in the water balance of the Baltic Sea watershed

The Baltic Sea watershed includes the territories of 14 countries in Northern, Central, and Eastern Europe. Long-term observations have shown that the climate in this area is characterised by a pronounced multidecadal variability, with a period of about 30 years, but its origin is thus far unknown. We propose that the observed ~30-year fluctuations in Baltic Sea salinity are caused by the Atlantic Multidecadal Variability and the North Atlantic Oscillation, which together modulate precipitation over the watershed and hence the river discharge into the Baltic Sea. The return of a large portion of the outflowing brackish Baltic Sea water with the inflowing salt water, due to mixing at the entrance area results in a positive feedback mechanism that amplifies the multidecadal variations in salinity. The strength of this self-amplification is considerable since atmospheric forcing has nearly the same periodicity as the response time of the freshwater content to external freshwater inputs.

Microplastics in Harbour Seawaters: A Case Study in the Port of Gdynia, Baltic Sea

An important source of microplastics (MPs) in the Baltic Sea waters is plastic waste, which is fragmented in the natural environment. The pilot research on the identification of microplastics in the surface waters of the Port of Gdynia is presented. In this paper, microplastics of particle sizes 0.3–5 mm in harbour seawaters were investigated. Microplastics were collected from five harbour basins using an unmanned mobile research unit, HydroDron-1. Sampling of microplastics on the surface port water was conducted over four seasons. The collected plastic particles were separated by chemical oxidation and flotation in the NaCl solution (density 1.2 g/cm3). Polymer identification was carried out by visual and microscopic observations, as well as using the Total Reflection Fourier Transform Infrared spectroscopy. Based on tows conducted in five basins of the Port of Gdynia, in total, the concentration of microplastics identified ranged from 0.082 mg/m3 to 0.524 mg/m3, depending on the investigated basin. Four groups of microplastic shapes (fragments, films, fibres and spheres) were detected in all the investigated harbour basins. Fragments and fibres were prevalent when categorised by particle shape, whereas when categorised by colour, transparent, white and black particles were dominant. The predominant type of the identified polymers was polyolefins (PE, PP, PS) and their derivatives.

Relative abundance of harbour porpoises (Phocoena phocoena) from acoustic and visual surveys of the Baltic Sea and adjacent waters during 2001 and 2002

Boat-based acoustic and visual surveys for harbour porpoises (Phocoena phocoena) were conducted during the summers of 2001 and 2002 in order to investigate their distribution and relative abundance in the Baltic Sea, and to compare the results with the adjacent Kiel and Mecklenburg Bights and the Little Belt. Harbour porpoises are subject to year-round bycatch in gillnets and other fishing gear in these waters. This is of particular concern in the Baltic Sea where a survey carried out in 1995 indicated that the population is low and current levels of anthropogenic mortality are believed to be unsustainable. Polish coastal waters were not included in the 1995 survey and it has been hypothesised that these unsurveyed waters may contain a significant uncounted part of the Baltic Sea population. Results show that the porpoise detection rate was two orders of magnitude lower in the Baltic Sea than in other waters surveyed. No evidence was found that Polish waters contain a significant, previously uncounted part of the Baltic Sea population. The results confirm the endangered status of the Baltic Sea population, and stress the urgency of preventing future anthropogenic mortalities that threaten the survival of the population.