Isolation and characterization of phage–host systems from the Baltic Sea ice

In search for sea ice bacteria and their phages from the Baltic Sea ice, two ice samples were collected from land-fast ice in a south-west Finland coastal site in February and March 2011. Bacteria were isolated from the melted sea ice samples and phages were screened from the same samples for 43 purified isolates. Plaque-producing phages were found for 15 bacterial isolates at 3 °C. Ten phage isolates were successfully plaque purified and eight of them were chosen for particle purification to analyze their morphology and structural proteins. Phage 1/32 infecting an isolate affiliated to phylum Bacteroidetes (Flavobacterium sp.) is a siphovirus and six phages infecting isolates affiliated to γ-Proteobacteria (Shewanella sp.) hosts were myoviruses. Cross titrations between the hosts showed that all studied phages are host specific. Phage solutions, host growth and phage infection were tested in different temperatures revealing phage temperature tolerance up to 45 °C, whereas phage infection was in most of the cases retarded above 15 °C. This study is the first to report isolation and cultivation of ice bacteria and cold-active phages from the Baltic Sea ice.     

Degradation of Crude Oil and PAHs in Iron–Manganese Concretions and Sediment from the Northern Baltic Sea

The ability of different sea bottom types to recover from oil contamination under oxic and anoxic conditions is poorly known in the brackish Baltic Sea. We carried out microcosm experiments to examine the capacity of iron–manganese concretions and sediment to remove petroleum compounds at 10°C. The biological degradation potential of polycyclic aromatic hydrocarbons (PAHs) was indicated by the 1000-fold increase in the copy numbers of PAH-degradation genes resulting in 2.2 × 10⁶ gene copies g^?1 DW. In the experiments 35?81% of the crude oil and 96% of PAHs disappeared through abiotic and biotic pathways, and there was little difference between the concretions and sediment. Bacterial community analysis revealed that the bacterial sequences obtained from the oil-treated concretions were affiliated to groups typical for concretions and metal-rich environments, whereas oil-treated sediment sequences were similar to those originating from sediments and oil-contaminated environments. The high frequency of concretion clones affiliated with specific taxonomic groups of α-, β-, γ-, and δ-proteobacteria may indicate the existence of new clades of bacteria within the Rhizobiales and Rhodospirillales of the α-proteobacteria, Burkholderiales—incertae sedis of the β-proteobacteria, Chromatiales of the γ-proteobacteria and the Syntrophobacteriales of the δ-proteobacteria. Our study suggests that concretions and bottom sediment maintain rich, distinct bacterial communities under oil exposure that have the potential to remove petroleum compounds in oxic and anoxic conditions.     

Scenario simulations of future salinity and ecological consequences in the Baltic Sea and adjacent North Sea areas–implications for environmental monitoring

Substantial ecological changes occurred in the 1970s in the Northern Baltic during a temporary period of low salinity (S). This period was preceded by an episodic increase in the rainfall over the Baltic Sea watershed area. Several climate models, both global and regional, project an increase in the runoff of the Northern latitudes due to proceeding climate change. The aim of this study is to model, firstly, the effects on Baltic Sea salinity of increased runoff due to projected global change and, secondly, the effects of salinity change on the distribution of marine species. The results suggest a critical shift in the S range 5–7, which is a threshold for both freshwater and marine species distributions and diversity. We discuss several topics emphasizing future monitoring, modelling, and fisheries research. Environmental monitoring and modelling are investigated because the developing alternative ecosystems do not necessarily show the same relations to environment quality factors as the retiring ones. An important corollary is that the observed and modelled S changes considered together with species’ ranges indicate what may appear under a future climate. Consequences could include a shift in distribution areas of marine benthic foundation species and some 40–50 other species, affiliated to these. This change would extend over hundreds of kilometres, in the Baltic Sea and the adjacent North Sea areas. Potential cascading effects, in coastal ecology, fish ecology and fisheries would be extensive, and point out the necessity to develop further the “ecosystem approach in the environmental monitoring”.     

Distribution of denitrifying bacterial communities in the stratified water column and sediment–water interface in two freshwater lakes and the Baltic Sea

We have studied the distribution and community composition of denitrifying bacteria in the stratified water column and at the sediment–water interface in lakes Plußsee and Schöhsee, and a near-shore site in the Baltic Sea in Germany. Although environmental changes induced by the stratification of the water column in marine environments are known to affect specific populations of denitrifying bacteria, little information is available for stratified freshwater lakes and brackish water. The aim of the present study was to fill this gap and to demonstrate specific distribution patterns of denitrifying bacteria in specific aquatic habitats using two functional markers for the nitrite reductase (nirK and nirS genes) as a proxy for the communities. The leading question to be answered was whether communities containing the genes nirK and nirS have similar, identical, or different distribution patterns, and occupy the same or different ecological niches. The genes nirK and nirS were analyzed by PCR amplification with specific primers followed by terminal restriction fragment length polymorphism (T-RFLP) and by cloning and sequence analysis. Overall, nirS-denitrifiers were more diverse than nirK-denitrifiers. Denitrifying communities in sediments were clearly different from those in the water column in all aquatic systems, regardless of the gene analyzed. A differential distribution of denitrifying assemblages was observed for each particular site. In the Baltic Sea and Lake Plußsee, nirK-denitrifiers were more diverse throughout the water column, while nirS-denitrifiers were more diverse in the sediment. In Lake Schöhsee, nirS-denitrifiers showed high diversity across the whole water body. Habitat-specific clusters of nirS sequences were observed for the freshwater lakes, while nirK sequences from both freshwater lakes and the Baltic Sea were found in common phylogenetic clusters. These results demonstrated differences in the distribution of bacteria containing nirS and those containing nirK indicating that both types of denitrifiers apparently occupy different ecological niches.     

A metabarcoding analysis of the wrackbed microbiome indicates a phylogeographic break along the North Sea–Baltic Sea transition zone

Sandy beaches are biogeochemical hotspots that bridge marine and terrestrial ecosystems via the transfer of organic matter, such as seaweed (termed wrack). A keystone of this unique ecosystem is the microbial community, which helps to degrade wrack and re-mineralize nutrients. However, little is known about this community. Here, we characterize the wrackbed microbiome as well as the microbiome of a primary consumer, the seaweed fly Coelopa frigida, and examine how they change along one of the most studied ecological gradients in the world, the transition from the marine North Sea to the brackish Baltic Sea. We found that polysaccharide degraders dominated both microbiomes, but there were still consistent differences between wrackbed and fly samples. Furthermore, we observed a shift in both microbial communities and functionality between the North and Baltic Sea driven by changes in the frequency of different groups of known polysaccharide degraders. We hypothesize that microbes were selected for their abilities to degrade different polysaccharides corresponding to a shift in polysaccharide content in the different seaweed communities. Our results reveal the complexities of both the wrackbed microbial community, with different groups specialized to different roles, and the cascading trophic consequences of shifts in the near shore algal community.     

Iron–Manganese Concretions Sustaining Microbial Life in the Baltic Sea: The Structure of the Bacterial Community and Enrichments in Metal-Oxidizing Conditions

The abundant deposits of spherical iron-manganese concretions in the Gulf of Finland are colonized by bacteria in vast numbers. Communities on the surface and in the porous interior have formed two separate clusters, in accordance with their genetic differences. The overall bacterial community in the concretions was highly diverse, representing 12 phyla. Half of the bacteria were affiliated with the most common classes of Proteobacteria, while a third of the bacteria were unclassified. Cloned 16S rRNA-gene sequences of the concretion bacteria showed high scores for similarity to the sequences obtained from sea sediments, metal-rich environments, and ocean crust. The clone library of native concretions was not dominated by known Fe- and Mn-oxidizing species. Known Mn-oxidizing bacteria Sphingomonas, Pseudomonas, and Bacillus were enriched in experiments with Mn²⁺-containing liquid media, whereas Prosthecobacter (Verrucomicrobia) and Rheinheimera were enriched in semisolid media possibly better simulating the natural conditions in the concretions. In a corresponding experiment, the Fe²⁺-oxygen gradient favored the enrichment of Shewanella baltica and Thalassolituus oleivorans, which are known to reduce Fe and to degrade petroleum hydrocarbons, respectively. An individual spherical concretion forms a microcosm for a diverse microbial community having potential to oxidize Fe and Mn as shown in cultivation experiments. Therefore, bacteria may significantly affect the formation of the concretions in the Gulf of Finland.     

Behavioral,Ecological and Genetic Differentiation in an Open Environment—A Study of a Mysid Population in the Baltic Sea

Diel vertical migration (DVM) is often assumed to encompass an entire population. However, bimodal nighttime vertical distributions have been observed in various taxa. Mysid shrimp populations also display this pattern with one group concentrated in the pelagia and the other near the bottom. This may indicate alternative migratory strategies, resembling the seasonal partial migrations seen in birds, fishes and amphibians, where only a subset of the population migrates. To assess the persistence of these alternative strategies, we analyzed the nitrogen and carbon stable isotope signatures (as proxies for diet), biochemical indices (as proxies for growth condition), and genetic population divergence in the Baltic mysid Mysis salemaai collected at night in the pelagia and close to the bottom. Stable isotope signatures were significantly different between migrants (pelagic samples) and residents (benthic samples), indicating persistent diet differences, with pelagic mysids having a more uniform and carnivorous diet. Sequencing of the mitochondrial cytochrome subunit I (COI) gene showed genetic differentiation attributable to geographic location but not between benthic and pelagic groups. Divergent migration strategies were however supported by significantly lower gene flow between benthic populations indicating that these groups have a lower predisposition for horizontal migrations compared to pelagic ones. Different migration strategies did not convey measurable growth benefits as pelagic and benthic mysids had similar growth condition indices. Thus, the combination of ecological, biochemical and genetic markers indicate that this partial migration may be a plastic behavioral trait that yields equal growth benefits.     

Production characteristics of bacteria and phytoplankton in the Sea of Okhotsk and Bering Sea during spring–summer

Production parameters for bacterioplankton were assessed during the spring–summer period in the western parts of the Sea of Okhotsk and the Bering Sea, as well as in northwestern Pacific Ocean. The lowest values of bacterial production were observed in early June during the spring phytoplankton bloom (0.08 mg C day^–1 m^–3), while the maximum values (up to 55 mg C day^–1 m^–3) occurred in late July?early August, 1.5 to 2 months after the bloom. The concentration of dissolved organic matter, the substrate for bacterioplankton, was assessed using satellite data. The ratio between bacterial and primary production in the surface samples varied from 0.5% at the peak of phytoplankton bloom to 180% at the peak of bacterioplankton development.     

Summer-autumn ichthyoplankton of the Sea of Okhotsk and the Sea of Japan and special traits of feeding of fish larvae and fry in 2003–2004

In summer-autumn of 2003–2004, the ichthyoplankton of the Sea of Okhotsk comprised 35 species. In this period the most widely distributed and numerous were larvae of the lord Hemilepidotus gilberti, the Pacific stout sand lance Ammodytes hexapterus, and the Sakhalin dab Limanda sakhalinensis. The maximum catches of fish larvae were attributed to coastal waters off eastern Sakhalin and to the shelf of the northern part of the Sea of Okhotsk. In November of 2003, the ichthyoplankton of the Sea of Japan was represented by fish larvae belonging mainly to the boreal ichthyocomplex. The catches consisted predominantly of larvae of the arabesque greenling Pleurogrammus azonus, the ronquil Bathymaster derjugini, and the rockfish Sebastes owstoni. Fish larvae and fry in the northwestern part of the Sea of Japan were caught principally within 43°–45° N and 137°–139° E above the depth 1500–2000 m. The food spectrum of fish larvae in the Sea of Okhotsk and the Sea of Japan comprised over 20 plankters of various size belonging to seven taxa. Irrespective of fish species, the food items common of all fish were copepods Pseudocalanus minutus and Oithona similis. The daily rations were calculated for mass species (Hemilepidotus gilberti, Ammodytes hexapterus, Hexagrammos stelleri, Pleurogrammus azonus, Bathymaster derjugini, and Sebastes owstoni). The larvae of all considered species in the Sea of Japan and in the Sea of Okhotsk fed predominantly in the light period of the day.     

Decreased Silica Land–sea Fluxes through Damming in the Baltic Sea Catchment – Significance of Particle Trapping and Hydrological Alterations

We tested the hypothesis that reservoirs with low water residence time and autochthonous production influence river biogeochemistry in eutrophied river systems draining cultivated watersheds. The effect of a single artificial water reservoir and consecutive reservoirs on silica (Si) river fluxes is exemplified by the moderately dammed Vistula River and the heavily regulated Daugava River that are compared with the practically undammed Oder River. The sum of the discharge weighted annual mean biogenic silica (BSi) and dissolved silicate (DSi) concentrations in the rivers Oder, Vistula and Daugava were about 160 μ M (40 + 120 μ M), 150 μ M (20 + 130 μ M) and 88 μ M (6 + 82 μ M), respectively. Assuming BSi and DSi concentrations as observed in the Oder River as typical for eutrophied but undammed rivers, complete trapping of this BSi could have lowered Si fluxes to the Baltic Sea from rivers with cultivated watersheds by 25%. The superimposed effect of hydrological alterations on reduced Si land–sea fluxes is demonstrated by studies in the boreal/subarctic and oligotrophic rivers Kalixälven and Lueälven. The DSi yield of the heavily dammed Luleälven (793 kg km^?2 yr^?1) constituted only 63% of that was found in the unregulated Kalixälven (1261 kg km^?2 yr^?1), despite the specific runoff of the Luleälven (672 mm m^?2 yr^?1) being 19% higher than that of theKalixälven (563 mm m^?2 yr^?1); runoff normalized DSi yield of the former, regulated watershed, was only half the DSi yield of the latter, unperturbed watershed. Based on these findings, it is hypothesized here that perturbed surface water–groundwater interactions are the major reasons for the reduced annual fluctuations in DSi concentrations as also seen in the heavily dammed and eutrophic river systems such as the Daugava and Danube.     

Long-term changes in the phytobenthos of the southern Åland Islands,northern Baltic Sea

Marine macrophytes and -algae have undergone major changes in abundance and species composition over the last decades, primarily due to eutrophication. However, comparable studies conducted in the mid 20th century are rare, but potentially valuable for enabling insight into changes in the benthic communities from the early onset of the eutrophication of the Baltic Sea. In the present study, the submerged phytobenthic community in the exposed southern archipelago of the Åland Islands was examined in 2018 and compared with surveys conducted in 1956 and 1993, respectively. The aim was to analyze long-term changes in the phytobenthic community in relation to the general large-scale anthropogenic drivers since the 1950s. Between 1956 and 1993, a decrease in the total number of species/taxa, an increase of filamentous algae coverage and a decrease in the depth range of Fucus vesiculosus was observed. These changes in the phytobenthic community continued between 1993 and 2018, suggesting no changes in the previously described negative trends. Between 1956 and 2018, a general shift in the distribution of phytobenthic functional groups, (grouped according to morphology and type of algae; green, brown and red) occurred, with increased coverage of filamentous brown and green algae, and decline in red algae coverage. The depth range of F. vesiculosus also decreased by >50% between 1956 and 2018. The results support findings that the eutrophication of the northern Baltic Sea is still at a high level, which slows down or prevents the recovery of offshore phytobenthic communities, despite the progress seen in other areas. Thus, the likely main drivers behind the changes are the direct and indirect effects of eutrophication in combination with warmer water, i.e. an effect of climate change.     

Diversity and abundance of “Pelagibacterales” (SAR11) in the Baltic Sea salinity gradient

The candidate order “Pelagibacterales” (SAR11) is one of the most abundant bacterial orders in ocean surface waters and, periodically, in freshwater lakes. The presence of several stable phylogenetic lineages comprising “Pelagibacterales” correlates with the physico-chemical parameters in aquatic environments. A previous amplicon sequencing study covering the bacterial community in the salinity gradient of the Baltic Sea suggested that pelagibacteral subclade SAR11-I was replaced by SAR11-IIIa in the mesohaline region of the Baltic Sea. In this current study, we investigated the cellular abundances of “Pelagibacterales” subclades along the Baltic Sea salinity gradient using catalyzed reporter deposition fluorescence in situ hybridization (CARD-FISH). The results obtained with a newly designed probe, which exclusively detected SAR11-IIIa, were compared to CARD-FISH abundances of the marine SAR11-I/II subclade and the freshwater lineage SAR11-IIIb (LD12). The results showed that SAR11-IIIa was abundant in oligohaline–mesohaline conditions (salinities 2.7–13.3), with maximal abundances at a salinity of 7 (up to 35% of total Bacteria, quantified with a universal bacterial probe EUB). As expected, SAR11-I/II was abundant (27% of EUB) in the marine parts of the Baltic Sea, whereas counts of the freshwater lineage SAR11-IIIb were below the detection limit at all stations. The shift from SAR11-IIIa to SAR11-I/II was confirmed in the vertical salinity gradient in the deeper basins of the Baltic Sea. These findings were consistent with an overlapping but defined distribution of SAR11-I/II and SAR11-IIIa in the salinity gradient of the Baltic Sea and suggested the adaptation of SAR11-IIIa for growth and survival in mesohaline conditions.     

Transport and accumulation of sediment and contaminants in the Lagoon of Kuršiųmarios (Lithuania) and Baltic Sea

In this paper an overview is given of earlier work on transport, deposition AND transformation of suspended matter, and contaminants (metals, hydrocarbons) in Lithuanian coastal waters as well as in other parts of the Baltic Sea. The Lithuanian river Nemunas dischargesc. 600.10⁶ kg suspended matter into the Kuršių Marios Lagoon annually, of which two thirds are accumulated in the lagoon. The remainder is exported to the Baltic Sea through the Klaipéda Strait influencing biological activity in the coastal zone. Sedimentation rate in Kuršių Marios Lagoon is estimated at 3.2 mm y⁻¹. In the last 50 years the surface area of the lagoon decreased by 0.7 km² y⁻¹. Concentration profiles of metals and hydrocarbons were measured in the Kuršių Marios Lagoon, the Baltic proper, and in the Gulf of Finland. Among hydrocarbons both anthropogenic and compounds from natural sources are present. It is argued that correct interpretation of concentration horizons in sediment may be hampered by various processes,e. g. early sedimentogenesis and diagenesis, and cyclic salinity changes in the Baltic Sea.     

The extensive bloom of alternate-stage Prymnesium polylepis (Haptophyta) in the Baltic Sea during autumn–spring 2007–2008

During autumn 2007, an unusual increase in an algal species belonging to the order Prymnesiales was observed throughout the Baltic Sea Proper during routine national monitoring. Electron microscopical examination of the blooming species showed two types of flat scales – small and large – that resembled those of the alternate stage of Prymnesium polylepis. No spine-bearing scales were found. The 18S rDNA sequence data (n?=?20, c. 1500?bp) verified the species identification as P. polylepis. There was up to 0.5% (7?bp) variability in the P. polylepis partial 18?S rDNA sequences from the Baltic Sea. These environmental sequences differed by 0–0.35% (0–4?bp) from cultured P. polylepis (isolate UIO036), and by 1.0–3.7% from other available Prymnesium sequences. The number of cells assumed to be P. polylepis began to increase in October 2007 coincidently with significantly calm and dry weather, and at their maximum the cells accounted for over 80% of the total phytoplankton biovolume in December–January. During February–April 2008, 95% of the Prymnesiales cells were in the size class of P. polylepis (>6?µm). The species attained bloom concentrations (>1?×?10⁶?cells?l^–1) from March to May 2008. The species was observed throughout the Baltic Sea, except the Bothnian Bay, Gulf of Riga and the Kattegat. No toxic effects of the bloom were observed.     

The northern Baltic Sea phytoplankton communities in 1903–1911 and 1993–2005: a comparison of historical and modern species data

Despite over 100 years of phytoplankton research in the Baltic Sea, little is known about how the species composition has changed during this period, characterised by severe anthropogenic eutrophication. We investigated the phytoplankton communities in the northern Baltic Sea using data from 1903 to 1911 and 1993 to 2005; to minimise effects of methodological differences we focused on occurrence frequencies. We found that the historical and modern communities differed regarding both species composition and the relative importance of taxonomical groups. The most obvious differences were the increase of dinoflagellates and decrease in the diatom to dinoflagellate ratio in all seasons. Contrary to the widely held view that cyanophytes have gained significance, our results indicate that in terms of occurrence the group has not increased in summer, and has lost ground in both spring and autumn. Several shifts in the occurrence frequency and seasonality of individual taxa transpired. Examining our results in relation to environmental conditions we found that some changes may be symptomatic of climate change related pressures. However, statistical analyses revealed that an undefined ‘period effect’ was the most important factor separating the historical and modern phytoplankton communities. We interpret this ‘period effect’ as evidence for the direct and/or indirect influence of eutrophication.     

Peculiarities of the state of phytoplankton in the Baltic Sea’s Vistula Lagoon at the turn of 21st century

In 1989–2005 the qualitative composition and seasonal and inter-annual dynamics of the total biomass of phytoplankton, chlorophyll a content, hydrological, and hydrochemical parameters were studied in the Russian zone of the Vistula Lagoon in the Baltic Sea. The results of these observations were compared to the data obtained in the 1950s and 1970s. The structural reorganization of phytoplankton was revealed, testifying to the negative changes in the ecosystem under conditions of anthropogenic pollution and eutrophication, climate warming, and increasing salinity.