Microbial community structure in polluted Baltic Sea sediments

Nearly half the seabed of the Baltic Proper is incapable of supporting life of higher organisms as a consequence of oxygen depletion resulting from eutrophication. However, these areas are actually teeming with microbial life. Here we used terminal-restriction fragment length polymorphism (T-RFLP) to investigate the dominant archaeal and bacterial groups, with respect to community structure, in surface layers of bottom sediments of the Baltic Sea along a coastal pollution gradient. Both archaeal and bacterial communities formed distinct clusters along the pollution gradient and the community compositions were different at the polluted sites compared with the relatively clean reference sites. The structures of the bacterial communities were most strongly correlated to water depth, followed by organic carbon, oxygen, salinity and silicate levels. In contrast, the structures of the archaeal communities were most strongly correlated to oxygen, salinity, organic carbon, silicate and nitrate levels. Some members of the microbial communities were identified using a combination of traditional and molecular approaches. Isolates obtained on different culture media were identified by partial sequencing of their 16S rRNA genes and some novel species were found. In addition, we developed a computer program, aplaus, to elucidate the putative identities of the most dominant community members by T-RFLP.     

Microbiological and biogeochemical processes in a pockmark of the Gdansk depression,Baltic Sea

Comprehensive microbiological and biogeochemical investigation of a pockmark within one of the sites of gas-saturated sediments in the Gdansk depression, Baltic Sea was carried out during the 87th voyage of the Professor Shtokman research vessel. Methane content in the near-bottom water and in the underlying sediments indicates stable methane flow from the sediment into the water. In the 10-m water layer above the pockmark, apart from methane anomalies, elevated numbers of microorganisms and enhanced rates of dark CO₂ fixation (up to 1.15 µmol C/(l day)) and methane oxidation (up to 2.14 nmol CH₄/(l day)) were revealed. Lightened isotopic composition of suspended organic matter also indicates high activity of the near-bottom microbial community. Compared to the background stations, methane content in pockmark sediments increased sharply from the surface to 40–60 ml/dm³ in the 20–30 cm horizon. High rates of bacterial sulfate reduction (SR) were detected throughout the core (0–40 cm); the maximum of 74 µmol S/(dm³ day) was located in subsurface horizons (15–20 cm). The highest rates of anaerobic methane oxidation (AMO), up to 80 µmol/dm³ day), were detected in the same horizon. Good coincidence of the AMO and SR profiles with stoichiometry close to 1: 1 is evidence in favor of a close relation between these processes performed by a consortium of methanotrophic archaea and sulfate-reducing bacteria. Methane isotopic composition in subsurface sediments of the pockmark (from ?53.0 to ?56.5‰) does not rule out the presence of methane other than the biogenic methane from the deep horizons of the sedimentary cover.     

Bacterioplankton of the Gdansk Basin,Baltic Sea

The numbers, biomass, and production of bacterioplankton were determined in the Russian Sector of the Gdansk Basin (Baltic Sea) in 2007–2009. Significant spatial and temporal variations were determined. During the year, bacterial activity increased with increasing water temperature and higher availability of organic substrates. The lowest bacterial production (0.01–31.63 mg C m⁻³ day⁻¹) was observed in late winter and late autumn, while the highest (0.17–341.70 mg C m⁻³ day⁻¹) occurred in spring and summer. Since bacterial numbers and biomass were found to depend on the weather conditions and the terrigenous inflow, significant variations were observed from year to year. The highest and lowest numbers and biomass of bacterioplankton determined in summer were 0.09–1.10 × 10⁶ cells mL⁻¹ and 2–22 mg C m⁻³ for July 2007 and 1.96–11.23 × 10⁶ cells mL⁻¹ and 23–123 mg C m^–3 for July 2009. The values of these parameters were the highest along the coast and decreased towards the open sea.     

Linking denitrifier community structure and prevalent biogeochemical parameters in the pelagial of the central Baltic Proper (Baltic Sea)

The oxic-anoxic interface of the water column of the Gotland Basin (central Baltic Sea) is characterised by defined biogeochemical gradients and is hypothesised to be a zone of pronounced denitrification. Our aim was to analyse the composition and distribution of pelagic denitrifying microorganisms in relation to the physico-chemical gradients in the water column. PCR-amplified nirS genes--coding for dissimilatory nitrite reductase--were analysed as functional markers by terminal restriction fragment length polymorphism and cloning. The overall nirS diversity was low, with the lowest levels found at the oxic-anoxic interface. Only a few terminal restriction fragments dominated the denitrifier communities throughout the water column, and these could be assigned to several new Baltic Sea clusters that were revealed by phylogenetic analysis. The novel clusters were separated in two groups corresponding to the oxygen concentrations within specific layers of the water column. Gradients of prevalent biogeochemical parameters (H(2)S, NH(4) (+), NO(3) (-) and O(2)) largely determined the composition of the nirS-type denitrifier communities within the water column of the Gotland Basin.     

Trace elements in the muscle,ova and seminal fluid of key clupeid representatives from the Gdansk Bay (South Baltic Sea) and Iberian Peninsula (North-East Atlantic)

BackgroundBaltic herring and European sardine are pelagic, fish of particular ecological importance, on the one hand control numbers of planktonic organisms, and on the other hand exist as food for predators on higher trophic levels. Moreover, these fish are among the main species caught for human consumption. Rare earth elements (REEs) come mainly from geogenic sources but, due to their use in technology, agriculture and medicine, the importance of anthropogenic sources is growing steadily.MethodsSamples used for the study were available on the market. Fresh materials of fish muscle, ova and seminal fluid were mineralized and elements were determined by means of inductively coupled plasma – mass spectrometry (ICP-MS).ResultsThe conducted research indicated the presence of REEs in the muscles of the Baltic herring (∑REE = 0.076 ± 0.047 mg/kg) and European sardine (∑REE = 0.191 ± 0.163 mg/kg), with a clear dominance of heavy REEs in both fish species. Trace elements (TE) in the muscles of the tested fish demonstrated a similar system of concentration (Baltic herring: Zn > As > Se > Cu > Cr > Ni > Pb > Cd; European sardine: Zn > As > Se > Cu > Ni > Cr > Pb > Cd). REEs and TEs in these fish were presence in ova and seminal fluid indicates intergenerational transfer.ConclusionChanges in the concentrations of some trace elements (As, Cu, Cd) in the muscles of herring indicate increases compared to the historical data. The availability of metals in the aquatic environment may be determined by ongoing climate changes, effected water salinity and warming increased availability of labile forms of trace metals. Decline trends in the condition of pelagic fish need to extend the research in the context of contemporary environmental threats.     

Steryl chlorin esters in sediments of the southern Baltic Sea

Sediments of the southern Baltic Sea were analysed for content of steryl chlorin esters, the chlorin compounds discovered recently in the marine environment. The chlorin esters occur in the Baltic sediments in substantial amounts and form a considerable fraction of the total chlorin content. Among the physicochemical parameters studied the highest correlation with the steryl chlorins showed organic carbon content in sediments and the content of fraction of sediments smaller than 10 μm. A significant correlation was observed between the steryl chlorins content and other chlorins as chlorophylla, phaeophytina, pyrophaeophytina as well as with β-carotene, the distinctly less significant correlation was with phaeophorbidea. This indicates an other way of formation of the steryl chlorins from algae than zooplankton grazing.     

Diatom assemblages in superficial sediments from the Gulf of Riga,eastern Baltic Sea

Twenty one superficial sediment samples from areas of high and moderate eutrophication in the Gulf of Riga were studied with respect to siliceous microfossils, mainly diatoms.The results seem to imply that the number of taxa and the abundance of the frustules are affected by runoff from rivers and the degree of eutrophication in different parts of the Gulf. Areas with high eutrophication, e.g. the river estuaries, have diatom assemblages of varying composition, while in areas with moderate eutrophication the composition is almost constant and the influx of freshwater diatoms and littoral periphyton small. The high abundance and low diversity of brackish-marine and brackish, planktonic diatoms seem to be a result of an influx of nutrients and pollutants in the water and bottom sediments. The sea ice diatoms occurring in the Baltic waters and also in the Gulf of Riga tend to be resistant to eutrophication or are even favoured by it.     

Microbial community shift with decabromodiphenyl ether (BDE 209) in sediments of the Pearl River estuary, China

To compare the effect of decabromodiphenyl ether (BDE 209) on microbial community from the Pearl River estuary, the microbial community at three in situ sites and the responses of microbial community to BDE-209 stressor were investigated. Denaturing gradient gel electrophoresis analysis of 16S rRNA gene showed that microbial community at site A2 has less diversity than sites A1 and A3. Physicochemical parameters (NH₄-N, salinity and SiO₃-Si) could significantly impact the microbial community composition in this estuary. In laboratory-incubated experiments, results indicated high concentration of BDE 209 (100 mg/kg) could increase the microbial diversity at sites A1 and A2, whereas reduced the microbial diversity at site A3. The unweighted pair group method with arithmetic means cluster analysis and principal component analysis demonstrated that the community structure changes at sites A1 and A2 were driven by the BDE 209 concentration, whereas at site A3 they depended on the incubation time. Thirty-five days after the addition of 100 mg/kg BDE 209, Firmicutes were found to be the dominant bacteria at sites A1 and A2. These data suggest the BDE 209 may have different effects on the microbial community in the Pearl River estuary.     

Trace fossils as indicators of environmental change in Holocene sediments of the Archipelago Sea, northern Baltic Sea

Biogenic structures in Holocene sediments from the Archipelago Sea, northern Baltic Sea, were characterized through the analysis of X-ray images of four cores collected from water depths between 32 and 66 m. In the area, initial colonization of endobenthic invertebrates occurred at 7800 ± 80 calendar years BP. The trace assemblage at this level is low-diversity, small-diameter, shallowly tiered, and Palaeophycus-dominated; rare Arenicolites are also observed. Early colonization coincides with increasing marine influence in the post-glacial lacustrine setting just before the dramatic onset of brackish-water conditions established after 7600 BP. The post-incursion brackish-water assemblage possesses a higher diversity of traces (Planolites, Arenicolites, Lockeia, Teichichnus), which is taken to reflect the enhanced salinity and trophic state of the basin. The shift from Palaeophycus-mottling to a Planolites-dominated fabric represents changed behavioural patterns in the endobenthic community due to changed substrate properties. The ethology of the succeeding trace assemblage also represents a switch from domicile-based activities, such as predation, scavenging and interface-dominated deposit feeding to shallow-tier deposit feeding. Finally, traces are excluded from thinly laminated intervals, demonstrating that seafloor oxygen deficiency commonly reached levels that were detrimental to colonization of the sediment substrate.     

Argyrophilic nucleolar organizer regions (AgNORs) in interphases and metaphases of normal and neoplastic gill cells of Macoma balthica (Bivalvia: Tellinidae) from the Gulf of Gdansk, Baltic Sea

Chromosome analysis of gill cells of different populations of Macoma balthica (L.) from the Bay of Gdansk (Baltic Sea) revealed 2 clam categories, 1 with neoplastic features and 1 without. Silver-staining was performed on interphase and metaphase cells of both categories. The mean argyrophilic nucleolar organizer region (AgNOR) count per abnormal interphase cell was significantly higher than in normal interphase cells. Normal silver-stained metaphases had 3 nucleolar organizer region (NOR) chromosome phenotypes. The location of the NORs in the most frequent phenotype (55.6% in 54 metaphases scored) was interstitial on the largest metacentric chromosome pair, Pair No. 1. Abnormal silver-stained metaphases had a higher number of active NOR sites. Different phenotypes were observed (frequency greater than 10% for 67 metaphases scored); 2 were similar to those in normal metaphases and 5 were ectopic. The higher activity of AgNORs observed in abnormal cells confirmed the diagnosis of malignant neoplasia.     

Planktonic ciliates of the Baltic Sea (a review)

The data on the ciliates species composition are given for the Baltic Sea, a brackish-water semi-closed water body where a considerable part of the planktonic fauna is presented by freshwater species. During the observation period, 789 species of ciliates were found, 160 of which are typical planktonic forms. The ecological characteristics of ciliates are given, along with an assessment of their role in the productivity of the Baltic Sea pelagic communities.     

Copepod eggs survive a decade in the sediments of the Baltic Sea

Many planktonic calanoid copepod species have been proved to spend a part of their life cycle as benthic resting eggs. In addition to avoiding seasonally occurring unfavourable conditions resting stages may also be used as a long-term survival strategy. The aim of this study was to find out for how long eggs of calanoid copepods retain their viability in the sediments of the Baltic Sea. The occurrence of viable copepod eggs in sea bottom sediment was studied in Pojovik Bay, SW coast of Finland. Eggs were found throughout a 25 cm deep core but deeper than 20 cm they were very scarce. Eggs were incubated at 12 °C in order to check the viability, and their age was estimated by determining the sediment accumulation rate with ¹³⁷Cs-method. Viable eggs were estimated to be 10–13 yrs old, some possibly even 18–19 yrs. Most eggs in the top 8 cm were viable, their age being up to 7–8 yrs. Nauplii that hatched from the eggs belonged to Acartia bifilosa and Eurytemora affinis, A. bifilosa dominating the hatchers of the top sedment layers and E. affinis the deeper layers. Preliminary evidence is presented that E. affinis produces true diapause eggs in the Baltic Sea.     

Diatoms in surface sediments of the Gotland Basin in the Baltic Sea

A sediment core, 55 cm long, from station F81 in the Gotland Basin of the Baltic Sea was analysed for diatoms and ebridians. Chrysophyte stomatocysts found in the core were also counted but not identified. The aim was to trace environmental changes, e.g. eutrophication and salinity variations. There is evidence that eutrophication has been increasing in the Baltic Sea in recent decades.Brackish-marine plankton diatoms dominate the entire core and reflect the local planktonic taxa rather well. The dominant taxon is the polyhalobous Actinocyclus octonarius. The main biostratigraphical change within the core analysed takes place at a depth of about 22 cm, where the abundance of diatoms, and especially of Chaetoceros spp., Thalassiosira hyberborea var. pelagica and T. baltica start to increase. This may reflect eutrophication which can be estimated to have started c. 200 years ago.     

Density of Monoporeia affinis and biogeochemistry in Baltic Sea sediments

This study focused on effects from Monoporeia affinis reworking and ventilation activities on benthic fluxes and mineralization processes during a simulated bloom event. The importance of M. affinis density for benthic solute (O₂, ΣNO₂⁻ + NO₃⁻, NH₄⁺ and HPO₄²⁻) fluxes and sediment reactivity (mobilization of NH₄⁺ and HPO₄²⁻) following additions of organic material to the sediment surface was experimentally investigated using sediment-water and closed sediment (jar) incubations. Three different densities of M. affinis were used to resemble a low, medium and high density situation (1300, 2500 and 6400 ind. m^− 2, respectively) of a natural amphipod community. The degradation of phytodetritus (Tetraselmis sp., 5 g C m^− 2) added to the sediment surface was followed over a period of 20 days. Benthic solute fluxes of O₂, ΣNO₂⁻ + NO₃⁻ and NH₄⁺ were generally progressively stimulated with increasing number of M. affinis, while no such correlation was found for HPO₄²⁻. Solute fluxes were initially enhanced 1 to 2 days after the addition of phytodetritius, caused by mineralization of the most labile organic material and a food-stimulated irrigation by the amphipods. There was no effect from the activity of M. affinis on total denitrification (Dtot = Dn + Dw) or denitrification utilizing nitrate from coupled nitrification/denitrification (Dn) for any of the densities examined. Denitrification utilizing overlying water nitrate (Dw) was only about 10% of Dtot. Dw was significantly enhanced for the highest M. affinis density investigated. The reactivity of the sediment decreased progressively with increasing density of M. affinis and with time of the experiment. However, enhanced ammonium production at least 6 days after the organic addition indicated excretion of N-containing organic compounds by M. affinis. In conclusion, large spatial and temporal variations in density of M. affinis may be of significant importance for benthic solute fluxes and overall mineralization of organic material in Baltic Sea sediments.     

The Microbial Food Web in Eutrophic Shallow Estuaries of the Baltic Sea

Microbial food webs are responsible for the main carbon flow in shallow eutrophic estuaries of the Baltic Sea. Bacteria account for respirative use most of the autotrophic production. Bottom-up influences are mainly directed to the phytoplankton. Massive increase of phytoplankton biomass has only little effect on the biomasses of the heterotrophic plankton. The investigated ecosystem obviously differs by its high bacteria/non-bacteria heterotrophs-relation from other aquatic ecosystems.     

Effects of nonindigenous species on diversity and community functioning in the eastern Gulf of Finland (Baltic Sea)

An increase of xenodiversity in plankton and benthos in the eastern Gulf of Finland was observed from 1998 to 2004. Nonindigenous species account for 4.8% of all species found and up to 96% of total biomass. Invasive benthic omnivores, the alien amphipods Gmelinoides fasciatus and Pontogammarus robustoides and the predaceous fish Perccottus glenii with their versatile diets strongly affect the community structure. Invasive sessile seston-feeders that directly (through grazing and water clearance) and indirectly (through recycling of nutrients) interact with other ecosystem components, are mainly represented by the zebra mussel Dreissena polymorpha, which affect the structure of benthic and planktonic communities as well as benthic-pelagic coupling. The invasive predatory cladocerans Cercopagis pengoi and Evadne anonyx and larvae of D. polymorpha are only temporary components in the zooplankton, which is limiting their overall effect. Alien benthic bioturbators, the polychaetes Marenzelleria neglecta and the oligochaete Tubificoides pseudogaster account for a high proportion of total abundance and biomass but their effects on native species need further research.