Horizontal Variation of Bacterioplankton in the Baltic Sea

Variations in the thymidine incorporation rate, bacterial abundance, and mean cell volumes in the surface water (0.5 m) of the Baltic Sea in spring and summer were compared in studies with different spatial scales (570 nautical miles [nmi] [ca. 1056 km], 220 nmi [ca. 407 km], 24 nmi [ca. 44 km], 12 nmi [ca. 22 km], and 200 m). The objective of the comparison was to investigate whether a single sample taken at one sampling point is representative enough for researchers to make generalizations about a larger water area. Bacterioplankton variation was connected more to seasonal characteristics than to the spatial scale of sampling. Variation was greater and more random in spring than in summer. The state variables (bacterial abundance and mean cell volume) varied less than the rate variable (thymidine incorporation). The results suggest that the sampling design for bacterioplankton studies in northern temperate seas should be planned primarily according to the season and that more stress should be put on rate variable measurements than on those of state variables.     

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.     

Microbial community of reduced pockmark sediments (Gdansk Deep,Baltic Sea)

The microbial community of reduced pockmark sediments in the Russian sector of the Gdansk Deep, Baltic Sea, was investigated by molecular biological techniques. Fluorescent in situ hybridization was used to determine the numbers of eubacteria, archaea, and sulfate-reducing bacteria. Eubacteria were found to predominate in the upper 10 cm of the sediment (up to 5.3 × 10⁹ cells/g wet sediment), while the number of archaea increased in the 10- to 30-cm layers (up to 2.8 × 10⁹ cells/g wet sediment, which is higher than the number of eubacteria in the same horizons). Analysis of 16S rRNA gene fragments revealed members of the following phyla: Proteobacteria, Chloroflexi, Firmicutes, Planctomycetales, and high-G + C gram-positive bacteria. Sulfate-reducing bacteria (SRBs) of the families Syntrophaceae, Desulfuromonadaceae, and Actinobacteria of the genera Kocuria and Rothia were the predominant groups. Molecular probes were used to determine predominance of Desulfovibrionales in the SRB enrichment cultures obtained from different horizons of pockmark sediments. Three archaeal phylotypes were revealed, belonging to Euryarchaeota. One of these fell into the group of uncultured methanotrophic archaea (ANME-1a), while the other two were most closely related to uncultured methanogens.     

Benthic zonation of the Eastern Gotland Basin, Baltic Sea

In this paper recent benthic biological studies in the Eastern Gotland Basin area of the Baltic Sea are summarised. A general pattern of vertical distribution of macrofauna is presented and special reference is made to sharp temporal changes in macrofauna of deeper, subhalocline areas of the basin. Information on faunal sediment reworking ability is compiled. The environmental factors driving benthic zonation are discussed and the vertical benthic zones are defined on the basis of their major biological and abiotic features. This analysis shows that due to sharp gradients in environment and clear differences in composition of macrofauna, the ecological functioning of the Eastern Gotland Basin benthic zones is clearly different. Therefore, in the biogeochemical models of benthic-pelagic interaction, these zones (together with water layers they underlie) should be treated separately, as different sub-systems.     

The Native Bacterioplankton Community in the Central Baltic Sea Is Influenced by Freshwater Bacterial Species

The Baltic Sea is one of the largest brackish environments on Earth. Despite extensive knowledge about food web interactions and pelagic ecosystem functioning, information about the bacterial community composition in the Baltic Sea is scarce. We hypothesized that due to the eutrophic low-salinity environment and the long water residence time (>5 years), the bacterioplankton community from the Baltic proper shows a native “brackish” composition influenced by both freshwater and marine phylotypes. The bacterial community composition in surface water (3-m depth) was examined at a single station throughout a full year. Denaturing gradient gel electrophoresis (DGGE) showed that the community composition changed over the year. Further, it indicated that at the four extensive samplings (16S rRNA gene clone libraries and bacterial isolates from low- and high-nutrient agar plates and seawater cultures), different bacterial assemblages associated with different environmental conditions were present. Overall, the sequencing of 26 DGGE bands, 160 clones, 209 plate isolates, and 9 dilution culture isolates showed that the bacterial assemblage in surface waters of the central Baltic Sea was dominated by Bacteroidetes but exhibited a pronounced influence of typical freshwater phylogenetic groups within Actinobacteria, Verrucomicrobia, and Betaproteobacteria and a lack of typical marine taxa. This first comprehensive analysis of bacterial community composition in the central Baltic Sea points to the existence of an autochthonous estuarine community uniquely adapted to the environmental conditions prevailing in this brackish environment.     

Importance of Viral Lysis and Dissolved DNA for Bacterioplankton Activity in a P-Limited Estuary,Northern Baltic Sea

Through lysis of bacterioplankton cells, viruses mediate an important, but poorly understood, pathway of carbon and nutrients from the particulate to the dissolved form. Via this activity, nutrient-rich cell lysates may become available to noninfected cells and support significant growth. However, the nutritional value of lysates for noninfected bacteria presumably depends on the prevailing nutrient limitation. In the present study, we examined dynamics of dissolved DNA (D-DNA) and viruses along a transect in the phosphorus (P)-limited Ore Estuary, northern Baltic Sea. We found that viruses were an important mortality factor for bacterioplankton and that their activity mediated a significant recycling of carbon and especially of P. Uptake of dissolved DNA accounted for up to 70% of the bacterioplankton P demand, and about a quarter of the D-DNA pool was supplied through viral lysis of bacterial cells. Generally, the importance of viral lysates and uptake of D-DNA was highest at the estuarine and offshore stations and was positively correlated with P limitation measured as alkaline phosphatase activity. Our results highlight the importance of viral activity for the internal recycling of principal nutrients and pinpoints D-DNA as a particularly relevant compound in microbial P dynamics.     

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.     

Ecology of mysid shrimps in the Bornholm Basin (central Baltic Sea)

Mysid shrimps are an important trophic link in the food web of the Baltic Sea. In 2002 and 2003 we investigated species composition, distribution, life cycle and prey in the Bornholm Basin (central Baltic). Three species and one genus were identified: Mysis mixta, Neomysis integer, Mesopodopsis slabberi and Praunus sp. The dominant M. mixta and N. integer occurred in the whole study area but were more abundant in the peripheral, more shallow regions. Size frequency distribution indicated one generation for M. mixta and probably two for N. integer. Main prey of all size classes in both species was the cladoceran Bosmina coregoni maritima during summer and autumn. In spring and winter also copepods of the species Temora longicornis and Pseudocalanus acuspes were important prey items. Detritus and phytoplankton cells were of minor importance and many individuals had empty guts. Mysid shrimps in the deep basin might be advected from more shallow areas, as the abundance of all species was much lower than in coastal regions. The deep Bornholm Basin does not seem to be a favourable habitat, probably due to the inaccessibility of the oxygen deficient bottom layer. Under current hydrographic conditions mysids are probably not important predators of zooplankton and thus not competitors of planktivorous fish in the Bornholm Basin.     

Spatio-temporal distribution of Oithona similis in the Bornholm Basin (Central Baltic Sea)

Oithona similis is an abundant but poorly studied cyclopoidcopepod in the brackish Central Baltic Sea. We describe thespatio-temporal distribution of O. similis in a Central Balticdeep basin (Bornholm Basin) during spring and summer 1999. Usingvertically resolving sampling in parallel with hydrographicmeasurements, we found the copepod to dwell in the permanenthalocline characteristic of a Central Baltic deep basin. Thehabitat of O. similis is thus limited from above by low salinityand from below by low oxygen conditions, both characteristicfor the area. Horizontally resolving sampling yielded abundancesurfaces which were compared by analysis of variance showingsimilar patterns among sampling dates. Comparison with flowfields from a three-dimensional hydrodynamic model suggeststhat the horizontal distribution is primarily the result ofcirculation in the dwelling depth. The study shows how the physicalenvironment in the area determines the spatial distributionwhich might affect abundance and production of this copepod.     

Eutrophication in the Baltic Sea

Fish consumption is increasing globally. Overfishing puts pressure on fisheries, but aquaculture provides an alternative to satisfy the growing need for seafood. However, nutrient emissions from aquaculture contribute to eutrophication, and raising fish from the top of the food chain is inefficient. Here we use the approach of industrial ecology and report ImPACT decomposition analysis of the drivers of nutrient emissions to the Baltic Sea from rainbow trout aquaculture in Finland during 1980?2007. During this period, the nitrogen load studied increased markedly and was 522 tonnes in 2007. The phosphorus load quadrupled and then returned to its original level of about 65 tonnes. The Finnish population increased slightly, while the average affluence level increased significantly. Total salmonid consumption increased substantially during the period. The increasing percentage of imported salmonids and improvements in domestic aquaculture technology ended the period of strong growth of emissions in the 1980s. Decreasing the nutrient load through reductions in salmonid consumption in the future is unlikely, due to health benefits and consumer preferences. Replacing domestic production with import of salmonids raises questions regarding outsourcing of the environmental impact, and regarding rural development in Finland. Major improvements in production technology are not in sight. New perspectives on rainbow trout aquaculture may be needed, including using feed from the Baltic Sea, thus closing the nutrient cycle or changing consumption and production to herbivorous fish species.     

Relationship between Bacterioplankton Richness, Respiration, and Production in the Southern North Sea

We investigated the relationship between bacterioplankton production (BP), respiration (BR), and community composition measured by terminal restriction fragment length polymorphism in the southern North Sea over a seasonal cycle. Major changes in bacterioplankton richness were apparent from April to December. While cell-specific BP decreased highly significantly with increasing bacterioplankton richness, cell-specific BR was found to be variable along the richness gradient, suggesting that bacterioplankton respiration is rather independent from shifts in the bacterial community composition. As a consequence, the bacterial growth efficiency [BGE = BP/(BP + BR)] was negatively related to bacterioplankton richness, explaining ~43% of the variation in BGE. Our results indicate that despite the observed shifts in the community composition, the main function of the bacterioplankton, the remineralization of dissolved organic carbon to CO₂, is rather stable.     

Status of Biodiversity in the Baltic Sea

The brackish Baltic Sea hosts species of various origins and environmental tolerances. These immigrated to the sea 10,000 to 15,000 years ago or have been introduced to the area over the relatively recent history of the system. The Baltic Sea has only one known endemic species. While information on some abiotic parameters extends back as long as five centuries and first quantitative snapshot data on biota (on exploited fish populations) originate generally from the same time, international coordination of research began in the early twentieth century. Continuous, annual Baltic Sea-wide long-term datasets on several organism groups (plankton, benthos, fish) are generally available since the mid-1950s. Based on a variety of available data sources (published papers, reports, grey literature, unpublished data), the Baltic Sea, incl. Kattegat, hosts altogether at least 6,065 species, including at least 1,700 phytoplankton, 442 phytobenthos, at least 1,199 zooplankton, at least 569 meiozoobenthos, 1,476 macrozoobenthos, at least 380 vertebrate parasites, about 200 fish, 3 seal, and 83 bird species. In general, but not in all organism groups, high sub-regional total species richness is associated with elevated salinity. Although in comparison with fully marine areas the Baltic Sea supports fewer species, several facets of the system''s diversity remain underexplored to this day, such as micro-organisms, foraminiferans, meiobenthos and parasites. In the future, climate change and its interactions with multiple anthropogenic forcings are likely to have major impacts on the Baltic biodiversity.     

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.