Abundance, depth distribution, and composition of aerobic bacteriochlorophyll a-producing bacteria in four basins of the central Baltic Sea

The abundance, vertical distribution, and diversity of aerobic anoxygenic phototrophic bacteria (AAP) were studied at four basins of the Baltic Sea. AAP were enumerated by infrared epifluorescence microscopy, and their diversity was analyzed by using pufM gene clone libraries. In addition, numbers of CFU containing the pufM gene were determined, and representative strains were isolated. Both approaches indicated that AAP reached maximal abundance in the euphotic zone. Maximal AAP abundance was 2.5 x 10(5) cells ml(-1) (11% of total prokaryotes) or 1.0 x 10(3) CFU ml(-1) (9 to 10% of total CFU). Environmental pufM clone sequences were grouped into 11 operational taxonomic units phylogenetically related to cultivated members of the Alpha-, Beta-, and Gammaproteobacteria. In spite of varying pufM compositions, five clones were present in all libraries. Of these, Jannaschia-related clones were always found in relative abundances representing 25 to 30% of the total AAP clones. The abundances of the other clones varied. Clones potentially affiliated with typical freshwater Betaproteobacteria sequences were present at three Baltic Sea stations, whereas clones grouping with Loktanella represented 40% of the total cell numbers in the Gotland Basin. For three alphaproteobacterial clones, probable pufM phylogenetic relationships were supported by 16S rRNA gene analyses of Baltic AAP isolates, which showed nearly identical pufM sequences. Our data indicate that the studied AAP assemblages represented a mixture of marine and freshwater taxa, thus characterizing the Baltic Sea as a "melting pot" of abundant, polyphyletic aerobic photoheterotrophic bacteria.     

Recruitment of members from the rare biosphere of marine bacterioplankton communities after an environmental disturbance

A bacterial community may be resistant to environmental disturbances if some of its species show metabolic flexibility and physiological tolerance to the changing conditions. Alternatively, disturbances can change the composition of the community and thereby potentially affect ecosystem processes. The impact of disturbance on the composition of bacterioplankton communities was examined in continuous seawater cultures. Bacterial assemblages from geographically closely connected areas, the Baltic Sea (salinity 7 and high dissolved organic carbon [DOC]) and Skagerrak (salinity 28 and low DOC), were exposed to gradual opposing changes in salinity and DOC over a 3-week period such that the Baltic community was exposed to Skagerrak salinity and DOC and vice versa. Denaturing gradient gel electrophoresis and clone libraries of PCR-amplified 16S rRNA genes showed that the composition of the transplanted communities differed significantly from those held at constant salinity. Despite this, the growth yields (number of cells ml(-1)) were similar, which suggests similar levels of substrate utilization. Deep 454 pyrosequencing of 16S rRNA genes showed that the composition of the disturbed communities had changed due to the recruitment of phylotypes present in the rare biosphere of the original community. The study shows that members of the rare biosphere can become abundant in a bacterioplankton community after disturbance and that those bacteria can have important roles in maintaining ecosystem processes.     

Diversity and seasonal dynamics of Actinobacteria populations in four lakes in northeastern Germany

The phylogenetic diversity and seasonal dynamics of freshwater Actinobacteria populations in four limnologically different lakes of the Mecklenburg-Brandenburg Lake District (northeastern Germany) were investigated. Fluorescence in situ hybridization was used to determine the seasonal abundances and dynamics of total Actinobacteria (probe HGC69a) and the three actinobacterial subclusters acI, acI-A, and acI-B (probes AcI-852, AcI-840-1, and AcI-840-2). Seasonal means of total Actinobacteria abundances in the epilimnia of the lakes varied from 13 to 36%, with maximum values of 30 to 58%, of all DAPI (4',6'-diamidino-2-phenylindole)-stained cells. Around 80% of total Actinobacteria belonged to the acI cluster. The two subclusters acI-A and acI-B accounted for 60 to 91% of the acI cluster and showed seasonal means of 49% (acI-B) and 23% (acI-A) in relation to the acI cluster. Total Actinobacteria and members of the clusters acI and acI-B showed distinct seasonal changes in their absolute abundances, with maxima in late spring and fall/winter. In eight clone libraries constructed from the lakes, a total of 76 actinobacterial 16S rRNA gene sequences were identified from a total of 177 clones. The majority of the Actinobacteria sequences belonged to the acI and acIV cluster. Several new clusters and subclusters were found (acSTL, scB1-4, and acIVA-D). The majority of all obtained 16S rRNA gene sequences are distinct from those of already-cultured freshwater Actinobacteria.     

Biodiversity gradient in the Baltic Sea: a comprehensive inventory of macrozoobenthos data

In the Helsinki Commission Red List project 2009–2012, taxonomic and distributional data of benthic (macro) invertebrates were compiled by the present authors in a comprehensive checklist of the Baltic Sea fauna. Based on the most recent and comprehensive data, this paper presents the diversity patterns observed among benthic invertebrates in the Baltic Sea. As expected, the total number of species per sub-region generally declined along the salinity gradient from the Danish Straits to the northern Baltic Sea. This relationship is well known from the Baltic Sea and has resulted in a general assumption of an exponentially positive relationship between species richness and salinity for marine species, and a negative relationship for freshwater species. In 1934, Remane produced a diagram to describe the hypothetical distribution of benthic invertebrate diversity along a marine–freshwater salinity gradient. Our results clearly indicated the validity of this theory for the macrozoobenthic diversity pattern within the Baltic Sea. Categorisation of sub-regions according to species composition showed both separation and grouping of some sub-regions and a strong alignment of similarity patterns of zoobenthic species composition along the salinity gradient.     

Bacterial Community of the Largest Oligosaline Lake,Namco on the Tibetan Plateau

Bacterial abundances and diversity in the surface water of Lake Namco, the largest oligosaline lake on the Tibetan Plateau, were examined using flow cytometry approach and constructing 16S rRNA gene clone libraries. Bacterial abundances were from 0.08 × 10⁶ to 1.6 × 10⁶ cells mL^?1, and were in the reported range of other lakes of the Tibetan Plateau and high mountain regions. Bacterial abundances were significantly correlated with the concentrations of chlorophyll a (chl a), but showed no significant relationship with the dissolved organic carbon (DOC), which suggested that the amount of DOC released by algae was the key factor determining the bacterial abundance rather than the total DOC. The total trace elements concentrations also obviously connected with bacterial abundances, and 9 of 20 elements showed significant relationship. Bacterial 16S rRNA gene clone sequences were affiliated to the α-, β-, γ-, δ-, and ?-Proteobacteria, Actinobacteria, Bacteroidetes, Cyanobacteria, Firmicutes, Acidobacteria, Planctomycetes, Verrucomicrobia, Candidate division OD1, or unclassified, and among these the β-Proteobacteria dominated. Bacteria in Lake Namco were most closely related to those retrieved from freshwater habitats. Relatively few sequences were closely related to those recovered from saline habitats. Eleven of 34 typical freshwater bacterial clusters were detected in the oligosaline Lake Namco. Bacterial diversity within the lake varied and was connected with the concentrations of DOC and chl a.     

Origin and fate of dissolved organic matter in four shallow Baltic Sea estuaries

Coastal waters have strong gradients in dissolved organic matter (DOM) quantity and characteristics, originating from terrestrial inputs and autochthonous production. Enclosed seas with high freshwater input therefore experience high DOM concentrations and gradients from freshwater sources to more saline waters. The brackish Baltic Sea experiences such salinity gradients from east to west and from river mouths to the open sea. Furthermore, the catchment areas of the Baltic Sea are very diverse and vary from sparsely populated northern areas to densely populated southern zones. Coastal systems vary from enclosed or open bays, estuaries, fjords, archipelagos and lagoons where the residence time of DOM at these sites varies and may control the extent to which organic matter is biologically, chemically or physically modified or simply diluted with transport off-shore. Data of DOM with simultaneous measurements of dissolved organic (DO) nitrogen (N), carbon (C) and phosphorus (P) across a range of contrasting coastal systems are scarce. Here we present data from the Roskilde Fjord, Vistula and Öre estuaries and Curonian Lagoon; four coastal systems with large differences in salinity, nutrient concentrations, freshwater inflow and catchment characteristics. The C:N:P ratios of DOM of our data, despite high variability, show site specific significant differences resulting largely from differences residence time. Microbial processes seemed to have minor effects, and only in spring did uptake of DON in the Vistula and Öre estuaries take place and not at the other sites or seasons. Resuspension from sediments impacts bottom waters and the entire shallow water column in the Curonian Lagoon. Finally, our data combined with published data show that land use in the catchments seems to impact the DOC:DON and DOC:DOP ratios of the tributaries most.

     

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.     

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.     

A Less Saline Baltic Sea Promotes Cyanobacterial Growth,Hampers Intracellular Microcystin Production,and Leads to Strain-Specific Differences in Allelopathy

Salinity is one of the main factors that explain the distribution of species in the Baltic Sea. Increased precipitation and consequent increase in freshwater inflow is predicted to decrease salinity in some areas of the Baltic Sea. Clearly such changes may have profound effects on the organisms living there. Here we investigate the response of the commonly occurring cyanobacterium Dolichospermum spp. to three salinities, 0, 3 and 6. For the three strains tested we recorded growth, intracellular toxicity (microcystin) and allelopathic properties. We show that Dolichospermum can grow in all the three salinities tested with highest growth rates in the lowest salinity. All strains showed allelopathic potential and it differed significantly between strains and salinities, but was highest in the intermediate salinity and lowest in freshwater. Intracellular toxin concentration was highest in salinity 6. In addition, based on monitoring data from the northern Baltic Proper and the Gulf of Finland, we show that salinity has decreased, while Dolichospermum spp. biomass has increased between 1979 and 2013. Thus, based on our experimental findings it is evident that salinity plays a large role in Dolichospermum growth, allelopathic properties and toxicity. In combination with our long-term data analyses, we conclude that decreasing salinity is likely to result in a more favourable environment for Dolichospermum spp. in some areas of the Baltic Sea.     

Chinese mitten crab <Emphasis Type="Italic">Eriocheir sinensis</Emphasis> in the Baltic Sea—a supply-side invader?

Although the Chinese mitten crab Eriocheir sinensis (H. Milne-Edwards, 1853) (Crustacea, Decapoda, Varunidae) invaded the Baltic Sea about 80 years ago, published information on its present distribution and abundance in this region is lacking. We provide here information on its Baltic-wide distribution and long-term population dynamics. The species has been found all over the coastal Baltic Sea and also in some adjacent rivers and lakes. The Chinese mitten crab appears to have increased in abundance in recent years in the northeastern part of the Baltic Sea (Gulf of Finland, Gulf of Riga, northern Baltic Proper). Higher catch rates were observed in spring (April–June) and autumn (September–November). The size variation of crabs in different samples was low (mean carapace width 6.1–6.3 cm). Despite findings of gravid females, the reproduction of the mitten crab in the central, northern and eastern Baltic region is considered unlikely due to low salinity and the individuals caught are assumed to actively migrate into the region from the species’ main European distribution area (southeastern North Sea), certainly over 1500 km migration distance. Thus, the dynamics of the North Sea population is probably regulating, at least in part, the occurrence of the Chinese mitten crab in the Baltic Sea area.     

Salinity gradient of the Baltic Sea limits the reproduction and population expansion of the newly invaded comb jelly Mnemiopsis leidyi

The recent invasion of the comb jelly Mnemiopsis leidyi into northern European waters is of major public and scientific concern. One of the key features making M. leidyi a successful invader is its high fecundity combined with fast growth rates. However, little is known about physiological limitations to its reproduction and consequent possible abiotic restrictions to its dispersal. To evaluate the invasion potential of M. leidyi into the brackish Baltic Sea we studied in situ egg production rates in different regions and at different salinities in the laboratory, representing the salinity gradient of the Baltic Sea. During October 2009 M. leidyi actively reproduced over large areas of the Baltic Sea. Egg production rates scaled with animal size but decreased significantly with decreasing salinity, both in the field (7-29) and in laboratory experiments (6-33). Temperature and zooplankton, i.e. food abundance, could not explain the observed differences. Reproduction rates at conditions representing the Kattegat, south western and central Baltic Sea, respectively, were 2.8 fold higher at the highest salinities (33 and 25) than at intermediate salinities (10 and 15) and 21 times higher compared from intermediate to the lowest salinity tested (6). Higher salinity areas such as the Kattegat, and to a lower extent the south western Baltic, seem to act as source regions for the M. leidyi population in the central Baltic Sea where a self-sustaining population, due to the low salinity, cannot be maintained.     

Further expansion of the genus Cercopagis (Crustacea,Branchiopoda, Onychopoda) in the Baltic Sea,with notes on the taxa present and their ecology

The onychopod cladoceran Cercopagis that recently invaded the Baltic Sea is reported from new zones of the northern Baltic proper. Because of successful survival and an expanding distribution range, the addition of Cercopagis to the Baltic fauna is considered to be permanent. What has previously been cited as Cercopagis pengoi encompasses the morphology of several other species, subspecies and forms. Either a number of morphologically similar species is present, or there is a number of spurious species in Cercopagis. The last hypothesis is favoured. The spatial distribution pattern of Cercopagis, as well as that of total zooplankton, was correlated with depth. Deep (>100 m) and shallow (<10 m) stations had significantly lower abundance than stations of intermediate depth (<100 m). An overview of the distribution of C. pengoi group in fresh and brackish waters suggests a high tolerance to environmental factors, but with differences among taxa. Due to this ecological flexibility, the colonization of the Baltic is not unexpected. Increasing salinity may restrict dispersal of cercopagids to the southern areas of the Baltic and to the North Sea, but inland lakes (e.g. in Sweden) present an ecological profile suitable for colonization.     

Comparative analysis of ammonia monooxygenase (amoA) genes in the water column and sediment-water interface of two lakes and the Baltic Sea

The functional gene amoA was used to compare the diversity of ammonia-oxidizing bacteria (AOB) in the water column and sediment-water interface of the two freshwater lakes Plusssee and Sch?hsee and the Baltic Sea. Nested amplifications were used to increase the sensitivity of amoA detection, and to amplify a 789-bp fragment from which clone libraries were prepared. The larger part of the sequences was only distantly related to any of the cultured AOB and is considered to represent new clusters of AOB within the Nitrosomonas/Nitrosospira group. Almost all sequences from the water column of the Baltic Sea and from 1-m depth of Sch?hsee were related to different Nitrosospira clusters 0 and 2, respectively. The majority of sequences from Plusssee and Sch?hsee were associated with sequences from Chesapeake Bay, from a previous study of Plusssee and from rice roots in Nitrosospira-like cluster A, which lacks sequences from Baltic Sea. Two groups of sequences from Baltic Sea sediment were related to clonal sequences from other brackish/marine habitats in the purely environmental Nitrosospira-like cluster B and the Nitrosomonas-like cluster. This confirms previous results from 16S rRNA gene libraries that indicated the existence of hitherto uncultivated AOB in lake and Baltic Sea samples, and showed a differential distribution of AOB along the water column and sediment of these environments.     

Photosynthesis and UV-B Tolerance of the Marine Alga Fucus vesiculosus at Different Sea Water Salinities

The marine algal species in the Baltic Sea are few due to the low sea water salinity. One of the few species that can be found is Fucus vesiculosus. Even this species is affected by the low salinity and becomes smaller in size in the Baltic. In present work the photosynthesis of F. vesiculosus in the northern Baltic (Bothnian Sea) was compared to the photosynthesis of F. vesiculosus in the Atlantic. Oxygen evolution was measured before and after exposure to 2.3 W of UV-B (280–320 nm) radiation for 5 h, as well as after 48 h recovery in low light. The plants were kept in their own sea water salinity as well as in a changed salinity, this to examine possible correlations between salinity and photosynthesis. The results show a significant higher initial maximal photosynthesis (P _max) for Atlantic plants (10.3 nmol O₂ g⁻¹ FW s⁻¹) compared to Baltic plants (4.0 nmol O₂ g⁻¹ FW s⁻¹). The Baltic plants were found more sensitive to UV-B with a 40–50% decrease of P _max as well as a lower degree of recovery (60–70% compared to 75–95% for the Atlantic plants). The higher salinity (35 psu) had a positive effect on the Baltic F. vesiculosus with increased P _max as well as increased tolerance to UV-B. The lower salinity (5 psu) had a negative effect on the Atlantic plants with a decreased P _max as well as a lower tolerance to UV-B. Pigment content was found higher in Atlantic F. vesiculosus. The pigment content decreased then the Atlantic plants were transferred to 5 psu. The concentration of Chl a as well as the total content of violaxanthin, diadinoxanthin and zeaxanthin in Baltic plants increased when transferred to 35 psu. The Atlantic F. vesiculosus can not survive the low salinity in the northern Baltic (died within 8 weeks). It is likely that a long time acclimation or adaptation to low salinity has taken place for F. vesiculosus in northern Baltic. If this is an ecotypic or genotypic development it is too early to say.     

Atlantic climatic factors control decadal dynamics of a Baltic Sea copepod Temora longicornis

We discovered, using transfer functions, that climatic changes in the Atlantic control the abundance of Temora longicornis , a dominant pelagic copepod of the Baltic Sea. The seawater salinity was increasing and copepod numbers were high from 1960s up to 1970s. Then the freshwater runoff started to increase, which resulted in decreasing salinities and abundance of the copepod. At the end of 1990s, runoffs remained at a high level, and the decrease of surface salinities and Temora leveled off. Due to time lags between variables studied, we also make predictions of changes expectable in early 2000s. The total freshwater runoff to the Baltic Sea followed the North Atlantic Oscillation with an immediate lag. Salinity followed the runoff non-linearly with a lag of 4–9 months. Temora longicornis followed the salinity with a lag of 1–3 months. Predicted abundance of T. longicornis will remain low implicating poor feeding conditions for planktivores. Our study points out the importance of physical factors in control of pelagic environments compared to ecological interactions, such as top-down and bottom-up.     

Diversity of microbial communities colonizing the walls of a Karstic cave in Slovenia

Karstic cave systems in Slovenia receive substantial amounts of organic input from adjacent forest and freshwater systems. These caves host microbial communities that consist of distinct small colonies differing in colour and shape. Visible to the naked eye, the colonies cover cave walls and are strewn with light-reflecting water droplets. In this study, the diversity of prokaryotes constituting these unusual microbial communities in Pajsarjeva jama cave was examined. A molecular survey based on small subunit rRNA diversity showed a high diversity within the Bacteria , while members of Archaea were not recovered. A total of eight bacterial phyla were detected. The application of various species richness estimators confirmed the diverse nature of the microbial community sample. Members of Gammaproteobacteria were most abundant in the clone libraries constructed and were followed in abundance by members of Actinobacteria and Nitrospira . In addition, members of Alphaproteobacteria, Betaproteobacteria and Deltaproteobacteria as well as Acidobacteria, Verrucomicrobia, Planctomycetes, Chloroflexi and Gemmatimonadetes were identified in clone libraries. The high number of clones most closely related to environmental 16S rRNA gene clones showed the broad spectrum of unknown and yet to be cultivated microorganisms inhabiting these cave systems.     

Evidence for Selective Bacterial Community Structuring in the Freshwater Sponge Ephydatia fluviatilis

To understand the functioning of sponges, knowledge of the structure of their associated microbial communities is necessary. However, our perception of sponge-associated microbiomes remains mainly restricted to marine ecosystems. Here, we report on the molecular diversity and composition of bacteria in the freshwater sponge Ephydatia fluviatilis inhabiting the artificial lake Vinkeveense Plassen, Utrecht, The Netherlands. Polymerase chain reaction-denaturing gradient gel electrophoresis (PCR-DGGE) fingerprints revealed that the apparent diversities within the domain Bacteria and the phylum Actinobacteria were lower in E. fluviatilis than in bulk water. Enrichment of specific PCR-DGGE bands in E. fluviatilis was detected. Furthermore, sponge- and bulk water-derived bacterial clone libraries differed with respect to bacterial community composition at the phylum level. E. fluviatilis-derived sequences were affiliated with six recognized phyla, i.e., Proteobacteria, Planctomycetes, Actinobacteria, Bacteroidetes, Chlamydiae and Verrucomicrobia, in order of relative abundance; next to the uncultured candidate phylum TM7 and one deeply rooted bacterial lineage of undefined taxonomy (BLUT). Actinobacteria, Proteobacteria, and Bacteroidetes were the dominant bacterial phyla in the freshwater clone library whereas sequences affiliated with Planctomycetes, Verrucomicrobia, Acidobacteria and Armatimonadetes were found at lower frequencies. Fine-tuned phylogenetic inference showed no or negligible overlaps between the E. fluviatilis and water-derived phylotypes within bacterial taxa such as Alphaproteobacteria, Bacteroidetes and Actinobacteria. We also ascertained the status of two alphaproteobacterial lineages as freshwater sponge-specific phylogenetic clusters, and report on high distinctiveness of other E. fluviatilis specific phylotypes, especially within the Bacteroidetes, Planctomycetes and Chlamydia taxa. This study supports the contention that the composition and diversity of bacteria in E. fluviatilis is partially driven by the host organism.     

Long-term dynamics of zooplankton in the southeastern Baltic Sea

Long-term research in the Baltic Sea revealed the basic trends of zooplankton community variations depending on oceanographic processes. Alternation of the periods of increase and decrease in salinity of the Baltic Sea against the background of climate changes (temperature increase) and eutrophication affect the state of the entire Baltic ecosystem, including zooplankton. For these periods, the dynamics of zooplankton in the Baltic Sea were analyzed based on literature data and results of regular research in the southeastern Baltic Sea during 1998–2007. The changes in the hydrological situation were accompanied by significant changes in the zooplankton community. In the 1990s–2000s, the abundance and biomass of brackish-water and thermophilous species primarily of Cladocera and Copepoda increased markedly. The role of the previously dominant marine copepod Pseudocalanus elongatus decreased due to salinity reduction in the deep-water part of the Baltic Sea. Maximum development of zooplankton occurred in years of the greatest warming-up of the water (2001, 2005–2007) against the background of a general positive trend of zooplankton abundance in the last decade.     

Changes in community structure of active protistan assemblages from the lower Pearl River to coastal Waters of the South China Sea

Protists make up an important component of aquatic ecosystems, playing crucial roles in biogeochemical processes on local and global scales. To reveal the changes of diversity and community structure of protists along the salinity gradients, community compositions of active protistan assemblages were characterized along a transect from the lower Pearl River estuary to the open waters of the South China Sea (SCS), using high-throughput sequencing of the hyper-variable V9 regions of 18S rRNA. This study showed that the alpha diversity of protists, both in the freshwater and in the coastal SCS stations was higher than that in the estuary. The protist community structure also changed along the salinity gradient. The relative sequence abundance of Stramenopiles was highest at stations with lower salinity and decreased with the increasing of salinity. By contrast, the contributions of Alveolata, Hacrobia and Rhizaria to the protistan communities generally increased with the increasing of salinity. The composition of the active protistan community was strongly correlated with salinity, indicating that salinity was the dominant factor among measured environmental parameters affecting protistan community composition and structure.     

Salinity Impact on Bacterial Community Composition in Five High-Altitude Lakes from the Tibetan Plateau,Western China

The influence of salinity and geographical distance on bacterial community composition (BCC) in five freshwater, oligosaline or polysaline lakes located at altitudes higher than 4400 m on the central and southern Tibetan Plateau were investigated using the 16S rRNA gene clone library approach together with multivariate analysis of environmental variables. A total of 10 clone libraries were constructed with two libraries in each lake, one in the epilimnion and the other in the hypolimnion. Geographical distance was not found to impact BCC significantly, but salinity, chl a and lake hydraulic retention time were significant factors influencing the BCC. Bacteria in lakes located on the central and southern Plateau owned the same community composition as that observed from the eastern Tibetan lakes. They were both predominated by Bacteroidetes and Cyanobacteria, had low taxon richness, and similar typical freshwater clusters and distributed characteristics. Supplemental materials are available for this article. Go to the publisher's online edition of Geomicrobiology Journal to view the supplemental file.