Ocean acidification resulting from the uptake of anthropogenic carbon dioxide (CO2) by the ocean is considered a major threat to marine ecosystems. Here we examined the effects of ocean acidification on microbial community dynamics in the eastern Baltic Sea during the summer of 2012 when inorganic nitrogen and phosphorus were strongly depleted. Large-volume in situ mesocosms were employed to mimic present, future and far future CO2 scenarios. All six groups of phytoplankton enumerated by flow cytometry ( < 20 µm cell diameter) showed distinct trends in net growth and abundance with CO2 enrichment. The picoeukaryotic phytoplankton groups Pico-I and Pico-II displayed enhanced abundances, whilst Pico-III, Synechococcus and the nanoeukaryotic phytoplankton groups were negatively affected by elevated fugacity of CO2 (fCO2). Specifically, the numerically dominant eukaryote, Pico-I, demonstrated increases in gross growth rate with increasing fCO2 sufficient to double its abundance. The dynamics of the prokaryote community closely followed trends in total algal biomass despite differential effects of fCO2 on algal groups. Similarly, viral abundances corresponded to prokaryotic host population dynamics. Viral lysis and grazing were both important in controlling microbial abundances. Overall our results point to a shift, with increasing fCO2, towards a more regenerative system with production dominated by small picoeukaryotic phytoplankton.
Posts Tagged 'Baltic'
Alterations in microbial community composition with increasing fCO2: a mesocosm study in the eastern Baltic Sea (update)
Published 30 August 2017 Science ClosedTags: abundance, Baltic, biological response, BRcommunity, community composition, field, growth, mesocosms, mortality, otherprocess, phytoplankton, prokaryotes, virus, zooplankton
Seasonal variations of Fucus vesiculosus fertility under ocean acidification and warming in the western Baltic Sea
Published 15 August 2017 Science ClosedTags: algae, Baltic, biological response, chemistry, field, laboratory, mesocosms, morphology, multiple factors, reproduction, temperature
Ocean warming and acidification may substantially affect the reproduction of keystone species such as Fucus vesiculosus (Phaeophyceae). In four consecutive benthic mesocosm experiments, we compared the reproductive biology and quantified the temporal development of Baltic Sea Fucus fertility under the single and combined impact of elevated seawater temperature and pCO2 (1100 ppm). In an additional experiment, we investigated the impact of temperature (0–25°C) on the maturation of North Sea F. vesiculosus receptacles. A marked seasonal reproductive cycle of F. vesiculosus became apparent in the course of 1 year. The first appearance of receptacles on vegetative apices and the further development of immature receptacles of F. vesiculosus in autumn were unaffected by warming or elevated pCO2. During winter, elevated pCO2 in both ambient and warmed temperatures increased the proportion of mature receptacles significantly. In spring, warming and, to a lesser extent, elevated pCO2 accelerated the maturation of receptacles and advanced the release of gametes by up to 2 weeks. Likewise, in the laboratory, maturation and gamete release were accelerated at 15–25°C relative to colder temperatures. In summary, elevated pCO2 and/or warming do not influence receptacle appearance in autumn, but do accelerate the maturation process during spring, resulting in earlier gamete release. Temperature and, to a much lesser extent, pCO2 affect the temporal development of Fucus fertility. Thus, rising temperatures will mainly shift or disturb the phenology of F. vesiculosus in spring and summer, which may alter and/or hamper its ecological functions in shallow coastal ecosystems of the Baltic Sea.
Macroalgae may mitigate ocean acidification effects on mussel calcification by increasing pH and its fluctuations
Published 15 August 2017 Science ClosedTags: abundance, algae, Baltic, biogeochemistry, biological response, BRcommunity, calcification, communityMF, field, laboratory, mollusks, multiple factors, otherprocess, phanerogams
Ocean acidification (OA) is generally assumed to negatively impact calcification rates of marine organisms. At a local scale however, biological activity of macrophytes may generate pH fluctuations with rates of change that are orders of magnitude larger than the long-term trend predicted for the open ocean. These fluctuations may in turn impact benthic calcifiers in the vicinity. Combining laboratory, mesocosm and field studies, such interactions between OA, the brown alga Fucus vesiculosus, the sea grass Zostera marina and the blue mussel Mytilus edulis were investigated at spatial scales from decimetres to 100s of meters in the western Baltic. Macrophytes increased the overall mean pH of the habitat by up to 0.3 units relative to macrophyte-free, but otherwise similar, habitats and imposed diurnal pH fluctuations with amplitudes ranging from 0.3 to more than 1 pH unit. These amplitudes and their impact on mussel calcification tended to increase with increasing macrophyte biomass to bulk water ratio. At the laboratory and mesocosm scales, biogenic pH fluctuations allowed mussels to maintain calcification even under acidified conditions by shifting most of their calcification activity into the daytime when biogenic fluctuations caused by macrophyte activity offered temporal refuge from OA stress. In natural habitats with a low biomass to water body ratio, the impact of biogenic pH fluctuations on mean calcification rates of M. edulis was less pronounced. Thus, in dense algae or seagrass habitats, macrophytes may mitigate OA impact on mussel calcification by raising mean pH and providing temporal refuge from acidification stress.
Effect of ocean acidification and elevated temperature on growth of calcifying tubeworm shells (Spirorbis spirorbis): an in-situ benthocosm approach
Published 10 July 2017 Science ClosedTags: annelids, Baltic, biological response, dissolution, field, growth, mesocosms, morphology, multiple factors, temperature
The calcareous tubeworm Spirorbis spirorbis is a wide-spread serpulid species in the Baltic Sea, where it commonly grows as an epibiont on brown macroalgae (genus Fucus). It lives within a Mg-calcite shell and could be affected by ocean acidification and temperature rise induced by the predicted future atmospheric CO2 increase. However, Spirorbis tubes grow in a chemically modified boundary layer around the algae, which may mitigate acidification. In order to investigate how increasing temperature and rising pCO2 may influence S. spirorbis shell growth we carried out four seasonal experiments in the ‘Kiel Outdoor Benthocosms’ at elevated pCO2 and temperature conditions. Compared to laboratory batch culture experiments the benthocosm approach provides a better representation of natural conditions for physical and biological ecosystem parameters, including seasonal variations. We find that growth rates of S. spirorbis are significantly controlled by ontogenetic and seasonal effects. The length of the newly grown tube is inversely related to the initial diameter of the shell. Our study showed no significant difference of the growth rates between ambient atmospheric and elevated (1100 ppm) pCO2 conditions. No influence of daily average CaCO3 saturation state on the growth rates of S. spirorbiswas observed. We found, however, net growth of the shells even in temporarily undersaturated bulk solutions, under conditions that concurrently favored selective shell surface dissolution. The results suggest an overall resistance of S. spirorbis growth to acidification levels predicted for the year 2100 in the Baltic Sea. In contrast, S. spirorbis did not survive at mean seasonal temperatures exceeding 24 °C during the summer experiments. In the autumn experiments at ambient pCO2, the growth rates of juvenile S. spirorbis were higher under elevated temperature conditions. The results reveal that S. spirorbis may prefer moderately warmer conditions during their early life stages but will suffer from an excessive temperature increase and from increasing shell corrosion as a consequence of progressing ocean acidification.
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Organic matter export to the seafloor in the Baltic Sea: Drivers of change and future projections
Published 4 July 2017 Science ClosedTags: Baltic, biogeochemistry, methods, review
The impact of environmental change and anthropogenic stressors on coastal marine systems will strongly depend on changes in the magnitude and composition of organic matter exported from the water column to the seafloor. Knowledge of vertical export in the Baltic Sea is synthesised to illustrate how organic matter deposition will respond to climate warming, climate-related changes in freshwater runoff, and ocean acidification. Pelagic heterotrophic processes are suggested to become more important in a future warmer climate, with negative feedbacks to organic matter deposition to the seafloor. This is an important step towards improved oxygen conditions in the near-bottom layer that will reduce the release of inorganic nutrients from the sediment and hence counteract further eutrophication. The evaluation of these processes in ecosystem models, validated by field observations, will significantly advance the understanding of the system’s response to environmental change and will improve the use of such models in management of coastal areas.
Ocean acidification in the Baltic Sea : implications for the bivalve Macoma balthica
Published 16 May 2017 Science ClosedTags: abundance, Baltic, biological response, BRcommunity, chemistry, field, laboratory, mesocosms, mollusks, morphology, mortality, otherprocess, performance, physiology, respiration
The Baltic Sea is one of the most human-impacted sea areas in the world and its ecosystems are exposed to a variety of stressors of anthropogenic origin. Large changes in the environmental conditions, species and communities of the Baltic Sea are predicted to occur due to global climate change, but the extent and magnitude of the future changes are challenging to estimate due to the multiple stressors simultaneously impacting the system. As an additional threat, future ocean acidification will play a role in modifying the environmental conditions, and these CO2-induced changes are predicted to be fast in the Baltic Sea. This is especially of concern for the species-poor, but functionally essential benthic communities where key species such as bivalve Macoma balthica live at the limits of their tolerance range, and are already regularly disturbed by environmental stressors such as hypoxia. Currently, only very limited knowledge about the effects of future ocean acidification exists for this species.
The overall aim of my thesis was to develop an understanding of the effects of CO2 increase on the vulnerability of Baltic Sea key species, and how this is related to other effects of climate change, e.g. an increase in bottom-water hypoxia. Specifically, I investigated how different life stages of the infaunal bivalve M. balthica could be affected by future ocean acidification. Survival, growth, behaviour and physiological responses were assessed in a combination of laboratory and mesocosm experiments by exposing different life stages of M. balthica to different pH levels over different time periods depending on the life stage in question. While some life stage-based differences in vulnerability and survival were found, the results indicate that reduced pH has a negative effect on all life stages. In larval M. balthica, even a slight pH decrease was found to cause significant negative changes during that delicate life stage, both by slowing growth and by decreasing survival. Other observed impacts included delayed settling of the post-larvae and increasing energetic demand of adult bivalves.
The results suggest consistent negative effects at all life stages with potential major implications for the resilience of M. Balthica populations, which are currently under threat from a range of anthropogenic stressors such as increasing hypoxia. The kind of experimental studies conducted in this thesis are useful for pinpointing mechanisms, but they are always simplifications of reality, however, and are usually conducted over time scales that are short in relation to the time scales over which ocean acidification is affecting populations, communities and ecosystems. To fully understand and to be able to estimate how the complex ecosystems are about to change in the future, incorporating more of the biotic interactions, impacting stressors and relevant environmental conditions are needed for increasing the level of realism in the experiments.
Naturally acidified habitat selects for ocean acidification–tolerant mussels
Published 3 May 2017 Science ClosedTags: adaptation, Baltic, biological response, BRcommunity, calcification, chemistry, field, growth, mollusks, morphology, mortality, otherprocess, reproduction
Ocean acidification severely affects bivalves, especially their larval stages. Consequently, the fate of this ecologically and economically important group depends on the capacity and rate of evolutionary adaptation to altered ocean carbonate chemistry. We document successful settlement of wild mussel larvae (Mytilus edulis) in a periodically CO2-enriched habitat. The larval fitness of the population originating from the CO2-enriched habitat was compared to the response of a population from a nonenriched habitat in a common garden experiment. The high CO2–adapted population showed higher fitness under elevated PCO2 (partial pressure of CO2) than the non-adapted cohort, demonstrating, for the first time, an evolutionary response of a natural mussel population to ocean acidification. To assess the rate of adaptation, we performed a selection experiment over three generations. CO2 tolerance differed substantially between the families within the F1 generation, and survival was drastically decreased in the highest, yet realistic, PCO2 treatment. Selection of CO2-tolerant F1 animals resulted in higher calcification performance of F2 larvae during early shell formation but did not improve overall survival. Our results thus reveal significant short-term selective responses of traits directly affected by ocean acidification and long-term adaptation potential in a key bivalve species. Because immediate response to selection did not directly translate into increased fitness, multigenerational studies need to take into consideration the multivariate nature of selection acting in natural habitats. Combinations of short-term selection with long-term adaptation in populations from CO2-enriched versus nonenriched natural habitats represent promising approaches for estimating adaptive potential of organisms facing global change.
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The future for microplankton in the Baltic Sea – Effects of SWS and climate change
Published 2 May 2017 Science ClosedTags: abundance, Baltic, biological response, BRcommunity, chemistry, community composition, field, laboratory, multiple factors, otherprocess, photosynthesis, phytoplankton, prokaryotes, protists, salinity, temperature, zooplankton
The Baltic Sea is located between 53°N to 66°N and from 10°E to 30°E and is the second largest brackish water body in the world. It consists of several basins where the Baltic Proper is the major water mass. Around 85 million people live in the catchment area of the Baltic Sea, which subjects it to a range of environmental pressures, such as increased nutrient inputs from human activities (eutrophication), shipping, over-fishing, acid rain and trace metals released from anti-fouling paint. All these stressors, combined with low alkalinity, variable salinity and limited water exchange, makes the Baltic Sea a very sensitive area that may be less resilient to future stressors such as climate change or increased shipping activities. Microplankton communities consist of small heterotrophic bacteria, picoplankton, phytoplankton, cyanobacteria and smaller grazers, such as ciliates and zooplankton. In the Baltic Proper, there is a succession of blooms, within the microplankton community, from diatoms and dinoflagellates in the early spring to cyanobacteria during summer and ending with a second diatom and dinoflagellate bloom in the autumn. The cyanobacteria of the Baltic Proper bloom every summer and are dominated by Aphanizomenon sp. and Nodularia spumigena. Dolichospermum spp. is present but is less abundant. The effects of climate change were tested on a natural microplankton community, as well as on isolated cyanobacteria species from the Baltic Sea. To simulate effects of climate change, the temperature was increased from 12°C to 16°C, salinity decreased from 6-7 to 3-4 and atmospheric pCO2-levels was increased from 380 ppm to 960 ppm. The biovolume of Aphanizomenon sp. and N. spumigena increased when temperature was increased by 4°C. When salinity was decreased by three units, both the growth and photosynthetic activity of N. spumigena were reduced while Aphanizomenon sp. was unaffected, and the growth of Dolichospermum sp. was increased. Furthermore, present-day salinities were beneficial, in terms of increased biovolumes, of diatoms, dinoflagellates and ciliates, compared to reduced future salinity. Increased atmospheric pCO2 had no effect on any of the species in the microplankton community. These results show that the future microplankton community may be positive, in terms of increased biovolume, for the cyanobacteria species Aphanizomenon sp. and Dolichospermum spp. An increase of cyanobacteria blooms may open up to the possibility to grow and/or harvest these species as a source of biofuel or fatty acids (FA). Dolichospermum sp. yielded higher total FA content per biovolume, compared to the other two cyanobacteria species in phosphorus-depleted medium and Aphanizomenon sp. in nitrogen-depleted medium. Natural nutrient levels in the Baltic Proper are low both in nitrogen and phosphorus, which indicates a possible future market for biofuel and FA technologies. Additionally, the effects of seawater scrubbing (SWS) were tested on a natural summer-bloom microplankton community. Three different concentrations of scrubber water were added; 1%, 3% and 10%. To elucidate effects of decreased pH alone, water acidified with H2SO4 was added in equal concentrations. The six treatments were compared to a control without acidifying substances. SWS or the corresponding pH treatments, did not have a direct effect on microplankton species composition and biovolume. However, the increased amount of Cu and Zn in the scrubber water, combined with significant decrease in pH and alkalinity already at the 1% scrubber water treatment calls for precaution when implementing scrubber units on the shipping fleet of the Baltic Sea. The accumulated effects of long-term repeated addition constantly throughout the year, i.e. in a shipping lane, are yet to be elucidated.
Climate change can cause complex responses in Baltic Sea macroalgae: A systematic review
Published 28 March 2017 Science ClosedTags: algae, Baltic, biological response, review
Estuarine macroalgae are important primary producers in aquatic ecosystems, and often foundation species providing structurally complex habitat. Climate change alters many abiotic factors that affect their long-term persistence and distribution. Here, we review the existing scientific literature on the tolerance of key macroalgal species in the Baltic Sea, the world’s largest brackish water body. Elevated temperature is expected to intensify coastal eutrophication, further promoting growth of opportunistic, filamentous species, especially green algae, which are often species associated with intensive filamentous algal blooms. Declining salinities will push the distributions of marine species towards south, which may alter the Baltic Sea community compositions towards a more limnic state. Together with increasing eutrophication trends this may cause losses in marine-originating foundation species such as Fucus, causing severe biodiversity impacts. Experimental results on ocean acidification effects on macroalgae are mixed, with only few studies conducted in the Baltic Sea. We conclude that climate change can alter the structure and functioning of macroalgal ecosystems especially in the northern Baltic coastal areas, and can potentially act synergistically with eutrophication. We briefly discuss potential adaptation measures.
Changes in wintertime pH and hydrography of the Gulf of Finland (Baltic Sea) with focus on depth layers
Published 15 March 2017 Science ClosedTags: Baltic, chemistry, field
We studied changes in sea water pH, temperature and salinity with focus on two depth layers, along the Gulf of Finland (the Baltic Sea) using long-term monitoring data from 1979 to 2015. Data from the most frequently sampled monitoring stations between western and eastern Gulf of Finland were used. The main result of the study reveals that pH has decreased both in surface and deep-water in the western Gulf of Finland with values ranging between −0.005 and −0.008 units year−1. We also demonstrate a rise in temperature (~2 °C) and decrease in salinity (~−0.7 g kg−1) at several stations over the last 36 years. In general, the changes are shown to be more pronounced in the western part of the gulf. This paper also stresses the importance of improving the sampling frequency and quality of monitoring measurements.
Climate change, zooplankton and fisheries
Published 6 March 2017 Science ClosedTags: Baltic, biological response, fisheries, review, zooplankton
We summarize responses to and mechanisms by which zooplankton cope with climate change. Effects of ocean warming include altered phenology, body size reduction, decline of tropical zooplankton biomass, functional group shifts in Polar Regions, and poleward expansion of zooplankton distributions. Thermal specialists (zooplankton from tropical and Polar Regions) may already perform near their limits and will be more vulnerable to warming. Evolutionary adaptation may mitigate, but not always fully offset the adverse effects of warming; thus, dispersal may play a prevalent role in the future distribution of species. While direct negative effects of ocean acidification is largely confined to calcifying organisms, early life stages of noncalcifying species (e.g., copepods, fish larvae) are susceptible to sublethal effects, particularly in combination with increasing temperature. Evidence is emerging for a large adaptation potential to hypercapnia in zooplankton. Hypoxia negatively affects physiology and life history traits. Despite zooplankton physiological and behavioral adaptations to hypoxia, shoaling of hypoxic waters likely increases predation mortality. Combined effects of warming, hypercapnia and hypoxia are poorly characterized or understood, but will likely depress performance and narrow the thermal performance curve. Climate change could result in different kinds of mismatches between zooplankton and fish larvae, i.e., (i) temporal, (ii) spatial, (iii) bioenergetic, and (iv) evolutionary mistmatches that individually or in combination, would result in altered larval fish growth and survival. Linkages between climate, zooplankton and fisheries are explored using the Baltic Sea as a case study.
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Acidification and warming affect prominent bacteria in two seasonal phytoplankton bloom mesocosms
Published 24 February 2017 Science ClosedTags: abundance, Baltic, biological response, BRcommunity, community composition, laboratory, mesocosms, multiple factors, otherprocess, primary production, prokaryotes, temperature
In contrast to clear stimulatory effects of rising temperature, recent studies of the effects of CO2 on planktonic bacteria have reported conflicting results. To better understand the potential impact of predicted climate scenarios on the development and performance of bacterial communities, we performed bifactorial mesocosm experiments (pCO2 and temperature) with Baltic Sea water, during a diatom dominated bloom in autumn and a mixed phytoplankton bloom in summer. The development of bacterial community composition (BCC) followed well-known algal bloom dynamics. A principal coordinate analysis (PCoA) of bacterial OTUs (operational taxonomic units) revealed that phytoplankton succession and temperature were the major variables structuring the bacterial community whereas the impact of pCO2 was weak. Prokaryotic abundance and carbon production, and organic matter concentration and composition were partly affected by temperature but not by increased pCO2. However, pCO2 did have significant and potentially direct effects on the relative abundance of several dominant OTUs; in some cases, these effects were accompanied by an antagonistic impact of temperature. Our results suggest the necessity of high-resolution BCC analyses and statistical analyses at the OTU level to detect the strong impact of CO2 on specific bacterial groups, which in turn might also influence specific organic matter degradation processes.
The influence of CO2 enrichment on net photosynthesis of seagrass Zostera marina in a brackish water environment
Published 21 February 2017 Science ClosedTags: Baltic, biological response, field, light, mesocosms, multiple factors, phanerogams, photosynthesis, temperature
Seagrasses are distributed across the globe and their communities may play key roles in the coastal ecosystems. Seagrass meadows are expected to benefit from the increased carbon availability which might be used in photosynthesis in a future high CO2 world. The main aim of this study was to examine the effect of elevated pCO2 on the net photosynthesis of seagrass Zostera marina in a brackish water environment. The short-term mesocosm experiments were conducted in Kõiguste Bay (northern part of Gulf of Riga, the Baltic Sea) in June–July 2013 and 2014. As the levels of pCO2 naturally range from ca. 150 μatm to well above 1000 μatm under summer conditions in Kõiguste Bay we chose to operate in mesocosms with the pCO2 levels of ca. 2000, ca. 1000, and ca. 200 μatm. Additionally, in 2014 the photosynthesis of Z. marina was measured outside of the mesocosm in the natural conditions. In the shallow coastal Baltic Sea seagrass Z. marina lives in a highly variable environment due to seasonality and rapid changes in meteorological conditions. This was demonstrated by the remarkable differences in water temperatures between experimental years of ca. 8°C. Thus, the current study also investigated the effect of elevated pCO2 in combination with short-term natural fluctuations of environmental factors, i.e., temperature and PAR on the photosynthesis of Z. marina. Our results show that elevated pCO2 alone did not enhance the photosynthesis of the seagrass. The photosynthetic response of Z. marina to CO2 enrichment was affected by changes in water temperature and light availability.
Intra-population variability of ocean acidification impacts on the physiology of Baltic blue mussels (Mytilus edulis): integrating tissue and organism response
Published 9 February 2017 Science ClosedTags: adaptation, Baltic, biological response, laboratory, mollusks, mortality, otherprocess, physiology, respiration
Increased maintenance costs at cellular, and consequently organism level, are thought to be involved in shaping the sensitivity of marine calcifiers to ocean acidification (OA). Yet, knowledge of the capacity of marine calcifiers to undergo metabolic adaptation is sparse. In Kiel Fjord, blue mussels thrive despite periodically high seawater PCO2, making this population interesting for studying metabolic adaptation under OA. Consequently, we conducted a multi-generation experiment and compared physiological responses of F1 mussels from ‘tolerant’ and ‘sensitive’ families exposed to OA for 1 year. Family classifications were based on larval survival; tolerant families settled at all PCO2 levels (700, 1120, 2400 µatm) while sensitive families did not settle at the highest PCO2 (≥99.8% mortality). We found similar filtration rates between family types at the control and intermediate PCO2 level. However, at 2400 µatm, filtration and metabolic scope of gill tissue decreased in tolerant families, indicating functional limitations at the tissue level. Routine metabolic rates (RMR) and summed tissue respiration (gill and outer mantle tissue) of tolerant families were increased at intermediate PCO2, indicating elevated cellular homeostatic costs in various tissues. By contrast, OA did not affect tissue and routine metabolism of sensitive families. However, tolerant mussels were characterised by lower RMR at control PCO2 than sensitive families, which had variable RMR. This might provide the energetic scope to cover increased energetic demands under OA, highlighting the importance of analysing intra-population variability. The mechanisms shaping such difference in RMR and scope, and thus species’ adaptation potential, remain to be identified.
Impact of environmental factors on bacterioplankton communities
Published 1 February 2017 Science ClosedTags: abundance, Baltic, biological response, BRcommunity, chemistry, community composition, communityMF, field, mesocosms, multiple factors, otherprocess, primary production, prokaryotes, temperature
Aquatic bacteria are main drivers of biogeochemical cycles and contribute predominantly to organic matter and nutrient recycling. As a high biodiversity is assumed to stabilize ecosystem functioning, it is necessary to understand the bacterial community dynamics and their structuring factors. It is known that different taxa are dominant across different habitats and seasons. This indicates an occurrence of species sorting by community structuring environmental factors. A first attempt for the understanding of bacterial distribution is to test for a correlation between microbial composition and measured environmental variables. In order to get further insights into the impact of environmental factors on bacterial communities, this thesis assessed the influence of major structuring drivers by using 16S rRNA gene amplicon sequencing, bacterial bulk parameters and interdisciplinary approaches in laboratory experiments and field studies.
In a field study in the Benguela upwelling system, the influence of different levels of primary production and the planktonic succession on bacterial community composition and its development was investigated. Community analysis revealed a clustering of different microbial assemblages along aging upwelled water. This zonation was mainly driven by phytoplankton composition and abundance and the spatial differences were comparable with a temporal succession that occurs during phytoplankton blooms in temperate coastal waters. A dominance of Bacteroidetes and Gammaproteobacteria was observed during algal blooming and high abundance of “Pelagibacterales” was found in regions with low algal abundance. Overall, this study highlightes the strong impact of quality and quantity of phytoplankton and nutrients on the bacterial communities.
A laboratory experiment with Baltic Sea water was performed to better understand the potential impact of rising temperature and CO2 on planktonic bacteria. The development of the bacterial community composition was followed in bifactorial mesocosm experiments during a diatom bloom in autumn and a phytoplankton bloom in summer. The results confirmed that phytoplankton succession and temperature were the major variables structuring the bacterial community. The impact of CO2 on the broad community was weak but high-resolution community analyses revealed a strong effect on specific bacterial groups, which might play important roles in specific organic matter degradation processes.
The response of bacterial communities to a disturbance by a saline intrusion could be investigated during a major Baltic inflow event. Community structuring factors were dominated by mixing of the inflow water with the former bottom water. Although the inflow had a selecting effect on the bacterial community, some immigrated taxa showed increased potential activity and seem to profit from changing environmental conditions. These results suggest a potential impact of inflow events on bacterial functions and therefore on biogeochemical processes.
Altogether, the results confirm the strong structuring effects of environmental conditions on bacterial community composition. Furthermore, high-resolution sequencing enabled an identification of specific affected taxa, which in turn give first clues for the impact of the investigated factors on specific bacterial functions.
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Ciliate and mesozooplankton community response to increasing CO2 levels in the Baltic Sea: insights from a large-scale mesocosm experiment (update)
Published 30 January 2017 Science ClosedTags: abundance, Baltic, biogeochemistry, biological response, BRcommunity, community composition, crustaceans, field, mesocosms, mollusks, otherprocess, zooplankton
Community approaches to investigating ocean acidification (OA) effects suggest a high tolerance of micro- and mesozooplankton to carbonate chemistry changes expected to occur within this century. Plankton communities in the coastal areas of the Baltic Sea frequently experience pH variations partly exceeding projections for the near future both on a diurnal and seasonal basis. We conducted a large-scale mesocosm CO2 enrichment experiment ( ∼ 55 m3) enclosing the natural plankton community in Tvärminne–Storfjärden for 8 weeks during June–August 2012 and studied community and species–taxon response of ciliates and mesozooplankton to CO2 elevations expected for this century. In addition to the response to fCO2, we also considered temperature and chlorophyll a variations in our analyses. Shannon diversity of ciliates significantly decreased with fCO2 and temperature with a greater dominance of smaller species. The mixotrophic Myrionecta rubra seemed to indirectly and directly benefit from higher CO2 concentrations in the post-bloom phase through increased occurrence of picoeukaryotes (most likely Cryptophytes) and Dinophyta at higher CO2 levels. With respect to mesozooplankton, we did not detect significant effects for either total abundance or for Shannon diversity. The cladocera Bosmina sp. occurred at distinctly higher abundance for a short time period during the second half of the experiment in three of the CO2-enriched mesocosms except for the highest CO2 level. The ratio of Bosmina sp. with empty to embryo- or resting-egg-bearing brood chambers, however, was significantly affected by CO2, temperature, and chlorophyll a. An indirect CO2 effect via increased food availability (Cyanobacteria) stimulating Bosmina sp. reproduction cannot be ruled out. Although increased regenerated primary production diminishes trophic transfer in general, the presence of organisms able to graze on bacteria such as cladocerans may positively impact organic matter transfer to higher trophic levels. Thus, under increasing OA in cladoceran-dominated mesozooplankton communities, the importance of the microbial loop in the pelagic zone may be temporarily enhanced and carbon transfer to higher trophic levels may be stimulated.
The adaptive potential of early life-stage Fucus vesiculosus under multifactorial environmental change
Published 26 January 2017 Science ClosedTags: adaptation, algae, Baltic, biological response, BRcommunity, field, growth, laboratory, mesocosms, morphology, mortality, multiple factors, nutrients, otherprocess, oxygen, performance, review, temperature
Multiple global and local stressors threaten populations of the bladderwrack Fucus vesiculosus (Phaeophyceae). Baltic F. vesiculosus populations presumably have a lower genetic diversity compared to other populations. I investigated the adaptive potential under multifactorial environmental change in F. vesiculosus germlings. Effects of warming and acidification were crossed during one year at the two levels “present” and “future” (according to the year 2110) at the “Kiel Outdoor Benthocosms” by applying delta-treatments. Effects of warming varied with season while acidification showed generally weak effects. The two factors “ocean acidification and warming” (OAW) and nutrients were crossed showing that nutrient enrichment mitigated heat stress. Germlings previously treated under the OAW x nutrient experiment were subsequently exposed to a simulated hypoxic upwelling. Sensitivity to hypoxia was enhanced by the previous OAW conditions. Difference in the performance of genetically different sibling groups and diversity level were observed indicating an increased adaptive potential at higher genetic diversity. Different sibling groups were analysed under multiple factors to test correlations of genotypic sensitivities. Sensitivity towards warming, acidification and nutrient enrichment correlated positively while sensitivities towards OAW and hypoxia showed a negative correlation demonstrating that genotypes previously selected under OAW are sensitive to hypoxic upwelling. In a literature review, responses of marine organisms to climate change were analysed through different levels of biological organisation showing that climate change has different effects on each single level of biological organisation. This study highlights that global change research requires an upscaling approach with regard to multiple factors, seasons, natural fluctuations, different developmental stages and levels of biological organisation in the light of the adaptive potential.
Ocean acidification impacts bacteria–phytoplankton coupling at low-nutrient conditions (update)
Published 3 January 2017 Science ClosedTags: abundance, Baltic, biogeochemistry, biological response, BRcommunity, community composition, field, mesocosms, multiple factors, nutrients, otherprocess, physiology, primary production, prokaryotes, respiration
The oceans absorb about a quarter of the annually produced anthropogenic atmospheric carbon dioxide (CO2), resulting in a decrease in surface water pH, a process termed ocean acidification (OA). Surprisingly little is known about how OA affects the physiology of heterotrophic bacteria or the coupling of heterotrophic bacteria to phytoplankton when nutrients are limited. Previous experiments were, for the most part, undertaken during productive phases or following nutrient additions designed to stimulate algal blooms. Therefore, we performed an in situ large-volume mesocosm ( ∼ 55 m3) experiment in the Baltic Sea by simulating different fugacities of CO2 (fCO2) extending from present to future conditions. The study was conducted in July–August after the nominal spring bloom, in order to maintain low-nutrient conditions throughout the experiment. This resulted in phytoplankton communities dominated by small-sized functional groups (picophytoplankton). There was no consistent fCO2-induced effect on bacterial protein production (BPP), cell-specific BPP (csBPP) or biovolumes (BVs) of either free-living (FL) or particle-associated (PA) heterotrophic bacteria, when considered as individual components (univariate analyses). Permutational Multivariate Analysis of Variance (PERMANOVA) revealed a significant effect of the fCO2 treatment on entire assemblages of dissolved and particulate nutrients, metabolic parameters and the bacteria–phytoplankton community. However, distance-based linear modelling only identified fCO2 as a factor explaining the variability observed amongst the microbial community composition, but not for explaining variability within the metabolic parameters. This suggests that fCO2 impacts on microbial metabolic parameters occurred indirectly through varying physicochemical parameters and microbial species composition. Cluster analyses examining the co-occurrence of different functional groups of bacteria and phytoplankton further revealed a separation of the four fCO2-treated mesocosms from both control mesocosms, indicating that complex trophic interactions might be altered in a future acidified ocean. Possible consequences for nutrient cycling and carbon export are still largely unknown, in particular in a nutrient-limited ocean.
Effect of ocean acidification on the structure and fatty acid composition of a natural plankton community in the Baltic Sea (update)
Published 19 December 2016 Media coverage , Science ClosedTags: Baltic, biological response, BRcommunity, community composition, field, mesocosms, otherprocess, physiology, phytoplankton
Increasing atmospheric carbon dioxide (CO2) is changing seawater chemistry towards reduced pH, which affects various properties of marine organisms. Coastal and brackish water communities are expected to be less affected by ocean acidification (OA) as these communities are typically adapted to high fluctuations in CO2 and pH. Here we investigate the response of a coastal brackish water plankton community to increasing CO2 levels as projected for the coming decades and the end of this century in terms of community and biochemical fatty acid (FA) composition. A Baltic Sea plankton community was enclosed in a set of offshore mesocosms and subjected to a CO2 gradient ranging from natural concentrations ( ∼ 347 µatm fCO2) up to values projected for the year 2100 ( ∼ 1333 µatm fCO2). We show that the phytoplankton community composition was resilient to CO2 and did not diverge between the treatments. Seston FA composition was influenced by community composition, which in turn was driven by silicate and phosphate limitation in the mesocosms and showed no difference between the CO2 treatments. These results suggest that CO2 effects are dampened in coastal communities that already experience high natural fluctuations in pCO2. Although this coastal plankton community was tolerant of high pCO2 levels, hypoxia and CO2 uptake by the sea can aggravate acidification and may lead to pH changes outside the currently experienced range for coastal organisms.
Highly sensitive poisoning-resistant optical carbon dioxide sensors for environmental monitoring
Published 16 December 2016 Science ClosedTags: Baltic, chemistry, field, methods
A new optical carbon dioxide sensor for marine applications is presented. It combines a robust and long-term stable sensing material with a compact read-out device. The sensing material relies on a NIR pH indicator immobilized into ethyl cellulose along with a quaternary ammonium base. The perfluorinated polymer Hyflon AD 60 used as a protection layer significantly enhances the long-term and mechanical stability of the sensor foils, as well as the robustness against poisoning gases, e.g. hydrogen sulfide. The sensor can be stored at ambient conditions for more than six weeks whereas sensors covered with silicone rubber deteriorate within one week under the same conditions. The complete sensor device is applicable after a three-point (re)calibration without a preconditioning step. The carbon dioxide production and consumption of the water plant Egeria densa was measured in the laboratory. Furthermore, results of profiling carbon dioxide measurements during a research cruise on the Baltic Sea at water depths up to 225 m are presented.
