Ocean acidification and warming (OAW) are occurring globally. Additionally, at a more local scale the spreading of hypoxic conditions is promoted by eutrophication and warming. In the semi-enclosed brackish Baltic Sea, occasional upwelling in late summer and autumn may expose even shallow-water communities including the macroalga Fucus vesiculosus to particularly acidified, nutrient-rich and oxygen-poor water bodies. During summer 2014 (July–September) sibling groups of early life-stage F. vesiculosus were exposed to OAW in the presence and absence of enhanced nutrient levels and, subsequently to a single upwelling event in a near-natural scenario which included all environmental fluctuations in the Kiel Fjord, southwestern Baltic Sea, Germany (54°27 ´N, 10°11 ´W). We strove to elucidate the single and combined impacts of these potential stressors, and how stress sensitivity varies among genetically different sibling groups. Enhanced by a circumstantial natural heat wave, warming and acidification increased mortalities and reduced growth in F. vesiculosus germlings. This impact, however, was mitigated by enhanced nutrient conditions. Survival under OAW conditions strongly varied among sibling groups hinting at a substantial adaptive potential of the natural Fucus populations in the Western Baltic. A three-day experimental upwelling caused severe mortality of Fucus germlings, which was substantially more severe in those sibling groups which previously had been exposed to OAW. Our results show that global (OAW), regional (nutrient enrichment) and local pressures (upwelling), both alone and co-occurring may have synergistic and antagonistic effects on survival and/or growth of Fucus germlings. This result emphasizes the need to consider combined stress effects.
Posts Tagged 'Baltic'
Buffering and amplifying interactions among OAW (ocean acidification & warming) and nutrient enrichment on early life-stage Fucus vesiculosus L. (Phaeophyceae) and their carry over effects to hypoxia impact
Published 6 April 2016 Science ClosedTags: algae, Baltic, biological response, growth, laboratory, mortality, multiple factors, nutrients, physiology, temperature
Ocean acidification indirectly alters trophic interaction of heterotrophic bacteria at low nutrient conditions
Published 14 March 2016 Science ClosedTags: Baltic, biological response, BRcommunity, community composition, field, mesocosms, multiple factors, nutrients, otherprocess, primary production, prokaryotes, respiration
Annually, the oceans absorb about one fourth of the anthropogenically produced atmospheric carbon dioxide (CO2) resulting in a drop in surface water pH, a process termed ocean acidification (OA). Surprisingly little is known about how OA affects physiology as well as food web interactions of heterotrophic bacteria when essential nutrients are limited, since most previous experiments were carried out during productive phases or even after nutrient additions to stimulate algal blooms. Therefore, we conducted 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 carried out after the spring-bloom in July–August to maintain low-nutrient conditions throughout the experiment, which resulted in a small-sized phytoplankton community dominated by picophytoplankton. Several positive as well as negative effects on free-living (FL) and particle-associated (PA) bacterial protein production (BPP) and biovolume (BV) could be related to fCO2-induced differences in phytoplankton composition and subsequent the availability of phytoplankton-derived organic matter. However, dynamics of BV and cell-specific BPP (csBPP) of FL heterotrophic bacteria could not be explained exclusively by the availability of phytoplankton-derived organic carbon. The dynamics were also related to enhanced grazing on DNA rich (HDNA) bacterial cells at higher fCO2 as revealed by flow cytometry. Additionally, a decoupling of autotrophic production and heterotrophic consumption during the last third of the experiment resulted in low, but significantly higher accumulation of DOC at enhanced fCO2. Interestingly we could not detect any consistent and direct fCO2-induced effect on BPP, csBPP nor BV of either FL or PA heterotrophic bacteria. In contrast, our results reveal several indirect fCO2-induced effects on BPP and bacterial BV with potential consequences for oceanic carbon cycling, in particular in a low nutrient and high fCO2 future ocean.
Effects of ocean acidification on pelagic carbon fluxes in a mesocosm experiment
Published 8 March 2016 Science ClosedTags: abundance, Baltic, biogeochemistry, biological response, BRcommunity, field, mesocosms, morphology, otherprocess, phytoplankton, primary production, prokaryotes, respiration
About a quarter of anthropogenic CO2 emissions are currently taken up by the oceans decreasing seawater pH. We performed a mesocosm experiment in the Baltic Sea in order to investigate the consequences of increasing CO2 levels on pelagic carbon fluxes. A gradient of different CO2 scenarios, ranging from ambient (~ 370 µatm) to high (~ 1200 µatm), were set up in mesocosm bags (~ 55 m3). We determined standing stocks and temporal changes of total particulate carbon (TPC), dissolved organic (DOC), dissolved inorganic (DIC) and particulate organic carbon (POC) of specific plankton groups. We also measured carbon flux via CO2 exchange with the atmosphere and sedimentation (export); and biological rate measurements of primary production, bacterial production and total respiration. The experiment lasted for 44 days and was divided into three different phases (I: t0–t16; II: t17–t30; III: t31–t43). Pools of TPC, DOC and DIC were approximately 420, 7200 and 25 200 mmol C m−2 at the start of the experiment, and the initial CO2 additions increased the DIC pool by ~ 7 % in the highest CO2 treatment. Overall, there was a decrease in TPC and increase of DOC over the course of the experiment. The decrease in TPC was lower, and increase in DOC higher, in treatments with added CO2. During Phase I the estimated gross primary production (GPP) was ~ 100 mmol C fixed m−2 d−1; from which 75–95 % were respired, ~ 1 % ended up in the TPC (including export) and 5–25 % added to the DOC pool. During Phase II, the respiration loss increased to ~ 100 % of GPP at the ambient CO2 concentration, whereas respiration was lower (85–95 % of GPP) in the highest CO2 treatment. Bacterial production was ~ 30 % lower, on average, at the highest CO2 concentration compared with the controls during Phases II and III. This resulted in a higher accumulation DOC standing stock and lower reduction in TPC in the elevated CO2 treatments at the end of Phase II extending throughout Phase III. The “extra” organic carbon at high CO2 remained fixed in an increasing biomass of small-sized plankton and in the DOC pool, and did not transferred into large, sinking aggregates. Our results revealed a clear effect of increasing CO2 on carbon production and mineralization, in particular under nutrient limited conditions. Lower carbon loss processes (respiration and bacterial remineralization) at elevated CO2 levels resulted in higher TPC and DOC pools compared with the ambient CO2 concentration. These results highlight the importance to address not only net changes in carbon standing stocks, but also carbon fluxes and budgets to better disentangle the effects of ocean acidification.
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Negligible effects of ocean acidification on Eurytemora affinis (Copepoda) offspring production
Published 24 February 2016 Science ClosedTags: abundance, Baltic, biogeochemistry, biological response, crustaceans, laboratory, mesocosms, otherprocess, physiology, phytoplankton, protists, reproduction, zooplankton
Ocean acidification is caused by increasing amounts of carbon dioxide dissolving in the oceans leading to lower seawater pH. We studied the effects of lowered pH on the calanoid copepod Eurytemora affinis during a mesocosm experiment conducted in a coastal area of the Baltic Sea. We measured copepod reproductive success as a function of pH, chlorophyll a concentration, diatom and dinoflagellate biomass, carbon to nitrogen (C : N) ratio of suspended particulate organic matter, as well as copepod fatty acid composition. The laboratory-based experiment was repeated four times during 4 consecutive weeks, with water and copepods sampled from pelagic mesocosms enriched with different CO2 concentrations. In addition, oxygen radical absorbance capacity (ORAC) of animals from the mesocosms was measured weekly to test whether the copepod’s defence against oxidative stress was affected by pH. We found no effect of pH on offspring production. Phytoplankton biomass, as indicated by chlorophyll a concentration and dinoflagellate biomass, had a positive effect. The concentration of polyunsaturated fatty acids in the females was reflected in the eggs and had a positive effect on offspring production, whereas monounsaturated fatty acids of the females were reflected in their eggs but had no significant effect. ORAC was not affected by pH. From these experiments we conclude that E. affinis seems robust against direct exposure to ocean acidification on a physiological level, for the variables covered in the study. E. affinis may not have faced acute pH stress in the treatments as the species naturally face large pH fluctuations.
Shifts in the microbial community in the Baltic Sea with increasing CO2
Published 3 February 2016 Science ClosedTags: abundance, Baltic, biogeochemistry, biological response, BRcommunity, field, mesocosms, otherprocess, phytoplankton, prokaryotes, virus, zooplankton
Ocean acidification, due to dissolution of anthropogenically produced carbon dioxide is considered a major threat to marine ecosystems. The Baltic Sea, with extremely low salinity and thus low pH buffering capacity, is likely to experience stronger variation in pH than the open ocean with increasing atmospheric carbon dioxide. We examined the effects of ocean acidification on the microbial community during summer using large volume in situ mesocosms to simulate present to future and far future scenarios. We saw distinct trends with increasing CO2 in each of the 6 groups of phytoplankton with diameters below 20 μm that we enumerated by flow cytometry. Of these groups two picoeukaryotic groups increased in abundance whilst the other groups, including prokaryotic Synechococcus spp., decreased with increasing CO2. Gross growth rates increased with increasing CO2 in the dominant picoeukaryote group sufficient to double their abundances whilst reduced grazing allowed the other picoeukaryotes to flourish at higher CO2. Significant increases in lysis rates were seen at higher CO2 in these two picoeukaryote groups. Converting abundances to particulate organic carbon we saw a large shift in the partitioning of carbon between the size fractions which lasted throughout the experiment. The heterotrophic prokaryotes largely followed the algal biomass with responses to increasing CO2 reflecting the altered phytoplankton community dynamics. Similarly, higher viral abundances at higher CO2 seemed related to increased prokaryote biomass. Viral lysis and grazing were equally important controlling prokaryotic abundances. Overall our results point to a shift towards a more regenerative system with potentially increased productivity but reduced carbon export.
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Effect of ocean acidification and elevated fCO2 on trace gas production by a Baltic Sea summer phytoplankton community
Published 29 January 2016 Science ClosedTags: abundance, Baltic, biogeochemistry, biological response, BRcommunity, community composition, field, mesocosms, otherprocess, phytoplankton, prokaryotes
The Baltic Sea is a unique environment as the largest body of brackish water in the world. Acidification of the surface oceans due to absorption of anthropogenic CO2 emissions is an additional stressor facing the pelagic community of the already challenging Baltic Sea. To investigate its impact on trace gas biogeochemistry, a large-scale mesocosm experiment was performed off Tvärminne Research Station, Finland in summer 2012. During the second half of the experiment, dimethylsulphide (DMS) concentrations in the highest fCO2 mesocosms (1075–1333 μatm) were 34 % lower than at ambient CO2 (350 μatm). However the net production (as measured by concentration change) of seven halocarbons analysed was not significantly affected by even the highest CO2 levels after 5 weeks exposure. Methyl iodide (CH3I) and diiodomethane (CH2I2) showed 15 % and 57 % increases in mean mesocosm concentration (3.8 ± 0.6 pmol L−1 increasing to 4.3 ± 0.4 pmol L−1 and 87.4 ± 14.9 pmol L−1 increasing to 134.4 ± 24.1 pmol L−1 respectively) during Phase II of the experiment, which were unrelated to CO2 and corresponded to 30 % lower Chl-ɑ concentrations compared to Phase I. No other iodocarbons increased or showed a peak, with mean chloroiodomethane (CH2ClI) concentrations measured at 5.3 (± 0.9) pmol L−1 and iodoethane (C2H5I) at 0.5 (± 0.1) pmol L−1. Of the concentrations of bromoform (CHBr3; mean 88.1 ± 13.2 pmol L−1), dibromomethane (CH2Br2; mean 5.3 ± 0.8 pmol L−1) and dibromochloromethane (CHBr2Cl, mean 3.0 ± 0.5 pmol L−1), only CH2Br2 showed a decrease of 17 % between Phases I and II, with CHBr3 and CHBr2Cl showing similar mean concentrations in both Phases. Outside the mesocosms, an upwelling event was responsible for bringing colder, high CO2, low pH water to the surface starting on day t16 of the experiment; this variable CO2 system with frequent upwelling events implies the community of the Baltic Sea is acclimated to regular significant declines in pH caused by up to 800 μatm fCO2. After this upwelling, DMS concentrations declined, but halocarbon concentrations remained similar or increased compared to measurements prior to the change in conditions. Based on our findings, with future acidification of Baltic Sea waters, biogenic halocarbon emissions are likely to remain at similar values to today, however emissions of biogenic sulphur could significantly decrease from this region.
Genotypic variation influences tolerance to warming and acidification of early life-stage Fucus vesiculosus L. (Phaeophyceae) in a seasonally fluctuating environment
Published 22 January 2016 Science ClosedTags: algae, Baltic, biological response, laboratory, morphology, mortality
Global change exposes brown algal Fucus vesiculosus populations to increasing temperature and pCO2, which may threaten individuals, in particular the early life-stages. Genetic diversity of F. vesiculosus populations is low in the Baltic compared to Atlantic populations. This might jeopardise their potential for adaptation to environmental changes. Here, we report on the responses of early life-stage F. vesiculosus to warming and acidification in a near-natural scenario maintaining natural and seasonal variation (spring 2013–2014) of the Kiel Fjord in the Baltic Sea, Germany (54°27ʹN, 10°11ʹW). We assessed how stress sensitivity differed among sibling groups and how genetic diversity of germling populations affected their stress tolerance. Warming increased growth rates of Fucus germlings in spring and in early summer, but led to higher photoinhibition in spring and decreased their survival in late summer. Acidification increased germlings’ growth in summer but otherwise showed much weaker effects than warming. During the colder seasons (autumn and winter), growth was slow while survival was high compared to spring and summer, all at ambient temperatures. A pronounced variation in stress response among genetically different sibling groups (full-sib families) suggests a genotypic basis for this variation and thus a potential for adaptation for F. vesiculosus populations to future conditions. Corroborating this, survival in response to warming in populations with higher diversity was better than the mean survival of single sibling groups. We conclude that impacts on early life-stages depend on the combination of stressors and season and that genetic variation is crucial for the tolerance to global change stress.
Ocean acidification decreases plankton respiration: evidence from a mesocosm experiment
Published 20 January 2016 Science ClosedTags: algae, Baltic, biogeochemistry, biological response, BRcommunity, community composition, crustaceans, field, mesocosms, otherprocess, phytoplankton, primary production, prokaryotes, protists, respiration, zooplankton
Anthropogenic carbon dioxide (CO2) emissions are reducing the pH in the world’s oceans. The plankton community is a key component driving biogeochemical fluxes, and the effect of increased CO2 on plankton is critical for understanding the ramifications of ocean acidification on global carbon fluxes. We determined the plankton community composition and measured primary production, respiration rates and carbon export (defined here as carbon sinking out of a shallow, coastal area) during an ocean acidification experiment. Mesocosms (~ 55 m3) were set up in the Baltic Sea with a gradient of CO2 levels initially ranging from ambient (~ 240 μatm), used as control, to high CO2 (up to ~ 1330 μatm). The phytoplankton community was dominated by dinoflagellates, diatoms, cyanobacteria and chlorophytes, and the zooplankton community by protozoans, heterotrophic dinoflagellates and cladocerans. The plankton community composition was relatively homogenous between treatments. Community respiration rates were lower at high CO2 levels. The carbon-normalized respiration was approximately 40 % lower in the high CO2 environment compared with the controls during the latter phase of the experiment. We did not, however, detect any effect of increased CO2 on primary production. This could be due to measurement uncertainty, as the measured total particular carbon (TPC) and combined results presented in this special issue suggest that the reduced respiration rate translated into higher net carbon fixation. The percent carbon derived from microscopy counts (both phyto- and zooplankton), of the measured total particular carbon (TPC) decreased from ~ 26 % at t0 to ~ 8 % at t31, probably driven by a shift towards smaller plankton (< 4 μm) not enumerated by microscopy. Our results suggest that reduced respiration lead to increased net carbon fixation at high CO2. However, the increased primary production did not translate into increased carbon export, and did consequently not work as a negative feedback mechanism for increasing atmospheric CO2 concentration.
Effect of ocean acidification on the structure and fatty acid composition of a natural plankton community in the Baltic Sea
Published 19 January 2016 Science ClosedTags: abundance, Baltic, biological response, BRcommunity, community composition, crustaceans, field, mesocosms, otherprocess, physiology, phytoplankton, zooplankton
Increasing atmospheric carbon dioxide (CO2) is changing seawater chemistry towards reduced pH, which consequently 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 off-shore mesocosms and subjected to a CO2 gradient ranging from natural concentrations (~347 μatm pCO2) up to values projected for the year 2100 (~1333 μatm pCO2). 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 to 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.
Larval development and settling of Macoma balthica in a large-scale mesocosm experiment at different fCO2 levels
Published 22 December 2015 Science ClosedTags: Baltic, biological response, field, mesocosms, mollusks, morphology, reproduction
Anthropogenic carbon dioxide (CO2) emissions are causing severe changes in the global inorganic carbon balance of the oceans. Associated ocean acidification is expected to impose a major threat to marine ecosystems worldwide, and it is also expected to be amplified in the Baltic Sea where the system is already at present exposed to relatively large natural seasonal and diel pH fluctuations. The response of organisms to future ocean acidification has primarily been studied in single-species experiments, whereas the knowledge of community-wide responses is still limited. To study responses of the Baltic Sea pelagic community to a range of future CO2-scenarios, six ∼ 55 m3 pelagic mesocosms were deployed in the northern Baltic Sea in June 2012. In this specific study we focused on the tolerance, development and subsequent settlement process of the larvae of the benthic key-species Macoma balthica when exposed to different levels of future CO2. We found that the settling of M. balthica was delayed along the increasing CO2 gradient of the mesocosms. Also, when exposed to increasing CO2 levels larvae settled at a larger size, indicating a developmental delay. With on-going climate change, both the frequency and extent of regularly occurring high CO2 conditions is likely to increase, and a permanent pH decrease will likely occur. The strong impact of increasing CO2 levels on early-stage bivalves is alarming as these stages are crucial for sustaining viable populations, and a failure in their recruitment would ultimately lead to negative effects on the population.
Micro- and mesozooplankton community response to increasing CO2 levels in the Baltic Sea: insights from a large-scale mesocosm experiment
Published 16 December 2015 Science ClosedTags: abundance, Baltic, biogeochemistry, biological response, BRcommunity, community composition, crustaceans, field, mesocosms, mollusks, otherprocess, zooplankton
Community approaches 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, thus some level of tolerance/adaptation may be expected. We conducted a large-scale mesocosm CO2 enrichment experiment (~ 55 m3) enclosing the natural plankton community in Tvärminne/Storfjärden for eight weeks during June–August 2012 and studied community and species/taxon response of microzooplankton (ciliates) and mesozooplankton to CO2 elevations expected for this century. Besides the response to fCO2 and associate changes in carbonate chemistry speciation, we also considered temperature and chlorophyll a variations in our analyses. Shannon diversity of microzooplankton significantly decreased with fCO2 and temperature with a greater dominance of smaller species. Small sized ciliates (Myrionecta rubra, Balanion comatum, Strombidium cf. epidemum, Strobilidium sp.) showed significant relations with one or more of the factors. The phototrophic Myrionecta rubra seemed to directly benefit from higher CO2 concentrations and showed increased abundance in the pre-bloom phase. With respect to meszooplankton, we neither detected significant effects for total abundance nor for Shannon diversity. The cladocera Bosmina occurred at distinctly higher abundance (more than twice as high compared to the control mesocosms) 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 with empty to embryo/resting egg bearing brood chambers, however, was significantly affected by all three factors. An indirect CO2 effect via increased food availability stimulating Bosmina reproduction is suggested, but too low sampling frequency of this highly flexible organism probably entailed proving a significant relation with fCO2. Filter-feeding cladocerans effectively transfer microbial loop carbon 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 enhanced and carbon transfer to higher trophic levels stimulated.
Season exerts differential effects of ocean acidification and warming on growth and carbon metabolism of the seaweed Fucus vesiculosus in the western Baltic Sea
Published 15 December 2015 Science ClosedTags: abundance, algae, Baltic, biogeochemistry, biological response, BRcommunity, chemistry, field, growth, light, mesocosms, mollusks, multiple factors, otherprocess, physiology, temperature
Warming and acidification of the oceans as a consequence of increasing CO2-concentrations occur at large scales. Numerous studies have shown the impact of single stressors on individual species. However, studies on the combined effect of multiple stressors on a multi-species assemblage, which is ecologically much more realistic and relevant, are still scarce. Therefore, we orthogonally crossed the two factors warming and acidification in mesocosm experiments and studied their single and combined impact on the brown alga Fucus vesiculosus associated with its natural community (epiphytes and mesograzers) in the Baltic Sea in all seasons (from April 2013 to April 2014). We superimposed our treatment factors onto the natural fluctuations of all environmental variables present in the Benthocosms in so-called delta-treatments. Thereby we compared the physiological responses of F. vesiculosus (growth and metabolites) to the single and combined effects of natural Kiel Fjord temperatures and pCO2 conditions with a 5 °C temperature increase and/or pCO2 increase treatment (1100 ppm in the headspace above the mesocosms). Responses were also related to the factor photoperiod which changes over the course of the year. Our results demonstrate complex seasonal pattern. Elevated pCO2 positively affected growth of F. vesiculosus alone and/or interactively with warming. The response direction (additive, synergistic or antagonistic), however, depended on season and daylength. The effects were most obvious when plants were actively growing during spring and early summer. Our study revealed for the first time that it is crucial to always consider the impact of variable environmental conditions throughout all seasons. In summary, our study indicates that in future F. vesiculosus will be more affected by detrimental summer heat-waves than by ocean acidification although the latter consequently enhances growth throughout the year. The mainly negative influence of rising temperatures on the physiology of this keystone macroalga may alter and/or hamper its ecological functions in the shallow coastal ecosystem of the Baltic Sea.
The effect of CO2-induced seawater acidification on the behaviour and metabolic rate of the Baltic clam Macoma balthica
Published 2 December 2015 Science ClosedTags: Baltic, biological response, laboratory, mollusks, mortality, performance, physiology
The aim of this study was to investigate the effect of CO2-induced seawater acidification (pH 8.1; control pH 7.0 and 6.0) on the survival, behaviour and metabolic rate of the Baltic clam Macoma balthica during short- (36 hours) and long-term (14 days) exposures. Total metabolic rate and gaping behaviour (shell opening and closing) were determined based on heat dissipation measurements using an isothermal twin calorimeter of the Calvet type. The survival and burrowing behaviour during long-term exposure were observed every day. Short-term exposure to reduced pH did not significantly affect the resting or active metabolic rate. Neither were there any significant changes in gaping behaviour. However, long-term exposure significantly affected burrowing behaviour. In the lowest-pH treatment, both resting and active metabolic rates were also significantly higher than in the control.
Ocean acidification challenges copepod reproductive plasticity
Published 19 November 2015 Science ClosedTags: Baltic, biogeochemistry, biological response, crustaceans, laboratory, mesocosms, morphology, physiology, reproduction, zooplankton
Ocean acidification is challenging phenotypic plasticity of individuals and populations. Calanoid copepods (zooplankton) are shown to be fairly plastic against altered pH conditions, and laboratory studies indicate that transgenerational effects are one mechanism behind this plasticity. We studied phenotypic plasticity of the copepod Acartia bifilosa in the course of a pelagic, large-volume mesocosm study that was conducted to investigate ecosystem and biogeochemical responses to ocean acidification. We measured copepod egg production rate, egg hatching success, adult female size and adult female antioxidant capacity (ORAC) as a function of acidification (fCO2 ~ 365–1231 μatm), and as a function of quantity and quality of their diet. We used an egg transplant experiment to reveal if transgenerational effects can alleviate the possible negative effects of ocean acidification on offspring development. We found significant negative effects of ocean acidification on adult female copepod size and egg hatching success. In addition, we found a threshold of fCO2 concentration (~ 1000 μatm), above which adaptive maternal effects cannot alleviate the negative effects of acidification on egg hatching and nauplii development. We did not find support for the hypothesis that insufficient food quantity (total particulate carbon ~ 55 μm) or quality (C : N) weakens the transgenerational effects. However, females with high ORAC produced eggs with high hatching success. Overall, these results indicate that A. bifilosa could be affected by projected near future CO2 levels.
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Effects of high CO2 and warming on a Baltic Sea microzooplankton community
Published 9 November 2015 Science ClosedTags: abundance, Baltic, biological response, BRcommunity, community composition, laboratory, mesocosms, multiple factors, otherprocess, temperature, zooplankton
Global warming and ocean acidification are among the most important stressors for aquatic ecosystems in the future. To investigate their direct and indirect effects on a near-natural plankton community, a multiple-stressor approach is needed. Hence, we set up mesocosms in a full-factorial design to study the effects of both warming and high CO2 on a Baltic Sea autumn plankton community, concentrating on the impacts on microzooplankton (MZP). MZP abundance, biomass, and species composition were analysed over the course of the experiment. We observed that warming led to a reduced time-lag between the phytoplankton bloom and an MZP biomass maximum. MZP showed a significantly higher growth rate and an earlier biomass peak in the warm treatments while the biomass maximum was not affected. Increased pCO2 did not result in any significant effects on MZP biomass, growth rate, or species composition irrespective of the temperature, nor did we observe any significant interactions between CO2 and temperature. We attribute this to the high tolerance of this estuarine plankton community to fluctuations in pCO2, often resulting in CO2 concentrations higher than the predicted end-of-century concentration for open oceans. In contrast, warming can be expected to directly affect MZP and strengthen its coupling with phytoplankton by enhancing its grazing pressure.
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No observed effect of ocean acidification on nitrogen biogeochemistry in a summer Baltic Sea plankton community
Published 30 October 2015 Science ClosedTags: abundance, Baltic, biogeochemistry, biological response, BRcommunity, field, mesocosms, nitrogen fixation, otherprocess, prokaryotes
Nitrogen fixation by filamentous cyanobacteria supplies significant amounts of new nitrogen (N) to the Baltic Sea. This balances N loss processes such as denitrification and anammox and forms an important N source supporting primary and secondary production in N-limited post-spring bloom plankton communities. Laboratory studies suggest that filamentous diazotrophic cyanobacteria growth and N2-fixation rates are sensitive to ocean acidification with potential implications for new N supply to the Baltic Sea. In this study, our aim was to assess the effect of ocean acidification on diazotroph growth and activity as well as the contribution of diazotrophically-fixed N to N supply in a natural plankton assemblage. We enclosed a natural plankton community in a summer season in the Baltic Sea near the entrance to the Gulf of Finland in six large-scale mesocosms (volume ~ 55 m3) and manipulated fCO2 over a range relevant for projected ocean acidification by the end of this century (average treatment fCO2: 365–1231 μatm). The direct response of diazotroph growth and activity was followed in the mesocosms over a 47 day study period during N-limited growth in the summer plankton community. Diazotrophic filamentous cyanobacteria abundance throughout the study period and N2-fixation rates (determined only until day 21 due to subsequent use of contaminated commercial 15N-N2 gas stocks) remained low. Thus estimated new N inputs from diazotrophy were too low to relieve N limitation and stimulate a summer phytoplankton bloom. Instead regeneration of organic N sources likely sustained growth in the plankton community. We could not detect significant CO2-related differences in inorganic or organic N pools sizes, or particulate matter N : P stoichiometry. Additionally, no significant effect of elevated CO2 on diazotroph activity was observed. Therefore, ocean acidification had no observable impact on N cycling or biogeochemistry in this N-limited, post-spring bloom plankton assemblage in the Baltic Sea.
Effect of elevated CO2 on organic matter pools and fluxes in a summer Baltic Sea plankton community (update)
Published 29 October 2015 Science ClosedTags: abundance, Baltic, biogeochemistry, biological response, BRcommunity, community composition, field, mesocosms, otherprocess, phytoplankton
Ocean acidification is expected to influence plankton community structure and biogeochemical element cycles. To date, the response of plankton communities to elevated CO2 has been studied primarily during nutrient-stimulated blooms. In this CO2 manipulation study, we used large-volume (~ 55 m3) pelagic in situ mesocosms to enclose a natural summer, post-spring-bloom plankton assemblage in the Baltic Sea to investigate the response of organic matter pools to ocean acidification. The carbonate system in the six mesocosms was manipulated to yield average fCO2 ranging between 365 and ~ 1230 μatm with no adjustment of naturally available nutrient concentrations. Plankton community development and key biogeochemical element pools were subsequently followed in this nitrogen-limited ecosystem over a period of 7 weeks. We observed higher sustained chlorophyll a and particulate matter concentrations (~ 25 % higher) and lower inorganic phosphate concentrations in the water column in the highest fCO2 treatment (1231 μatm) during the final 2 weeks of the study period (Phase III), when there was low net change in particulate and dissolved matter pools. Size-fractionated phytoplankton pigment analyses indicated that these differences were driven by picophytoplankton (< 2 μm) and were already established early in the experiment during an initial warm and more productive period with overall elevated chlorophyll a and particulate matter concentrations. However, the influence of picophytoplankton on bulk organic matter pools was masked by high biomass of larger plankton until Phase III, when the contribution of the small size fraction (< 2 μm) increased to up to 90 % of chlorophyll a. In this phase, a CO2-driven increase in water column particulate carbon did not lead to enhanced sinking material flux but was instead reflected in increased dissolved organic carbon concentrations. Hence ocean acidification may induce changes in organic matter partitioning in the upper water column during the low-nitrogen summer period in the Baltic Sea.
Negligible effects of ocean acidification on Eurytemora affinis (Copepoda) offspring production
Published 26 October 2015 Science ClosedTags: abundance, Baltic, biogeochemistry, biological response, crustaceans, laboratory, mesocosms, otherprocess, physiology, phytoplankton, protists, reproduction, zooplankton
Ocean acidification is caused by increasing amounts of carbon dioxide dissolving in the oceans leading to lower seawater pH. We studied the effects of lowered pH on the calanoid copepod Eurytemora affinis during a mesocosm experiment conducted in a coastal area of the Baltic Sea. We measured copepod reproductive success as a function of pH, chlorophyll a concentration, diatom and dinoflagellate biomass, carbon to nitrogen (C : N) ratio of suspended particulate organic matter, as well as copepod fatty acid composition. The laboratory-based experiment was repeated four times during four consecutive weeks, with water and copepods sampled from pelagic mesocosms enriched with different CO2 concentrations. In addition, oxygen radical absorbance capacity (ORAC) of animals from the mesocosms was measured weekly to test whether the copepod’s defence against oxidative stress was affected by pH. We found no effect of pH on offspring production. Phytoplankton biomass, as indicated by chlorophyll a concentration, had a strong positive effect. The concentration of polyunsaturated fatty acids in the females were reflected in the eggs and had a positive effect on offspring production, whereas monounsaturated fatty acids of the females were reflected in their eggs but had no significant effect. ORAC was not affected by pH. From these experiments we conclude that E. affinis seems robust against direct exposure to ocean acidification on a physiological level, for the variables covered in the study. E. affinis may not have faced acute pH stress in the treatments as the species naturally face large pH fluctuations.
Modelling the contributions to marine acidification from deposited SOx, NOx, and NHx in the Baltic SEA: Past and present situations
Published 17 September 2015 Science ClosedTags: Baltic, biogeochemistry, chemistry, field, modeling, regionalmodeling
We have examined the effects of historical atmospheric depositions of sulphate, nitrate, and ammonium from land and shipping on the acid–base balance in the Baltic Sea. The modelling considers the 1750–2014 period, when land and ship emissions changed greatly, with increasing carbon dioxide concentrations, SOx, NOx, and NHx emissions, and nutrient loads.
The present results indicate that Baltic Sea acidification due to the atmospheric deposition of acids peaked around 1980, with a pH cumulative decrease of approximately 10−2 in surface waters. This is one order of magnitude less than the cumulative acidification due to increased atmospheric CO2. The acidification contribution of shipping is one order of magnitude less than that of land emissions. However, the pH trend due to atmospheric acids has started to reverse due to reduced land emissions, though the effect of shipping is ongoing.
The effect of strong atmospheric acids on Baltic Sea water depends on the region and period studied. The largest total alkalinity sink per surface area is in the south-western Baltic Sea where shipping is intense. Considering the entire Baltic Sea over the 2001–2010 period, the pH changes are approximately −3×10−3 to −11×10−3 and −4×10−4 to −16×10−4 pH units attributable to all emissions and ship emissions only, respectively. The corresponding changes in total alkalinity are approximately −10 to −30 µmol kg−1 and −1 to −4 µmol kg−1 attributable to all emissions and ship emissions only, respectively.
The effects of elevated CO2 and ocean acidification on the production of marine biogenic trace gases
Published 18 August 2015 Science ClosedTags: Baltic, biogeochemistry, biological response, BRcommunity, field, laboratory, mesocosms, North Atlantic, prokaryotes
The human-induced increases in atmospheric carbon dioxide since the beginning of the industrial revolution have led to increasing oceanic carbon uptake and changes in seawater carbonate chemistry, resulting in lowering of surface water pH. To date, surface ocean acidity has increased by 30% compared with pre-industrial times. The aim of this study was to investigate the relationship between increasing pCO2, decreasing pH and changes in volatile dimethylsulphide (DMS) and halocarbon concentrations, through 70,000 litre, high pCO2 mesocosm experiments and laboratory culture studies. DMS is a climatically important trace gas produced by marine algae: it transfers sulphur into the atmosphere and is a major influence on biogeochemical climate feedbacks. Halocarbons are also important biogenic trace gases which undergo atmospheric photochemical degradation, releasing halide radicals to participate in atmospheric ozone cycling, and transfer halogens from sea to land. Evidence is presented from a Norwegian coastal study which showed a 60% DMS, 30% DMSP and 40% iodocarbon reduction in high pCO2 mesocosms, and in the Baltic Sea, known for its low-salinity, cyanobacterial dominated community, where DMS concentrations showed an 80% reduction under high pCO2 but halocarbon concentrations were unaffected. No decrease in DMS or DMSP concentrations were identified in high pCO2 laboratory cultures of the DMSproducing species Emiliania huxleyi RCC1229, and halocarbons were undetectable. Changes in trace gas concentrations may arise due to pH effects on the interactions between microbial producers and consumers. Other effects may arise from cell biochemistry due to long-term adaptation to increased ρCO2 and reduced pH on the enzymatic activity production of the compounds. Further studies should determine the nature of the pCO2 and pH effect on bacterial interactions with DMS, DMSP and halocarbon production and breakdown. There should also be attention given to the DMS source in the cyanobacterial-dominated community of the Baltic Sea.
