Posts Tagged 'Baltic'

Warming, but not acidification, restructures epibacterial communities of the Baltic macroalga Fucus vesiculosus with seasonal variability

Due to ocean acidification and global warming, surface seawater of the western Baltic Sea is expected to reach an average of ∼1100 μatm pCO2 and an increase of ∼5°C by the year 2100. In four consecutive experiments (spanning 10–11 weeks each) in all seasons within 1 year, the abiotic factors temperature (+5°C above in situ) and pCO2 (adjusted to ∼1100 μatm) were tested for their single and combined effects on epibacterial communities of the brown macroalga Fucus vesiculosus and on bacteria present in the surrounding seawater. The experiments were set up in three biological replicates using the Kiel Outdoor Benthocosm facility (Kiel, Germany). Phylogenetic analyses of the respective microbiota were performed by bacterial 16S (V1-V2) rDNA Illumina MiSeq amplicon sequencing after 0, 4, 8, and 10/11 weeks per season. The results demonstrate (I) that the bacterial community composition varied in time and (II) that relationships between operational taxonomic units (OTUs) within an OTU association network were mainly governed by the habitat. (III) Neither single pCO2 nor pCO2:Temperature interaction effects were statistically significant. However, significant impact of ocean warming was detected varying among seasons. (IV) An indicator OTU (iOTU) analysis identified several iOTUs that were strongly influenced by temperature in spring, summer, and winter. In the warming treatments of these three seasons, we observed decreasing numbers of bacteria that are commonly associated with a healthy marine microbial community and—particularly during spring and summer—an increase in potentially pathogenic and bacteria related to intensified microfouling. This might lead to severe consequences for the F. vesiculosus holobiont finally affecting the marine ecosystem.

Continue reading ‘Warming, but not acidification, restructures epibacterial communities of the Baltic macroalga Fucus vesiculosus with seasonal variability’

The characteristics of the CO2 system of the Oder River estuary (Baltic Sea)


• The CO2 system in the Oder River Estuary was investigated for the first time.

• OM production and remineralization affect the CO2 system in the Oder River Estuary.

• Extreme primary production may initiate mineral precipitation of calcite in high AT.

• Estuarine processes may modify the riverine loads of AT and CT to the Baltic Sea.


This study examined the CO2 system in the estuary of the Oder River, one of the largest rivers entering the Baltic Sea. Three measurable parameters describing the CO2 system, namely total alkalinity (AT), total CO2 (CT), and the partial pressure of CO2 (pCO2), were investigated together with dissolved oxygen, salinity (S), and temperature during two RV Oceania cruises, in May and November of 2016. Large spatial variabilities of AT (1771–2940 μmol kg−1) and CT (1676–2972 μmol kg−1) were determined along the S gradient between the open Baltic Sea and river mouth. In November, the relationships of AT–S and CT-S indicated conservative mixing whereas in May both were strongly affected by biomass production and calcium carbonate formation. The waters of the Oder were oversaturated with CO2 compared to the atmosphere, irrespective of the season, with pCO2 values of 1351 ± 42 μatm in May and 1120 ± 32 μatm in November. In the Szczecin Lagoon, however, pCO2 levels dropped significantly, to 63 μatm, in May, accompanied by an O2 saturation of up to 134% during the same period. The inverse correlation of pCO2 and O2 saturation indicated that the distribution of CO2 and O2 in the estuary at the time of sampling was controlled mostly by biological activity. The very large drop in the pCO2 of the Szczecin Lagoon induced an extreme oversaturation of CaCO3 that triggered mineral calcite precipitation. The mineral precipitation of carbonates in the lagoon may have accounted for as much as 40% of the CT depletion determined in May, with the remaining 60% attributed to the joint effect of net ecosystem production and CO2 air/water gas exchange.

Continue reading ‘The characteristics of the CO2 system of the Oder River estuary (Baltic Sea)’

Multimarker response of the ragworm Hediste diversicolor (Polychaeta) to seawater acidification derived from potential CO2 leakage from the CCS sub-seabed storage site in the Baltic Sea


• Seawater acidification affected physiological traits, LPO and growth of Hediste diversicolor from the southern Baltic Sea.

• Moderate hypercapnia (pH 7.5–7.1) induced an increase in metabolic rate of the polychaetes and a decline of their growth.

• The most acidic environment (pH 6.5) caused metabolic slow down limiting energy turnover and growth.

• Reduced seawater pH did not impact energetic reserves so, proteins were not used as substrates under acidic conditions.

• High tolerance of the ragworms to hypercapnia stems probably from pre-adaptation to natural pH reduction events in sediment.


Sub-seabed Carbon Capture and Storage (CCS) is conceived as safe technology with small likehood of negative consequences to the marine ecosystem but CO2 escape from geological reservoir still poses potential environmental risk. If carbon dioxide leakage occurs carbonate chemistry in the bottom zone and sessile benthic fauna are expected to be the most likely affected by elevated levels of CO2. Though generic mechanisms and advisory conclusions on the presumable impact of increased acidity on the marine benthic biota were formulated they cannot be applied uniformly across different environmental variables as specific local conditions may alter biological response to hypercapnia. A laboratory experiment was conducted to quantify the effects of medium-term (8 wk) exposure to seawater acidification (pH 7.7–6.5) on the infaunal polychaete Hediste diversicolor from the southern Baltic Sea using multimarker approach. Under moderate acidity (pH 7.5 and 7.1) the polychaetes were found to increase metabolic rate (by 13.4% and 19.6%, respectively) and reduce their body mass (by 8.1% and 5.5% wet weight, respectively and by 6.1% and 3.0% dry weight, respectively) whilst enhancing synthesis of antioxidant malondialdehyde (by 22.8% and 65.3%, respectively). In the most acidic environment (pH 6.5) the ragworms showed overall metabolic slow down (by 34.8%) and impaired growth (e.g. by 10.2% for length of the first three segments) indicative of low vulnerability to hypercapnia. High implicit tolerance of the polychaetes to increased acidity in the environment stems inevitably from a certain level of pre-adaptation to pH reduction events which occur in organic-rich stratified sediments due to intense aerobic biomineralization leading often to oxygen depletion and formation of toxic hydrogen sulphide. Acidification did not affect energetic reserves suggesting that costs of acid-base maintenance were covered mainly from assimilated food and that proteins were not used as metabolic substrates.

Continue reading ‘Multimarker response of the ragworm Hediste diversicolor (Polychaeta) to seawater acidification derived from potential CO2 leakage from the CCS sub-seabed storage site in the Baltic Sea’

Future acidification of the Baltic Sea – A sensitivity study


• Sensitivity of pH and the carbonate system to potential future changes in the Baltic Sea

• pH response to future atmospheric CO2, climate change, and changes in the catchment

• CO2-induced acidification can be enhanced or mitigated by other processes in coastal seas.

• Unlikely that acidification of the Baltic Sea can be counteracted unless CO2 emissions decline


Future acidification of coastal seas will depend not only on the development of atmospheric CO2 partial pressure (pCO2), but also on changes in the catchment areas, exchange with the adjacent ocean, and internal cycling of carbon and nutrients. Here we use a coupled physical-biogeochemical Baltic Sea model to quantify the sensitivity of pH to changes both in external forcing and internal processes. The experiments include changes in runoff, supply of dissolved inorganic carbon (DIC) and total alkalinity (AT), nutrient loads, exchange between the Baltic and North Seas, and atmospheric pCO2. We furthermore address the potential different future developments of runoff and river loads in boreal and continental catchments, respectively. Changes in atmospheric pCO2 exert the strongest control on future pH according to our calculations. This CO2-induced acidification could be further enhanced in the case of desalination of the Baltic Sea, although increased concentrations of AT in the river runoff due to increased weathering to some extent could counteract acidification. Reduced nutrient loads and productivity would reduce the average annual surface water pH but at the same time slightly increase wintertime surface water pH (the annual pH minimum). The response time of surface water pH to sudden changes in atmospheric pCO2 is approximately one month, whereas response times to changes in e.g. runoff and AT/DIC loads are more related to residence times of water and salt (>30 years). It seems unlikely that the projected future increase in atmospheric pCO2 and associated pH reduction could be fully counteracted by any of the other processes addressed in our experiments.

Continue reading ‘Future acidification of the Baltic Sea – A sensitivity study’

Spatial risk assessment of global change impacts on Swedish seagrass ecosystems

Improved knowledge on the risk in ecologically important habitats on a regional scale from multiple stressors is critical for managing functioning and resilient ecosystems. This risk assessment aimed to identify seagrass ecosystems in southern Sweden that will be exposed to a high degree of change from multiple global change stressors in mid- and end-of-century climate change conditions. Risk scores were calculated from the expected overlap of three stressors: sea surface temperature increases, ocean acidification and wind driven turbid conditions. Three high-risk regions were identified as areas likely to be exposed to a particularly high level of pressure from the global stressors by the end of the century. In these areas it can be expected that there will be a large degree of stressor change from the current conditions. Given the ecological importance of seagrass meadows for maintaining high biodiversity and a range of other ecosystem services, these risk zones should be given high priority for incorporation into management strategies, which can attempt to reduce controllable stressors in order to mitigate the consequences of some of the impending pressures and manage for maintained ecosystem resilience.

Continue reading ‘Spatial risk assessment of global change impacts on Swedish seagrass ecosystems’

Technical note: Seamless gas measurements across Land-Ocean Aquatic Continuum – corrections and evaluation of sensor data for CO2, CH4 and O2 from field deployments in contrasting environments

Comparatively the ocean and inland waters are two separate worlds, with concentrations in greenhouse gases having orders of magnitude in difference between the two. Together they create the Land-Ocean Aquatic Continuum (LOAC), which comprises itself largely of areas with little to no data in regards to understanding the global carbon system. Reasons for this include remote and inaccessible sample locations, often tedious methods that require collection of water samples and subsequent analysis in the lab, as well as the complex interplay of biological, physical and chemical processes. This has led to large inconsistencies, increasing errors and inevitably leading to potentially false upscaling. Here we demonstrate successful deployment in oceanic to remote inland regions, over extreme concentration ranges with multiple pre-existing oceanographic sensors combined set-up, allowing for highly detailed and accurate measurements. The set-up consists of sensors measuring pCO2pCH4 (both flow-through, membrane-based NDIR or TDLAS sensors), O2, and a thermosalinograph at high-resolution from the same water source simultaneously. The flexibility of the system allowed deployment from freshwater to open ocean conditions on varying vessel sizes, where we managed to capture day-night cycles, repeat transects and also delineate small scale variability. Our work demonstrates the need for increased spatiotemporal monitoring, and shows a way to homogenize methods and data streams in the ocean and limnic realms.

Continue reading ‘Technical note: Seamless gas measurements across Land-Ocean Aquatic Continuum – corrections and evaluation of sensor data for CO2, CH4 and O2 from field deployments in contrasting environments’

Contemporary trends in hydrophysical and hydrochemical parameters in the NE Baltic Sea

The current study focuses on trends in hydrophysical and ­chemical parameters (e.g. temperature, salinity, dissolved oxygen, chlorophyll a (Chl a), pH and nutrients) in the Estonian coastal sea and offshore areas in relation to the biogeochemical processes and marine carbon dioxide system of the Baltic Sea. Analysis of 586 time series of these parameters, retrieved during national monitoring activities in 1993–2017, revealed a number of significant trends, which characterize the changes in the northeastern (NE) Baltic Sea. The number of significant trends in the surface layer was slightly higher in the coastal sea area than in the offshore area. No significant (e.g. climate change­related) temperature trends were revealed in the surface layers of the Estonian offshore area. Over a longer time frame (since the 1970s–1980s), the trends in hydrochemical parameters have shown improved ecological conditions in the Estonian coastal waters, however, further improvement is not so obvious. In fact, most nutrient trends were positive over the last two decades. A positive Chl a trend was detected in the offshore area of the Baltic Proper. Dissolved oxygen trends in the bottom layers were all negative. So far, not enough parameters have been monitored for the evaluation of marine acidification processes. Several important recommendations for further improvement of monitoring programmes are suggested.

Continue reading ‘Contemporary trends in hydrophysical and hydrochemical parameters in the NE Baltic Sea’

High CO2 and warming affect microzooplankton food web dynamics in a Baltic Sea summer plankton community

Aquatic ecosystems face a multitude of environmental stressors, including warming and acidification. While warming is expected to have a pronounced effect on plankton communities, many components of the plankton seem fairly robust towards realistic end-of-century acidification conditions. However, interactions of the two stressors and the inclusion of further factors such as nutrient concentration and trophic interactions are expected to change this outcome. We investigated the effects of warming and high CO2 on a nutrient-deplete late summer plankton community from the Kiel Fjord, Baltic Sea, using a mesocosm setup crossing two temperatures with a gradient of CO2. Phytoplankton and microzooplankton (MZP) growth rates as well as biomass, taxonomic composition, and grazing rates of MZP were analysed. We observed effects of high CO2, warming, and their interactions on all measured parameters. The occurrence and direction of the effects were dependent on the phytoplankton or MZP community composition. In addition, the abundance of small-sized phytoplankton was identified as one of the most important factors in shaping the MZP community composition. Overall, our results indicate that an estuarine MZP community used to strong natural fluctuations in CO2 can still be affected by a moderate increase in CO2 if it occurs in combination with warming and during a nutrient-deplete post-bloom situation. This highlights the importance of including trophic interactions and seasonality aspects when assessing climate change effects on marine zooplankton communities.

Continue reading ‘High CO2 and warming affect microzooplankton food web dynamics in a Baltic Sea summer plankton community’

Skeletal integrity of a marine keystone predator (Asterias rubens) threatened by ocean acidification


• Common sea star from Kiel Fjord was acclimated to two future levels of ocean acidification.

• Corrosion on spines and plates was recorded at pHT-SW 7.4 and below.

• Low seawater pH affected skeletal integrity of ambulacral plates.

• With OA, altered skeleton might impair locomotion and feeding behaviour of A. rubens.

• Limited scope for future adaptation or acclimation of Kiel Fjord A. rubens population.


The current increase in atmospheric CO2 concentration induces changes in the seawater carbonate system resulting in decreased pH and calcium carbonate saturation state, a phenomenon called ocean acidification (OA). OA has long been considered as a major threat to echinoderms because their extensive endoskeleton is made of high‑magnesium calcite, one of the most soluble forms of calcium carbonate. Numerous studies addressed this question in sea urchins, but very few questioned the impact of OA on the sea star skeleton, although members of this taxon do not compensate their extracellular pH, contrary to most sea urchins. In the present study, adults of the common sea star, Asterias rubens from Kiel Fjord, a site experiencing natural acidification events exceeding pCO2 levels of 2500 μatm, were chronically exposed to different levels of simulated ocean acidification (pHT-SW 8.0, 7.4, 7.2), encompassing present and future conditions, for the duration of 109 days. Corrosion and mechanical properties of skeletal elements were studied using scanning electron microscopy, three-point bending tests as well as nanoindentation. The spines were significantly corroded at pHT-SW 7.4 and below while the ambulacral plates were only affected at pHT-SW 7.2. Nanoindentation of newly formed spines and ambulacral plates did not reveal significant CO2-induced differences in skeleton hardness or elasticity across treatments. Results of three-point bending tests revealed significantly reduced characteristic strength and fracture force of ambulacral plates from the median arm segment at pHT-SW 7.4 and below. These plates are those supporting the tube feet involved in the opening of bivalves during feeding and in the animal attachment to the substrate. Under reduced seawater pH, this might result in fracture of sea star plates during predation on mussel. The present results predict a possible impact of ocean acidification on the skeletal integrity of a marine keystone predator.

Continue reading ‘Skeletal integrity of a marine keystone predator (Asterias rubens) threatened by ocean acidification’

Intra-specific variation of ocean acidification effects in marine mussels and oysters: integrative physiological studies on tissue and organism responses

Uptake of increasing anthropogenic CO2 emissions by ocean surface waters is causing an increase of seawater PCO2 accompanied by a decrease of seawater pH and carbonate ion concentrations. This process, termed ocean acidification (OA), is predicted to negatively affect many marine organisms with likely consequences for marine ecosystems and the services they provide. Calcifying mussels and oysters, and particularly their early life stages, are predicted to be among the most OA sensitive taxa, as OA interferes with the calcification process. In addition, mussels and oysters possess a relatively low ability to compensate for CO2 induced disturbances in extracellular body fluid pH with potential physiological downstream effects such as elevated metabolic maintenance costs. As mussels and oysters are key habitat forming organisms in many highly productive temperate coastal communities, negative OA effects may translate into deleterious effects at an ecosystem scale. In particular, the relative long generation time of most marine bivalves raises the concern that the rapid rate at which OA occurs may outpace species’ ability to genetically adapt, leaving pre-existing genetic variation as a potential key to species resilience under OA. Against this backdrop, this thesis contributes to the understanding of physiological mechanisms that underpin and define the OA vulnerability of ecologically and economically important mussels and oysters. Thereby, emphasis was placed on investigating intra-specific variance as a proxy for potential adaptive capacities. Kiel Fjord is located in the Western Baltic Sea and is characterised by strong seasonal and diurnal fluctuations in seawater PCO2. These fluctuations are caused by upwelling events of acidified bottom waters with peak PCO2 values (>2300 μatm) that are already by far exceeding those projected for open ocean surface waters by the end of this century. Despite these unfavourable conditions, blue mussels (Mytilus edulis) dominate the benthic community, which makes this population particularly interesting in the context of metabolic adaptation to OA. Consequently, a long-term multi-generation CO2 acclimation experiment with different family lines of M. edulis from Kiel Fjord formed the first part of this thesis. Offspring of 16 different family lines were transferred to three different PCO2 conditions, representing present and predicted PCO2 levels in Kiel Fjord (700 μatm (control), 1120 μatm (intermediate) and 2400 μatm (high)). Larval survival rates were substantially different between family lines at the highest PCO2 level. Based on these differences, families were classified as either ‘tolerant’ (i.e. successful settlement at all PCO2 levels) or ‘sensitive’ (i.e. successful settlement only at control and intermediate PCO2 level). Subsequently, the offspring were raised for over one year at respective PCO2 levels, followed by measurements of physiological parameters at the whole-animal, tissue (gill and outer mantle) and biochemical level (key metabolic enzymes). The results revealed that routine metabolic rates (RMR) and summed tissue respiration were increased in tolerant families at intermediate PCO2, indicating elevated homeostatic costs. However, this higher energy demand at the intermediate PCO2 level was not accompanied by a simultaneous increase in energy assimilation (i.e. clearance rates (CR)), indicating an incipient imbalance in energy demand and supply. Consequently, RMRs at the highest PCO2 were not different to control RMRs but associated with reduced CRs, which correlated with a lower gill metabolic scope, reduced gill mitochondrial capacities (lower capacities for citrate synthase (CS) and cytochrome c oxidase (COX)) as well as an increased capacity for anaerobic energy production (lower ratio of pyruvate kinase to phospoenolpyruvate carboxykinase). In conjunction with a lower COX to CS ratio observed in outer mantle tissue, this suggested a CO2-induced shift of metabolic pathways in tolerant families at the highest PCO2 level. By contrast, sensitive families had an unchanged RMR, tissue respiration and CR at the intermediate CO2. However, a higher control RMR in sensitive than tolerant families at similar CR suggested a lower, CO2 independent metabolic efficiency in sensitive families. This was also reflected in their lower gill mitochondrial scope at control conditions compared to tolerant families. These findings suggested that sensitive families lack the metabolic scope to cover OA induced higher maintenance costs and have to rely on energy reallocation and thus, energy trade-offs which may also have prevented survival at the highest experimental PCO2 level. Accordingly, investigations of 3-hydroxyacyl-CoA dehydrogenase (HADH) capacities, which catalyses a key step in lipid oxidation, suggested an increased reliance on lipids as metabolic fuel in sensitive families at elevated PCO2. If this was also prevalent during the larval phase, a quicker depletion of lipid reserves before completion of metamorphosis may have contributed to the higher larval mortality at the highest PCO2 treatment in sensitive compared to tolerant mussels. The second part of the thesis aimed to clarify whether a higher OA tolerance in Sydney rock oysters (Saccostrea glomerata) is directly correlated with an increased capacity to compensate for CO2 induced extracellular acid-base disturbances, and whether such a capacity is driven by higher metabolic and ion-regulatory costs at the tissue level. Earlier studies focusing on two different populations of Sydney rock oysters demonstrated that oysters that were selectively bred for increased growth and disease resistance (‘selected oysters’) have a higher CO2 resilience compared to the wild population (‘wild oysters’). To unravel the underlying physiological mechanisms, oysters of both populations were acclimated at control and elevated PCO2 (1100 μatm) levels for seven weeks, followed by determinations of extracellular acidbase parameters (pHe, PeCO2, [HCO3 -]e), tissue respiration and indirect determination of energy demands of major ion regulatory transport proteins. Indeed, at elevated PCO2, wild oysters had a lower pHe and an increased PeCO2 whereas extracellular acid-base status of selected oysters remained unaffected. However, differing pHe values between oyster types were not driven by elevated metabolic costs of major ion regulators at tissue level. Selected oysters rather exhibited an increased systemic capacity to eliminate metabolic CO2, which likely came through higher and energetically more efficient filtration rates and associated facilitation of gas exchange, suggesting that effective filtration and CO2 resilience might be positively correlated traits in oysters. In conclusion, the findings of this thesis contribute to the growing evidence that ongoing OA will likely impair the physiology of marine mussels and oysters with potentially associated downstream consequences for the respective ecosystems. However, the results also suggest adaptive capacities in both species studied. The higher CO2 resilience of selected Sydney rock oysters was expressed within the – in evolutionary terms – rapid time span of only a few generations of selective breeding, which indicates that rapid adaptation to OA may be possible in marine bivalves. The observed intra-specific variation of OA responses in blue mussels suggests standing genetic variation within this population, which is likely to be key for the persistence of populations under rapidly occurring OA. However, as global change is not limited to OA, future research will have to reassess potential resilience traits and adaptive capacities to OA when combined with changes in other environmental drivers.

Continue reading ‘Intra-specific variation of ocean acidification effects in marine mussels and oysters: integrative physiological studies on tissue and organism responses’

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Ocean acidification in the IPCC AR5 WG II

OUP book