Ocean Acidification Affects Redox-Balance and Ion-Homeostasis in the Life-Cycle Stages of Emiliania huxleyi

Ocean Acidification (OA) has been shown to affect photosynthesis and calcification in the coccolithophore Emiliania huxleyi, a cosmopolitan calcifier that significantly contributes to the regulation of the biological carbon pumps. Its non-calcifying, haploid life-cycle stage was found to be relatively unaffected by OA with respect to biomass production. Deeper insights into physiological key processes and their dependence on environmental factors are lacking, but are required to understand and possibly estimate the dynamics of carbon cycling in present and future oceans. Therefore, calcifying diploid and non-calcifying haploid cells were acclimated to present and future CO2 partial pressures (pCO2; 38.5 Pa vs. 101.3 Pa CO2) under low and high light (50 vs. 300 µmol photons/m**2 /s). Comparative microarray-based transcriptome profiling was used to screen for the underlying cellular processes and allowed to follow up interpretations derived from physiological data. In the diplont, the observed increases in biomass production under OA are likely caused by stimulated production of glycoconjugates and lipids. The observed lowered calcification under OA can be attributed to impaired signal-transduction and ion-transport. The haplont utilizes distinct genes and metabolic pathways, reflecting the stage-specific usage of certain portions of the genome. With respect to functionality and energy-dependence, however, the transcriptomic OA-responses resemble those of the diplont. In both life-cycle stages, OA affects the cellular redox-state as a master regulator and thereby causes a metabolic shift from oxidative towards reductive pathways, which involves a reconstellation of carbon flux networks within and across compartments. Whereas signal transduction and ion-homeostasis appear equally OA-sensitive under both light intensities, the effects on carbon metabolism and light physiology are clearly modulated by light availability. These interactive effects can be attributed to the influence of OA and light on the redox equilibria of NAD and NADP, which function as major sensors for energization and stress. This generic mode of action of OA may therefore provoke similar cell-physiological responses in other protists.

Seawater carbonate chemistry and effects of CO2 and their modulation by light in the life-cycle stages of the coccolithophore Emiliania huxleyi strains RCC 1216 and 1217 during experiments, 2012

The effects of ocean acidification on the life-cycle stages of the coccolithophore Emiliania huxleyi and their by light were examined. Calcifying diploid and noncalcifying haploid cells (Roscoff culture collection 1216 and 1217) were acclimated to present-day and elevated CO2 partial pressures (PCO2; 38.5 vs. 101.3 Pa, ., 380 vs. 1000 matm) under low and high light (50 vs. 300 mmol photons m-2 s-1). Growth rates as well as quotas and production rates of C and N were measured. Sources of inorganic C for biomass buildup were using a 14C disequilibrium assay. Photosynthetic O2 evolution was measured as a function of dissolved inorganic C and light by means of membrane-inlet mass spectrometry. The diploid stage responded to elevated PCO2 by shunting resources from the production of particulate inorganic C toward organic C yet keeping the production of total particulate C constant. As the effect of ocean acidification was stronger under low light, the diploid stage might be less affected by increased acidity when energy availability is high. The haploid stage maintained elemental composition and production rates under elevated PCO2. Although both life-cycle stages involve different ways of dealing with elevated PCO2, the responses were generally modulated by energy availability, being typically most pronounced under low light. Additionally, PCO2 responses resembled those induced by high irradiances, indicating that ocean acidification affects the interplay between energy-generating processes (photosynthetic light reactions) and processes competing for energy (biomass buildup and calcification). A conceptual model is put forward explaining why the magnitude of single responses is determined by energy availability.

Characterisation factors for life cycle impact assessment of sound emissions

abstract to be added by authors

Effects of ocean acidification on different life-cycle stages of the kelp Laminaria hyperborea (Phaeophyceae), link to supplementary data

Our objective for this study was to evaluate the influence of preindustrial and expected future atmospheric CO2 concentrations (280 µatm and 700 µatm pCO2, respectively) on different life-cycle stages of the kelp Laminaria hyperborea from Helgoland (Germany, North Sea). Zoospore germination, gametogenesis, vegetative growth, sorus formation and photosynthetic performance of vegetative and fertile tissue were examined. The contribution of external carbonic anhydrase (exCA) to C-supply for net-photosynthesis (net-PS) and the Chla- and phlorotannin content were investigated. Female gametogenesis and vegetative growth of sporophytes were significantly enhanced under the expected future pCO2. rETR(max) and net-PS of young vegetative sporophytes tended to increase performance at higher pCO2. The trend towards elevated net-PS vanished after inhibition of exCA. In vegetative sporophytes, phlorotannin content and Chla content were not significantly affected by pCO2.

Seawater carbonate chemistry, Acropora digitifera growth and skeletal U/Ca ratios during experiments, 2011

The impact of ocean acidification caused by the increasing atmospheric CO2 has been studied in marine calcifiers, including hermatypic corals. However, the effect of elevated pCO2 on the early developmental life-cycle stage of corals has been little studied. In this study, we reared polyps of Acropora digitifera in seawater at pHT 6.55, 7.31, 7.64, 7.77, and 8.03, controlled by CO2 bubbling. We measured the dry weights of polyp skeletons after the 40-d experiment to investigate the relationship between the seawater aragonite saturation state and polyp growth. In addition, we measured skeletal U/Ca ratio to estimate their pH dependence. Skeletal weights of coral polyps increased with the aragonite saturation state and reached an apparent saturation plateau above pH 7.77. U/Ca ratios had a strong inverse relationship with pH and a negligible relationship with skeletal growth rate (polyp weight), suggesting that skeletal U/Ca could be useful for reconstructing paleo-pH.

Have we been underestimating the effects of ocean acidification in zooplankton?

Understanding how copepods may respond to ocean acidification (OA) is critical for risk assessments of ocean ecology and biogeochemistry. The perception that copepods are insensitive to OA is largely based on experiments with adult females. Their apparent resilience to increased carbon dioxide (pCO2) concentrations has supported the view that copepods are 'winners' under OA. Here, we show that this conclusion is not robust, that sensitivity across different life stages is significantly misrepresented by studies solely using adult females. Stage-specific responses to pCO2 (385-6000 µatm) were studied across different life stages of a calanoid copepod, monitoring for lethal and sublethal responses. Mortality rates varied significantly across the different life stages, with nauplii showing the highest lethal effects; nauplii mortality rates increased threefold when pCO2 concentrations reached 1000 µatm (year 2100 scenario) with LC50 at 1084 µatm pCO2. In comparison, eggs, early copepodite stages, and adult males and females were not affected lethally until pCO2 concentrations >= 3000 µatm. Adverse effects on reproduction were found, with >35% decline in nauplii recruitment at 1000 µatm pCO2. This suppression of reproductive scope, coupled with the decreased survival of early stage progeny at this pCO2 concentration, has clear potential to damage population growth dynamics in this species. The disparity in responses seen across the different developmental stages emphasizes the need for a holistic life-cycle approach to make species-level projections to climate change. Significant misrepresentation and error propagation can develop from studies which attempt to project outcomes to future OA conditions solely based on single life history stage exposures.

Strong shift from HCO3- to CO2 uptake in Emiliania huxleyi with acidification: new approach unravels acclimation versus short-term pH effects

Effects of ocean acidification on Emiliania huxleyi strain RCC 1216 (calcifying, diploid life-cycle stage) and RCC 1217 (non-calcifying, haploid life-cycle stage) were investigated by measuring growth, elemental composition, and production rates under different pCO2 levels (380 and 950 µatm). In these differently acclimated cells, the photosynthetic carbon source was assessed by a (14)C disequilibrium assay, conducted over a range of ecologically relevant pH values (7.9-8.7). In agreement with previous studies, we observed decreased calcification and stimulated biomass production in diploid cells under high pCO2, but no CO2-dependent changes in biomass production for haploid cells. In both life-cycle stages, the relative contributions of CO2 and HCO3 (-) uptake depended strongly on the assay pH. At pH values =< 8.1, cells preferentially used CO2 (>= 90 % CO2), whereas at pH values >= 8.3, cells progressively increased the fraction of HCO3 (-) uptake (~45 % CO2 at pH 8.7 in diploid cells; ~55 % CO2 at pH 8.5 in haploid cells). In contrast to the short-term effect of the assay pH, the pCO2 acclimation history had no significant effect on the carbon uptake behavior. A numerical sensitivity study confirmed that the pH-modification in the (14)C disequilibrium method yields reliable results, provided that model parameters (e.g., pH, temperature) are kept within typical measurement uncertainties. Our results demonstrate a high plasticity of E. huxleyi to rapidly adjust carbon acquisition to the external carbon supply and/or pH, and provide an explanation for the paradoxical observation of high CO2 sensitivity despite the apparently high HCO3 (-) usage seen in previous studies.

Seawater carbonate chemistry and Strongylocentrotus droebachiensis larval and juvenile survival and reporductive processes, 2012

Anthropogenic CO2 emissions are acidifying the world's oceans. A growing body of evidence demonstrates that ocean acidification can impact survival, growth, development and physiology of marine invertebrates. Here we tested the impact of long term (up to 16 months) and trans life-cycle (adult, embryo/larvae and juvenile) exposure to elevated pCO2 (1200 µatm, compared to control 400 µatm) on the green sea urchin Strongylocentrotus droebachiensis. Female fecundity was decreased 4.5 fold when acclimated to elevated pCO2 for 4 months during reproductive conditioning while no difference was observed in females acclimated for 16 months. Moreover, adult pre-exposure for 4 months to elevated pCO2, had a direct negative impact on subsequent larval settlement success. Five to nine times fewer offspring reached the juvenile stage in cultures using gametes collected from adults previously acclimated to high pCO2 for 4 months. However, no difference in larval survival was observed when adults were pre-exposed for 16 months to elevated pCO2. pCO2 had no direct negative impact on juvenile survival except when both larvae and juveniles were raised in elevated pCO2. These negative effects on settlement success and juvenile survival can be attributed to carry-over effects from adults to larvae and from larvae to juveniles. Our results support the contention that adult sea urchins can acclimate to moderately elevated pCO2 in a matter of a few months and that carry-over effects can exacerbate the negative impact of ocean acidification on larvae and juveniles.

Response of benthic foraminifera to ocean acidification in their natural sediment environment: a long-term culturing experiment

Calcifying foraminifera are expected to be endangered by ocean acidification; however, the response of a complete community kept in natural sediment and over multiple generations under controlled laboratory conditions has not been constrained to date. During 6 months of incubation, foraminiferal assemblages were kept and treated in natural sediment with pCO2-enriched seawater of 430, 907, 1865 and 3247 µatm pCO2. The fauna was dominated by Ammonia aomoriensis and Elphidium species, whereas agglutinated species were rare. After 6 months of incubation, pore water alkalinity was much higher in comparison to the overlying seawater. Consequently, the saturation state of Omega calc was much higher in the sediment than in the water column in nearly all pCO2 treatments and remained close to saturation. As a result, the life cycle (population density, growth and reproduction) of living assemblages varied markedly during the experimental period, but was largely unaffected by the pCO2 treatments applied. According to the size-frequency distribution, we conclude that foraminifera start reproduction at a diameter of 250 µm. Mortality of living Ammonia aomoriensis was unaffected, whereas size of large and dead tests decreased with elevated pCO2 from 285 µm (pCO2 from 430 to 1865 µatm) to 258 µm (pCO2 3247 µatm). The total organic content of living Ammonia aomoriensis has been determined to be 4.3% of CaCO3 weight. Living individuals had a calcium carbonate production rate of 0.47 g/m**2/a, whereas dead empty tests accumulated a rate of 0.27 g /m**2/a. Although Omega calc was close to 1, approximately 30% of the empty tests of Ammonia aomoriensis showed dissolution features at high pCO2 of 3247 µatm during the last 2 months of incubation. In contrast, tests of the subdominant species, Elphidium incertum, stayed intact. Our results emphasize that the sensitivity to ocean acidification of the endobenthic foraminifera Ammonia aomoriensis in their natural sediment habitat is much lower compared to the experimental response of specimens isolated from the sediment.

Seawater chemistry, nutrients, chlorophyll a, and growth rate of Phaeocystis globosa during experiments

Phaeocystis globosa (Prymnesiophyceae) is an ecologically dominating phytoplankton species in many areas around the world. It plays an important role in both the global sulfur and carbon cycles, by the production of dimethylsulfide (DMS) and the drawdown of inorganic carbon. Phaeocystis globosa has a polymorphic life cycle and is considered to be a harmful algal bloom (HAB) forming species. All these aspects make this an interesting species to study the effects of increasing carbon dioxide (CO2) concentrations, due to anthropogenic carbon emissions. Here, the combined effects of three different dissolved carbon dioxide concentrations (CO2(aq)) (low: 4 µmol/kg, intermediate: 6-10 µmol/kg and high CO2(aq): 21-24 µmol/kg) and two different light intensities (low light, suboptimal: 80 µmol photons/m**2/s and high light, light saturated: 240 µmol photons/m**2/s) are reported. The experiments demonstrated that the specific growth rate of P. globosa in the high light cultures decreased with increasing CO2(aq) from 1.4 to 1.1 /d in the low and high CO2 cultures, respectively. Concurrently, the photosynthetic efficiency (Fv/Fm) increased with increasing CO2(aq) from 0.56 to 0.66. The different light conditions affected photosynthetic efficiency and cellular chlorophyll a concentrations, both of which were lower in the high light cultures as compared to the low light cultures. These results suggest that in future inorganic carbon enriched oceans, P. globosa will become less competitive and feedback mechanisms to global change may decrease in strength.

Seawater carbonate chemistry and giant kelp Macrocystis pyrifera reproduction processes during experiments, 2011

The worldwide effects of ocean acidification (OA) on marine species are a growing concern. In temperate coastal seas, seaweeds are dominant primary producers that create complex habitats and supply energy to higher trophic levels. Studies on OA and macroalgae have focused on calcifying species and adult stages but, critically, they have overlooked the microscopic stages of the reproductive life cycle, which, for other anthropogenic stress e.g. UV-B radiation, are the most susceptible life-history phase. Also, environmental cues and stressors can cause changes in the sex ratio which has implications for the mating system and recruitment success. Here, we report the effects of pH (7.59-8.50) on meiospore germination and sex determination for the giant kelp, Macrocystis pyrifera (Laminariales), in the presence and absence of additional dissolved inorganic carbon (DIC). Lowered pH (7.59-7.60, using HCl-only) caused a significant reduction in germination, while added DIC had the opposite effect, indicating that increased CO2 at lower pH ameliorates physiological stress. This finding also highlights the importance of appropriate manipulation of seawater carbonate chemistry when testing the effects of ocean acidification on photosynthetic organisms. The proportion of male to female gametophytes did not vary significantly between treatments suggesting that pH was not a primary environmental modulator of sex. Relative to the baseline (pH 8.19), gametophytes were 32% larger under moderate OA (pH 7.86) compared to their size (10% increase) under extreme OA (pH 7.61). This study suggests that metabolically-active cells can compensate for the acidification of seawater. This homeostatic function minimises the negative effects of lower pH (high H+ ions) on cellular activity. The 6-9% reduction in germination success under extreme OA suggests that meiospores of M.pyrifera may be resistant to future ocean acidification.

Does Encapsulation Protect Embryos from the Effects of Ocean Acidification? The Example of Crepidula fornicata

Early life history stages of marine organisms are generally thought to be more sensitive to environmental stress than adults. Although most marine invertebrates are broadcast spawners, some species are brooders and/or protect their embryos in egg or capsules. Brooding and encapsulation strategies are typically assumed to confer greater safety and protection to embryos, although little is known about the physico-chemical conditions within egg capsules. In the context of ocean acidification, the protective role of encapsulation remains to be investigated. To address this issue, we conducted experiments on the gastropod Crepidula fornicata. This species broods its embryos within capsules located under the female and veliger larvae are released directly into the water column. C. fornicata adults were reared at the current level of CO2 partial pressure (pCO2) (390 µatm) and at elevated levels (750 and 1400 µatm) before and after fertilization and until larval release, such that larval development occurred entirely at a given pCO2. The pCO2 effects on shell morphology, the frequency of abnormalities and mineralization level were investigated on released larvae. Shell length decreased by 6% and shell surface area by 11% at elevated pCO2 (1400 µatm). The percentage of abnormalities was 1.5- to 4-fold higher at 750 µatm and 1400 µatm pCO2, respectively, than at 390 µatm. The intensity of birefringence, used as a proxy for the mineralization level of the larval shell, also decreased with increasing pCO2. These negative results are likely explained by increased intracapsular acidosis due to elevated pCO2 in extracapsular seawater. The encapsulation of C. fornicata embryos did not protect them against the deleterious effects of a predicted pCO2 increase. Nevertheless, C. fornicata larvae seemed less affected than other mollusk species. Further studies are needed to identify the critical points of the life cycle in this species in light of future ocean acidification.

Synergistic effects of ocean acidification and warming on overwintering pteropods in the Arctic

Ocean acidification and warming will be most pronounced in the Arctic Ocean. Aragonite shell-bearing pteropods in the Arctic are expected to be among the first species to suffer from ocean acidification. Carbonate undersaturation in the Arctic will first occur in winter and because this period is also characterized by low food availability, the overwintering stages of polar pteropods may develop into a bottleneck in their life cycle. The impacts of ocean acidification and warming on growth, shell degradation (dissolution), and mortality of two thecosome pteropods, the polar Limacina helicina and the boreal L. retroversa, were studied for the first time during the Arctic winter in the Kongsfjord (Svalbard). The abundance of L. helicina and L. retroversa varied from 23.5 to 120 ind /m2 and 12 to 38 ind /m2, and the mean shell size ranged from 920 to 981 µm and 810 to 823 µm, respectively. Seawater was aragonite-undersaturated at the overwintering depths of pteropods on two out of ten days of our observations. A 7-day experiment [temperature levels: 2 and 7 °C, pCO2 levels: 350, 650 (only for L. helicina) and 880 ?atm] revealed a significant pCO2 effect on shell degradation in both species, and synergistic effects between temperature and pCO2 for L. helicina. A comparison of live and dead specimens kept under the same experimental conditions indicated that both species were capable of actively reducing the impacts of acidification on shell dissolution. A higher vulnerability to increasing pCO2 and temperature during the winter season is indicated compared with a similar study from fall 2009. Considering the species winter phenology and the seasonal changes in carbonate chemistry in Arctic waters, negative climate change effects on Arctic thecosomes are likely to show up first during winter, possibly well before ocean acidification effects become detectable during the summer season.

Seawater carbonate chemistry and protein sports of barnicle Balanus amphitrite during experiments, 2011

The majority of benthic marine invertebrates have a complex life cycle, during which the pelagic larvae select a suitable substrate, attach to it, and then metamorphose into benthic adults. Anthropogenic ocean acidification (OA) is postulated to affect larval metamorphic success through an altered protein expression pattern (proteome structure) and post-translational modifications. To test this hypothesis, larvae of an economically and ecologically important barnacle species Balanus amphitrite, were cultured from nauplius to the cyprid stage in the present (control) and in the projected elevated concentrations of CO2 for the year 2100 (the OA treatment). Cyprid response to OA was analyzed at the total proteome level as well as two protein post-translational modification (phosphorylation and glycosylation) levels using a 2-DE based proteomic approach. The cyprid proteome showed OA-driven changes. Proteins that were differentially up or down regulated by OA come from three major groups, namely those related to energy-metabolism, respiration, and molecular chaperones, illustrating a potential strategy that the barnacle larvae may employ to tolerate OA stress. The differentially expressed proteins were tentatively identified as OA-responsive, effectively creating unique protein expression signatures for OA scenario of 2100. This study showed the promise of using a sentinel and non-model species to examine the impact of OA at the proteome level.