Seawater carbonate chemistry, mass, size and regenerative capacity of Luidia clathrata during experiments, 2011

The present study examines sublethal effects of near-future (year 2100) ocean acidification (OA) on regenerative capacity, biochemical composition, and behavior of the sea star Luidia clathrata, a predominant predator in sub-tropical soft-bottom habitats. Two groups of sea stars, each with two arms excised, were maintained on a formulated diet in seawater bubbled with air alone (pH 8.2, approximating a pCO2 of 380 µatm) or with a controlled mixture of air/C02 (pH 7.8, approximating a pCO2 of 780 µatm). Arm length, total body wet weight, and righting responses were measured weekly. After 97 days, a period of time sufficient for 80% arm regeneration, pyloric caecal indices, and protein, carbohydrate, lipid, and ash levels were determined for body wall and pyloric caecal tissues of intact and regenerating arms of individuals held in both seawater pH treatments. The present study indicates that predicted near-term levels of ocean acidification (seawater pH 7.8) do not significantly impact whole animal growth, arm regeneration rates, biochemical composition, or righting behavior in this common soft bottom sea star.

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.

Seawater carbonate chemistry and Globigerinoides sacculifer biological processes during experiments, 2010

The effect of carbonate ion concentration ([CO3]) on calcification rates estimated from shell size and weight was investigated in the planktonic foraminifera Orbulina universa and Globigerinoides sacculifer. Experiments on G. sacculifer were conducted under two irradiance levels (35 and 335 µmol photons m-2 s-1). Calcification was ca. 30% lower under low light than under high light, irrespective of the [CO3]. Both O. universa and G. sacculifer exhibited reduced final shell weight and calcification rate under low [CO3]. For the [CO3] expected at the end of the century, the calcification rates of these two species are projected to be 6 to 13% lower than the present conditions, while the final shell weights are reduced by 20 to 27% for O. universa and by 4 to 6% for G. sacculifer. These results indicate that ocean acidification would impact on calcite production by foraminifera and may decrease the calcite flux contribution from these organisms.

Seawater carbonate chemistry and processes during experiments with crabs Chionoecetes tanneri and Cancer magister, 2007

Rising levels of atmospheric carbon dioxide could be curbed by large-scale sequestration of CO2 in the deep sea. Such a solution requires prior assessment of the impact of hypercapnic, acidic seawater on deep-sea fauna. Laboratory studies were conducted to assess the short-term hypercapnic tolerance of the deep-sea Tanner crab Chionoecetes tanneri, collected from 1000 m depth in Monterey Canyon off the coast of central California, USA. Hemolymph acid- base parameters were monitored over 24 h of exposure to seawater equilibrated with ~1% CO2 (seawater PCO2 ~6 torr or 0.8 kPa, pH 7.1), and compared with those of the shallow-living Dungeness crab Cancer magister. Short-term hypercapnia-induced acidosis in the hemolymph of Chionoecetes tanneri was almost uncompensated, with a net 24 h pH reduction of 0.32 units and a net bicarbonate accumulation of only 3 mM. Under simultaneous hypercapnia and hypoxia, short-term extracellular acidosis in Chionoecetes tanneri was completely uncompensated. In contrast, Cancer magister fully recovered its hemolymph pH over 24 h of hypercapnic exposure by net accumulation of 12 mM bicarbonate from the surrounding medium. The data support the hypothesis that deep-sea animals, which are adapted to a stable environment and exhibit reduced metabolic rates, lack the short-term acid-base regulatory capacity to cope with the acute hypercapnic stress that would accompany large-scale CO2 sequestration. Additionally, the data indicate that sequestration in oxygen-poor areas of the ocean would be even more detrimental to deep-sea fauna.

Seawater carbonate chemistry during experiments with Mytilus edulis, 2008

The effects of medium term (32 d) hypercapnia on the immune response of Mytilus edulis were investigated in mussels exposed to acidified (using CO2) sea water (pH 7.7, 7.5 or 6.7; control: pH 7.8). Levels of phagocytosis increased significantly during the exposure period, suggesting an immune response induced by the experimental set-up. However, this induced stress response was suppressed when mussels were exposed to acidified sea water. Acidified sea water did not have any significant effects on other immuno-surveillance parameters measured (superoxide anion production, total and differential cell counts). These results suggest that ocean acidification may impact the physiological condition and functionality of the haemocytes and could have a significant effect on cellular signalling pathways, particularly those pathways that rely on specific concentrations of calcium, and so may be disrupted by calcium carbonate shell dissolution.

Impact of elevated pCO2 on paralytic shellfish poisoning toxin content and composition in Alexandrium tamarense

Ocean acidification is considered a major threat to marine ecosystems and may particularly affect primary producers. Here we investigated the impact of elevated pCO2 on paralytic shellfish poisoning toxin (PST) content and composition in two strains of Alexandrium tamarense, Alex5 and Alex2. Experiments were carried out as dilute batch to keep carbonate chemistry unaltered over time. We observed only minor changes with respect to growth and elemental composition in response to elevated pCO2. For both strains, the cellular PST content, and in particular the associated cellular toxicity, was lower in the high CO2 treatments. In addition, Alex5 showed a shift in its PST composition from a nonsulfated analogue towards less toxic sulfated analogues with increasing pCO2. Transcriptomic analyses suggest that the ability of A. tamarense to maintain cellular homeostasis is predominantly regulated on the post-translational level rather than on the transcriptomic level. Furthermore, genes associated to secondary metabolite and amino acid metabolism in Alex5 were down-regulated in the high CO2 treatment, which may explain the lower PST content. Elevated pCO2 also induced up-regulation of a putative sulfotransferase sxtN homologue and a substantial down-regulation of several sulfatases. Such changes in sulfur metabolism may explain the shift in PST composition towards more sulfated analogues. All in all, our results indicate that elevated pCO2 will have minor consequences for growth and elemental composition, but may potentially reduce the cellular toxicity of A. tamarense.

Seawater carbonate chemistry and nutrient fluxes during experiments with brittlestar Amphiura filiformis, 2009

Rising levels of atmospheric carbon dioxide and the concomitant increased uptake of this by the oceans is resulting in hypercapnia-related reduction of ocean pH. Research focussed on the direct effects of these physicochemical changes on marine invertebrates has begun to improve our understanding of impacts at the level of individual physiologies. However, CO2-related impairment of organisms' contribution to ecological or ecosystem processes has barely been addressed. The burrowing ophiuroid Amphiura filiformis, which has a physiology that makes it susceptible to reduced pH, plays a key role in sediment nutrient cycling by mixing and irrigating the sediment, a process known as bioturbation. Here we investigate the role of A. filiformis in modifying nutrient flux rates across the sediment-water boundary and the impact of CO2- related acidification on this process. A 40 day exposure study was conducted under predicted pH scenarios from the years 2100 (pH 7.7) and 2300 (pH 7.3), plus an additional treatment of pH 6.8. This study demonstrated strong relationships between A. filiformis density and cycling of some nutrients; activity increases the sediment uptake of phosphate and the release of nitrite and nitrate. No relationship between A. filiformis density and the flux of ammonium or silicate were observed. Results also indicated that, within the timescale of this experiment, effects at the individual bioturbator level appear not to translate into reduced ecosystem influence. However, long term survival of key bioturbating species is far from assured and changes in both bioturbation and microbial processes could alter key biogeochemical processes in future, more acidic oceans.

Simulated changes in ocean physics and carbon cycle for LGM experiments with shifting positions of the Southern Hemisphere westerly winds using the MITgcm, links to model results in NetCDF format

We explore the impact of a latitudinal shift in the westerly wind belt over the Southern Ocean on the Atlantic meridional overturning circulation (AMOC) and on the carbon cycle for Last Glacial Maximum background conditions using a state-of-the-art ocean general circulation model. We find that a southward (northward) shift in the westerly winds leads to an intensification (weakening) of no more than 10% of the AMOC. This response of the ocean physics to shifting winds agrees with other studies starting from preindustrial background climate, but the responsible processes are different. In our setup changes in AMOC seemed to be more pulled by upwelling in the south than pushed by downwelling in the north, opposite to what previous studies with different background climate are suggesting. The net effects of the changes in ocean circulation lead to a rise in atmospheric pCO2 of less than 10 atm for both northward and southward shift in the winds. For northward shifted winds the zone of upwelling of carbon- and nutrient-rich waters in the Southern Ocean is expanded, leading to more CO2 outgassing to the atmosphere but also to an enhanced biological pump in the subpolar region. For southward shifted winds the upwelling region contracts around Antarctica, leading to less nutrient export northward and thus a weakening of the biological pump. These model results do not support the idea that shifts in the westerly wind belt play a dominant role in coupling atmospheric CO2 rise and Antarctic temperature during deglaciation suggested by the ice core data.

Seawater carbonate chemistry and biological processes of Limacina helicina during experiments, 2011

Due to their aragonitic shell, thecosome pteropods may be particularly vulnerable to ocean acidification driven by anthropogenic CO2 emissions. This applies specifically to species inhabiting Arctic surface waters that are projected to become temporarily and locally undersaturated with respect to aragonite as early as 2016. This study investigated the effects of rising partial pressure of CO2 (pCO2) and elevated temperature on pre-winter juveniles of the polar pteropod Limacina helicina. After a 29 day experiment in September/October 2009 at three different temperatures and under pCO2 scenarios projected for this century, mortality, shell degradation, shell diameter and shell increment were investigated. Temperature and pCO2 had a significant effect on mortality, but temperature was the overriding factor. Shell diameter, shell increment and shell degradation were significantly impacted by pCO2 but not by temperature. Mortality was 46% higher at 8 °C than at in situ temperature (3 °C), and 14% higher at 1100 ?atm than at 230 ?atm. Shell diameter and increment were reduced by 10 and 12% at 1100 ?atm and 230 ?atm, respectively, and shell degradation was 41% higher at elevated compared to ambient pCO2. We conclude that pre-winter juveniles will be negatively affected by both rising temperature and pCO2 which may result in a possible decline in abundance of the overwintering population, the basis for next year's reproduction.

Impact of temperature and species interaction on filamentous cyanobacteria may be more important than salinity and increased pCO2 levels

A future business-as-usual scenario (A1FI) was tested on two bloom-forming cyanobacteria of the Baltic Proper, Nodularia spumigena and Aphanizomenon sp., growing separately and together. The projected scenario was tested in two laboratory experiments where (a) interactive effects of increased temperature and decreased salinity and (b) interactive effects of increased temperature and elevated levels of pCO2 were tested. Increased temperature, from 12 to 16 °C, had a positive effect on the biovolume and photosynthetic activity (F v/F m) of both species. Compared when growing separately, the biovolume of each species was lower when grown together. Decreased salinity, from 7 to 4, and elevated levels of pCO2, from 380 to 960 ppm, had no effect on the biovolume, but on F v/F m of N. spumigena with higher F v/F m in salinity 7. Our results suggest that the projected A1FI scenario might be beneficial for the two species dominating the extensive summer blooms in the Baltic Proper. However, our results further stress the importance of studying interactions between species.

Seawater carbonate chemistry and biological processes of oysters Crassostrea virginica during experiments, 2010

Estuarine organisms are exposed to periodic strong fluctuations in seawater pH driven by biological carbon dioxide (CO2) production, which may in the future be further exacerbated by the ocean acidification associated with the global rise in CO2. Calcium carbonate-producing marine species such as mollusks are expected to be vulnerable to acidification of estuarine waters, since elevated CO2 concentration and lower pH lead to a decrease in the degree of saturation of water with respect to calcium carbonate, potentially affecting biomineralization. Our study demonstrates that the increase in CO2 partial pressure (pCO2) in seawater and associated decrease in pH within the environmentally relevant range for estuaries have negative effects on physiology, rates of shell deposition and mechanical properties of the shells of eastern oysters Crassostrea virginica (Gmelin). High CO2 levels (pH ~7.5, pCO2 ~3500 µatm) caused significant increases in juvenile mortality rates and inhibited both shell and soft-body growth compared to the control conditions (pH ~8.2, pCO2 ~380 µatm). Furthermore, elevated CO2 concentrations resulted in higher standard metabolic rates in oyster juveniles, likely due to the higher energy cost of homeostasis. The high CO2 conditions also led to changes in the ultrastructure and mechanical properties of shells, including increased thickness of the calcite laths within the hypostracum and reduced hardness and fracture toughness of the shells, indicating that elevated CO2 levels have negative effects on the biomineralization process. These data strongly suggest that the rise in CO2 can impact physiology and biomineralization in marine calcifiers such as eastern oysters, threatening their survival and potentially leading to profound ecological and economic impacts in estuarine ecosystems.

Seawater carbonate chemistry and biological processes of mussel Crassostrea gigas during experiments, 2011

Climate change with increasing temperature and ocean acidification (OA) poses risks for marine ecosystems. According to Pörtner and Farrell [1], synergistic effects of elevated temperature and CO2-induced OA on energy metabolism will narrow the thermal tolerance window of marine ectothermal animals. To test this hypothesis, we investigated the effect of an acute temperature rise on energy metabolism of the oyster, Crassostrea gigas chronically exposed to elevated CO2 levels (partial pressure of CO2 in the seawater ~0.15 kPa, seawater pH ~ 7.7). Within one month of incubation at elevated PCO2 and 15 °C hemolymph pH fell (pHe = 7.1 ± 0.2 (CO2-group) vs. 7.6 ± 0.1 (control)) and PeCO2 values in hemolymph increased (0.5 ± 0.2 kPa (CO2-group) vs. 0.2 ± 0.04 kPa (control)). Slightly but significantly elevated bicarbonate concentrations in the hemolymph of CO2-incubated oysters ([HCO-3]e = 1.8 ± 0.3 mM (CO2-group) vs. 1.3 ± 0.1 mM (control)) indicate only minimal regulation of extracellular acid-base status. At the acclimation temperature of 15 °C the OA-induced decrease in pHe did not lead to metabolic depression in oysters as standard metabolism rates (SMR) of CO2-exposed oysters were similar to controls. Upon acute warming SMR rose in both groups, but displayed a stronger increase in the CO2-incubated group. Investigation in isolated gill cells revealed a similar temperature-dependence of respiration between groups. Furthermore, the fraction of cellular energy demand for ion regulation via Na+/K+-ATPase was not affected by chronic hypercapnia or temperature. Metabolic profiling using 1H-NMR spectroscopy revealed substantial changes in some tissues following OA exposure at 15 °C. In mantle tissue alanine and ATP levels decreased significantly whereas an increase in succinate levels was observed in gill tissue. These findings suggest shifts in metabolic pathways following OA-exposure. Our study confirms that OA affects energy metabolism in oysters and suggests that climate change may affect populations of sessile coastal invertebrates such as mollusks

Seawater carbonate chemistry and biological processes of Mytilus edulis during experiments, 2011

Progressive ocean acidification due to anthropogenic CO2 emissions will alter marine ecosytem processes. Calcifying organisms might be particularly vulnerable to these alterations in the speciation of the marine carbonate system. While previous research efforts have mainly focused on external dissolution of shells in seawater under saturated with respect to calcium carbonate, the internal shell interface might be more vulnerable to acidification. In the case of the blue mussel Mytilus edulis, high body fluid pCO2 causes low pH and low carbonate concentrations in the extrapallial fluid, which is in direct contact with the inner shell surface. In order to test whether elevated seawater pCO2 impacts calcification and inner shell surface integrity we exposed Baltic M. edulis to four different seawater pCO2 (39, 142, 240, 405 Pa) and two food algae (310-350 cells mL-1 vs. 1600-2000 cells mL-1) concentrations for a period of seven weeks during winter (5°C). We found that low food algae concentrations and high pCO2 values each significantly decreased shell length growth. Internal shell surface corrosion of nacreous ( = aragonite) layers was documented via stereomicroscopy and SEM at the two highest pCO2 treatments in the high food group, while it was found in all treatments in the low food group. Both factors, food and pCO2, significantly influenced the magnitude of inner shell surface dissolution. Our findings illustrate for the first time that integrity of inner shell surfaces is tightly coupled to the animals' energy budget under conditions of CO2 stress. It is likely that under food limited conditions, energy is allocated to more vital processes (e.g. somatic mass maintenance) instead of shell conservation. It is evident from our results that mussels exert significant biological control over the structural integrity of their inner shell surfaces.

Seawater carbonate chemistry, growth rate and light sensitivity of marine diatom Chaetoceros muelleri (strain CSIRO CS-176) during experiments, 2011

This study investigated the impact of photon flux and elevated CO2 concentrations on growth and photosynthetic electron transport on the marine diatom Chaetoceros muelleri and looked for evidence for the presence of a CO2-concentrating mechanism (CCM). pH drift experiments clearly showed that C. muelleri has the capacity to use bicarbonate to acquire inorganic carbon through one or multiple CCMs. The final pH achieved in unbuffered cultures was not changed by light intensity, even under very low photon flux, implying a low energy demand of bicarbonate use via a CCM. In short-term pH drift experiments, only treatment with the carbonic anhydrase inhibitor ethoxyzolamide (EZ) slowed down the rise in pH considerably. EZ was also the only inhibitor that altered the final pH attained, although marginally. In growth experiments, CO2 availability was manipulated by changing the pH in closed flasks at a fixed dissolved inorganic carbon (DIC) concentration. Low-light-treated samples showed lower growth rates in elevated CO2conditions. No CO2 effect was recorded under high light exposure. The maximal photosynthetic capacity, however, increased with CO2 concentration in saturating, but not in subsaturating, light intensities. Growth and photosynthetic capacity therefore responded in opposite ways to increasing CO2 availability. The capacity to photoacclimate to high and low photon flux appeared not to be affected by CO2treatments. However, photoacclimation was restricted to growth photon fluxes between 30 and 300 µmol photons m-2 s-1. The light saturation points for photosynthetic electron transport and for growth coincided at 100 µmol photons m-2 s-1. Below 100 µmol photons m-2 s-1 the light saturation point for photosynthesis was higher than the growth photon flux (i.e. photosynthesis was not light saturated under growth conditions), whereas at higher growth photon flux, photosynthesis was saturated below growth light levels.

Seawater carbonate chemistry, shell linear extension and calcification during calcein staining and 45Ca experiments with pteropod Limacina helicina, 2009

Thecosome pteropods (shelled pelagic molluscs) can play an important role in the food web of various ecosystems and play a key role in the cycling of carbon and carbonate. Since they harbor an aragonitic shell, they could be very sensitive to ocean acidification driven by the increase of anthropogenic CO2 emissions. The impact of changes in the carbonate chemistry was investigated on Limacina helicina, a key species of Arctic ecosystems. Pteropods were kept in culture under controlled pH conditions corresponding to pCO2 levels of 350 and 760 µatm. Calcification was estimated using a fluorochrome and the radioisotope 45Ca. It exhibits a 28 % decrease at the pH value expected for 2100 compared to the present pH value. This result supports the concern for the future of pteropods in a high-CO2 world, as well as of those species dependent upon them as a food resource. A decline of their populations would likely cause dramatic changes to the structure, function and services of polar ecosystems.