Posts Tagged 'dissolution'

Effects of ocean acidification on calcification of the sub-Antarctic pteropod Limacina retroversa

Ocean acidification is expected to impact the high latitude oceans first, as CO2 dissolves more easily in colder waters. At the current rate of anthropogenic CO2 emissions, the sub-Antarctic Zone will start to experience undersaturated conditions with respect to aragonite within the next few decades, which will affect marine calcifying organisms. Shelled pteropods, a group of calcifying zooplankton, are considered to be especially sensitive to changes in carbonate chemistry because of their thin aragonite shells. Limacina retroversa is the most abundant pteropod in sub-Antarctic waters, and plays an important role in the carbonate pump. However, not much is known about its response to ocean acidification. In this study, we investigated differences in calcification between L. retroversa individuals exposed to ocean carbonate chemistry conditions of the past (pH 8.19; mid-1880s), present (pH 8.06), and near-future (pH 7.93; predicted for 2050) in the sub-Antarctic. After 3 days of exposure, calcification responses were quantified by calcein staining, shell weighing, and Micro-CT scanning. In pteropods exposed to past conditions, calcification occurred over the entire shell and the leading edge of the last whorl, whilst individuals incubated under present and near-future conditions mostly invested in extending their shells, rather than calcifying over their entire shell. Moreover, individuals exposed to past conditions formed larger shell volumes compared to present and future conditions, suggesting that calcification is already decreased in today’s sub-Antarctic waters. Shells of individuals incubated under near-future conditions did not increase in shell weight during the incubation, and had a lower density compared to past and present conditions, suggesting that calcification will be further compromised in the future. This demonstrates the high sensitivity of L. retroversa to relatively small and short-term changes in carbonate chemistry. A reduction in calcification of L. retroversa in the rapidly acidifying waters of the sub-Antarctic will have a major impact on aragonite-CaCO3 export from oceanic surface waters to the deep sea.

Continue reading ‘Effects of ocean acidification on calcification of the sub-Antarctic pteropod Limacina retroversa’

Ocean acidification reduces skeletal density of hardground‐forming high‐latitude crustose coralline algae

Crustose coralline algae (CCA) function as foundation species by creating marine carbonate hardground habitats. High‐latitude species may be vulnerable to regional warming and acidification. Here, we report the results of an experiment investigating the impacts of CO2‐induced acidification (pCO2 ∼350, 490, 890, 3200 µatm) and temperature (∼6.5, 8.5, 12.5°C) on the skeletal density of two species of high‐latitude CCA: Clathromorphum compactum (CC) and C. nereostratum (CN). Skeletal density of both species significantly declined with pCO2. In CN, the density of previously deposited skeleton declined in the highest pCO2 treatment. This species was also unable to precipitate new skeleton at 12.5°C, suggesting that CN will be particularly sensitive to future warming and acidification. The decline in skeletal density exhibited by both species under future pCO2 conditions could reduce their skeletal strength, potentially rendering them more vulnerable to disturbance, and impairing their production of critical habitat in high‐latitude systems.

Continue reading ‘Ocean acidification reduces skeletal density of hardground‐forming high‐latitude crustose coralline algae’

Calcification does not necessarily protect articulated coralline algae from urchin grazing

Calcification is widely thought to be an adaptation that reduces the impact of herbivory. Recent work has shown that ocean acidification may negatively impact calcification of marine organisms, including coralline red algae, which could theoretically increase the susceptibility of corallines to benthic grazers. By manipulating calcium carbonate content of three articulated coralline algal species, we demonstrated that calcification has a variable and species-specific effect on urchin grazing. For two species, Corallina vancouveriensis and Corallina officinalis var. chilensis, reductions in calcium carbonate content did not cause a significant increase in urchin grazing, raising questions about the benefit of calcification in these species. For Calliarthron tuberculosum, reduced calcium carbonate content caused an increase in urchin grazing rates but only after calcium carbonate had been reduced by more than 15%, suggesting that only dramatic shifts in calcification would make C. tuberculosum more susceptible to urchin grazing. We hypothesize that the herbivory-reducing benefits of calcification likely depend upon coralline thallus morphology. Negative impacts of ocean acidification on calcification in coralline algae may not necessarily increase herbivory rates.

Continue reading ‘Calcification does not necessarily protect articulated coralline algae from urchin grazing’

Coccolithophore calcification studied by single-cell impedance cytometry: towards single-cell PIC:POC measurements

Since the industrial revolution 30% of the anthropogenic CO2 is absorbed by oceans, resulting in ocean acidification, which is a threat to calcifying algae. As a result, there has been profound interest in the study of calcifying algae, because of their important role in the global carbon cycle. The coccolithophore Emiliania huxleyi is considered to be globally the most dominant calcifying algal species, which creates a unique exoskeleton from inorganic calcium carbonate platelets. The PIC (particulate inorganic carbon): POC (particulate organic carbon) ratio describes the relative amount of inorganic carbon in the algae and is a critical parameter in the ocean carbon cycle.

In this research we explore the use of microfluidic single-cell impedance spectroscopy in the field of calcifying algae. Microfluidic impedance spectroscopy enables us to characterize single-cell electrical properties in a noninvasive and label-free way. We use the ratio of the impedance at high frequency vs. low frequency, known as opacity, to discriminate between calcified coccolithophores and coccolithophores with a calcite exoskeleton dissolved by acidification (decalcified).

We have demonstrated that using opacity we can discriminate between calcified and decalcified coccolithophores with an accuracy of 94.1%. We have observed a correlation between the measured opacity and the cell height in the channel, which is supported by FEM simulations. The difference in cell density between calcified and decalcified cells can explain the difference in cell height and therefore the measured opacity.

Continue reading ‘Coccolithophore calcification studied by single-cell impedance cytometry: towards single-cell PIC:POC measurements’

Late afternoon seasonal transition to dissolution in a coral reef: an early warning of a net dissolving ecosystem?

There are concerns that reefs will transition from net calcifying to net dissolving in the near future due to decreasing calcification and increasing dissolution rates. Here we present in situ rates of net ecosystem calcification (NEC) and net ecosystem production (NEP) on a coral reef flat using a slack‐water approach. Up until dusk, the reef was net calcifying in most months but shifted to net dissolution in austral summer, coinciding with high respiration rates and a lower aragonite saturation state (Ωarag). The estimated sediment contribution to NEC ranged from 8 – 21 % during the day and 45 – 78 % at night, indicating that high rates of sediment dissolution may cause the transition to reef dissolution. This late afternoon seasonal transition to negative NEC may be an early warning sign of the reef shifting to a net dissolving state and may be occurring on other reefs.

Continue reading ‘Late afternoon seasonal transition to dissolution in a coral reef: an early warning of a net dissolving ecosystem?’

Pteropods make thinner shells in the upwelling region of the California Current ecosystem

Shelled pteropods are widely regarded as bioindicators for ocean acidification, because their fragile aragonite shells are susceptible to increasing ocean acidity. While short-term incubations have demonstrated that pteropod calcification is negatively impacted by ocean acidification, we know little about net calcification in response to varying ocean conditions in natural populations. Here, we examine in situ calcification of Limacina helicina pteropods collected from the California Current Ecosystem, a coastal upwelling system with strong spatial gradients in ocean carbonate chemistry, dissolved oxygen and temperature. Depth-averaged pH ranged from 8.03 in warmer offshore waters to 7.77 in cold CO2-rich waters nearshore. Based on high-resolution micro-CT technology, we showed that shell thickness declined by ~ 37% along the upwelling gradient from offshore to nearshore water. Dissolution marks covered only ~ 2% of the shell surface area and were not associated with the observed variation in shell thickness. We thus infer that pteropods make thinner shells where upwelling brings more acidified and colder waters to the surface. Probably the thinner shells do not result from enhanced dissolution, but are due to a decline in calcification. Reduced calcification of pteropods is likely to have major ecological and biogeochemical implications for the cycling of calcium carbonate in the oceans.

Continue reading ‘Pteropods make thinner shells in the upwelling region of the California Current ecosystem’

Ocean acidification alters properties of the exoskeleton in adult tanner crabs, Chionoecetes bairdi

Ocean acidification can affect the ability of calcifying organisms to build and maintain mineralized tissue. In decapod crustaceans, the exoskeleton is a multilayered structure composed of chitin, protein, and mineral, predominately magnesian calcite or amorphous calcium carbonate (ACC). We investigated the effects of acidification on the exoskeleton of mature (post-terminal-molt) female southern Tanner crabs, Chionoecetes bairdi. Crabs were exposed to one of three pH levels—8.1, 7.8, or 7.5—for two years. Reduced pH led to a suite of body-region-specific effects on the exoskeleton. Microhardness of the claw was 38% lower in crabs at pH 7.5 compared with those at pH 8.1, but carapace microhardness was unaffected by pH. In contrast, reduced pH altered elemental content in the carapace (reduced calcium, increased magnesium), but not the claw. Diminished structural integrity and thinning of the exoskeleton was observed at reduced pH in both body regions; internal erosion of the carapace was present in most crabs at pH 7.5, and the claws of these crabs showed substantial external erosion, with tooth-like denticles nearly or completely worn away. Using infrared spectroscopy, we observed a shift in the phase of calcium carbonate present in the carapace of pH-7.5 crabs: a mix of ACC and calcite was found in the carapace of crabs at pH 8.1, whereas the bulk of calcium carbonate had transformed to calcite in pH-7.5 crabs. With limited capacity for repair, the exoskeleton of long-lived crabs that undergo a terminal molt, such as Cbairdi, may be especially susceptible to ocean acidification.

Continue reading ‘Ocean acidification alters properties of the exoskeleton in adult tanner crabs, Chionoecetes bairdi’

Acidification stress effect on umbonate veliger larval development in Panopea globosa

Highlights

  • The pH significantly influenced the biometric variables in Panopea globosa larvae.
  • Larvae exposed to lower pH showed shell dissolution at the umbo level.
  • The metabolic rate was higher in larvae exposed to acidification compared to the control.
  • Nicotinamide adenine dinucleotide dehydrogenase expression levels to pH 7.5 suggest a higher energy requirement.

Abstract


Ocean acidification generates a decrease in calcium carbonate availability essential for biomineralization in organisms such as mollusks. This effect was evaluated on Panopea globosa exposing for 7 days umbonate veliger larvae to two pH treatments: experimental (pH 7.5) and control (pH 8.0). Exposure to pH 7.5 affected growth, reducing larval shell length from 5.15–13.34% compared to the control group. This size reduction was confirmed with electron microscopy, also showing shell damage. The physiological response showed an increase in oxygen consumption in larvae exposed to low pH with a maximum difference of 1.57 nmol O2 h−1 larvae−1 at day 7. The gene expression analyses reported high expression values for nicotinamide adenine dinucleotide (NADH) dehydrogenase and Perlucin in larvae at pH 7.5, suggesting a higher energetic cost in this larval group to maintain homeostasis. In conclusion, this study showed that acidification affected development of P. globosa umbonate veliger larvae.

Continue reading ‘Acidification stress effect on umbonate veliger larval development in Panopea globosa’

Juvenile Eastern oysters more resilient to extreme ocean acidification than their mud crab predators

Ocean acidification is predicted to impair marine calcifiers’ abilities to produce shells and skeletons. We conducted laboratory experiments investigating the impacts of CO2‐induced ocean acidification (pCO2 = 478 – 519, 734 – 835, 8980 – 9567; Ωcalcite = 7.3 – 5.7, 5.6 – 4.3, 0.6 – 0.7) on calcification rates of two estuarine calcifiers involved in a classic predator‐prey model system: adult Panopeus herbstii (Atlantic mud crab) and juvenile Crassostrea virginica (eastern oyster). Both oyster and crab calcification rates significantly decreased at the highest pCO2 level. Notably, however, oysters maintained positive net calcification rates in the highest pCO2 treatment that was undersaturated with respect to calcite, while mud crabs exhibited net dissolution (i.e., net loss of shell mass) in calcite‐undersaturated conditions. Secondary electron imaging of oyster shells revealed minor microstructural alterations in the moderate‐pCO2 treatment, and major micro‐ and macro‐structural changes (including shell dissolution, delamination of periostracum) in the high‐pCO2 treatment. These results underscore the threat that ocean acidification poses for marine organisms that produce calcium carbonate shells, illustrate the strong biological control that some marine calcifiers exert over their shell‐building process, and shows that ocean acidification differentially impacts the crab and oyster species involved in this classical predator‐prey model system.

Continue reading ‘Juvenile Eastern oysters more resilient to extreme ocean acidification than their mud crab predators’

Futureproofing the green-lipped mussel aquaculture industry against ocean acidification

Two mitigation strategies – waste shell and aeration – were tested in field experiments to see how effective they are at mitigating acidification around mussel farms. This report outlines the results and recommendations from this research. 


Primary results:

  • The inner Firth of Thames currently experiences the lowest seasonal pH of the sites monitored, with a daily minimum of 7.84 (7.79–7.96) in autumn, with short-term (15-minute) pH minima as low as 7.2. Time-series data in the inner and outer Firth of Thames, and also on a mussel farm in the western Firth, show episodic declines in carbonate saturation to the critical carbonate saturation state ΩAR = 1.0 at which solid aragonite (the form of carbonate in mussel shells) will start to dissolve. Consequently, mussels in the Firth of Thames experience episodic corrosive conditions.
  • The mean pH in the Marlborough Sounds region is projected to decrease by 0.15–0.4 by 2100 depending on future emission scenario. The corresponding decline of 0.5–1.25 in the saturation state of aragonite (ΩAR), results in the critical threshold of ΩAR =1 being reached by 2100 under the worst-case scenario. These projections are based only on future CO2 emission scenarios and do not consider other coastal sources of acidity in coastal waters which may also alter in the future.

Continue reading ‘Futureproofing the green-lipped mussel aquaculture industry against ocean acidification’

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