CO2-induced Reduction Research Articles

Effects of CO2 on the physicochemical, microbial, and sensory properties of pork patties packaged under optimized O2 levels

The storage quality characteristics of fresh pork patties were investigated under 80% O2 modified atmosphere packaging (MAP80:20 = 80% O2/20% CO2) and 40% O2 MAP with various CO2 levels (MAP40:20 = 40% O2/20% CO2/40% N2; MAP40:40 = 40% O2/40% CO2/20% N2; MAP40:60 = 40% O2/60% CO2). Packaged patties were stored for 16 days at 4 °C to monitor their physicochemical (pH, instrumental color, oxidative stability, and fatty acid profile), microbial, and sensorial changes. Results suggested that decreasing O2 levels from 80% to 40% significantly inhibited the lipid oxidation of patties but led to a lower (P < 0.05) color stability. Elevating CO2 levels from 20% to 60% in combination with 40% O2 significantly suppressed bacterial growth and total volatile basic nitrogen production, and thus rendered patties with a better sensory quality and a similar meat color to 80% O2. However, increased CO2 levels promoted lipid oxidation through reducing the antioxidant capacity of patties, which was attributed to a CO2-induced reduction in superoxide dismutase and glutathione peroxidase activities during storage rather than a pH reduction or changes in fatty acid composition. Overall, 40% O2/40% CO2/20% N2 is a realistic alternative for pork patties to improve meat quality and extend the shelf-life to over 16 days.

Combined effects of elevated air temperature and CO2 on growth, yield, and yield components of japonica rice (Oryza sativa L.)

In the region where heat stress has become evident, the elevation of air temperature could reduce yield of heat stress-susceptible crops, such as rice (Oryza sativa L.), which is a major food staple in Asia. In addition to air temperature, atmospheric CO2 is projected to be elevated in the future. To project rice yield in the future, it is necessary to clarify the responses of rice to concurrent elevations of air temperature and atmospheric CO2. In the present study, two japonica rice cultivars with different heat tolerance, Hinohikari (sensitive) and Nikomaru (tolerant), were grown in pots inside open-top chambers and exposed to elevated air temperature and/or CO2. The degrees of increase in the air temperature and CO2 concentration by the treatments were approximately 1 °C and 120 µmol mol−1 (ppm). The study was conducted in Nagasaki, Japan, where heat stress on rice has become evident. Elevated air temperature significantly decreased both whole-plant growth and grain yield. Elevated CO2 significantly increased the growth but significantly decreased the yield. The effects of elevated air temperature and elevated CO2 on growth and yield did not significantly differ between two cultivars. In both cultivars, the main cause of yield reduction by both treatments was reduction in spikelet fertility, which is typical heat stress on rice. The elevated CO2-induced reduction in spikelet fertility could be explained partially by high-temperature regime during flowering due to acceleration of heading and by increase in canopy temperature via stomatal closure in flag leaves. Because elevated air temperature and elevated CO2 treatments additively reduced spikelet fertility in both cultivars, concurrent elevations of air temperature and CO2 caused considerable reduction in grain yield.

Warming offsets the benefits of elevated CO2 in water relations while amplifies elevated CO2-induced reduction in forage nutritional value in the C4 grass Megathyrsus maximus.

Tropical grasslands are very important to global carbon and water cycles. C4 plants have increased heat tolerance and a CO2 concentrating mechanism that often reduces responses to elevated concentrations of CO2 ([CO2]). Despite the importance of tropical grasslands, there is a scarcity of studies that elucidate how managed tropical grasslands will be affected by elevated [CO2] and warming. In our study, we used a combination of a temperature-free air-controlled enhancement (T-FACE) and a free-air carbon dioxide enrichment (FACE) systems to increase canopy temperature and [CO2] under field conditions, respectively. We warmed a field-grown pasture dominated by the C4 tropical forage grass Megathyrsus maximus by 2°C above ambient under two levels of [CO2] (ambient (aC) and elevated (eC - 600 ppm) to investigate how these two factors isolated or combined regulate water relations through stomatal regulation, and how this combination affects PSII functioning, biochemistry, forage nutritive value, and digestibility. We demonstrated that the effects of warming negated the effects of eC in plant transpiration, water potential, proline content, and soil moisture conservation, resulting in warming canceling the eCO2-induced improvement in these parameters. Furthermore, there were additive effects between eC and warming for chlorophyll fluorescence parameters and aboveground nutritive value. Warming sharply intensified the eCO2-induced decrease in crude protein content and increases in forage fibrous fraction and lignin, resulting in a smaller forage digestibility under a warmer CO2-enriched atmosphere. Our results highlight the importance of multifactorial studies when investigating global change impacts on managed ecosystems and the potential consequences for the global carbon cycle like amplification in methane emissions by ruminants and feeding a positive climate feedback system.

Responses of Freshwater Calcifiers to Carbon-Dioxide-Induced Acidification

Increased anthropogenic carbon dioxide (CO2) in the atmosphere can enter surface waters and depress pH. In marine systems, this phenomenon, termed ocean acidification (OA), can modify a variety of physiological, ecological, and chemical processes. Shell-forming organisms are particularly sensitive to this chemical shift, though responses vary amongst taxa. Although analogous chemical changes occur in freshwater systems via absorption of CO2 into lakes, rivers, and streams, effects on freshwater calcifiers have received far less attention, despite the ecological importance of these organisms to freshwater systems. We exposed four common and widespread species of freshwater calcifiers to a range of pCO2 conditions to determine how CO2-induced reductions in freshwater pH impact calcium carbonate shell formation. We incubated the signal crayfish, Pacifastacus leniusculus, the Asian clam, Corbicula fluminea, the montane pea clam, Pisidium sp., and the eastern pearlshell mussel, Margaritifera margaritifera, under low pCO2 conditions (pCO2 = 616 ± 151 µatm; pH = 7.91 ± 0.11), under moderately elevated pCO2 conditions (pCO2 = 1026 ± 239 uatm; pH = 7.67 ± 0.10), and under extremely elevated pCO2 conditions (pCO2 = 2380 ± 693 uatm; pH = 7.32 ± 0.12). Three of these species exhibited a negative linear response to increasing pCO2 (decreasing pH), while the fourth, the pea clam, exhibited a parabolic response. Additional experiments revealed that feeding rates of the crayfish decreased under the highest pCO2 treatment, potentially contributing to or driving the negative calcification response of the crayfish to elevated pCO2 by depriving them of energy needed for biocalcification. These results highlight the potential for freshwater taxa to be deleteriously impacted by increased atmospheric pCO2, the variable nature of these responses, and the need for further study of this process in freshwater systems.

Impaired hatching exacerbates the high CO2 sensitivity of embryonic sand lance Ammodytes dubius

Rising oceanic partial pressure of CO2 (pCO2) could affect many traits in fish early life stages, but only few species to date have shown direct CO2-induced survival reductions. This might partly be because species from less CO2-variable, offshore environments in higher latitudes are currently underrepresented in the literature. We conducted new experimental work on northern sand lance Ammodytes dubius, a key forage fish on offshore Northwest Atlantic sand banks, which was recently suggested to be highly CO2-sensitive. In 2 complementary trials, we produced embryos from wild, Gulf of Maine spawners and reared them at several pCO2 levels (~400-2000 µatm) in combination with static (6, 7, 10°C) and dynamic (10→5°C) temperature treatments. Again, we consistently observed large, CO2-induced reductions in hatching success (-23% at 1000 µatm, -61% at ~2000 µatm), and the effects were temperature-independent. To distinguish pCO2 effects during development from potential impacts on hatching itself, some embryos were switched between high and control pCO2 treatments just prior to hatch. This indeed altered hatching patterns, consistent with the CO2-impaired hatching hypothesis. High CO2 also delayed the day of first hatch in one trial and peak hatch in the other, where later-hatched larvae were of similar size but with progressively less endogenous energy reserves. For context, we extracted seasonal pCO2 projections for Stellwagen Bank (Gulf of Maine) from regional ensemble simulations, which indicated a CO2-induced reduction in sand lance hatching success to 71% of contemporary levels by 2100. The species’ unusual CO2 sensitivity has large ecological and scientific ramifications that warrant future in-depth research.

Could CO2-induced changes to C4 grass flammability aggravate savanna woody encroachment?

Fire plays an important role in maintaining the savanna tree-grass balance by limiting the recruitment of heat-sensitive tree seedlings. However, fire behaviour may change under increasing CO2 concentrations, due to altered flammability of the grassy layer. Here, we determined the effect of predicted future CO2 concentrations, and how it interacts with water-availability, on grass flammability and traits influential to flammability, and uncovered the physiological mechanisms underpinning these responses. Using the widespread C4 savanna grass, Themeda triandra, as a model, we found that improved water-use efficiency under elevated CO2 (800 ppm) resulted in a larger (greater aboveground biomass), but wetter (higher moisture content) grass fuel load, that cured at a slower rate under drought conditions. These changes were associated with increased time to ignition, reduced flaming times and reduced predicted rate of spread. We modelled the effect of altered grass flammability on fire behaviour at a national level (South Africa), finding large-scale reductions in fire spread under elevated CO2, mitigating the converse effects of predicted increases in aridity, and marginal increases in fireline intensity. CO2-induced reductions in fire frequency, spread or intensity could have serious implications for savanna vegetation dynamics, possibly exacerbating the woody encroachment already seen in these ecosystems across the world.

Hybrid CO2-N2 huff-n-puff strategy in unlocking tight oil reservoirs

Increasing energy and environmental demands raise intensive interests on cleaner but challenging resource explorations, where unconventional tight reservoirs attract attentions due to its huge reserves but complex reservoir conditions. As commonly-used gas solvents for enhancing tight oil recovery, CO2 and N2 show their superb capabilities in each single usage, while their combinations, particularly utilizing of huff-n-puff (HnP) strategy, has been rarely investigated. In this paper, novel gas solvents, hybrid CO2-N2 gases with six molar ratios were synthesized and applied for a series of laboratory HnP tests using artificial cores. The proposed technology was specifically evaluated by analysing relevant properties, optimising production strategy, and examining the post-production residual oil saturation by means of nuclear magnetic resonance (NMR). Overall, our experiments validate the first three HnP cycles usually have higher oil recovery, while the subsequently further cycles would only be mildly beneficial. In this case, the hybrid CO2-N2 HnP simultaneously takes advantages of CO2-induced viscosity reduction and N2-induced elastic energy increase. The optimum proportion of CO2-N2 in the hybrid gas solvent is found to be 1:2, with the best HnP oil recovery of 39.0%. The NMR-assisted coreflood tests indicate largely uneven residual oil distributions. The effectivities of CO2 and N2 HnP are determined to be different in variation of pore scale in production tight oil, where the N2 HnP has better oil extraction ability in small pores.

Impacts of Surface Ozone Pollution on Global Crop Yields: Comparing Different Ozone Exposure Metrics and Incorporating Co-effects of CO2

Surface ozone (O3) pollution poses significant threats to crop production and food security worldwide, but an assessment of present-day and future crop yield losses due to exposure to O3 still abides with great uncertainties, mostly due: (1) to the large spatiotemporal variability and uncertain future projections of O3 concentration itself; (2) different methodological approaches to quantify O3 exposure and impacts; (3) difficulty in accounting for co-varying factors such as CO2 concentration and climatic conditions. In this paper, we explore these issues using a common framework: a consistent set of simulated present-day O3 fields from one chemical transport model, coupled with a terrestrial ecosystem-crop model to derive various O3 exposure metrics and impacts on relative crop yields worldwide, and examine the potential effects of elevated CO2 on O3-induced crop yield losses. Throughout, we review and explain the differences in formulation and parameterization in the various approaches, including the concentration-based metrics, flux-based metrics, and mechanistic biophysical crop modeling. We find that while the spatial pattern of yield losses for a given crop is generally consistent across metrics, the magnitudes can differ substantially. Pooling the concentration-based and flux-based metrics together, we estimate the present-day globally aggregated yield losses to be: 3.6 ± 1.1% for maize, 2.6 ± 0.8% for rice, 6.7 ± 4.1% for soybean, and 7.2 ± 7.3% for wheat; these estimates are generally consistent with previous studies but on the lower end of the uncertainty range covered. We attribute the large combined uncertainty mostly to the differences among methodological approaches, and secondarily to differences in O3 and meteorological inputs. Based on a biophysical crop model that mechanistically simulates photosynthetic and yield responses of crops to stomatal O3 uptake, we further estimate that increasing CO2 concentration from 390 to 600 ppm reduces the globally aggregated O3-induced yield loss by 21–52% for maize and by 27–38% for soybean, reflecting a CO2-induced reduction in stomatal conductance that in turn alleviates stomatal O3 uptake and thus crop damage. Rising CO2 may therefore render the currently used exposure-yield relationships less applicable in a future atmosphere, and we suggest approaches to address such issues.

Transgenerational responses to seawater pH in the edible oyster, with implications for the mariculture of the species under future ocean acidification

The majority of common edible oysters are projected to grow more slowly and have smaller impaired shells because of anthropogenic CO2-induced reductions in seawater carbonate ion concentration and pH, a process called ocean acidification (OA). Recent evidence has shown that OA has carryover effects, for example, larvae exposed to OA will also exhibit either positive or negative effects after metamorphosis. This study examined the hidden carryover effects of OA exposure during parental and larval stages on post-metamorphic traits of the commercially important oyster species Crassostrea hongkongensis. Adults of C. hongkongensis were exposed to control pH (pHNBS 8.0) and OA-induced low pH (pHNBS 7.4) conditions. Their larval offspring were then exposed to the same aquarium conditions before being out-planted as post-metamorphic juveniles at a mariculture site for 10 months. Initially, larval offspring were resilient to low pH with or without parental exposure. The larvae exposed to low pH had significantly faster development and higher percentage of settlement success compared to control groups. The out-planted juveniles with parental exposure had improved survival and growth compared to juveniles without parental exposure, regardless of the larval exposure history. This implies that transgenerational effects due to parental exposure not only persists but also have a greater influence than the within-generational effects of larval exposure. Our results shed light on the importance of linking the various life history stages when assessing the OA-induced carryover capacity of C. hongkongensis in the natural environment. Understanding these linked relationships helps us better predict the species rapid adaptation responses in the face of changing coastal conditions due to OA.

Role of photosynthesis and stomatal conductance on the long-term rising of intrinsic water use efficiency in dominant trees in three old-growth forests in Bosnia-Herzegovina and Montenegro

Old-growth forests have an important role in maintaining animal and plant diversity, are important carbon (C) reservoirs and are privileged sites to study long-term plant physiological responses, long-term forest dynamics and climate change impact on forest ecosystems. Several studies have highlighted how old-living trees undergo age-related declines with hydraulic limitations and reduction in photosynthesis, though some recent works have suggested that such a decline is not always observed. Our study aims at understanding the role of atmospheric CO2 increase on tree C uptake and stomatal conductance (gs) in old-living trees by analysing the long-term patterns of tree growth and intrinsic water use efficiency (iWUE) in three old-growth forests in the Balkans (Bosnia-Herzegovina and Montenegro), using dendrochronology and isotopic analysis. We hypothesised a long-term increase in iWUE in the studied old-growth forests, mostly related to enhanced photosynthesis rather than reduced stomatal conductance. Tree cores were sampled from dominant silver fir (Abies alba Mill.) trees in each forest. Tree-ring widths were measured and basal area increments (BAI) were assessed for each sampled tree and, from the six longest chronologies, five decades were chosen for cellulose extraction, its isotopic analysis (δ13C, δ18O), iWUE and leaf water 18O evaporative enrichment above the source water (Δ18OL) determination. We observed a continuous and significant increase in iWUE from 1800 to 2010 in the sampled dominant trees at all the three old-growth forests. Our BAI data and our estimates of Δ18OL across the study period support the idea that enhanced photosynthesis rather than reduced stomatal conductance is the major driver of the measured iWUE increase. Thus, our results support some recent findings challenging the hypothesis that iWUE in forests is primarily the result of a CO2-induced reduction in stomatal conductance as well as the so called hydraulic limitation hypothesis.

CO2-induced low pH in an eastern oyster (Crassostrea virginica) hatchery positively affects reproductive development and larval survival but negatively affects larval shape and size, with no intergenerational linkages

Abstract In North America, studies regarding effects of CO2-induced low pH in bivalve aquaculture are largely restricted to the US Pacific coast. Studies on species from the northwest Atlantic are lacking. Furthermore, information on the roles of intergenerational exposure and biological sex in bivalve responses to low pH, particularly in an aquaculture-specific context, is scant. We tested if short-term (1 month) exposure to CO2-induced reductions in pHNBS affected the reproductive development of male and female eastern oysters (Crassostrea virginica) during hatchery-specific reproductive conditioning and whether maternal and/or paternal exposure influenced larval responses. Reduced pH (7.5–7.7) increased the rate of reproductive development in both males and females. There was no indication of intergenerational effects; adult pH conditions did not affect early larval development. In contrast, low pH conditions experienced by gametes during spawning, fertilization, and embryo incubation (48 h) resulted in higher larval survival (+6–8% from control), reduced shell height (−2 to 3 µm), and increased deformities (abnormal shell shape; +3–5%). We suggest that local adaptation to acidic land runoff may account for the positive effects of low pH observed in this study. Bioeconomic assessments are now needed to understand the implications of reduced pH on aquaculture operations in these regions of Atlantic Canada.

Algal density alleviates the elevated CO2‐caused reduction on growth ofPorphyra haitanensis(Bangiales, Rhodophyta), a species farmed in China

Growing of Pyropia haitanensis, a commercially farmed macroalga, usually increases their densities greatly during cultivation in natural habitats. To explore how the increased algal densities affect their photosynthetic responses to rising CO2, we compared the growth, cell components and photosynthesis of the thalli of P. haitanensis under a matrix of pCO2 levels (ambient CO2, 400 ppm; elevated CO2, 1,000 ppm) and biomass densities [low, 1.0 g fresh weight (FW) L−1; medium, 2.0 g FW L−1; high, 4.0 g FW L−1]. Under ambient CO2, the relative growth rate (RGR) was 5.87% d−1, 2.32% d−1 and 1.51% d−1 in low, medium and high densities, and elevated CO2 reduced the RGR by 27%, 25% and 12% respectively. Maximal photochemical quantum yield of photosystem II (FV/FM) was higher in low than in high densities, so were the light-utilized efficiency (α), saturation irradiance (EK) and maximum relative electron transfer rate (rETRmax). Elevated CO2 enhanced the FV/FM in low density but not in higher densities, as well as the α, EK and rETRmax. In addition, elevated CO2 reduced the content of chlorophyll a and enhanced that of carotenoids, but unaffected phycoerythrin, phycocyanin and soluble proteins. Our results indicate that the increased algal densities reduced both the growth and the photosynthesis of P. haitanensis and alleviated the elevated CO2-induced negative impact on growth and positive impact on photosynthesis. Moreover, the elevated CO2-induced reduction on growth and promotion on photosynthesis indicates that rising CO2 may enhance the loss of photosynthetic products of P. haitanensis through releasing organic matters.

Ocean acidification changes the vertical movement of stone crab larvae.

Anthropogenic activities are increasing ocean temperature and decreasing ocean pH. Some coastal habitats are experiencing increases in organic runoff, which when coupled with a loss of vegetated coastline can accelerate reductions in seawater pH. Marine larvae that hatch in coastal habitats may not have the ability to respond to elevated temperature and changes in seawater pH. This study examined the response of Florida stone crab (Menippe mercenaria) larvae to elevated temperature (30°C control and 32°C treatment) and CO2-induced reductions in pH (8.05 pH control and 7.80 pH treatment). We determined whether those singular and simultaneous stressors affect larval vertical movement at two developmental stages. Geotactic responses varied between larval stages. The direction and rate of the vertical displacement of larvae were dependent on pH rather than temperature. Stage III larvae swam upwards under ambient pH conditions, but swam downwards at a faster rate under reduced pH. There was no observable change in the directional movement of Stage V larvae. The reversal in orientation by Stage III larvae may limit larval transport in habitats that experience reduced pH and could pose challenges for the northward dispersal of stone crabs as coastal temperatures warm.

Disentangling the role of photosynthesis and stomatal conductance on rising forest water-use efficiency.

Multiple lines of evidence suggest that plant water-use efficiency (WUE)-the ratio of carbon assimilation to water loss-has increased in recent decades. Although rising atmospheric CO2 has been proposed as the principal cause, the underlying physiological mechanisms are still being debated, and implications for the global water cycle remain uncertain. Here, we addressed this gap using 30-y tree ring records of carbon and oxygen isotope measurements and basal area increment from 12 species in 8 North American mature temperate forests. Our goal was to separate the contributions of enhanced photosynthesis and reduced stomatal conductance to WUE trends and to assess consistency between multiple commonly used methods for estimating WUE. Our results show that tree ring-derived estimates of increases in WUE are consistent with estimates from atmospheric measurements and predictions based on an optimal balancing of carbon gains and water costs, but are lower than those based on ecosystem-scale flux observations. Although both physiological mechanisms contributed to rising WUE, enhanced photosynthesis was widespread, while reductions in stomatal conductance were modest and restricted to species that experienced moisture limitations. This finding challenges the hypothesis that rising WUE in forests is primarily the result of widespread, CO2-induced reductions in stomatal conductance.

Climate change is expected to increase yield and water use efficiency of wheat in the North China Plain

Climate change impacts on winter wheat yield and water-use were assessed with the AquaCrop model for different representative concentration pathway (RCP) scenarios (RCP 2.6, RCP 4.5, RCP 6.0 and RCP 8.5) and time slices (2040s, 2060s, 2080s) using ensemble projections from 10 general circulation models (GCM) for a site in the North China Plain. To test the role of crop and soil management practices under climate change, simulations with deficit irrigation (DI) and mulching were also performed. DI was defined as a practice where soil water content was restored to field capacity after depleting 150% of readily available water (RAW). The chosen mulching practice had a fixed capacity to reduce evaporation by 60%. Simulated outputs were compared with the baseline simulations (baseline period: 1984–2015). The results indicate that yield and water use efficiency (WUE) of wheat will increase under all RCP scenarios and time slices. Analysis revealed that winter wheat in the NCP would benefit from both CO2 fertilization and warming. Warming will shorten the growing cycle but largely due to curbing of the overwintering period. Due to accelerated growth/development, flowering and maturity will be advanced compared to the baseline period. Warming will also ease the low-temperature stress on biomass production. The seasonal evapotranspiration will reduce mainly due to the shorter growing cycle and the CO2-induced reduction in transpiration. Increase in yield and WUE is expected even under DI, while mulching can further increase WUE. Projections using individual GCMs indicated that the variability in crop production would be higher for the high-end scenario (RCP 8.5) than for RCP 2.6. These findings imply that in general, wheat in the NCP is less vulnerable to climate change than in other parts of the world. In addition, the expected increase in the yield and WUE of wheat may positively affect current depletion rates of groundwater for irrigation; however, more work is needed to quantify this. In future, it will be possible to introduce short duration wheat and long duration maize (second crop in rotation) cultivars.

Constraints to Vegetation Growth Reduced by Region-Specific Changes in Seasonal Climate

We qualitatively and quantitatively assessed the factors related to vegetation growth using Earth system models and corroborated the results with historical climate observations. The Earth system models showed a systematic greening by the late 21st century, including increases of up to 100% in Gross Primary Production (GPP) and 60% in Leaf Area Index (LAI). A subset of models revealed that the radiative effects of CO2 largely control changes in climate, but that the CO2 fertilization effect dominates the greening. The ensemble of Earth system model experiments revealed that the feedback of surface temperature contributed to 17% of GPP increase in temperature-limited regions, and radiation increase accounted for a 7% increase of GPP in radiation-limited areas. These effects are corroborated by historical observations. For example, observations confirm that cloud cover has decreased over most land areas in the last three decades, consistent with a CO2-induced reduction in transpiration. Our results suggest that vegetation may thrive in the starkly different climate expected over the coming decades, but only if plants harvest the sort of hypothesized physiological benefits of higher CO2 depicted by current Earth system models.

Vulnerability of juvenile hermit crabs to reduced seawater pH and shading

Multiple simultaneous stressors induced by anthropogenic activities may amplify their impacts on marine organisms. The effects of ocean acidification, in combination with other anthropogenic impacts (apart from temperature) are poorly understood, especially in coastal regions. In these areas, shading caused by infrastructure development, such as harbor construction, may potentially interact with CO2-induced pH reduction and affect invertebrate populations. Here, we evaluated the effects of reduced pH (7.6) and shading (24h in darkness) on mortality, growth, calcification and displacement behavior to live predator (danger signal) and dead gastropod (resource availability signal) odors using juveniles of the hermit crab Pagurus criniticornis collected in Araçá Bay (São Paulo state, Southeastern Brazil). After a 98 day experimental period, both stressors had a significant interaction effect on mortality, and an additive effect on total growth. No difference in calcification was recorded among treatments, indicating that individuals were able to maintain calcification under reduced pH conditions. When exposed to odor of live predators, crab responses were only affected by shading. However, an interactive effect between both stressors was observed in response to gastropod odor, leading to reduced displacement behavior. This study shows how local disturbance impacts may enhance the effects of global environmental change on intertidal crustacean populations.

CO2-induced pH Reduction Hinders Shell Development of Early Larvae Donkey's Ear Abalone Haliotis asinina (Linnaeus 1758)

CO2-induced pH Reduction Hinders Shell Development of Early Larvae Donkey's Ear Abalone Haliotis asinina (Linnaeus 1758)

Ocean acidification does not limit squid metabolism via blood oxygen supply.

Ocean acidification is hypothesized to limit the performance of squid owing to their exceptional oxygen demand and pH sensitivity of blood-oxygen binding, which may reduce oxygen supply in acidified waters. The critical oxygen partial pressure (Pcrit), the PO2 below which oxygen supply cannot match basal demand, is a commonly reported index of hypoxia tolerance. Any CO2-induced reduction in oxygen supply should be apparent as an increase in Pcrit In this study, we assessed the effects of CO2 (46-143 Pa; 455-1410 μatm) on the metabolic rate and Pcrit of two squid species - Dosidicus gigas and Doryteuthis pealeii - through manipulative experiments. We also developed a model, with inputs for hemocyanin pH sensitivity, blood PCO2 and buffering capacity, that simulates blood oxygen supply under varying seawater CO2 partial pressures. We compare model outputs with measured Pcrit in squid. Using blood-O2 parameters from the literature for model inputs, we estimated that, in the absence of blood acid-base regulation, an increase in seawater PCO2 to 100 Pa (≈1000 μatm) would result in a maximum drop in arterial hemocyanin-O2 saturation by 1.6% at normoxia and a Pcrit increase of ≈0.5 kPa. Our live-animal experiments support this supposition, as CO2 had no effect on measured metabolic rate or Pcrit in either squid species.

CO2-induced pH reduction increases physiological toxicity of nano-TiO2 in the mussel Mytilus coruscus

The increasing usage of nanoparticles has caused their considerable release into the aquatic environment. Meanwhile, anthropogenic CO2 emissions have caused a reduction of seawater pH. However, their combined effects on marine species have not been experimentally evaluated. This study estimated the physiological toxicity of nano-TiO2 in the mussel Mytilus coruscus under high pCO2 (2500–2600 μatm). We found that respiration rate (RR), food absorption efficiency (AE), clearance rate (CR), scope for growth (SFG) and O:N ratio were significantly reduced by nano-TiO2, whereas faecal organic weight rate and ammonia excretion rate (ER) were increased under nano-TiO2 conditions. High pCO2 exerted lower effects on CR, RR, ER and O:N ratio than nano-TiO2. Despite this, significant interactions of CO2-induced pH change and nano-TiO2 were found in RR, ER and O:N ratio. PCA showed close relationships among most test parameters, i.e., RR, CR, AE, SFG and O:N ratio. The normal physiological responses were strongly correlated to a positive SFG with normal pH and no/low nano-TiO2 conditions. Our results indicate that physiological functions of M. coruscus are more severely impaired by the combination of nano-TiO2 and high pCO2.