Effects Of pCO2 Research Articles

Effects of slowed respiratory rate and elevated end-tidal PCO2 during jogging on physiological responses

Effects of slowed respiratory rate and elevated end-tidal PCO2 during jogging on physiological responses

Elevated pCO2 may increase the edible safety risk of clams exposed to toxic Alexandrium spp.

Toxic harmful algal blooms (HABs) have received increasing attention owing to their threat to the health of aquatic life and seafood consumers. This study evaluated the impacts of elevated atmospheric partial pressure of CO2 (pCO2) on the production of paralytic shellfish toxins (PSTs) in different Alexandrium spp. strains, together with its further effects on the bioaccumulation/elimination dynamics of PSTs in bivalves contaminated with PSTs from toxic dinoflagellates. Our results showed that elevated pCO2 stimulated the growth of the two Alexandrium spp. (A. catenella and A. pacificum) isolated from the northern and southern coastal areas of China, respectively, and affected PST production including content and toxicity of the two strains differently. Further PSTs bioaccumulation/elimination in PSTs-contaminated Manila clam, Ruditapes philippinarum under high pCO2 also occurred. It is worth noting the biotransformation of neosaxitoxin (NEO) with high toxicity through trophic transfer with effect of elevated pCO2. When in microalgae cultured under the control (410 ppm) and elevated pCO2 conditions (495 and 850 ppm), the proportion of NEO in the PST content produced by A. catenella was reduced from 11.1 to 6.4 and 2.6 %, while the proportion of NEO in A. pacificum was increased from 3.1 to 3.6 and 4.7 %, respectively. NEO accounted for >50 % of total PST contents in clams, which were biotransformed via transfer from dinoflagellates and higher pCO2 enhanced this biotransformation leading to increased NEO accumulation. The negatively affected elimination of PSTs, especially NEO, in clams fed with A. catenella or A. pacificum, indicates that the detoxification of PSTs-contaminated clams may be more difficult under elevated pCO2. This study provides reference for developing models to assess the safety of bivalves under the co-stress of environmental change and toxic HABs, suggesting that ocean acidification may lead to the higher safety risk of Manila clams exposed to toxic HAB dinoflagellates.

Effects of increasing atmospheric CO2 on leaf water δ18O values are small and are attenuated in grasses and amplified in dicotyledonous herbs and legumes when transferred to cellulose δ18O values.

The oxygen isotope composition of cellulose (δ18O values) has been suggested to contain information on stomatal conductance (gs) responses to rising pCO2. The extent by which pCO2 affects leaf water and cellulose δ18O values (δ18OLW and δ18OC) and the isotope processes that determine pCO2 effects on δ18OLW and δ18OC are, however, unknown. We tested the effects of pCO2 on gs, δ18OLW and δ18OC in a glasshouse experiment, where six plant species were grown under pCO2 ranging from 200 to 500 ppm. Increasing pCO2 caused a decline in gs and an increase in δ18OLW, as expected. Importantly, the effects of pCO2 on gs and δ18OLW were small and pCO2 effects on δ18OLW were not directly transferred to δ18OC but were attenuated in grasses and amplified in dicotyledonous herbs and legumes. This is likely because of functional group-specific pCO2 effects on the model parameter pxpex. Our study highlights important uncertainties when using δ18OC as a proxy for gs. Specifically, pCO2-triggered gs effects on δ18OLW and δ18OC are possibly too small to be detected in natural settings and a pCO2 effect on pxpex may render the commonly assumed negative linkage between δ18OC and gs to be incorrect, potentially confounding δ18OC based gs reconstructions.

The prokaryotic and eukaryotic microbiome of Pacific oyster spat is shaped by ocean warming but not acidification.

Pacific oysters (Magallana gigas, a.k.a. Crassostrea gigas), the most widely farmed oysters, are under threat from climate change and emerging pathogens. In part, their resilience may be affected by their microbiome, which, in turn, may be influenced by ocean warming and acidification. To understand these impacts, we exposed early-development Pacific oyster spat to different temperatures (18°C and 24°C) and pCO2 levels (800, 1,600, and 2,800 µatm) in a fully crossed design for 3 weeks. Under all conditions, the microbiome changed over time, with a large decrease in the relative abundance of potentially pathogenic ciliates (Uronema marinum) in all treatments with time. The microbiome composition differed significantly with temperature, but not acidification, indicating that Pacific oyster spat microbiomes can be altered by ocean warming but is resilient to ocean acidification in our experiments. Microbial taxa differed in relative abundance with temperature, implying different adaptive strategies and ecological specializations among microorganisms. Additionally, a small proportion (~0.2% of the total taxa) of the relatively abundant microbial taxa were core constituents (>50% occurrence among samples) across different temperatures, pCO2 levels, or time. Some taxa, including A4b bacteria and members of the family Saprospiraceae in the phyla Chloroflexi (syn. Chloroflexota) and Bacteroidetes (syn. Bacteroidota), respectively, as well as protists in the genera Labyrinthula and Aplanochytrium in the class Labyrinthulomycetes, and Pseudoperkinsus tapetis in the class Ichthyosporea were core constituents across temperatures, pCO2 levels, and time, suggesting that they play an important, albeit unknown, role in maintaining the structural and functional stability of the Pacific oyster spat microbiome in response to ocean warming and acidification. These findings highlight the flexibility of the spat microbiome to environmental changes.IMPORTANCEPacific oysters are the most economically important and widely farmed species of oyster, and their production depends on healthy oyster spat. In turn, spat health and productivity are affected by the associated microbiota; yet, studies have not scrutinized the effects of temperature and pCO2 on the prokaryotic and eukaryotic microbiomes of spat. Here, we show that both the prokaryotic and, for the first time, eukaryotic microbiome of Pacific oyster spat are surprisingly resilient to changes in acidification, but sensitive to ocean warming. The findings have potential implications for oyster survival amid climate change and underscore the need to understand temperature and pCO2 effects on the microbiome and the cascading effects on oyster health and productivity.

Effects of elevated pCO2 on bioenergetics and disease susceptibility in Pacific herring (Clupea pallasii)

Effects of elevated pCO2 on bioenergetics and disease susceptibility in Pacific herring (Clupea pallasii)

Thermal fluctuations and CO2 enrichment synergistically accelerate biomass yield of Neopyropia yezoensis

Due to the rising atmospheric pCO2, the greenhouse effect in the natural environment has intensified, leading to ocean acidification and frequently extreme temperature events. Limited research has been conducted on the effects of near-shore temperature fluctuations and ocean acidification on macroalgae. In this study, Neopyropia yezoensis (Bangiales, Rhodophyta) was cultured under two CO2 concentrations (LC: 400 μatm and HC: 1000 μatm) and three temperature conditions (10 ℃, 14 ℃, and fluctuation: increased from 10 ℃ to 14 ℃ and then decreased back to 10 ℃ with a fluctuation of 1 ℃ per day). The growth, chlorophyll fluorescence, photosynthetic pigments, and soluble carbohydrate of N. yezoensis were measured. The results showed that the relative growth rate, rETRmax, contents of chlorophyll a, phycoerythrin, and carotenoid in the thalli increased at 14 ℃ and thermal fluctuation, while the content of soluble carbohydrate were inhibited. Moreover, the effect of pCO2 on growth was significant only under temperature fluctuation. Even when the temperature dropped to 10 ℃, the physiological responses of N. yezoensis were still promoted by the thermal fluctuation condition. These findings indicate that the yield and quality of N. yezoensis could potentially improve in the future warming scenarios, and changes observed in N. yezoensis could serve as an early indicator for global climate change.

Transcriptomic Responses of a Lightly Calcified Echinoderm to Experimental Seawater Acidification and Warming during Early Development.

Ocean acidification (OA) and ocean warming (OW) are potential obstacles to the survival and growth of marine organisms, particularly those that rely on calcification. This study investigated the single and joint effects of OA and OW on sea cucumber Apostichopus japonicus larvae raised under combinations of two temperatures (19 °C or 22 °C) and two pCO2 levels (400 or 1000 μatm) that reflect the current and end-of-21st-century projected ocean scenarios. The investigation focused on assessing larval development and identifying differences in gene expression patterns at four crucial embryo-larval stages (blastula, gastrula, auricularia, and doliolaria) of sea cucumbers, using RNA-seq. Results showed the detrimental effect of OA on the early development and body growth of A. japonicus larvae and a reduction in the expression of genes associated with biomineralization, skeletogenesis, and ion homeostasis. This effect was particularly pronounced during the doliolaria stage, indicating the presence of bottlenecks in larval development at this transition phase between the larval and megalopa stages in response to OA. OW accelerated the larval development across four stages of A. japonicus, especially at the blastula and doliolaria stages, but resulted in a widespread upregulation of genes related to heat shock proteins, antioxidant defense, and immune response. Significantly, the negative effects of elevated pCO2 on the developmental process of larvae appeared to be mitigated when accompanied by increased temperatures at the expense of reduced immune resilience and increased system fragility. These findings suggest that alterations in gene expression within the larvae of A. japonicus provide a mechanism to adapt to stressors arising from a rapidly changing oceanic environment.

Brown seaweed Nemacystus decipiens intensifies the effects of ocean acidification on coral Montipora digitata

Photosynthetic marine macrophytes such as seaweeds have been proposed to provide habitat refugia for marine calcifiers against ocean acidification (OA) by increasing the local pH. However, the effectiveness of seaweed as a potential habitat refugia for marine calcifiers such as corals remains to be investigated. This study focused on the seaweed Nemacystus decipiens, which are widely farmed in the shallow reef lagoon of Okinawa coral reefs, Japan, and aimed to evaluate their response to high pCO2 and whether they can mitigate the effect of high pCO2 on the coral Montipora digitata. Corals were cultured with and without seaweed under control (300–400 μatm) or high pCO2 conditions (OA, 900–1000 μatm) for 2 weeks. Results showed that all photo-physiological parameters examined in the seaweed N. decipiens were not affected by high pCO2, suggesting that OA will not positively affect their productivity. The calcification rate of the coral M. digitata was found to decrease under OA and the effect was further exaggerated by the presence of seaweed. The present study suggests that farming seaweeds will not act as a potential habitat refugia for adjacent corals under future OA, but instead can exaggerate the negative effect of OA on coral calcification.

Respiratory rate responses to both hypercapnia and acidaemia are modified by age in patients with acidosis

ObjectiveTo explore the associations between arterial pO2, pCO2 and pH and how these are modified by age. MethodsAn analysis of 2598 patients admitted with a diagnosis of Covid-19 infection to a large UK teaching hospital. ResultsThere were inverse associations for arterial pO2, pCO2 and pH with respiratory rate. The effects of pCO2 and pH on respiratory rate were modified by age; older patients had higher respiratory rates at higher pCO2 (p = 0.004) and lower pH (p = 0.007) values. ConclusionsThis suggests that ageing is associated with complex changes in the physiological feedback loops that control respiratory rate. As well as having clinical relevance, this may also impact on the use of respiratory rate in early warning scores across the age range.

The promotion of stress tolerant Symbiodiniaceae dominance in juveniles of two coral species under simulated future conditions of ocean warming and acidification

The symbiotic relationship between coral and its endosymbiotic algae, Symbiodiniaceae, greatly influences the hosts’ potential to withstand environmental stress. To date, the effects of climate change on this relationship has primarily focused on adult corals. Uncovering the effects of environmental stress on the establishment and development of this symbiosis in early life stages is critical for predicting how corals may respond to climate change. To determine the impacts of future climate projections on the establishment of symbionts in juvenile corals, ITS2 amplicon sequencing of single coral juveniles was applied to Goniastrea retiformis and Acropora millepora before and after exposure to three climate conditions of varying temperature and pCO2 levels (current and RCP8.5 in 2050 and 2100). Compared to ambient conditions, juvenile corals experienced shuffling in the relative abundance of Cladocopium (C1m, decrease) to Durusdinium (D1 and D1a, increase) over time. We calculated a novel risk metric incorporating functional redundancy and likelihood of impact on host physiology to identify the loss of D1a as a “low risk” to the coral compared to the loss of “higher risk” taxa like D1 and C1m. Although the increase in stress tolerant Durusdinium under future warming was encouraging for A. millepora, by 2100, G. retiformis communities displayed signs of symbiosis de-regulation, suggesting this acclimatory mechanism may have species-specific thresholds. Whilst this study cannot specifically disentangle the individual effects of temperature and pCO2, it does provide valuable insights into the impacts of both stressors combined. These results emphasize the need for understanding of long-term effects of climate change induced stress on coral juveniles, and their potential for increased acclimation to heat tolerance through changes in symbiosis.

Separate and combined effects of elevated pCO2 and temperature on the branching reef corals Acropora digitifera and Montipora digitata

Ocean acidification (OA) and warming (OW) are major global threats to coral reef ecosystems; however, studies on their combined effects (OA + OW) are scarce. Therefore, we evaluated the effects of OA, OW, and OA + OW in the branching reef corals Acropora digitifera and Montipora digitata, which have been found to respond differently to environmental changes. Our results indicate that OW has a greater impact on A. digitifera and M. digitata than OA and that the former species is more vulnerable to OW than the latter. OW was the main stressor for increased mortality and decreased calcification in the OA + OW group, and the effect of OA + OW was additive in both species. Our findings suggest that the relative abundance and cover of M. digitata are expected to increase whereas those of A. digitifera may decrease in the near future in Okinawa.

Elevated dissolved carbon dioxide and associated acidification delays maturation and decreases calcification and survival in the freshwater crustacean Daphnia magna

AbstractIncreasing pCO2 in freshwaters across the globe will likely be accompanied by acidification. Although this has been linked to reduced calcification, growth, and survival in several marine species, similar responses in freshwater organisms remain largely unexplored. Here, we investigated the direct effects of elevated pCO2 and associated acidification on the water flea Daphnia magna. As a highly efficient filter feeder, this crustacean is a dominant primary consumer in freshwater zooplankton assemblages, capable of controlling algal growth. It has a high calcium content compared to other zooplankton species, which might make it particularly sensitive since calcification may be impaired under elevated pCO2. We exposed newly hatched individuals of four clonal lineages to 27,000 ppm pCO2 corresponding to a pH of 6.7 in a controlled laboratory experiment. Both survival and calcium content were reduced and juveniles grew slower and matured later under elevated pCO2. Adult growth rate was not affected by pCO2 suggesting that surviving adults are less sensitive or may acclimate over time but at the cost of reduced offspring size. We hypothesize that the combination of elevated pCO2 and low pH interferes with the calcification process, reflected in slower growth, smaller body size and reduced calcification in D. magna. In turn, this might lead to less efficient control of phytoplankton as an ecosystem service and reduce their competitive advantage over other zooplankters with less calcified bodies.

The effect of increasing temperature and pCO2 on experimental pelagic freshwater communities

AbstractAs the global climate is changing, average water temperatures and the supply of CO2 to water bodies are increasing. To determine how the effects of these changes on freshwater communities interact, we ran a month‐long factorial mesocosm experiment, in which we manipulated water temperature (heated, ambient) and pCO2 (preindustrial, ambient, future). We found that the total phytoplankton biomass responded positively to the pCO2 and temperature treatments but no interactive effects were detected. Green algae were positively affected by temperature and, over the course of the experiment, responded to pCO2 first positively, then negatively. Heterokonts, on the other hand, were unaffected by temperature but responded positively to pCO2. pCO2 enrichment also led to increases in seston C : N stoichiometry, although the experiment ended before we could observe any effects of pCO2 on the zooplankton community composition. Warming caused shifts in zooplankton community composition, primarily through higher abundances of the cladoceran Bosmina longirostris and the rotifer Conochilus unicornis, and lower abundances of the rotifer Polyarthra vulgaris. We found that, in contrast to the effects of temperature, which can be explained by temperature‐dependent plankton growth curves, the responses of algal groups to pCO2 enrichment were difficult to anticipate, despite the availability of priors from previous pCO2 enrichment experiments in the same lake mesocosms. We conclude that climate change‐induced increases in aquatic pCO2 and temperatures are likely to affect pelagic ecosystems, though further research in freshwater systems is needed before generalized claims regarding the simple and interactive effects of pCO2 can be made.

Effects of ocean acidification and warming on the specific dynamic action of California Grunion (Leuresthes tenuis) larvae

Ocean acidification (OA) and Ocean Warming (OW) are ongoing environmental changes that present a suite of physiological challenges to marine organisms. Larval stages may be especially sensitive to the effects of climate change because the larval phase is a time of critical growth and development. Of particular importance to growth is Specific Dynamic Action (SDA) – the energy used in digestion, absorption, and assimilation of food. Relatively little is known about the energetics of SDA for larval fishes and even less is known about how SDA may be affected by climate change. In this study we used feeding experiments and respirometry assays to characterize the functional form of SDA for California Grunion (Leuresthes tenuis). In a second set of experiments, we tested the independent and combined effects of ocean acidification and warming on SDA. Our first experiment revealed that an elevated metabolic rate was detectable within an hour of feeding, peaked at 3–6 h post feeding, and lasted about 24 h in total. Experiments testing the effects of acidification and warming revealed that temperature generally increased the maximum rate of postprandial respiration and the total amount of energy expended via SDA. In an experiment where feeding level was the same for fish held at different temperatures, elevated pCO2 increased the maximum rate of postprandial respiration and shortened the SDA response. However, in an experiment that allowed fish to consume more food at high temperatures, effects of pCO2 on SDA were minimal. The effects of OA on SDA may depend on a combination of temperature and food availability, and the disruption of SDA with OA may be part of a chain of events where digestion and assimilation efficiency are impaired with potential consequences for growth, survival, and population replenishment.

Response of drip water Mg/Ca and Sr/Ca variations in ventilated caves to hydroclimate

Mg/Ca and Sr/Ca in speleothems which record valuable information regarding past variations of precipitation and cave air pCO2 are promising proxies because the degrees of water-rock interaction (WRI) and prior calcite precipitation (PCP) are directly and indirectly related to these changes. However, the controls on Mg/Ca and Sr/Ca can be complex, and most studies ignored the combined effects of rainfall and cave air pCO2. Moreover, knowledge of the influence of seasonal rainfall and cave air pCO2 on seasonal fluctuations in drip water Mg/Ca and Sr/Ca are limited for caves with different regions and ventilation types. Drip water Mg/Ca and Sr/Ca were monitored for five years at Shawan Cave. The results indicate that the irregular seasonal oscillation in drip water Mg/Ca and Sr/Ca is controlled by inverse-phase seasonal changes between rainfall and cave air pCO2. The rainfall amount may be the primary controlling factor of the interannual variation in drip water Mg/Ca, whereas the interannual variation in drip water Sr/Ca is most likely controlled by cave air pCO2. Furthermore, we compared drip water Mg/Ca and Sr/Ca of caves in different regions to fully understand how drip water Mg/Ca and Sr/Ca respond to hydroclimate changes. The drip water element/Ca, for seasonal ventilation caves with a fairly narrow range of cave air pCO2 respond well to the local hydroclimate associated with rainfall variation. If the range of cave air pCO2 is considerably large, the element/Ca in seasonal ventilation caves of subtropical humid regions may not reflect hydroclimate and that of Mediterranean and semi-arid regions may be primarily controlled by cave air pCO2. The element/Ca in the low year-round pCO2 caves could reflect the hydroclimate associated with surface temperature. Therefore, observations of drip water monitoring and comparative analysis can provide a reference for the explanation of speleothems element/Ca ratios from seasonally ventilated caves worldwide.

Steering the product spectrum in high-pressure anaerobic processes: CO2 partial pressure as a novel tool in biorefinery concepts

BackgroundElevated CO2 partial pressure (pCO2) has been proposed as a potential steering parameter for selective carboxylate production in mixed culture fermentation. It is anticipated that intermediate product spectrum and production rates, as well as changes in the microbial community, are (in)directly influenced by elevated pCO2. However, it remains unclear how pCO2 interacts with other operational conditions, namely substrate specificity, substrate-to-biomass (S/X) ratio and the presence of an additional electron donor, and what effect pCO2 has on the exact composition of fermentation products. Here, we investigated possible steering effects of elevated pCO2 combined with (1) mixed substrate (glycerol/glucose) provision; (2) subsequent increments in substrate concentration to increase the S/X ratio; and (3) formate as an additional electron donor.ResultsMetabolite predominance, e.g., propionate vs. butyrate/acetate, and cell density, depended on interaction effects between pCO2–S/X ratio and pCO2–formate. Individual substrate consumption rates were negatively impacted by the interaction effect between pCO2–S/X ratio and were not re-established after lowering the S/X ratio and adding formate. The product spectrum was influenced by the microbial community composition, which in turn, was modified by substrate type and the interaction effect between pCO2–formate. High propionate and butyrate levels strongly correlated with Negativicutes and Clostridia predominance, respectively. After subsequent pressurized fermentation phases, the interaction effect between pCO2–formate enabled a shift from propionate towards succinate production when mixed substrate was provided.ConclusionsOverall, interaction effects between elevated pCO2, substrate specificity, high S/X ratio and availability of reducing equivalents from formate, rather than an isolated pCO2 effect, modified the proportionality of propionate, butyrate and acetate in pressurized mixed substrate fermentations at the expense of reduced consumption rates and increased lag-phases. The interaction effect between elevated pCO2 and formate was beneficial for succinate production and biomass growth with a glycerol/glucose mixture as the substrate. The positive effect may be attributed to the availability of extra reducing equivalents, likely enhanced carbon fixating activity and hindered propionate conversion due to increased concentration of undissociated carboxylic acids.

Deoxygenation enhances photosynthetic performance and increases N2 fixation in the marine cyanobacterium Trichodesmium under elevated pCO2.

Effects of changed levels of dissolved O2 and CO2 on marine primary producers are of general concern with respect to ecological effects of ongoing ocean deoxygenation and acidification as well as upwelled seawaters. We investigated the response of the diazotroph Trichodesmium erythraeum IMS 101 after it had acclimated to lowered pO2 (~60 μM O2) and/or elevated pCO2 levels (HC, ~32 μM CO2) for about 20 generations. Our results showed that reduced O2 levels decreased dark respiration significantly, and increased the net photosynthetic rate by 66 and 89% under the ambient (AC, ~13 μM CO2) and the HC, respectively. The reduced pO2 enhanced the N2 fixation rate by ~139% under AC and only by 44% under HC, respectively. The N2 fixation quotient, the ratio of N2 fixed per O2 evolved, increased by 143% when pO2 decreased by 75% under the elevated pCO2. Meanwhile, particulate organic carbon and nitrogen quota increased simultaneously under reduced O2 levels, regardless of the pCO2 treatments. Nevertheless, changed levels of O2 and CO2 did not bring about significant changes in the specific growth rate of the diazotroph. Such inconsistency was attributed to the daytime positive and nighttime negative effects of both lowered pO2 and elevated pCO2 on the energy supply for growth. Our results suggest that Trichodesmium decrease its dark respiration by 5% and increase its N2-fixation by 49% and N2-fixation quotient by 30% under future ocean deoxygenation and acidification with 16% decline of pO2 and 138% rise of pCO2 by the end of this century.

Impact of ultraviolet radiation nearly overrides the effects of elevated pCO2 on a prominent nitrogen‐fixing cyanobacterium

AbstractAlthough the marine N2‐fixers Trichodesmium spp. are affected by increasing pCO2 and by ultraviolet radiation (UVR) in their habitats, little is known on their potential responses to future ocean acidification in the presence of UVR. We grew Trichodesmium at two pCO2 levels (410 and 1000 μatm) under natural sunlight, documented the filament length, growth, and chlorophyll content after its acclimation to the pCO2 treatments, and measured its carbon and N2 fixation rates under different solar radiation treatments with or without UVR. We showed that the elevated pCO2 did not significantly alter the diazotroph's growth, filament length, or pigment content, and its photosynthetic rate was only affected by solar radiation treatments rather than the pCO2 levels. The presence of UV‐A and UV‐B inhibited photosynthesis by 10–22% and 17–21%, respectively. Inhibition of N2 fixation by UV‐B was proportional to its intensity, whereas UV‐A stimulated N2 fixation at low, but inhibited it at high, intensities. Elevated pCO2 only stimulated N2 fixation under moderate levels of solar radiation. The simulated depth profile of N2 fixation in the water column showed that UV‐induced inhibition dominated the combined effects of elevated pCO2 and UVR at 0–30 m depth and the combination of these factors enhanced N2 fixation at 30–60 m depth, but this effect diminished in deeper water. Our results suggest that Trichodesmium could be influenced more by UVR than by pCO2 and their combined action result in negative effects on N2 fixation under high solar radiation, but positive effects under low to moderate solar radiation.

Ocean acidification and ammonium enrichment interact to stimulate a short-term spike in growth rate of a bloom forming macroalga

IntroductionThe coastal macroalgal genus, Ulva, is found worldwide and is considered a nuisance algal genus due to its propensity for forming vast blooms. The response of Ulva to ocean acidification (OA) is of concern, particularly with nutrient enrichment, as these combined drivers may enhance algal blooms because of increased availability of dissolved inorganic resources.MethodsWe determined how a suite of physiological parameters were affected by OA and ammonium (NH4+) enrichment in 22-day laboratory experiments to gain a mechanistic understanding of growth, nutrient assimilation, and photosynthetic processes. We predicted how physiological parameters change across a range of pCO2 and NH4+ scenarios to ascertain bloom potential under future climate change regimes.ResultsDuring the first five days of growth, there was a positive synergy between pCO2 and NH4+ enrichment, which could accelerate initiation of an Ulva bloom. After day 5, growth rates declined overall and there was no effect of pCO2, NH4+, nor their interaction. pCO2 and NH4+ acted synergistically to increase NO3- uptake rates, which may have contributed to increased growth in the first five days. Under the saturating photosynthetically active radiation (PAR) used in this experiment (500 μmol photon m-2 s-1), maximum photosynthetic rates were negatively affected by increased pCO2, which could be due to increased sensitivity to light when high CO2 reduces energy requirements for inorganic carbon acquisition. Activity of CCMs decreased under high pCO2 and high NH4+ conditions indicating that nutrients play a role in alleviating photodamage and regulating CCMs under high-light intensities.DiscussionThis study demonstrates that OA could play a role in initiating or enhancing Ulva blooms in a eutrophic environment and highlights the need for understanding the potential interactions among light, OA, and nutrient enrichment in regulating photosynthetic processes.

A positive temperature‐dependent effect of elevated CO2 on growth and lipid accumulation in the planktonic copepod, Calanus finmarchicus

AbstractCalanus finmarchicus were reared from eggs to adults at 12°C and 16°C with non‐limiting food in combination with ambient (600 μatm) and high (1100 μatm) pCO2. These conditions are likely to be encountered by the species at the southern margins of its biogeographical range by the end of the century. Dry weight (DW), carbon (C) and nitrogen (N) mass, oil‐sac volume (OSV), fatty acid composition (FA), and oxygen consumption rates (OCR) were measured on newly molted stage CV copepodites and recently molted adult females. By focusing our measurements on these precise events in the life cycle, we were able to obtain a more accurate comparison of growth and respiration across treatments. Copepods raised at 12°C had a significantly greater DW, OSV, and C and N mass than those raised at 16°C High pCO2, independent of temperature, was associated with a further increase in the DW and C content of the copepods. Interactive effects of temperature and pCO2 resulted in a larger OSV at low temperature and high pCO2. Mass‐specific respiration rates were significantly lower at lower temperatures and elevated pCO2 suggesting that the increase in mass (DW, C, and OSV) resulted from reduced metabolic cost. The composition of fatty acids in the copepods varied mainly with temperature. Two fatty acids varied with pCO2: 16:0 tended to decrease with higher pCO2 and 18:3n−3 tended to increase with higher pCO2. These observations suggest that elevated pCO2/lower pH in future oceans may have a beneficial effect on C. finmarchicus.