Posts Tagged 'growth'



Responses of seaweeds that use CO2 as their sole inorganic carbon source to ocean acidification: differential effects of fluctuating pH but little benefit of CO2 enrichment

Laboratory studies that test the responses of coastal organisms to ocean acidification (OA) typically use constant pH regimes which do not reflect coastal systems, such as seaweed beds, where pH fluctuates on diel cycles. Seaweeds that use CO2 as their sole inorganic carbon source (non-carbon dioxide concentrating mechanism species) are predicted to benefit from OA as concentrations of dissolved CO2 increase, yet this prediction has rarely been tested, and no studies have tested the effect of pH fluctuations on non-CCM seaweeds. We conducted a laboratory experiment in which two ecologically dominant non-CCM red seaweeds (Callophyllis lambertii and Plocamium dilatatum) were exposed to four pH treatments: two static, pHT 8.0 and 7.7 and two fluctuating, pHT 8.0 ± 0.3 and 7.7 ± 0.3. Fluctuating pH reduced growth and net photosynthesis in C. lambertii, while P. dilatatum was unaffected. OA did not benefit P. dilatatum, while C. lambertii displayed elevated net photosynthetic rates. We provide evidence that carbon uptake strategy alone cannot be used as a predictor of seaweed responses to OA and highlight the importance of species-specific sensitivity to [H+]. We also emphasize the importance of including realistic pH fluctuations in experimental studies on coastal organisms.

Continue reading ‘Responses of seaweeds that use CO2 as their sole inorganic carbon source to ocean acidification: differential effects of fluctuating pH but little benefit of CO2 enrichment’

Tipping points of gastric pH regulation and energetics in the sea urchin larva exposed to CO2 induced seawater acidification

Highlights

• We determined the sensitivity thresholds for survival development and growth in sea urchin larvae exposed to acidified conditions.

• Determination of physiological parameters including midgut pH homeostasis, metabolic rates and expression of midgut acid-base transporters demonstrates a physiological tipping point at pH 7.2.

• This work demonstrates substantial resilience of an important environmental engineer to the ongoing phenomenon of ocean acidification.

Abstract

Sea urchin larvae reduce developmental rates accompanied by changes in their energy budget when exposed to acidified conditions. The necessity to maintain highly alkaline conditions in their digestive systems led to the hypothesis that gastric pH homeostasis is a key trait affecting larval energy budgets leading to distinct tipping points for growth and survival.

To test this hypothesis, sea urchin larvae were reared for 10 days in different pH conditions ranging from pH 7.0 to pH 8.2. Survival, development and growth rates were determined demonstrating severe impacts < pH 7.2. To test the effects of pH on midgut alkalization we measured midgut pH and monitored the expression of acid-base transporters. While larvae were able to maintain their midgut pH at 8.9–9.1 up to an acidification level of pH 7.2, midgut pH was decreased in the lower pH treatments. The maintenance of midgut pH under low pH conditions was accompanied by dynamic changes in the expression level of midgut acid-base transporters. Metabolic rates of the larvae increased with decreasing pH and reached a threshold between pH 7.0 and pH 7.3 where metabolic rates decreased again. Methylation analyses on promoter CpG islands were performed for midgut acid-base transporter genes to test for possible epigenetic modifications after 10-day exposure to different pH conditions. This analysis demonstrated no correlation between methylation level and pH treatments suggesting low potential for epigenetic modification of acid-base transporters upon short-term exposure. Since a clear tipping point was identified at pH 7.2, which is much lower than near-future OA scenarios, this study suggests that the early development of the purple sea urchin larva has a comparatively high tolerance to seawater acidification with substantial acclimation capacity and plasticity in a key physiological trait under near-future OA conditions.

Continue reading ‘Tipping points of gastric pH regulation and energetics in the sea urchin larva exposed to CO2 induced seawater acidification’

Responses of carbonic anhydrases and Rubisco to abrupt CO2 changes of seawater in two marine diatoms

Diatoms are experiencing striking fluctuations in seawater carbonate chemistry in the natural marine environment, especially in coastal seawaters. Here, we show that the diatoms Thalassiosira weissflogii and Phaeodactylum tricornutum, which utilize different carbon acquisition mechanisms, respond differently to short-term changes in seawater carbonate chemistry. Our results showed that T. weissflogii showed significantly higher photosynthetic oxygen evolution rates than that of P. tricornutum at low levels of CO2 or HCO3−. This suggests that T. weissflogii had higher affinities for CO2 or HCO3− when their concentrations were not sufficient to support saturated growth and photosynthesis. While the activity of Rubisco in P. tricornutum positively correlated with carbonic anhydrases (CA), we observed negative relationship between Rubisco and CA activity in the diatom T. weissflogii. These contrasting physiological responses of diatoms with varied carbon acquisition mechanisms indicate different abilities to cope up with abrupt changes in seawater carbonate chemistry. We propose that the ability to respond to varying carbonate chemistry may act as one determinant of the diatom distributions and phytoplankton community structures.

Continue reading ‘Responses of carbonic anhydrases and Rubisco to abrupt CO2 changes of seawater in two marine diatoms’

Effect of increased CO2 concentration on the growth rate of Isopora palifera and Acropora hyacinthus from different cross-shelf reef zones

The rise in atmospheric carbon dioxide (CO2) concentration due to emissions
associated with economic development is altering ocean chemistry, a process known as ocean acidification. The resultant decrease in oceanic pH will affect marine organisms, in particular those which build their skeletons through calcification such as scleractinian corals. The aim of this research was to analyse the likely impact of changing CO2 concentrations and thus seawater pH on the growth rate of two common corals, Isopora palifera and Acropora hyacinthus. This research was conducted at the Marine, Coastal and Small Island Research
Centre, Universitas Hasanuddin, Indonesia. Samples of Isopora palifera and Acropora hyacinthus were collected along an inshore-offshore cross-shelf gradient from 3 sites: Pulau Karanrang (inner zone), Pulau Badi (intermediate zone), and Pulau Kapoposang (outer zone). A fully randomised research design was used with three replicates for each of three CO2 treatments: 390 ppm (control), 550 ppm (2030 prediction), 1000 ppm (2050 prediction). The samples were weighed weekly for 1 month (digital balance, accuracy 0.1 mg). ANOVA analysis with post hoc Tukey Test showed a significant (p < 0.05) between treatment difference in growth rate for both Isopora palifera and Acropora hyacinthus (P<0,05). The corals from all three zones exhibited positive growth at 390 ppm CO2, and negative growth at CO2 concentrations of 550 ppm and 1000 ppm.

Continue reading ‘Effect of increased CO2 concentration on the growth rate of Isopora palifera and Acropora hyacinthus from different cross-shelf reef zones’

Common Caribbean corals exhibit highly variable responses to future acidification and warming

We conducted a 93-day experiment investigating the independent and combined effects of acidification (280−3300 µatm pCO2) and warming (28°C and 31°C) on calcification and linear extension rates of four key Caribbean coral species (Siderastrea sidereaPseudodiploria strigosaPorites astreoidesUndaria tenuifolia) from inshore and offshore reefs on the Belize Mesoamerican Barrier Reef System. All species exhibited nonlinear declines in calcification rate with increasing pCO2. Warming only reduced calcification in Ps. strigosa. Of the species tested, only S. siderea maintained positive calcification in the aragonite-undersaturated treatment. Temperature and pCO2 had no effect on the linear extension of S. siderea and Po. astreoides, and natal reef environment did not impact any parameter examined. Results suggest that S. siderea is the most resilient of these corals to warming and acidification owing to its ability to maintain positive calcification in all treatments, Ps. strigosa and U. tenuifolia are the least resilient, and Po. astreoides falls in the middle. These results highlight the diversity of calcification responses of Caribbean corals to projected global change.

Continue reading ‘Common Caribbean corals exhibit highly variable responses to future acidification and warming’

Diverse responses of sporophytic photochemical efficiency and gametophytic growth for two edible kelps, Saccharina japonica and Undaria pinnatifida, to ocean acidification and warming

Highlights

• Increased pCO2 enhanced sporophytic photosynthesis of S. japonica and U. pinnatifida.
• Increased pCO2 inhibited gametophytic growth of these two kelps.
• Ocean acidification and warming represent major threats to kelp mariculture.
• U. pinnatifida showed higher productivity in warmer ocean than S. japonica.

Abstract

Ocean acidification and warming represent major environmental threats to kelp mariculture. In this study, sporophytic photochemical efficiency and gametophytic growth of Saccharina japonica and Undaria pinnatifidawere evaluated under different pCO2 levels (360, 720, and 980 ppmv) and temperatures (5, 10, 15, and 20 °C for sporophytes; 15 and 20 °C for gametophytes). Sporophytic photochemical efficiencies of both kelps were significantly greater at 720 ppmv than at 360 and 980 ppmv. Female gametophytes of both kelps grew significantly better at 360 ppmv than at higher pCO2 levels. The growth of U. pinnatifida gametophytes was significantly greater at 20 °C than at 15 °C, while no significant difference was observed for the growth of S. japonica. These results indicate that increased pCO2 stimulated sporophytic photochemical efficiency while inhibited gametophytic growth of these kelps, which might negatively affect their seedling cultivation. U. pinnatifida exhibited higher productivity in warmer ocean than S. japonica.

Continue reading ‘Diverse responses of sporophytic photochemical efficiency and gametophytic growth for two edible kelps, Saccharina japonica and Undaria pinnatifida, to ocean acidification and warming’

Knockdown of carbonate anhydrase elevates Nannochloropsis productivity at high CO2 level

Highlights

• In the industrial oleaginous microalga Nannochloropsis oceanica, a cytosolic carbonic anhydrase (CA2) was identified as a key Carbon Concentrating Mechanism (CCM) component induced in response to lowered CO2 level.

• Knockdown of CA2 resulted in ~40% elevation of biomass accumulation rate under 5% CO2 (versus the wild type), which is reproducible across photobioreactor types and cultivation scales.

• The higher pH tolerance of CA2-knockdown mutant is underpinned by reduced biophysical CCM, sustained pH hemostasis, stimulated energy intake and enhanced photosynthesis.

• “Inactivation of CCM” is an effective strategy to generate hyper-CO2-assimilating and autonomously containable industrial microalgae for flue gas-based oil production.

Abstract

Improving acid tolerance is pivotal to the development of microalgal feedstock for converting flue gas to biomass or oils. In the industrial oleaginous microalga Nannochloropsis oceanica, transcript knockdown of a cytosolic carbonic anhydrase (CA2), which is a key Carbon Concentrating Mechanism (CCM) component induced under 100 ppm CO2 (very low carbon, or VLC), results in ∼45%, ∼30% and ∼40% elevation of photosynthetic oxygen evolution rate, growth rate and biomass accumulation rate respectively under 5% CO2 (high carbon, or HC), as compared to the wild type. Such high-CO2-level activated biomass over-production is reproducible across photobioreactor types and cultivation scales. Transcriptomic, proteomic and physiological changes of the mutant under high CO2 (HC; 5% CO2) suggest a mechanism where the higher pH tolerance is coupled to reduced biophysical CCM, sustained pH hemostasis, stimulated energy intake and enhanced photosynthesis. Thus “inactivation of CCM” can generate hyper-CO2-assimilating and autonomously containable industrial microalgae for flue gas-based oil production.

Continue reading ‘Knockdown of carbonate anhydrase elevates Nannochloropsis productivity at high CO2 level’


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OA-ICC HIGHLIGHTS

Ocean acidification in the IPCC AR5 WG II

OUP book