Posts Tagged 'laboratory'

Interactive effects of seawater carbonate chemistry, light intensity and nutrient availability on physiology and calcification of the coccolithophore Emiliania huxleyi

Rising atmospheric carbonate dioxide (CO2) levels lead to increasing CO2 concentration and declining pH in seawater, as well as ocean warming. This enhances stratification and shoals the upper mixed layer (UML), hindering the transport of nutrients from deeper waters and exposing phytoplankton to increased light intensities. In the present study, we investigated combined impacts of CO2 levels (410 μatm (LC) and 925 μatm (HC)), light intensities (80–480 μmol photons m−2 s−1) and nutrient concentrations [101 μmol L−1 dissolved inorganic nitrogen (DIN) and 10.5 μmol L−1 dissolved inorganic phosphate (DIP) (HNHP); 8.8 μmol L−1 DIN and 10.5 μmol L−1 DIP (LN); 101 μmol L−1 DIN and 0.4 μmol L−1 DIP (LP)] on growth, photosynthesis and calcification of the coccolithophore Emiliania huxleyi. HC and LN synergistically decreased growth rates of E. huxleyi at all light intensities. High light intensities compensated for inhibition of LP on growth rates at LC, but exacerbated inhibition of LP at HC. These results indicate that the ability of E. huxleyi to compete for nitrate and phosphate may be reduced in future oceans with high CO2 and high light intensities. Low nutrient concentrations increased particulate inorganic carbon quotas and the sensitivity of maximum electron transport rates to light intensity. Light-use efficiencies for carbon fixation and calcification rates were significantly larger than that of growth. Our results suggest that interactive effects of multiple environmental factors on coccolithophores need to be considered when predicting their contributions to the biological carbon pump and feedbacks to climate change.

Continue reading ‘Interactive effects of seawater carbonate chemistry, light intensity and nutrient availability on physiology and calcification of the coccolithophore Emiliania huxleyi’

Simultaneous shifts in elemental stoichiometry and fatty acids of Emiliania huxleyi in response to environmental changes

Climate-driven changes in environmental conditions have significant and complex effects on marine ecosystems. Variability in phytoplankton elements and biochemicals can be important for global ocean biogeochemistry and ecological functions, while there is currently limited understanding on how elements and biochemicals respond to the changing environments in key coccolithophore species such as Emiliania huxleyi. We investigated responses of elemental stoichiometry and fatty acids (FAs) in a strain of E. huxleyi under three temperatures (12, 18 and 24 °C), three N : P supply ratios (molar ratios 10:1, 24:1 and 63:1) and two pCO2 levels (560 and 2400 µatm). Overall, C : N : P stoichiometry showed the most pronounced response to N : P supply ratios, with high ratios of particulate organic carbon vs. particulate organic nitrogen (POC : PON) and low ratios of PON vs. particulate organic phosphorus (PON : POP) in low-N media, and high POC : POP and PON : POP in low-P media. The ratio of particulate inorganic carbon vs. POC (PIC : POC) and polyunsaturated fatty acid proportions strongly responded to temperature and pCO2, both being lower under high pCO2 and higher with warming. We observed synergistic interactions between warming and nutrient deficiency (and high pCO2) on elemental cellular contents and docosahexaenoic acid (DHA) proportion in most cases, indicating the enhanced effect of warming under nutrient deficiency (and high pCO2). Our results suggest differential sensitivity of elements and FAs to the changes in temperature, nutrient availability and pCO2 in E. huxleyi, which is to some extent unique compared to non-calcifying algal classes. Thus, simultaneous changes of elements and FAs should be considered when predicting future roles of E. huxleyi in the biotic-mediated connection between biogeochemical cycles, ecological functions and climate change.

Continue reading ‘Simultaneous shifts in elemental stoichiometry and fatty acids of Emiliania huxleyi in response to environmental changes’

Dimethylsulfide (DMS) production in polar oceans may be resilient to ocean acidification

Emissions of dimethylsulfide (DMS) from the polar oceans play a key role in atmospheric processes and climate. Therefore, it is important we increase our understanding of how DMS production in these regions may respond to environmental change. The polar oceans are particularly vulnerable to ocean acidification (OA). However, our understanding of the polar DMS response is limited to two studies conducted in Arctic waters, where in both cases DMS concentrations decreased with increasing acidity. Here, we report on our findings from seven summertime shipboard microcosm experiments undertaken in a variety of locations in the Arctic Ocean and Southern Ocean. These experiments reveal no significant effects of short term OA on the net production of DMS by planktonic communities. This is in contrast to identical experiments from temperate NW European shelf waters where surface ocean communities responded to OA with significant increases in dissolved DMS concentrations. A meta-analysis of the findings from both temperate and polar waters (n = 18 experiments) reveals clear regional differences in the DMS response to OA. We suggest that these regional differences in DMS response reflect the natural variability in carbonate chemistry to which the respective communities may already be adapted. Future temperate oceans could be more sensitive to OA resulting in a change in DMS emissions to the atmosphere, whilst perhaps surprisingly DMS emissions from the polar oceans may remain relatively unchanged. By demonstrating that DMS emissions from geographically distinct regions may vary in response to OA, our results may facilitate a better understanding of Earth’s future climate. Our study suggests that the way in which processes that generate DMS respond to OA may be regionally distinct and this should be taken into account in predicting future DMS emissions and their influence on Earth’s climate.

Continue reading ‘Dimethylsulfide (DMS) production in polar oceans may be resilient to ocean acidification’

The effects of warming and ocean acidification on growth, photosynthesis, and bacterial communities for the marine invasive macroalga Caulerpa taxifolia

Caulerpa taxifolia is a pantropical green benthic marine macroalga, and one of the best known marine invasive species in temperate coastal habitats. In Australia, this species has been introduced to seven estuaries along New South Wales and one in South Australia. How this alga will perform under future climate change scenarios is however not well defined. This study experimentally assessed the effects of ocean acidification and global warming on the growth, photosynthetic performance and the bacterial community on two populations of C. taxifolia, one native and one invasive. A range of complex significant interactive effects between pH, temperature, and initial plant size on the growth of C. taxifolia were observed, but no effect of population origin and photosystem II (PSII) fluorescence quantum yield parameters were detected. No significant effects of the treatment combinations were observed on bacterial community richness or diversity. Only one bacterial species out of 1087 present on the algae showed significant changes between pH treatments at high temperature (24°C). This bacterium belonged to the genus Planctomyces and its relative abundance was more than 10 times higher in samples with low pH compared to the control. Higher plant growth was observed under all higher pCO2 and lower pH conditions suggesting that C. taxifolia will benefit from climate change, posing a potential higher risk in invaded locations.

Continue reading ‘The effects of warming and ocean acidification on growth, photosynthesis, and bacterial communities for the marine invasive macroalga Caulerpa taxifolia’

Resilience by diversity: large intraspecific differences in climate change responses of an Arctic diatom

The potential for adaptation of phytoplankton to future climate is often extrapolated based on single strain responses of a representative species, ignoring variability within and between species. The aim of this study was to approximate the range of strain-specific reaction patterns within an Arctic diatom population, which selection can act upon. In a laboratory experiment, we first incubated natural communities from an Arctic fjord under present and future conditions. In a second step, single strains of the diatom Thalassiosira hyalina were isolated from these selection environments and exposed to a matrix of temperature (3°C and 6°C) and pCO2 levels (180 μatm, 370 μatm, 1000 μatm, 1400 μatm) to establish reaction norms for growth, production rates, and elemental quotas. The results revealed interactive effects of temperature and pCO2 as well as wide tolerance ranges. Between strains, however, sensitivities and optima differed greatly. These strain-specific responses corresponded well with their respective selection environments of the previous community incubation. We therefore hypothesize that intraspecific variability and the selection between coexisting strains may pose an underestimated source of species’ plasticity. Thus, adaptation of phytoplankton assemblages may also occur by selection within rather than only between species, and species-wide inferences from single strain experiments should be treated with caution.

Continue reading ‘Resilience by diversity: large intraspecific differences in climate change responses of an Arctic diatom’

Ocean acidification but not warming alters sex determination in the Sydney rock oyster, Saccostrea glomerata

Whether sex determination of marine organisms can be altered by ocean acidification and warming during this century remains a significant, unanswered question. Here, we show that exposure of the protandric hermaphrodite oyster, Saccostrea glomerata to ocean acidification, but not warming, alters sex determination resulting in changes in sex ratios. After just one reproductive cycle there were 16% more females than males. The rate of gametogenesis, gonad area, fecundity, shell length, extracellular pH and survival decreased in response to ocean acidification. Warming as a sole stressor slightly increased the rate of gametogenesis, gonad area and fecundity, but this increase was masked by the impact of ocean acidification at a level predicted for this century. Alterations to sex determination, sex ratios and reproductive capacity will have flow on effects to reduce larval supply and population size of oysters and potentially other marine organisms.

Continue reading ‘Ocean acidification but not warming alters sex determination in the Sydney rock oyster, Saccostrea glomerata’

Rapid evolution of highly variable competitive abilities in a key phytoplankton species

Climate change challenges plankton communities, but evolutionary adaptation could mitigate the potential impacts. Here, we tested with the phytoplankton species Emiliania huxleyi whether adaptation to a stressor under laboratory conditions leads to equivalent fitness gains in a more natural environment. We found that fitness advantages that had evolved under laboratory conditions were masked by pleiotropic effects in natural plankton communities. Moreover, new genotypes with highly variable competitive abilities evolved on timescales significantly shorter than climate change.

Continue reading ‘Rapid evolution of highly variable competitive abilities in a key phytoplankton species’


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