Posts Tagged 'light'

A niche comparison of Emiliania huxleyi and Gephyrocapsa oceanica and potential effects of climate change

Coccolithophore responses to changes in carbonate chemistry speciation such as CO2 and H+ are highly modulated by light intensity and temperature. Here we fit an analytical equation, accounting for simultaneous changes in carbonate chemistry speciation, light and temperature, to published and original data for Emiliania huxleyi, and compare the projections with those for Gephyrocapsa oceanica. Based on our analysis, the two most abundant coccolithophores in today’s oceans appear to be adapted for a similar fundamental light niche but slightly different ones for temperature and CO2, with E. huxleyi having a tolerance to lower temperatures and higher CO2 levels than G. oceanica. Based on growth rates, a dominance of E. huxleyi over G. oceanica is projected below temperatures of 22 °C at current atmospheric CO2 levels. This is similar to a global surface sediment compilation of E. huxleyi and G. oceanica coccolith abundances suggesting temperature dependent dominance shifts. For a future RCP 8.5 climate change scenario (1000 μatm fCO2 and +4.8 °C) we project a niche contraction for G. oceanica then being restricted to regions of even higher temperatures. Finally, we compare satellite derived particulate inorganic carbon estimates in the surface ocean with a recently proposed metric for potential coccolithophore success on the community level i.e. the temperature, light and carbonate chemistry dependent CaCO3 production potential (CCPP). Excluding the Antarctic province from the analysis we found a good correlation between CCPP and satellite derived PIC in the other regions with an R2 of 0.73 for Austral winter/Boreal summer and 0.85 for Austral summer/Boreal winter.

Continue reading ‘A niche comparison of Emiliania huxleyi and Gephyrocapsa oceanica and potential effects of climate change’

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’

Environmental controls on the elemental composition of a Southern Hemisphere strain of the coccolithophore Emiliania huxleyi (update)

A series of semi-continuous incubation experiments were conducted with the coccolithophore Emiliania huxleyi strain NIWA1108 (Southern Ocean isolate) to examine the effects of five environmental drivers (nitrate and phosphate concentrations, irradiance, temperature, and partial pressure of CO2 (pCO2)) on both the physiological rates and elemental composition of the coccolithophore. Here, we report the alteration of the elemental composition of E. huxleyi in response to the changes in these environmental drivers. A series of dose–response curves for the cellular elemental composition of E. huxleyi were fitted for each of the five drivers across an environmentally representative gradient. The importance of each driver in regulating the elemental composition of E. huxleyi was ranked using a semi-quantitative approach. The percentage variations in elemental composition arising from the change in each driver between present-day and model-projected conditions for the year 2100 were calculated. Temperature was the most important driver controlling both cellular particulate organic and inorganic carbon content, whereas nutrient concentrations were the most important regulator of cellular particulate nitrogen and phosphorus of E. huxleyi. In contrast, elevated pCO2 had the greatest influence on cellular particulate inorganic carbon to organic carbon ratio, resulting in a decrease in the ratio. Our results indicate that the different environmental drivers play specific roles in regulating the elemental composition of E. huxleyi with wide-reaching implications for coccolithophore-related marine biogeochemical cycles, as a consequence of the regulation of E. huxleyi physiological processes.

Continue reading ‘Environmental controls on the elemental composition of a Southern Hemisphere strain of the coccolithophore Emiliania huxleyi (update)’

Reduced spore germination explains sensitivity of reef-building algae to climate change stressors

Reduced seawater pH and changes in carbonate chemistry associated with ocean acidification (OA) decrease the recruitment of crustose coralline algae (CCAcf.), an important coral-reef builder. However, it is unclear whether the observed decline in recruitment is driven by impairment of spore germination, or post-settlement processes (e.g. space competition). To address this, we conducted an experiment using a dominant CCA, Porolithon cf. onkodes to test the independent and combined effects of OA, warming, and irradiance on its germination success and early development. Elevated CO2 negatively affected several processes of spore germination, including formation of the germination disc, initial growth, and germling survival. The magnitude of these effects varied depending on the levels of temperature and irradiance. For example, the combination of high CO2 and high temperature reduced formation of the germination disc, but this effect was independent of irradiance levels, while spore abnormalities increased under high CO2 and high temperature particularly in combination with low irradiance intensity. This study demonstrates that spore germination of CCA is impacted by the independent and interactive effects of OA, increasing seawater temperature and irradiance intensity. For the first time, this provides a mechanism for how the sensitivity of critical early life history processes to global change may drive declines of adult populations of key marine calcifiers.

Continue reading ‘Reduced spore germination explains sensitivity of reef-building algae to climate change stressors’

Global warming interacts with ocean acidification to alter PSII function and protection in the diatom Thalassiosira weissflogii


  • Global warming increases the photoinactivation rate.
  • Ocean acidification alleviates the effect of global warming on photoinactivation.
  • Global warming does not affect PsbA removal but ocean acidification enhances it.
  • Ocean acidification induces high nonphotochemical quenching.
  • Global warming increases antioxidant systems, but ocean acidification does not


Diatoms, as important contributors to aquatic primary production, are critical to the global carbon cycle. They tend to dominate phytoplankton communities experiencing rapid changes of underwater light. However, little is known regarding how climate change impacts diatoms’ capacity in coping with variable light environments. Here we grew a globally abundant diatom T. weissflogii, under two levels of temperature (18, 24 °C) and pCO2 (400, 1000 μatm), and then treated it with a light challenge to understand the combined effects of ocean warming and acidification on its exploitation of variable light environments. The higher temperature increased the photoinactivation rate at 400 μatm pCO2 and the higher pCO2 alleviated the negative effect of the higher temperature on PSII photoinactivation. Temperature did not affect the PsbA removal rate, but higher pCO2 stimulated PsbA removal. Photoinactivation outran repair, leading to decreased maximum photochemical yield in PSII. The higher pCO2 induced high sustained phase of nonphotochemical quenching when cells were less photoinhibited. The high light exposure induced the activity of both superoxide dismutase (SOD) and catalase (CAT) and the higher temperature stimulated them further, with insignificant effect of pCO2. Our findings suggest that ocean warming, ocean acidification and high light exposure would interact on PSII function and protection, and combination of these three environmental factors would lead to a reduced PSII activity in T. weissflogii. This study provides helpful insight into how climate change variables combined with local stressor impact diatoms’ photosynthetic physiology.

Continue reading ‘Global warming interacts with ocean acidification to alter PSII function and protection in the diatom Thalassiosira weissflogii’

Elevated pCO2 affects tissue biomass composition, but not calcification, in a reef coral under two light regimes

Ocean acidification (OA) is predicted to reduce reef coral calcification rates and threaten the long-term growth of coral reefs under climate change. Reduced coral growth at elevated pCO2 may be buffered by sufficiently high irradiances; however, the interactive effects of OA and irradiance on other fundamental aspects of coral physiology, such as the composition and energetics of coral biomass, remain largely unexplored. This study tested the effects of two light treatments (7.5 versus 15.7 mol photons m−2 d−1) at ambient or elevated pCO2 (435 versus 957 µatm) on calcification, photopigment and symbiont densities, biomass reserves (lipids, carbohydrates, proteins), and biomass energy content (kJ) of the reef coral Pocillopora acuta from Kāne‘ohe Bay, Hawai‘i. While pCO2 and light had no effect on either area- or biomass-normalized calcification, tissue lipids gdw−1 and kJ gdw−1 were reduced 15% and 14% at high pCO2, and carbohydrate content increased 15% under high light. The combination of high light and high pCO2 reduced protein biomass (per unit area) by approximately 20%. Thus, under ecologically relevant irradiances, P. acuta in Kāne‘ohe Bay does not exhibit OA-driven reductions in calcification reported for other corals; however, reductions in tissue lipids, energy content and protein biomass suggest OA induced an energetic deficit and compensatory catabolism of tissue biomass. The null effects of OA on calcification at two irradiances support a growing body of work concluding some reef corals may be able to employ compensatory physiological mechanisms that maintain present-day levels of calcification under OA. However, negative effects of OA on P. acuta biomass composition and energy content may impact the long-term performance and scope for growth of this species in a high pCO2 world.

Continue reading ‘Elevated pCO2 affects tissue biomass composition, but not calcification, in a reef coral under two light regimes’

Effects of the interaction of ocean acidification, solar radiation, and warming on biogenic dimethylated sulfur compounds cycling in the Changjiang River Estuary

Ocean acidification (OA) affects marine primary productivity and community structure, and therefore may influence the biogeochemical cycles of volatile biogenic dimethyl sulfide (DMS) and its precursor dimethylsulfoniopropionate (DMSP) and photochemical oxidation product dimethyl sulfoxide (DMSO). A 23-day incubation experiment on board was conducted to investigate the short-term response of biogenic sulfur compounds production and cycling to OA in the Changjiang River Estuary and further understand its effects on biogenic sulfur compounds. Result showed that phytoplankton abundance and species presented remarkable differences under three different pH levels in the late stage of the experiment. A significant reduction in chlorophyll a (Chl-a), DMS, particulate DMSP (DMSPp), and dissolved DMSO (DMSOd) concentrations was identified under high CO2 levels. Moreover, minimal change was observed in the production of dissolved DMSP (DMSPd) and particulate DMSO (DMSOp) among treatments. The ratios of DMS, total DMSP (DMSPt), and total DMSO (DMSOt) to Chl-a were also not affected by a change in pH. In addition, DMS and DMSOd were highly related to mean bacterial abundance under three pH levels. Additional incubation experiments on light and temperature showed that the influence of pH on productions of dimethylated sulfur compounds also depended on solar radiation and temperature conditions. DMS photodegradation rate increased with decreasing pH under full-spectrum natural light and UVB light. Thus, OA may lead to decreasing DMS concentrations in the surface seawater. Light and temperature conditions also play an important role in the production and cycling of biogenic sulfur compounds.

Continue reading ‘Effects of the interaction of ocean acidification, solar radiation, and warming on biogenic dimethylated sulfur compounds cycling in the Changjiang River Estuary’

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Ocean acidification in the IPCC AR5 WG II

OUP book