Posts Tagged 'primary production'

Common reef-building coral in the Northern Red Sea resistant to elevated temperature and acidification

Coral reefs are currently experiencing substantial ecological impoverishment as a result of anthropogenic stressors, and the majority of reefs are facing immediate risk. Increasing ocean surface temperatures induce frequent coral mass bleaching events—the breakdown of the nutritional photo-symbiosis with intracellular algae (genus: Symbiodinium). Here, we report that Stylophora pistillata from a highly diverse reef in the Gulf of Aqaba showed no signs of bleaching despite spending 1.5 months at 1–2°C above their long-term summer maximum (amounting to 11 degree heating weeks) and a seawater pH of 7.8. Instead, their symbiotic dinoflagellates exhibited improved photochemistry, higher pigmentation and a doubling in net oxygen production, leading to a 51% increase in primary productivity. Nanoscale secondary ion mass spectrometry imaging revealed subtle cellular-level shifts in carbon and nitrogen metabolism under elevated temperatures, but overall host and symbiont biomass proxies were not significantly affected. Now living well below their thermal threshold in the Gulf of Aqaba, these corals have been evolutionarily selected for heat tolerance during their migration through the warm Southern Red Sea after the last ice age. This may allow them to withstand future warming for a longer period of time, provided that successful environmental conservation measures are enacted across national boundaries in the region.

Continue reading ‘Common reef-building coral in the Northern Red Sea resistant to elevated temperature and acidification’

Effects of ocean acidification on the physiological performance and carbon production of the Antarctic sea ice diatom Nitzschia sp. ICE-H

Ocean acidification (OA) resulting from increasing atmospheric CO2 strongly influences marine ecosystems, particularly in the polar ocean due to greater CO2 solubility. Here, we grew the Antarctic sea ice diatom Nitzschia sp. ICE-H in a semicontinuous culture under low (~ 400 ppm) and high (1000 ppm) CO2 levels. Elevated CO2 resulted in a stimulated physiological response including increased growth rates, chlorophyll a contents, and nitrogen and phosphorus uptake rates. Furthermore, high CO2 enhanced cellular particulate organic carbon production rates, indicating a greater shift from inorganic to organic carbon. However, the cultures grown in high CO2 conditions exhibited a decrease in both extracellular and intracellular carbonic anhydrase activity, suggesting that the carbon concentrating mechanisms of Nitzschia sp. ICE-H may be suppressed by elevated CO2. Our results revealed that OA would be beneficial to the survival of this sea ice diatom strain, with broad implications for global carbon cycles in the future ocean.

Continue reading ‘Effects of ocean acidification on the physiological performance and carbon production of the Antarctic sea ice diatom Nitzschia sp. ICE-H’

Elevated CO2 and associated seawater chemistry do not benefit a model diatom grown with increased availability of light

Elevated CO2 is leading to a decrease in pH in marine environments (ocean acidification [OA]), altering marine carbonate chemistry. OA can influence the metabolism of many marine organisms; however, no consensus has been reached on its effects on algal photosynthetic carbon fixation and primary production. Here, we found that when the diatom Phaeodactylum tricornutum was grown under different pCO2 levels, it showed different responses to elevated pCO2 levels under growth-limiting (20 µmol photons m-2 s-1, LL) compared with growth-saturating (200 µmol photons m-2 s-1, HL) light levels. With pCO2 increased up to 950 µatm, growth rates and primary productivity increased, but in the HL cells, these parameters decreased significantly at higher concentrations up to 5000 µatm, while no difference in growth was observed with pCO2 for the LL cells. Elevated CO2 concentrations reduced the size of the intracellular dissolved inorganic carbon (DIC) pool by 81% and 60% under the LL and HL levels, respectively, with the corresponding photosynthetic affinity for DIC decreasing by 48% and 55%. Little photoinhibition was observed across all treatments. These results suggest that the decreased growth rates under higher CO2 levels in the HL cells were most likely due to acid stress. Low energy demand of growth and energy saving from the down-regulation of the CO2 concentrating mechanisms (CCM) minimized the effects of acid stress on the growth of the LL cells. These findings imply that OA treatment, except for down-regulating CCM, caused stress on the diatom, reflected in diminished C assimilation and growth rates.

Continue reading ‘Elevated CO2 and associated seawater chemistry do not benefit a model diatom grown with increased availability of light’

The regulation of coralline algal physiology, an in-situ study of Corallina officinalis (Corallinales, Rhodophyta)

Calcified macroalgae are critical components of marine ecosystems worldwide, but face considerable threat both from climate change (increasing water temperatures) and ocean acidification (decreasing ocean pH and carbonate saturation). It is thus fundamental to constrain the relationships between key abiotic stressors and the physiological processes that govern coralline algal growth and survival. Here we characterize the complex relationships between the abiotic environment of rock pool habitats, and the physiology of the geniculate red coralline alga, Corallina officinalis (Corallinales, Rhodophyta). Paired assessment of irradiance, water temperature and carbonate chemistry, with C. officinalis net production (NP), respiration (R) and net calcification (NG) was performed in a south-west UK field site, at multiple temporal scales (seasonal, diurnal and tidal). Strong seasonality was observed in NP and night-time R, with a Pmax of 22.35 μmol DIC gDW−1 h−1, Ek of 300 μmol photons m−2 s−1 and R of 3.29 μmol DIC gDW−1 −1 determined across the complete annual cycle. NP showed a significant exponential relationship with irradiance (R2 = 0.67), although was temperature dependent given ambient irradiance > Ek for the majority of the annual cycle. Over tidal emersion periods, dynamics in NP highlighted the ability of C. officinalis to acquire inorganic carbon despite significant fluctuations in carbonate chemistry. Across all data, NG was highly predictable (R2 = 0.80) by irradiance, water temperature and carbonate chemistry, providing a NGmax of 3.94  μmol CaCO3 gDW−1 h−1, and Ek of 113 μmol photons m−2 s−1. Light-NG showed strong seasonality and significant coupling to NP (R2 = 0.65), as opposed to rock pool water carbonate saturation. In contrast, the direction of dark-NG (dissolution vs. precipitation) was strongly related to carbonate saturation, mimicking abiotic precipitation dynamics. Data demonstrated that C. officinalis is adapted to both long-term (seasonal) and short-term (tidal) variability in environmental stressors, although the balance between metabolic processes and the external environment may be significantly impacted by future climate change.

Continue reading ‘The regulation of coralline algal physiology, an in-situ study of Corallina officinalis (Corallinales, Rhodophyta)’

Independence of nutrient limitation and carbon dioxide impacts on the Southern Ocean coccolithophore Emiliania huxleyi

Future oceanic conditions induced by anthropogenic greenhouse gas emissions include warming, acidification and reduced nutrient supply due to increased stratification. Some parts of the Southern Ocean are expected to show rapid changes, especially for carbonate mineral saturation. Here we compare the physiological response of the model coccolithophore Emiliania huxleyi (strain EHSO 5.14, originating from 50oS, 149oE) with pH/CO2 gradients (mimicking ocean acidification ranging from 1 to 4 × current pCO2 levels) under nutrient-limited (nitrogen and phosphorus) and -replete conditions. Both nutrient limitations decreased per cell photosynthesis (particulate organic carbon (POC) production) and calcification (particulate inorganic carbon (PIC) production) rates for all pCO2 levels, with more than 50% reductions under nitrogen limitation. These impacts, however, became indistinguishable from nutrient-replete conditions when normalized to cell volume. Calcification decreased three-fold and linearly with increasing pCO2 under all nutrient conditions, and was accompanied by a smaller ~30% nonlinear reduction in POC production, manifested mainly above 3 × current pCO2. Our results suggest that normalization to cell volume allows the major impacts of nutrient limitation (changed cell sizes and reduced PIC and POC production rates) to be treated independently of the major impacts of increasing pCO2 and, additionally, stresses the importance of including cell volume measurements to the toolbox of standard physiological analysis of coccolithophores in field and laboratory studies.

Continue reading ‘Independence of nutrient limitation and carbon dioxide impacts on the Southern Ocean coccolithophore Emiliania huxleyi’

Boosted food web productivity through ocean acidification collapses under warming

Future climate is forecast to drive bottom-up (resource driven) and top-down (consumer driven) change to food web dynamics and community structure. Yet, our predictive understanding of these changes is hampered by an over-reliance on simplified laboratory systems centred on single trophic levels. Using a large mesocosm experiment, we reveal how future ocean acidification and warming modify trophic linkages across a three-level food web: that is, primary (algae), secondary (herbivorous invertebrates) and tertiary (predatory fish) producers. Both elevated CO2 and elevated temperature boosted primary production. Under elevated CO2, the enhanced bottom-up forcing propagated through all trophic levels. Elevated temperature, however, negated the benefits of elevated CO2 by stalling secondary production. This imbalance caused secondary producer populations to decline as elevated temperature drove predators to consume their prey more rapidly in the face of higher metabolic demand. Our findings demonstrate how anthropogenic CO2 can function as a resource that boosts productivity throughout food webs, and how warming can reverse this effect by acting as a stressor to trophic interactions. Understanding the shifting balance between the propagation of resource enrichment and its consumption across trophic levels provides a predictive understanding of future dynamics of stability and collapse in food webs and fisheries production.

Continue reading ‘Boosted food web productivity through ocean acidification collapses under warming’

Moving ocean acidification research beyond a simple science: investigating ecological change and their stabilizers

The response of complex ecological communities to ocean acidification reflects interactions among species that propagate or dampen ecological change. Yet, most studies have been based on short-term experiments with limited numbers of interacting species. Both limitations tend to exaggerate measured effects and when combined with our predisposition for investigating change, we reduce insight into pathways of stability, acclimation and adaptation. Here, we review accepted and emerging insights into processes that drive ecological change (top-down and bottom-up) and the stabilizing processes by which ecological complexity may dampen change. With an emphasis on kelp forest examples, we show that boosted primary productivity from enriched CO2 creates competitive imbalances that drive habitat change, but we also recognise intensifying herbivory on these habitats dampens this change. Foraging herbivores thrive on CO2 enriched plants and over successive generations their populations expand. When we consider such population level responses, we open new questions regarding density-effects (e.g. competition, susceptibility to predation and disease), as well as the bottom-up benefits to predators. Nevertheless, research on predators has lagged behind because their wide-ranging behaviour typically imposes logistical difficulties for observational and experimental research. We know that ocean warming imposes elevated metabolic costs on their foraging whilst acidification hampers navigation of their larvae towards suitable habitat and impairs their hunting and avoidance of predators as adults. Connecting such top-down with bottom-up responses is fundamental for progress, and is also contingent on understanding the mechanisms that dampen change. These stabilizers have the potential to keep pace with abiotic change and thereby influence the drivers of acclimation and adaption. Certainly, we acknowledge that investigating change is often simpler and associated bold messages appeal to citation impact. Yet, if we are to anticipate the ability of complex ecological communities to persist in changing environments, then understanding the shifting balance between the propagation of resource enrichment and its consumption across trophic levels is central to this challenge.

Continue reading ‘Moving ocean acidification research beyond a simple science: investigating ecological change and their stabilizers’


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OA-ICC HIGHLIGHTS

Ocean acidification in the IPCC AR5 WG II

OUP book