Short-term effects of CO2-induced low pH exposure on target gene expression in Platynereis dumerilii

Objective: Increasing atmospheric CO2 concentration are causing changes to the seawater carbonate chemistry, lowering the pH and we study potential impacts of these changes at the molecular level in a non-calcifying, marine polychaete species Platynereis dumerilii.

Methods: We investigate the relative expression of carbonic anhydrase (CA), Na+/H+ exchangers (NHE), and calmodulin (CaM) genes from P. dumerilii under acidified seawater conditions (pH 7.8) induced by CO2 using qPCR.

Results: mRNA expression of CA in the CO2-induced worms was significantly up-regulated at low pH conditions (pH 7.8, 1h), suggesting changes in acid-base balance. In contrast, the expression of NHE and CaM showed no significant change. In addition, we compare these results to a previous study using inorganic acid (HCl)-induced pH changes.

Conclusions: Results suggest that carbonate chemistry has an impact on gene expression that differs from pH-associated change. To our knowledge, this is the first study that compares low pH exposure experiments using HCl and CO2 as the inducing agents.

Continue reading ‘Short-term effects of CO2-induced low pH exposure on target gene expression in Platynereis dumerilii’

Impact of ocean acidification on Arctic phytoplankton blooms and dimethylsulfide production under simulated ice-free and under-ice conditions

In an experimental assessment of the potential impact of Arctic Ocean acidification on seasonal phytoplankton blooms and associated dimethylsulfide (DMS) dynamics, we incubated water from Baffin Bay under conditions representing an acidified Arctic Ocean. Using two light regimes simulating under-ice/ subsurface chlorophyll maxima (low light; Low PAR and no UVB) and ice-free (high light; High PAR + UVA + UVB) conditions, water collected at 38 m was exposed over 9 days to 6 levels of decreasing pH from 8.1 to 7.2. A phytoplankton bloom dominated by the centric diatoms Chaetoceros spp. reaching up to 7.5 µg chlorophyll a L−1 took place in all experimental bags. Total dimethylsulfoniopropionate (DMSPT) and DMS concentrations reached 155 nmol L−1 and 19 nmol L−1, respectively. Under both light regimes, chlorophyll a and DMS concentrations decreased linearly with increasing proton concentration at all pH tested. Concentrations of DMSPT also decreased but only under high light and over a smaller pH range (from 8.1 to 7.6). In contrast to nanophytoplankton (2–20 µm), picophytoplankton (≤ 2 µm) was stimulated by the decreasing pH. We furthermore observed no significant difference between the two light regimes tested in term of chlorophyll a, phytoplankton abundance/ taxonomy, and DMSP/ DMS net concentrations. These results show that OA could significantly decrease the algal biomass and inhibit DMS production during the seasonal phytoplankton bloom in the Arctic, with possible consequences for the regional climate.

Continue reading ‘Impact of ocean acidification on Arctic phytoplankton blooms and dimethylsulfide production under simulated ice-free and under-ice conditions’

Take the time and effort to correct misinformation

Scientists should challenge online falsehoods and inaccuracies — and harness the collective power of the Internet to fight back, argues Phil Williamson.

With the election of Donald Trump, his appointment of advisers who are on record as dismissing scientific evidence, and the emboldening of deniers on everything from climate change to vaccinations, the amount of nonsense written about science on the Internet (and elsewhere) seems set to rise. So what are we, as scientists, to do?

Most researchers who have tried to engage online with ill-informed journalists or pseudoscientists will be familiar with Brandolini’s law (also known as the Bullshit Asymmetry Principle): the amount of energy needed to refute bullshit is an order of magnitude bigger than that needed to produce it. Is it really worth taking the time and effort to challenge, correct and clarify articles that claim to be about science but in most cases seem to represent a political ideology?

I think it is. Challenging falsehoods and misrepresentation may not seem to have any immediate effect, but someone, somewhere, will hear or read our response. The target is not the peddler of nonsense, but those readers who have an open mind on scientific problems. A lie may be able to travel around the world before the truth has its shoes on, but an unchallenged untruth will never stop.

Continue reading ‘Take the time and effort to correct misinformation’

From the eMail Bag: CO2 in the air and oceans

We recently received an email from Jeffrey Middlebrook who asked about the dynamics of CO2 transport from the atmosphere to the oceans:

…as atmospheric water vapor increases with CO2-driven atmospheric warming, there will be more CO2 capture by the increased water vapor (yielding more carbonic acid) which will transfer more CO2 to the oceans, thereby decreasing the effects of atmospheric CO2 as a greenhouse gas, and with greater precipitation due to more atmospheric water vapor more atmospheric heat will be transferred to the oceans and terrestrial landscapes. It seems plausible that the increases in atmospheric water vapor due to increases in atmospheric CO2 might just produce a strong negative feedback.

About 46% of human emissions of CO2 stay in the atmosphere, while ~26% makes its way to the oceans, and ~28% is used by plants. Our emissions of CO2 may be good for plants (at least for now) but the additional CO2 in the oceans is leading to climate change’s “evil twin”: ocean acidification. (For much more about ocean acidification see our series: OA is not OK.)

Think of how large the world oceans are, and the vast ocean surface in contact with the equally vast atmosphere. The oceans primarily absorb CO2 directly from the atmosphere because of the differences in partial pressure across the ocean’s “cool skin” layer. If there is more CO2 in a parcel of air than there is in a parcel of water, then the water absorbs more CO2 until there is an equilibrium between the two (Henry’s law, see Figure 1). Temperature also plays a role since warmer water holds less CO2 than cooler water.

Continue reading ‘From the eMail Bag: CO2 in the air and oceans’

INTERVIEW – Le prince Albert explique au Figaro les raisons de son engagement pour la protection des mers (in French)

Du mardi 6 au vendredi 9 décembre se tient à Monaco la réunion préparatoire du rapport spécial du Giec (Groupe d’experts intergouvernemental sur l’évolution du climat) sur les océans et la cryosphère. Un événement organisé avec le soutien du gouvernement princier de Monaco, signe de la très forte implication du prince Albert II sur ces sujets environnementaux.

La question des océans et celle des glaciers sont des points essentiels dans la compréhension des enjeux climatiques. En dehors du sixième rapport général du Giec dont les trois volumes seront présentés en 2021 et 2022, trois rapports spéciaux sont en préparation. «Nous avons reçu 31 propositions de rapports spéciaux, raconte la paléoclimatologue Valérie Masson-Delmotte (CEA/CNRS/IPSL) qui est l’une des vice-présidentes du groupe de travail, et plusieurs de ces propositions avaient un lien avec ces deux enjeux que sont les océans et … (…)

Continue reading ‘INTERVIEW – Le prince Albert explique au Figaro les raisons de son engagement pour la protection des mers (in French)’

The reproductive and physiological condition of a deep-sea mussel (Bathymodiolus septemdierum Hashimoto and Okutani, 1994) living in extremely acidic conditions

Oceanic uptake of anthropogenic CO2 emissions is causing wholesale shifts seawater carbonate chemistry towards a state of decreased carbonate ion concentration and reduced ocean pH. This change in water chemistry has potentially dire implications for marine organisms, especially those that build and maintain calcium carbonate structures. Our understanding of how ocean acidification may affect marine organisms is limited, as most studies have been short-term laboratory experiments. The CO2 flux from hydrothermal vent fluids on NW Eifuku submarine volcano (Mariana Volcanic Arc) provides a natural setting to investigate the effects of acidification. Here, the vent mussel, Bathymodiolus septemdierum, lives in water with pH as low as 5.22. This study was designed to examine the consequences of a low pH environment on reproduction, calcification and somatic growth in B. septemdierum, since the presumed elevated cost of acid-base regulation may diminish available energy for these processes. Histological analysis reveals both females and males display synchronous gametogenesis across collection sites with spawning occurring between late winter and early spring. Mussels are functionally dioecious, although evidence of protogynous hermaphroditism was found– a first record for the genus. In comparison with mussels at near normal pH, we find no evidence that the pattern of gametogenesis is affected by low pH conditions. However, calcification is compromised: at a given shell volume, shells from NW Eifuku weigh about half those from sites with near normal pH mussels. The condition index (CI = body ash free dry weight/ shell volume) was assessed in mussels collected from four low pH sites on Northwest Eifuku and two control sites from Lau Basin and Nifonea Ridge; we show that low pH conditions negatively affect CI, especially when energy availability is limited. Bathymodiolus septemdierum acquires energy from chemoautotrophic symbionts in the specialized gill epithelial cells. Using a gill condition index (GCI = gill ash free dry weight/ shell volume) and transmission electron microscopy to determine symbiont abundances in gill tissues, we show that NW Eifuku mussels with healthy gills and abundant symbionts have a higher CI than mussels from NW Eifuku with unhealthy gills. Optimal environmental sulphide concentrations appear to sustain higher symbiont abundances. While the survival of mussels on NW Eifuku is remarkable, it can come at a considerable cost to body and shell condition when during periods of energy limitation. Bathymodiolus septemdierum shows substantial resilience to low pH conditions when energy availability is sufficient due to energy budget adjustments that maximize fitness.

Continue reading ‘The reproductive and physiological condition of a deep-sea mussel (Bathymodiolus septemdierum Hashimoto and Okutani, 1994) living in extremely acidic conditions’

Seagrass (Posidonia oceanica) seedlings in a high-CO2 world: from physiology to herbivory

Under future increased CO2 concentrations, seagrasses are predicted to perform better as a result of increased photosynthesis, but the effects in carbon balance and growth are unclear and remain unexplored for early life stages such as seedlings, which allow plant dispersal and provide the potential for adaptation under changing environmental conditions. Furthermore, the outcome of the concomitant biochemical changes in plant-herbivore interactions has been poorly studied, yet may have important implications in plant communities. In this study we determined the effects of experimental exposure to current and future predicted CO2 concentrations on the physiology, size and defense strategies against herbivory in the earliest life stage of the Mediterranean seagrass Posidonia oceanica. The photosynthetic performance of seedlings, assessed by fluorescence, improved under increased pCO2 conditions after 60 days, although these differences disappeared after 90 days. Furthermore, these plants exhibited bigger seeds and higher carbon storage in belowground tissues, having thus more resources to tolerate and recover from stressors. Of the several herbivory resistance traits measured, plants under high pCO2 conditions had a lower leaf N content but higher sucrose. These seedlings were preferred by herbivorous sea urchins in feeding trials, which could potentially counteract some of the positive effects observed.

Continue reading ‘Seagrass (Posidonia oceanica) seedlings in a high-CO2 world: from physiology to herbivory’


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Ocean acidification in the IPCC AR5 WG II

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