Temporal biomass dynamics of an Arctic plankton bloom in response to increasing levels of atmospheric carbon dioxide

Ocean acidification and carbonation, driven by anthropogenic emissions of carbon dioxide (CO₂), have been shown to affect a variety of marine organisms and are likely to change ecosystem functioning. High latitudes, especially the Arctic, will be the first to encounter profound changes in carbonate chemistry speciation at a large scale, namely the under-saturation of surface waters with respect to aragonite, a calcium carbonate polymorph produced by several organisms in this region. During a CO₂ perturbation study in 2010, in the framework of the EU-funded project EPOCA, the temporal dynamics of a plankton bloom was followed in nine mesocosms, manipulated for CO₂ levels ranging initially from about 185 to 1420 μatm. Dissolved inorganic nutrients were added halfway through the experiment. Autotrophic biomass, as identified by chlorophyll a standing stocks (Chl a), peaked three times in all mesocosms. However, while absolute Chl a concentrations were similar in all mesocosms during the first phase of the experiment, higher autotrophic biomass was measured at high in comparison to low CO₂ during the second phase, right after dissolved inorganic nutrient addition. This trend then reversed in the third phase. There were several statistically significant CO₂ effects on a variety of parameters measured in certain phases, such as nutrient utilization, standing stocks of particulate organic matter, and phytoplankton species composition. Interestingly, CO₂ effects developed slowly but steadily, becoming more and more statistically significant with time. The observed CO₂ related shifts in nutrient flow into different phytoplankton groups (mainly diatoms, dinoflagellates, prasinophytes and haptophytes) could have consequences for future organic matter flow to higher trophic levels and export production, with consequences for ecosystem productivity and atmospheric CO₂.

Arctic microbial community dynamics influenced by elevated CO2 levels

The Arctic Ocean ecosystem is particular vulnerable for ocean acidification (OA) related alterations due to the relatively high CO₂ solubility and low carbonate saturation states of its cold surface waters. Thus far, however, there is only little known about the consequences of OA on the base of the food web. In a mesocosm CO₂-enrichment experiment (overall CO₂ levels ranged from ∼180 to 1100 μatm) in the Kongsfjord off Svalbard, we studied the consequences of OA on a natural pelagic microbial community. The most prominent finding of our study is the profound effect of OA on the composition and growth of the Arctic phytoplankton community, i.e. the picoeukaryotic photoautotrophs and to a lesser extent the nanophytoplankton prospered. A shift towards the smallest phytoplankton as a result of OA will have direct consequences for the structure and functioning of the pelagic food web and thus for the biogeochemical cycles. Furthermore, the dominant pico- and nanophytoplankton groups were found prone to viral lysis, thereby shunting the carbon accumulation in living organisms into the dissolved pools of organic carbon and subsequently affecting the efficiency of the biological pump in these Arctic waters.

Impact de l’acidification du milieu marin sur la formation coquillière de l’ormeau Européen Haliotis tuberculata (Mollusques, Vetigastéropodes) (job advert, in French)

Le développement des activités humaines a entraîné une augmentation exponentielle de la concentration en dioxyde de carbone (CO2) atmosphérique qui passerait de 280 ppm avant l’ère industrielle à 560 ppm en 2050 1. Un tiers de l’excès du CO2 est absorbé par les océans, ce qui entraîne une acidification de l’eau. A la fin du siècle, la concentration en CO2 pourrait atteindre selon les prévisions 450 à 650 ppm, et le pH océanique diminuerait encore de 0,2 à 0,3 unité. Il est désormais admis par la communauté scientifique que l’acidification des océans a un impact sur les populations marines, et en particulier sur les organismes calcifiants tels que les Coraux, les Mollusques ou les Echinodermes2. En effet, l’acidification diminue la concentration en ions carbonate, réduisant la capacité de calcification des organismes et induisant la formation d’un squelette plus fragile. Plusieurs études ont montré que l’acidification des océans pourrait entraîner une baisse de 11 à 44% de la calcification chez les métazoaires3. Les effets de l’acidification sur le développement, la croissance et la calcification des organismes marins ont été étudiés chez plusieurs espèces de mollusques marins. L’augmentation de la pCO2 entraîne une diminution significative de la croissance et de la calcification chez les Bivalves, en particulier les coquilles aragonitiques5. Les travaux sur les gastéropodes concernent principalement les effets sur le développement larvaire : chez l’ormeau Haliotis coccoradiata, la combinaison d’une élévation de la température et d’une baisse du pH entraîne une mortalité des embryons et les survivants produisent des larves sans coquille6. Chez l’ormeau californien Haliotis rufescens, l’acidification du milieu entraîne une plus grande sensibilité des larves aux variations de température7.

Ocean acidification and disease: how will a changing climate impact Vibrio tubiashii growth and pathogenicity to Pacific oyster larvae?

Vibrio tubiashii (Vt) is a causative agent of vibriosis in molluscan bivalves. Recent re-emergence of vibriosis in economically valuable shellfish, such as the Pacific oyster (Crassostrea gigas) in Washington State, has increased the urgency to understand the ecology of this pathogen. It is currently unknown how predicted environmental changes associated with ocean acidification, such as elevated surface seawater temperature, increased partial pressure of CO₂ (pCO₂), and Vt abundance will impact marine organismal health and disease susceptibility. This study investigates how environmental cues predicted with ocean acidification influence physiological changes and pathogenicity in Vt. Using laboratory experiments to manipulate temperature and pCO₂, we examined how these environmental factors influenced pathogen growth. Larval susceptibility to vibriosis was determined by exposing C. gigas larvae to a combination of elevated pCO₂ and Vt concentrations. These experiments provide insight into the environmental parameters that may drive pathogenicity or influence proliferation of the bacterium. Investigation of single and multivariate parameters such as temperature, pCO₂, and pathogen levels will help assess how predicted shifts in ocean conditions can impact shellfish survival and disease resistance.

Chance of saving most coral reefs is dwindling -study

70 pct of corals will suffer degradation by 2030
To protect half of reefs, temperature rise must be under 1.5C

LONDON, Sept 16 (Reuters) – The chance to save the world’s coral reefs from damage caused by climate change is dwindling as man-made greenhouse gas emissions continue to rise, scientists said in a study released on Sunday.

Around 70 percent of corals are expected to suffer from long-term degradation by 2030, even if strict emission cuts are enforced, according to the study.

World’s coral reefs at risk from warming waters

Almost all of the world’s coral reefs are at risk unless drastic action is taken to keep temperature rises below 2°C, according to new research.

The study, published in Nature Climate Change, found that unless effective emission reduction policies are implemented urgently approximately two thirds of corals could suffer by 2030.

Most coral reefs are at risk unless climate change is drastically limited

09/16/2012 – Coral reefs face severe challenges even if global warming is restricted to the 2 degrees Celsius commonly perceived as safe for many natural and man-made systems. Warmer sea surface temperatures are likely to trigger more frequent and more intense mass coral bleaching events. Only under a scenario with strong action on mitigating greenhouse-gas emissions and the assumption that corals can adapt at extremely rapid rates, could two thirds of them be safe, shows a study now published in Nature Climate Change. Otherwise all coral reefs are expected to be subject to severe degradation.

Coral reefs house almost a quarter of the species in the oceans and provide critical services –including coastal protection, tourism and fishing – to millions of people worldwide. Global warming and ocean acidification, both driven by human-caused CO2 emissions, pose a major threat to these ecosystems.

Limiting global warming to 2 °C is unlikely to save most coral reefs

Mass coral bleaching events have become a widespread phenomenon causing serious concerns with regard to the survival of corals. Triggered by high ocean temperatures, bleaching events are projected to increase in frequency and intensity. Here, we provide a comprehensive global study of coral bleaching in terms of global mean temperature change, based on an extended set of emissions scenarios and models. We show that preserving >10% of coral reefs worldwide would require limiting warming to below 1.5 °C (atmosphere–ocean general circulation models (AOGCMs) range: 1.3–1.8 °C) relative to pre-industrial levels. Even under optimistic assumptions regarding corals’ thermal adaptation, one-third (9–60%, 68% uncertainty range) of the world’s coral reefs are projected to be subject to long-term degradation under the most optimistic new IPCC emissions scenario, RCP3-PD. Under RCP4.5 this fraction increases to two-thirds (30–88%, 68% uncertainty range). Possible effects of ocean acidification reducing thermal tolerance are assessed within a sensitivity experiment.