La Méditerranée concernée par l’acidification des océans (in French)

Une étude inédite est en préparation près de Nice : elle vise à déterminer comment les coquillages et les plantes aquatiques méditerranéennes réagissent à l’acidification des océans dûe au CO2.

Le gaz carbonique (CO2), émis en quantités de plus en plus importantes par l’homme, est le principal gaz à effet de serre. S’il est à l’origine de la hausse de la température mondiale, il est aussi responsable d’une acidification rapide des océans qui absorbent le quart du CO2 émis.

Ainsi, de 8,2 en 1800, le pH moyen des océans pourrait atteindre 7,75 vers 2100. Une baisse a priori peu spectaculaire mais qui signifie en fait que l’acidité océanique pourrait avoir été multipliée par 2,5 en 300 ans, selon Jean-Pierre Gattuso, directeur de recherche au Laboratoire d’océanographie de Villefranche.

Fish learn to cope in a high CO2 world

Some coral reef fish may be better prepared to cope with rising CO2 in the world’s oceans – thanks to their parents.

Researchers at the ARC Centre of Excellence for Coral Reef Studies (CoECRS) today reported in the journal Nature Climate Change, encouraging new findings that some fish may be less vulnerable to high CO2 and an acidifying ocean than previously feared.

“There has been a lot of concern around the world about recent findings that baby fish are highly vulnerable to small increases in acidity, as more CO2 released by human activities dissolves into the oceans,” says Dr Gabi Miller of CoECRS and James Cook University.

Et si les poissons s’adaptaient au changement climatique ? (in French)

Les poissons pourraient s’adapter mieux que prévu à des températures et à une acidité plus élevées des océans, conséquences attendues du changement climatique, estime une étude publiée dimanche 1er juillet dans la revue Nature Climate Change.

Des études menées en Australie sur des poissons clown montrent que les juvéniles résistent mieux à une température et une acidité plus élevée de l’eau si leurs parents ont eux-mêmes fait face à des conditions similaires.

Parental environment mediates impacts of increased carbon dioxide on a coral reef fish

Carbon dioxide concentrations in the surface ocean are increasing owing to rising CO₂ concentrations in the atmosphere¹. Higher CO₂ levels are predicted to affect essential physiological processes of many aquatic organisms^{2, 3}, leading to widespread impacts on marine diversity and ecosystem function, especially when combined with the effects of global warming^{4, 5, 6}. Yet the ability for marine species to adjust to increasing CO₂ levels over many generations is an unresolved issue. Here we show that ocean conditions projected for the end of the century (approximately 1,000 μatm CO₂ and a temperature rise of 1.5–3.0 °C) cause an increase in metabolic rate and decreases in length, weight, condition and survival of juvenile fish. However, these effects are absent or reversed when parents also experience high CO₂ concentrations. Our results show that non-genetic parental effects can dramatically alter the response of marine organisms to increasing CO₂ and demonstrate that some species have more capacity to acclimate to ocean acidification than previously thought.

Calcium carbonate production response to future ocean warming and acidification (update)

Anthropogenic carbon dioxide (CO₂) emissions are acidifying the ocean, affecting calcification rates in pelagic organisms, and thereby modifying the oceanic carbon and alkalinity cycles. However, the responses of pelagic calcifying organisms to acidification vary widely between species, contributing uncertainty to predictions of atmospheric CO₂ and the resulting climate change. At the same time, ocean warming caused by rising CO₂ is expected to drive increased growth rates of all pelagic organisms, including calcifiers. It thus remains unclear whether anthropogenic CO₂ emissions will ultimately increase or decrease pelagic calcification rates. Here, we assess the importance of this uncertainty by introducing a dependence of calcium carbonate (CaCO₃) production on calcite saturation state (Ω_CaCO3) in an intermediate complexity coupled carbon-climate model. In a series of model simulations, we examine the impact of several variants of this dependence on global ocean carbon cycling between 1800 and 3500 under two different CO₂ emissions scenarios. Introducing a calcification-saturation state dependence has a significant effect on the vertical and surface horizontal alkalinity gradients, as well as on the removal of alkalinity from the ocean through CaCO₃ burial. These changes result in an additional oceanic uptake of carbon when calcification depends on Ω_CaCO3 (of up to 270 Pg C), compared to the case where calcification does not depend on acidification. In turn, this response causes a reduction of global surface air temperature of up to 0.4 °C in year 3500. Different versions of the model produced varying results, and narrowing this range of uncertainty will require better understanding of both temperature and acidification effects on pelagic calcifiers. Nevertheless, our results suggest that alkalinity observations can be used to constrain model results, and may not be consistent with the model versions that simulated stronger responses of CaCO₃ production to changing saturation state.

Seagrass solution theory for endangered coral reefs

Research headed by a Swansea University marine biologist has offered potential solution to endangered coral reefs around the world’s oceans.

Dr Richard Unsworth’s team included scientists from Oxford University and James Cook University in Australia. They found varieties of seagrass which may reduce the acidity of water around reefs, protecting them from erosion.

Tropical seagrass meadows modify seawater carbon chemistry: implications for coral reefs impacted by ocean acidification

Highly productive tropical seagrasses often live adjacent to or among coral reefs and utilize large amounts of inorganic carbon. In this study, the effect of seagrass productivity on seawater carbonate chemistry and coral calcification was modelled on the basis of an analysis of published data.

Published data (11 studies, 64 records) reveal that seagrass meadows in the Indo-Pacific have an 83% chance of being net autotrophic, resulting in an average net sink of 155 gC m⁻² yr⁻¹. The capacities for seagrass productivity were analysed using an empirical model to examine the effect on seawater carbonate chemistry. Our analyses indicate that increases in pH of up to 0.38 units, and Ω_arag increases of 2.9 are possible in the presence of seagrass meadows (compared to their absence) with the precise values of these increases dependent on water residence time (tidal flushing) and water depth. In shallow water reef environments, Scleractinian coral calcification downstream of seagrass has the potential to be ≈18% greater than in an environment without seagrass. If this potential benefit to reef calcifiers is supported by further study it offers a potential tool in marine park management at a local scale. The applicability of this will depend upon local physical conditions as well as the spatial configuration of habitats, and the factors that influence their productivity. This novel study suggests that, in addition to their importance to fisheries, sediment stabilization and primary production, seagrass meadows may enhance coral reef resilience to future ocean acidification.