The response of marine picoplankton to ocean acidification

Since industrialization global CO₂ emissions have increased, and as a consequence oceanic pH is predicted to drop by 0.3–0.4 units before the end of the century – a process coined ‘ocean acidification’. Consequently, there is significant interest in how pH changes will affect the ocean’s biota and integral processes. We investigated marine picoplankton (0.2–2 µm diameter) community response to predicted end of century CO₂ concentrations, via a ‘high-CO₂’ (∼ 750 ppm) large-volume (11 000 l) contained seawater mesocosm approach. We found little evidence of changes occurring in bacterial abundance or community composition due to elevated CO₂ under both phytoplankton pre-bloom/bloom and post-bloom conditions. In contrast, significant differences were observed between treatments for a number of key picoeukaryote community members. These data suggested a key outcome of ocean acidification is a more rapid exploitation of elevated CO₂ levels by photosynthetic picoeukaryotes. Thus, our study indicates the need for a more thorough understanding of picoeukaryote-mediated carbon flow within ocean acidification experiments, both in relation to picoplankton carbon sources, sinks and transfer to higher trophic levels.

Maine voices: limit CO2 emissions to save Maine oceans

The absorption of the gas by the ocean makes seawater more acidic and less hospitable to seafood populations.

STANDISH – In recent years, carbon dioxide gas has received a lot of attention.

The biggest source of CO2 comes from fossil fuel combustion, which contributes more than 13 trillion pounds to the atmosphere annually. CO2 traps heat, and so this increase in atmospheric CO2 is the reason that Earth’s average temperature is warming.

Research discovers impact of ocean acidification on marine life

Summary

A Plymouth University academic researching the impact of ocean acidification on marine life is finding out exactly what we can expect as our seas soak up more and more carbon dioxide.

Further detail

PhD student Vivienne Johnston is working with Dr Jason Hall-Spencer at Plymouth focusing on the effects of ocean acidification on ecosystems close to volcanic carbon dioxide vents.

Her research published today (18th May) in the journal Global Change Biology found that seabeds in both temperate and tropical systems in the Mediterranean and Papua New Guinea had the same responses to ocean acidification, with some unexpected ecological winners in the corrosive waters.

Impacts of ocean acidification on respiratory gas exchange and acid–base balance in a marine teleost, Opsanus beta

The oceanic carbonate system is changing rapidly due to rising atmospheric CO₂, with current levels expected to rise to between 750 and 1,000 μatm by 2100, and over 1,900 μatm by year 2300. The effects of elevated CO₂ on marine calcifying organisms have been extensively studied; however, effects of imminent CO₂ levels on teleost acid–base and respiratory physiology have yet to be examined. Examination of these physiological processes, using a paired experimental design, showed that 24 h exposure to 1,000 and 1,900 μatm CO₂ resulted in a characteristic compensated respiratory acidosis response in the gulf toadfish (Opsanus beta). Time course experiments showed the onset of acidosis occurred after 15 min of exposure to 1,900 and 1,000 μatm CO₂, with full compensation by 2 and 4 h, respectively. 1,900-μatm exposure also resulted in significantly increased intracellular white muscle pH after 24 h. No effect of 1,900 μatm was observed on branchial acid flux; however, exposure to hypercapnia and HCO₃ ⁻ free seawater compromised compensation. This suggests branchial HCO₃ ⁻ uptake rather than acid extrusion is part of the compensatory response to low-level hypercapnia. Exposure to 1,900 μatm resulted in downregulation in branchial carbonic anhydrase and slc4a2 expression, as well as decreased Na⁺/K⁺ ATPase activity after 24 h of exposure. Infusion of bovine carbonic anhydrase had no effect on blood acid–base status during 1,900 μatm exposures, but eliminated the respiratory impacts of 1,000 μatm CO₂. The results of the current study clearly show that predicted near-future CO₂ levels impact respiratory gas transport and acid–base balance. While the full physiological impacts of increased blood HCO₃ ⁻ are not known, it seems likely that chronically elevated blood HCO₃ ⁻ levels could compromise several physiological systems and furthermore may explain recent reports of increased otolith growth during exposure to elevated CO₂

Response of two marine bacterial isolates to high CO2 concentration

Experimental results related to the effects of ocean acidification on planktonic marine microbes are still rather inconsistent and occasionally contradictory. Moreover, laboratory or field experiments that address the effects of changes in CO₂ concentrations on heterotrophic microbes are very scarce, despite the major role of these organisms in the marine carbon cycle. We tested the direct effect of an elevated CO₂ concentration (1000 ppmv) on the biomass and metabolic rates (leucine incorporation, CO₂ fixation and respiration) of 2 isolates belonging to 2 relevant marine bacterial families, Rhodobacteraceae (strain MED165) and Flavobacteriaceae (strain MED217). Our results demonstrate that, contrary to some expectations, high pCO₂ did not negatively affect bacterial growth but increased growth efficiency in the case of MED217. The elevated partial pressure of CO₂ ( pCO₂) caused, in both cases, higher rates of CO₂ fixation in the dissolved fraction and, in the case of MED217, lower respiration rates. Both responses would tend to increase the pH of seawater acting as a negative feedback between elevated atmospheric CO₂ concentrations and ocean acidification.

How human communities could ‘feel’ changing ocean biogeochemistry

Human-driven changes to ocean biogeochemistry affect multiple marine processes and species, thus altering the diverse array of ecosystem services that benefit human societies.

Changes in marine biogeochemistry such as pollution, ocean acidification, and deoxygenation often simultaneously affect marine environments and ecosystem services, often interacting synergistically to enhance one another. These biogeochemical shifts also occur in parallel with other anthropogenically driven changes, like rising temperature and altered circulation or reduced biodiversity and ecological shifts. Ecosystem services that experience multiple stressors could also therefore be more strongly harmed. Initial studies have estimated biogeochemistry-associated losses in some ecosystem services to which monetary values can be assigned, but the methods used fall short for measuring change in many other ecosystem services. Ecosystem assessments will provide a much broader accounting of how changing marine ecosystem services will affect human well-being by examining the natural and social science implications of marine biogeochemical change.

Prolonged exposure to elevated CO2 promotes growth of the algal symbiont Symbiodinium muscatinei in the intertidal sea anemone Anthopleura elegantissima

Some photosynthetic organisms benefit from elevated levels of carbon dioxide, but studies on the effects of elevated PCO₂ on the algal symbionts of animals are very few. This study investigated the impact of hypercapnia on a photosynthetic symbiosis between the anemone Anthopleura elegantissima and its zooxanthella Symbiodinium muscatinei. Anemones were maintained in the laboratory for 1 week at 37 Pa PCO₂ and pH 8.1. Clonal pairs were then divided into two groups and maintained for 6 weeks under conditions naturally experienced in their intertidal environment, 45 Pa PCO₂, pH 8.1 and 231 Pa PCO₂, pH 7.3. Respiration and photosynthesis were measured after the 1-week acclimation period and after 6 weeks in experimental conditions. Density of zooxanthellal cells, zooxanthellal cell size, mitotic index and chlorophyll content were compared between non-clonemate anemones after the 1-week acclimation period and clonal anemones at the end of the experiment. Anemones thrived in hypercapnia. After 6 weeks, A. elegantissima exhibited higher rates of photosynthesis at 45 Pa (4.2 µmol O₂ g⁻¹ h⁻¹) and 231 Pa (3.30 µmol O₂ g⁻¹ h⁻¹) than at the initial 37 Pa (1.53 µmol O₂ g⁻¹ h⁻¹). Likewise, anemones at 231 Pa received more of their respiratory carbon from zooxanthellae (CZAR  = 78.2%) than those at 37 Pa (CZAR  = 66.6%) but less than anemones at 45 Pa (CZAR  = 137.3%). The mitotic index of zooxanthellae was significantly greater in the hypercapnic anemones than in anemones at lower PCO₂. Excess zooxanthellae were expelled by their hosts, and cell densities, cell diameters and chlorophyll contents were not significantly different between the groups. The response of A. elegantissima to hypercapnic acidification reveals the potential adaptation of an intertidal, photosynthetic symbiosis for high PCO₂.

The Paleocene–Eocene thermal maximum (PETM) in shallow-marine successions of the Adriatic carbonate platform (SW Slovenia)

The Paleocene-Eocene thermal maximum represents one of the most rapid and extreme warming events in the Cenozoic. Shallow-water stratigraphic sections from the Adriatic carbonate platform offer a rare opportunity to learn about the nature of Paleocene-Eocene thermal maximum and the effects on shallow-water ecosystems. We use carbon and oxygen isotope stratigraphy, in conjunction with detailed larger benthic foraminiferal biostratigraphy, to establish a high-resolution paleoclimatic record for the Paleocene-Eocene thermal maximum. A prominent negative excursion in δ¹³C curves of bulk-rock (∼1‰–3‰), matrix (∼4‰), and foraminifera (∼6‰) is interpreted as the carbon isotope excursion during the Paleocene-Eocene thermal maximum. The strongly ¹³C-depleted δ¹³C record of our shallow-marine carbonates compared to open-marine records could result from organic matter oxidation, suggesting intensified weathering, runoff, and organic matter flux.

The Ilerdian larger benthic foraminiferal turnover is documented in detail based on high-resolution correlation with the carbon isotopic excursion. The turnover is described as a two-step process, with the first step (early Ilerdian) marked by a rapid diversification of small alveolinids and nummulitids with weak adult dimorphism, possibly as adaptations to fluctuating Paleocene-Eocene thermal maximum nutrient levels, and a second step (middle Ilerdian) characterized by a further specific diversification, increase of shell size, and well-developed adult dimorphism. Within an evolutionary scheme controlled by long-term biological processes, we argue that high seawater temperatures could have stimulated the early Ilerdian rapid specific diversification. Together, these data help elucidate the effects of global warming and associated feedbacks in shallow-water ecosystems, and by inference, could serve as an assessment analog for future changes.

Rio+20 side event: building marine ecosystem resilience to ocean acidification

Organizing partners

Pacific Small Island Developing States at the United Nations in New York (namely Fiji, the Republic of the Marshall Islands, the Federated States of Micronesia, Nauru, Palau, Papua New Guinea, Samoa, Solomon Islands, Tonga, Tuvalu and Vanuatu) together with Earthjustice.

Introduction

The Pacific Small Island Developing States in partnership with Earthjustice will host a side event on “Building Marine Ecosystem Resilience to Ocean Acidification” during the Rio+20 final PrepComm. A significant body of science and experience shows that reducing pollution, overfishing, and other stressors builds resilience to ocean acidification in sensitive species and ecosystems, including coral reefs, critical for marine biodiversity, global food security and sustainable livelihoods and development in the Pacific and around the world. Building resilience is fundamental to the three pillars of sustainable development on which the Pacific depends. Legal, policy, and financial solutions will be examined with special attention given to successful efforts to build marine ecosystem resilience in the Small Island Developing States.

The time for oysters

Next time you find yourself in the San Francisco Bay Area, which for your own sake will be soon, I hope, there are a few things you ought to do. Walk across the Golden Gate, go one of the Thursday “NightLife” events at the Academy of Sciences and drive north to Tomales Bay and feast on fresh oysters from one of the local hatcheries.

The bridge may be a touristy stop, but it’s a beautiful one that no one regrets. The museum after dark is hottest ticket in town — all the cool kids will be there, loving on science and displaying fashionable shoes. And the oyster feast is something to enjoy sooner rather than later, for oysters, and shellfish at large, may be on their way out.

The ocean’s acidity is increasing, fast enough to affect shellfish, so fast they may not be able to adapt and keep up.