Archive for July, 2015

New study exposes negative effects of climate change on Antarctic fish

Scientists at University of California Davis and San Francisco State University have discovered that the combination of elevated levels of carbon dioxide and an increase in ocean water temperature has a significant impact on survival and development of the Antarctic dragonfish (Gymnodraco acuticeps).

The research article was published today in the journal Conservation Physiology.

The study, which was the first to investigate the response to warming and increased pCO2 (partial pressure of carbon dioxide) in a developing Antarctic fish, assessed the effects of near-future ocean warming and acidification on early embryos of the naked dragonfish, a shallow benthic spawner exclusive to the circumpolar Antarctic. As the formation of their embryos takes longer than many species (up to ten months), this makes them particularly vulnerable to a change in chemical and physical conditions.

Continue reading ‘New study exposes negative effects of climate change on Antarctic fish’

Ocean acidification exerts negative effects during warming conditions in a developing Antarctic fish

Anthropogenic CO2 is rapidly causing oceans to become warmer and more acidic, challenging marine ectotherms to respond to simultaneous changes in their environment. While recent work has highlighted that marine fishes, particularly during early development, can be vulnerable to ocean acidification, we lack an understanding of how life-history strategies, ecosystems and concurrent ocean warming interplay with interspecific susceptibility. To address the effects of multiple ocean changes on cold-adapted, slowly developing fishes, we investigated the interactive effects of elevated partial pressure of carbon dioxide (pCO2) and temperature on the embryonic physiology of an Antarctic dragonfish (Gymnodraco acuticeps), with protracted embryogenesis (∼10 months). Using an integrative, experimental approach, our research examined the impacts of near-future warming [−1 (ambient) and 2°C (+3°C)] and ocean acidification [420 (ambient), 650 (moderate) and 1000 μatm pCO2 (high)] on survival, development and metabolic processes over the course of 3 weeks in early development. In the presence of increased pCO2 alone, embryonic mortality did not increase, with greatest overall survival at the highest pCO2. Furthermore, embryos were significantly more likely to be at a later developmental stage at high pCO2 by 3 weeks relative to ambient pCO2. However, in combined warming and ocean acidification scenarios, dragonfish embryos experienced a dose-dependent, synergistic decrease in survival and developed more slowly. We also found significant interactions between temperature, pCO2 and time in aerobic enzyme activity (citrate synthase). Increased temperature alone increased whole-organism metabolic rate (O2 consumption) and developmental rate and slightly decreased osmolality at the cost of increased mortality. Our findings suggest that developing dragonfish are more sensitive to ocean warming and may experience negative physiological effects of ocean acidification only in the presence of an increased temperature. In addition to reduced hatching success, alterations in development and metabolism due to ocean warming and acidification could have negative ecological consequences owing to changes in phenology (i.e. early hatching) in the highly seasonal Antarctic ecosystem.

Continue reading ‘Ocean acidification exerts negative effects during warming conditions in a developing Antarctic fish’

Effect of pH and temperature on antioxidant responses of the thick shell mussel Mytilus coruscus

This study evaluated the combined effects of seawater pH decrease and temperature increase on the activity of antioxidant enzymes in the thick shell mussel Mytilus coruscus, an ecological and economic bivalve species widely distributed along the East China Sea. Mussels were exposed to three pH levels (8.1, 7.7 and 7.3) and two temperatures (25°C and 30°C) for 14 days. Activities of superoxide dismutase (SOD), catalase (CAT), glutathione peroxidase (GPX), glutathione (GSH), acid phosphatase (ACP), alkaline phosphatase (AKP) and glutamic-pyruvic transaminase (GPT) were measured in gills and digestive glands after 1, 3, 7 and 14 days of exposure. All enzymatic activities were significantly impacted by pH, temperature. Enzymatic activities at the high temperature were significantly higher than those at the low temperature, and the mussels exposed to pH 7.3 showed significantly higher activities than those under higher pH condition for all enzymes except ACP. There was no interaction between temperature and pH in two third of the measured activities suggesting similar mode of action for both drivers. Interaction was only consistently significant for GPX. PCA revealed positive relationships between the measured biochemical indicators in both gills and digestive glands. Overall, our results suggest that decreased pH and increased temperature induce a similar anti-oxidative response in the thick shell mussel.

Continue reading ‘Effect of pH and temperature on antioxidant responses of the thick shell mussel Mytilus coruscus’

Elevated CO2 induces a bloom of microphytobenthos within a shell gravel mesocosm

The geological storage of carbon dioxide (CO2) is expected to be an important component of future global carbon emission mitigation, but there is a need to understand the impacts of a CO2 leak on the marine environment and to develop monitoring protocols for leakage detection. In the present study, sediment cores were exposed to CO2-acidified seawater at one of five pH levels (8.0, 7.5, 7.0, 6.5 and 6.0) for 10 weeks. A bloom of Spirulina sp. and diatoms appeared on sediment surface exposed to pH 7.0 and 7.5 seawater. Quantitative PCR measurements of the abundance of 16S rRNA also indicated an increase to the abundance of microbial 16S rRNA within the pH 7.0 and 7.5 treatments after 10 weeks incubation. More detailed analysis of the microbial communities from the pH 7.0, 7.5 and 8.0 treatments confirmed an increase in the relative abundance of Spirulina sp. and Navicula sp. sequences, with changes to the relative abundance of major archaeal and bacterial groups also detected within the pH 7.0 treatment. A decreased flux of silicate from the sediment at this pH was also detected. Monitoring for blooms of microphytobenthos may prove useful as an indicator of CO2 leakage within coastal areas.

Continue reading ‘Elevated CO2 induces a bloom of microphytobenthos within a shell gravel mesocosm’

Ocean warming and acidification modulate energy budget and gill ion regulatory mechanisms in Atlantic cod (Gadus morhua)

Ocean warming and acidification are threatening marine ecosystems. In marine animals, acidification is thought to enhance ion regulatory costs and thereby baseline energy demand, while elevated temperature also increases baseline metabolic rate. Here we investigated standard metabolic rates (SMR) and plasma parameters of Atlantic cod (Gadus morhua) after 3–4 weeks of exposure to ambient and future PCO2 levels (550, 1200 and 2200 µatm) and at two temperatures (10, 18 °C). In vivo branchial ion regulatory costs were studied in isolated, perfused gill preparations. Animals reared at 18 °C responded to increasing CO2 by elevating SMR, in contrast to specimens at 10 °C. Isolated gills at 10 °C and elevated PCO2 (≥1200 µatm) displayed increased soft tissue mass, in parallel to increased gill oxygen demand, indicating an increased fraction of gill in whole animal energy budget. Altered gill size was not found at 18 °C, where a shift in the use of ion regulation mechanisms occurred towards enhanced Na+/H+-exchange and HCO3 − transport at high PCO2 (2200 µatm), paralleled by higher Na+/K+-ATPase activities. This shift did not affect total gill energy consumption leaving whole animal energy budget unaffected. Higher Na+/K+-ATPase activities in the warmth might have compensated for enhanced branchial permeability and led to reduced plasma Na+ and/or Cl− concentrations and slightly lowered osmolalities seen at 18 °C and 550 or 2200 µatm PCO2 in vivo. Overall, the gill as a key ion regulation organ seems to be highly effective in supporting the resilience of cod to effects of ocean warming and acidification.

Continue reading ‘Ocean warming and acidification modulate energy budget and gill ion regulatory mechanisms in Atlantic cod (Gadus morhua)’

Impact of ocean acidification on aphotic biogeochemical production of reactive oxygen species

Reactive oxygen species (ROS) are critical to global maintenance of the global organic carbon cycle, sulfur cycle, oxygen cycle, and transition metal cycles. The primary source of ROS is commonly considered to be photolysis or photochemically driven reactions, however ROS also exist in aphotic zones. A geochemical mechanism for the same in dark environments based on the tidally driven, episodic movement of anoxic groundwaters through oxidized, Fe(III) rich sediments is shown. Predictive models were developed based on in vitro experiments and tested using sediment samples collected from a saline tidal creek in the estuary at Murrell’s Inlet, South Carolina. These sediments were air dried, resuspended in aerated solution, then exposed to aqueous sulfide at a range of concentrations chosen to replicate the conditions characteristic of a tidal cycle, beginning with low tide. No detectable ROS production occurred from this process in the dark until sulfide was added. Sulfide addition resulted in the rapid production of hydrogen peroxide. The mechanism of hydrogen peroxide production was tested using a simplified three factor representation of the system based on hydrogen sulfide, Fe(II) and Fe(III). We show that changes in marine pH associated with predicted ocean acidification are sufficient to quench hydrogen peroxide formation, potentially reducing it by an order of magnitude relative to current marine conditions (e.g. from 18.3×10-6 M to 2.01×10-6 M over the range of conditions studied).

Continue reading ‘Impact of ocean acidification on aphotic biogeochemical production of reactive oxygen species’

Antarctic phytoplankton down-regulate their carbon-concentrating mechanisms under high CO2 with no change in growth rates

High-latitude oceans, in particular the coastal Western Antarctic Peninsula (WAP) region of the Southern Ocean, are experiencing a rapidly changing environment due to rising surface ocean temperatures and CO2 concentrations. However, the direct effect of increasing CO2 on polar ocean primary production is unclear, with a number of experiments showing conflicting results. It has been hypothesized that increased CO2 may cause a reduction of the energy-intensive carbon concentrating mechanism (CCM) in phytoplankton, and these energy savings may lead to increased productivity. To test this hypothesis, we incubated natural phytoplankton communities in the WAP under high (800 ppm), current (400 ppm) and low (100 ppm) CO2 for 2 to 3 wk during the austral spring-summer of 2012/2013. In 2 incubations with diatom-dominated phytoplankton assemblages, high CO2 led to a clear down-regulation of CCM activity, as evidenced by an increase in half-saturation constants for CO2, a decrease in external carbonic anhydrase activity and a higher biological fractionation of stable carbon isotopes. In a third incubation, there was no observable regulation of the CCM, possibly because HCO3- served as the major inorganic carbon source in all treatments for this phytoplankton assemblage. We did not observe a significant effect of CO2 on growth rates or community composition in the diatom-dominated communities. The lack of a measureable effect on growth despite CCM down-regulation is likely explained by a very small energetic requirement to concentrate CO2 and saturate Rubisco at low temperatures.

Continue reading ‘Antarctic phytoplankton down-regulate their carbon-concentrating mechanisms under high CO2 with no change in growth rates’

Inventing an “easy button” for ocean acidification measurements

Measuring ocean acidification is tough — we can’t see it, and we have to use specialized instruments to measure it properly. Scientists use specialized laboratories to make the most accurate chemistry measurements of deep ocean waters. Worse, even the most affordable instruments to get this data still costs tens of thousands of dollars. This makes life difficult for shellfish growers, marine resource managers, and decision-makers who are trying to monitor ocean acidification and protect businesses, fisheries and local communities.

But these measurement hurdles are shrinking. Over the past two years, the Wendy Schmidt Ocean Health XPRIZE has hosted a competition for teams to develop devices that could most accurately or affordably detect ocean acidification conditions. In these two categories, 77 very different teams comprised of surfers, teenagers, and the more predictable engineers and scientists from around the world entered the competition. This video chronicles one team’s struggle to meet the competition deadlines and pass the performance tests, as well as how excited engineers get when making complicated gizmos.

Continue reading ‘Inventing an “easy button” for ocean acidification measurements’

Ocean warming ameliorates the negative effects of ocean acidification on Paracentrotus lividus larval development and settlement

Ocean warming and acidification both impact marine ecosystems. All organisms have a limited body temperature range, outside of which they become functionally constrained. Beyond the absolute extremes of this range, they cannot survive. It is hypothesized that some stressors can present effects that interact with other environmental variables, such as ocean acidification (OA) that have the potential to narrow the thermal range where marine species are functional. An organism’s response to ocean acidification can therefore be highly dependent on thermal conditions. This study evaluated the combined effects of predicted ocean warming conditions and acidification, on survival, development, and settlement, of the sea urchin Paracentrotus lividus. Nine combined treatments of temperature (19.0, 20.5 and 22.5ºC) and pH (8.1, 7.7 and 7.4 units) were carried out. All of the conditions tested were either within the current natural ranges of seawater pH and temperature or are within the ranges that have been predicted for the end of the century, in the sampling region (Canary Islands). Our results indicated that the negative effects of low pH on P. lividus larval development and settlement will be mitigated by a rise in seawater temperature, up to a thermotolerance threshold. Larval development and settlement performance of the sea urchin P. lividus was enhanced by a slight increase in temperature, even under lowered pH conditions. However, the species did show negative responses to the levels of ocean warming and acidification that have been predicted for the turn of the century.

Continue reading ‘Ocean warming ameliorates the negative effects of ocean acidification on Paracentrotus lividus larval development and settlement’

Environmental controls on the genesis of marine microbialites and dissolution surface associated with the end-Permian mass extinction: new sections and observations from the Nanpanjiang Basin, South China

A widespread marine microbialite and underlying truncation surface occur in Permian–Triassic sections of South China. We interpret the microbialite to have formed as a shallow, open-marine benthic framework stimulated by high seawater CaCO3 saturation. The widespread distribution across platform interiors and lack of asymmetry or thickening toward platform margins is incompatible with an alternative hypothesis, that microbialite deposition was stimulated by upwelling anoxic, alkaline waters. The truncation surface beneath the microbialite is irregular with overhangs and small caverns extending up to 30 cm beneath the surface indicating a dissolutional origin. Petrographic observations refute the interpretation that strata immediately beneath the surface contain pendant cements, meniscus cements, and vadose silt. Measurements of the anisopachous fibrous cements show that thickened areas have random, not downward orientations. Pores retain the pointed geometry consistent with isopachous cement. Carbon and oxygen isotope measurements, from immediately beneath the surface, do not show a negative shift as would be expected with subaerial exposure. Also incompatible with a subaerial origin is the occurrence of only one truncation surface within a subtidal succession ~ 50 m thick below the surface and the limited vertical penetration of dissolution. The surface closely resembles a hardground containing a micritized alteration zone with stromatolites encrusted on the surface. We interpret the surface to have formed by submarine dissolution driven by a pulse of ocean acidification associated with Siberian Traps eruptions and the end-Permian extinction. After a hiatus of ~ 30–100 kyr, seafloor dissolution would have brought seawater back to saturation coupled with increased delivery of calcium to the oceans as the result of elevated continental weathering and caused a rebound in carbonate saturation and precipitation of microbialites.

Continue reading ‘Environmental controls on the genesis of marine microbialites and dissolution surface associated with the end-Permian mass extinction: new sections and observations from the Nanpanjiang Basin, South China’

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Ocean acidification in the IPCC AR5 WG II

OUP book