Biogeochemical change in the water masses of the Southern Ocean, south of Tasmania, was assessed for the 16-year period between 1995 and 2011 using data from four summer repeats of the WOCE–JGOFS–CLIVAR–GO-SHIP (Key et al., 2015; Olsen et al., 2016) SR03 hydrographic section (at ∼ 140° E). Changes in temperature, salinity, oxygen, and nutrients were used to disentangle the effect of solubility, biology, circulation and anthropogenic carbon (CANT) uptake on the variability of dissolved inorganic carbon (DIC) for eight water mass layers defined by neutral surfaces (γn). CANT was estimated using an improved back-calculation method. Warming (∼ 0.0352 ± 0.0170 °C yr−1) of Subtropical Central Water (STCW) and Antarctic Surface Water (AASW) layers decreased their gas solubility, and accordingly DIC concentrations increased less rapidly than expected from equilibration with rising atmospheric CO2 (∼ 0.86 ± 0.16 µmol kg−1 yr−1 versus ∼ 1 ± 0.12 µmol kg−1 yr−1). An increase in apparent oxygen utilisation (AOU) occurred in these layers due to either remineralisation of organic matter or intensification of upwelling. The range of estimates for the increases in CANT were 0.71 ± 0.08 to 0.93 ± 0.08 µmol kg−1 yr−1 for STCW and 0.35 ± 0.14 to 0.65 ± 0.21 µmol kg−1 yr−1 for AASW, with the lower values in each water mass obtained by assigning all the AOU change to remineralisation. DIC increases in the Sub-Antarctic Mode Water (SAMW, 1.10 ± 0.14 µmol kg−1 yr−1) and Antarctic Intermediate Water (AAIW, 0.40 ± 0.15 µmol kg−1 yr−1) layers were similar to the calculated CANT trends. For SAMW, the CANT increase tracked rising atmospheric CO2. As a consequence of the general DIC increase, decreases in total pH (pHT) and aragonite saturation (ΩAr) were found in most water masses, with the upper ocean and the SAMW layer presenting the largest trends for pHT decrease (∼ −0.0031 ± 0.0004 yr−1). DIC increases in deep and bottom layers (∼ 0.24 ± 0.04 µmol kg−1 yr−1) resulted from the advection of old deep waters to resupply increased upwelling, as corroborated by increasing silicate (∼ 0.21 ± 0.07 µmol kg−1 yr−1), which also reached the upper layers near the Antarctic Divergence (∼ 0.36 ± 0.06 µmol kg−1 yr−1) and was accompanied by an increase in salinity. The observed changes in DIC over the 16-year span caused a shoaling (∼ 340 m) of the aragonite saturation depth (ASD, ΩAr = 1) within Upper Circumpolar Deep Water that followed the upwelling path of this layer. From all our results, we conclude a scenario of increased transport of deep waters into the section and enhanced upwelling at high latitudes for the period between 1995 and 2011 linked to strong westerly winds. Although enhanced upwelling lowered the capacity of the AASW layer to uptake atmospheric CO2, it did not limit that of the newly forming SAMW and AAIW, which exhibited CANT storage rates (∼ 0.41 ± 0.20 mol m−2 yr−1) twice that of the upper layers.
Archive for November, 2017
Carbon uptake and biogeochemical change in the Southern Ocean, south of Tasmania (update)
Published 23 November 2017 Science ClosedTags: Antarctic, chemistry, field, South Pacific
Ocean acidification affects mussels at early life stages
Published 23 November 2017 Press releases Closed
Two-day-old mussels larvae viewed by a polarizing microscope. Credit: F. Melzner, GEOMAR
Mussels are popular seafood in northern Germany. Mussels in their blue-black shells, are found in tidal regions of the coastal zones. Like many creatures in the oceans, which protect themselves with a calcareous shell from predators, mussels are endangered by the increasing acidification of seawater caused by the uptake of additional carbon dioxide from the atmosphere which is dissolved in seawater. Mussels are very sensitive to a decline in pH in early life stages. One important reason for this is the enormous calcification rate in the larval stage: between the first and second day of life they form a calcified shell, which corresponds to the weight of the rest of their body. This process is studied by scientists from Kiel and published in the international journal Nature Communications.
Continue reading ‘Ocean acidification affects mussels at early life stages’
Mussel larvae modify calcifying fluid carbonate chemistry to promote calcification
Published 23 November 2017 Science ClosedTags: Baltic, biological response, calcification, dissolution, laboratory, mollusks, morphology, physiology
Understanding mollusk calcification sensitivity to ocean acidification (OA) requires a better knowledge of calcification mechanisms. Especially in rapidly calcifying larval stages, mechanisms of shell formation are largely unexplored—yet these are the most vulnerable life stages. Here we find rapid generation of crystalline shell material in mussel larvae. We find no evidence for intracellular CaCO3 formation, indicating that mineral formation could be constrained to the calcifying space beneath the shell. Using microelectrodes we show that larvae can increase pH and [CO32−] beneath the growing shell, leading to a ~1.5-fold elevation in calcium carbonate saturation state (Ωarag). Larvae exposed to OA exhibit a drop in pH, [CO32−] and Ωarag at the site of calcification, which correlates with decreased shell growth, and, eventually, shell dissolution. Our findings help explain why bivalve larvae can form shells under moderate acidification scenarios and provide a direct link between ocean carbonate chemistry and larval calcification rate.
The effects of eutrophication and acidification on the ecophysiology of Ulva pertusa Kjellman
Published 23 November 2017 Science ClosedTags: algae, biogeochemistry, biological response, laboratory, morphology, multiple factors, nutrients, photosynthesis, physiology
In coastal environments, acidification and eutrophication affect the physiology of marine macroalgae. We investigated the responses of Ulva pertusa Kjellman (Ulvales, Chlorophyta) under such conditions. Samples were cultured at two different pH settings (low, 7.5; high, 8.0) and at three different ammonium levels (low, 4; medium, 60; high, 120 μM NH4+). Our objective was to analyze the influence that elevated CO2 and NH4+ might have on pH, oxygen evolution, rates of nutrient uptake, chlorophyll fluorescence, growth, and C/N ratio of that organism. Variability in pH value was enhanced under low pH/high NH4+ and was significantly different (p < 0.05) from changes measured when the high pH/low NH4+ combination was applied. Rates of NH4+ uptake and relative growth rates by U. pertusa were increased under low pH/high NH4+ conditions and that response was significantly different (p < 0.05) from the other treatments. The rate of photosynthetic oxygen evolution and chlorophyll fluorescence were increased under elevated NH4+ concentrations (p < 0.05). However, the C/N ratio of U. pertusa was not affected by higher concentrations of CO2 and NH4+ (p > 0.05). Our results indicated that the physiological reactions of this alga were heightened when exposed to either the elevated combination of CO2/NH4+ or even when only the level of NH4+ was raised. Although such excessive growth can lead to bloom formations in coastal areas, this species also has greater capacity for taking up nutrients and dissolved inorganic carbon.
Ocean acidification and Pacific oyster larval failures in the Pacific Northwest United States
Published 23 November 2017 Science ClosedTags: biological response, mollusks, North Pacific, policy, review, socio-economy
The Pacific Northwest coast of the United States (Figure 2.1) is home to a lucrative shellfish aquaculture industry that grows mainly (>80 percent) (Barton, et al. 2012) Pacific oysters (Crassostrea gigas). Washington States is the center of this industry. Its hatcheries produce oyster larvae, or spat, that are shipped all over the West Coast to be grown to market size in coastal water by aquaculturists. Washington’s hatcheries – along with its 125 farms, located throughout 12 coastal counties (Northern Economics, Inc.. 2013) – produce more shellfish than any other U.S. state, contributing around $270 million to the state economy and supporting about 3,200 jobs (Washington State Blue Ribbon Panel on Ocean Acidification 2012). The next greatest producer of shellfish in the United States is Connecticut, which has just 23 farms (United States Department of Agriculture 2014). Washington’s entire seafood industry generates more than 42,000 jobs in the state and contributes $1.7 billion to the gross state product via profits and jobs at restaurants, distributors and retailers (Washington State Blue Ribbon Panel on Ocean Acidification 2012). By comparison, the entire state hosts approximately 3 million jobs (Employment Security Department, Washington State) contributing to an approximately $446 billion gross state profit (U.S. Bureau of Economic Analysis). In other words, 1.4 percent of the state’s jobs are located in the shellfish industry, which creates 0.4 percent of the gross state profit. Shellfish generate more than two-thirds of the harvest value of the state’s wild commercial fisheries. Recreational shellfish harvesting in the Pacific Northwest also creates jobs and income for coastal counties. Recreational shellfish harvesting licenses generate $3 million annually in state revenue, and recreational oyster and clam harvesters contribute more than $27 million annually to coastal economies (Washington State Blue Ribbon Panel on Ocean Acidification 2012). Besides the economic impacts of shellfish harvesting, harvesting and eating seafood is an integral part of the culture and everyday life of many Washingtonians.
Meta-analysis identifies metabolic sensitivities to ocean acidification
Published 23 November 2017 Science ClosedTags: biological response, physiology, review
Ocean acidification is expected to have wide-ranging and complicated impacts on organismal physiology, notably metabolism. Effects on metabolism may have numerous consequences at the whole-organism level, in particular costs to growth, locomotion, reproductive output, and homeostasis. Negative effects on these metrics may further cascade up to impact ecosystem structure and function, and thus human society. As such, the study of metabolism in response to ocean acidification is a pivotal research avenue within the study of global ocean change. Here, the metabolic responses of marine species to ocean acidification are reviewed and examined through meta-analysis. We reviewed a total of 44 published studies and used a traditional meta-analysis to identify broad-scale trends in the metabolic responses of species to ocean acidification. Results from this study indicate varied metabolic strategies in response to OA, further complicating our predictive power to forecast ecosystem-level consequences of ongoing CO2 increases. However, strong effects were observed with respect to ontogeny, marine ecosystem, motility, and taxonomic origin, thereby reinforcing the need for a multi-faceted approach to both management of sensitive species and mitigation of future impacts.
Continue reading ‘Meta-analysis identifies metabolic sensitivities to ocean acidification’
Tidal and seasonal variation in carbonate chemistry, pH and salinity, for a mineral-acidified tropical estuarine system
Published 23 November 2017 Science ClosedTags: chemistry, field, North Pacific
- • This paper describes tidal fluxes and seasonal patterns in pH, salinity and carbonate chemistry attributes for a tropical Southeast Asian estuary, when heterotrophically generated CO2 and mineral acidification (through Acid Sulphate Soil (ASS) discharge) are likely to be of greater or lesser importance.
- • Heavy daily downpours had little effect on the estuarine water salinity and pH, whereas accumulative rainfall (and anticipated elevated ASS discharge) during the monsoon period distinctly lowered these parameters baselines across the system.
- • Remarkably low pH (relative to salinity), extraordinary pCO2 super-saturation, and carbonate under-saturation occurred extensively across our study system most of the time.
- • In addition to modifying pH, mineral acidification is implicated in shifting the carbonate equilibrium and elevating the already high pCO2 levels.
Abstract
Estuarine acidification and carbonate chemistry derive from multiple biogeochemical processes. Other than biogenic CO2−-acidification, estuaries can be acidified allochthonously through non-carbonate sources originating in freshwater and land ecosystems. The present study considered the carbonate chemistry of a nutrified, turbid, tropical mangrove estuary, influenced by acidic groundwater discharge from pyritic soils (Acid Sulphate Soils, ASS). We studied the spatial and temporal variation of the surface water pH, salinity, total alkalinity (TA), partial pressure carbon dioxide (pCO2), dissolved inorganic carbon (DIC), and calcite (Ωcal) and aragonite (Ωara) saturation in the Brunei Estuarine System (BES), Borneo, Southeast Asia. pH and salinity for tidal to seasonal timeframes were determined from data collected half-hourly, logged at three stations (upper, middle and lower estuary); these data were correlated with rainfall incidence and intensity. Carbonate parameters were calculated from TA using discrete samples collected from six stations. pH (6.8–7.9) and salinity (4.2–28.2) increased expectedly seawards, due to tidal forcing and freshwater dilution at opposite ends of the estuary; amplitudes within a tidal cycle became expanded landwards and during spring tides. While the overall effect of heavy daily downpours on estuarine salinity and pH was muted, cumulative rainfall during the monsoon season distinctly lowered parameter baselines; the response was again more pronounced in the upper estuary. In the mid-to-upper estuary, we observed a remarkably low pH relative to salinity, extraordinary pCO2super-saturation (13031 ± 4412 μatm) and carbonate undersaturation (Ωcal and Ωara were 0.006-1.431 and 0.004-0.928, respectively). Although the relative contributions of heterotrophic metabolism and ASS-discharge to the estuarine pH and pCO2 were not determined, both processes are implicated in increasing both acidity and CO2 levels. This study contributes to the understanding of carbonate fluxes in mineral-acidified estuaries.
Training on ocean acidification and first biological experiments in Costa Rica
Published 22 November 2017 Courses and training Closed
PhD candidate Celeste Sánchez Noguera from the Centro de Investigación en Ciencias del Mar y Limnología (CIMAR) at the University of Costa Rica and Dr. Sam Dupont from the University of Gothenburg met for the first time in Tasmania in May 2016 at the 4th Symposium on the Ocean in a High CO2 World and the 3d Science meeting of the Global Ocean Acidification Observing Network (GOA-ON). Ms Sánchez Noguera also participated in the training course on ocean acidification organized by the IAEA OA-ICC, the Centro de Investigación Científica y De Educación Superior de Ensenada (CICESE) and the University of Baja California (UABC) in Ensenada, Mexico, in September 2016. She then joined Dr. Dupont’s team in Kristineberg, Sweden, for one month in summer 2017 to work on an experiment aiming at evaluating ocean acidification tipping points on invertebrate larvae.
Since then, they have been exploring opportunities to develop ocean acidification work in Costa Rica. This was recently initiated through a SCOR visiting scholar grant allowing Dr. Dupont to visit Costa Rica for 2 weeks in November 2017 and with the support of CIMAR, the organization of a training on best practices in ocean acidification. They also built an experimental set-up allowing to manipulate the carbonate chemistry in a replicated aquarium system and they tested the impact on larval stages of invertebrates.
Continue reading ‘Training on ocean acidification and first biological experiments in Costa Rica’
Our view: ocean acidity threat warrants stronger state response
Published 22 November 2017 Media coverage ClosedIn 2014, with rising ocean acidity threatening Maine’s fishing and aquaculture industries, a state commission issued a series of recommendations for localized research that was delivered with optimism.
“While scientific research on the effects of ocean acidification on marine ecosystems and individual organisms is still in its infancy,” the report said, “Maine’s coastal communities need not wait for a global solution to address a locally exacerbated problem that is compromising their marine environment.”
Three years later, little progress has been made on those recommendations, and the work in implementing them has been left to volunteers — hardly the response warranted by such a threat to Maine’s marine economy.
Continue reading ‘Our view: ocean acidity threat warrants stronger state response’
A recent report shows rising CO2 levels in the atmosphere are about to make the world’s oceans uninhabitable for many sea creatures, threatening entire ocean ecosystems. What can be done?
(C) GEOMAR/JAGO-Team
Life on Earth began at sea. Over the billions of years since, the oceans have sustained a myriad of species, from world’s biggest mammals to the psychedelic profusion of life that makes up a coral reef.
But since the industrial revolution, the waters that cover more than two-thirds of our planet’s surface have become increasingly hostile to their inhabitants.
Overfishing, plastic pollution and warming waters all make it harder for marine life to survive.
But now, perhaps the biggest threat is also one of the most insidious effects of the carbon we pump into the atmosphere – ocean acidification.
Continue reading ‘Ocean acidification: climate change’s evil twin’
Image: Wikimedia Commons
Marine life is threatened by the actions of humankind; overfishing is killing off some aquatic species to the point of endangerment; fertiliser run-off is polluting water courses leading to algal blooms and eutrophication; vast swathes of mangrove forests have been cleared to make way for shrimp farming. To make matters worse, a recent key report suggests that another problem exacerbated by humans is affecting the majority of ocean life.
MoDIE: moderate dissolved inorganic carbon (DI13C) isotope enrichment for improved evaluation of DIC photochemical production in natural waters
Published 22 November 2017 Science ClosedTags: chemistry, methods
Highlights
- • MoDIE allows analysis of very small DIC changes against large seawater background.
- • MoDIE eliminates DIC-stripping to quantify photoproduced DIC in natural waters.
- • Initial DIC photoproduction rates in blue water are reported using MoDIE.
- • Ultra-precise DIC analysis via MoDIE could transform marine carbon cycle studies.
Abstract
Photochemical reactions in natural waters are a sink for dissolved organic carbon (DOC) and a source of dissolved inorganic carbon (DIC). Although considered significant to the carbon budget of the oceans, DIC photoproduction rates remain poorly constrained due to the analytical challenge involved in accurately measuring very low production rates (likely sub-μM h− 1 for blue ocean waters) relative to high background DIC concentrations (~ 2 mM). In an attempt to overcome this analytical limitation, almost all previous DIC photoproduction studies in marine systems have relied on the stripping of background DIC prior to irradiation, with unknown consequences for the integrity of the DOC pool and its photoreactivity, and none have resulted in a satisfactory determination of photoproduced DIC in open ocean waters. Here, we use small additions of NaH13CO3 (< 10% of background DIC concentrations) to achieve moderate DI13C isotope enrichment (MoDIE) of river, estuarine, and seawater samples. We then quantify the shift in δ13C of DIC in irradiated samples via liquid chromatography – isotope ratio mass spectrometry (LC-IRMS) and use these shifts to calculate photoproduced DIC. MoDIE provides a new method to more precisely (± 56 to ± 340 nM DIC) and more rapidly quantify DIC photoproduction compared to previous methods. MoDIE was evaluated by determining initial DIC photoproduction rates, along with associated broadband photochemical efficiency data (ranging from 144 to 280 μmol DIC per mol photons absorbed), in riverine to offshore waters, and produced the earliest time point and most precise measurement of DIC photoproduction in unmodified, low-CDOM, blue water (ag(325) = 0.30 m− 1) reported to date. In addition to measuring small DIC changes from photochemistry, the use of MoDIE could provide a major advance for other ocean carbon cycling studies, including examination of oceanic respiration, carbonate mineral precipitation/dissolution, and assessment of ocean acidification.
The effect of elevated carbon dioxide on the sinking and swimming of the shelled pteropod Limacina retroversa
Published 22 November 2017 Science ClosedTags: biological response, laboratory, mollusks, morphology, North Atlantic, performance, zooplankton
Shelled pteropods are planktonic molluscs that may be affected by ocean acidification. Limacina retroversa from the Gulf of Maine were used to investigate the impact of elevated carbon dioxide (CO2) on shell condition as well as swimming and sinking behaviours. Limacina retroversa were maintained at either ambient (ca. 400 µatm) or two levels of elevated CO2 (800 and 1200 µatm) for up to 4 weeks, and then examined for changes in shell transparency, sinking speed, and swimming behaviour assessed through a variety of metrics (e.g. speed, path tortuosity, and wing beat frequency). After exposures to elevated CO2 for as little as 4 d, the pteropod shells were significantly darker and more opaque in the elevated CO2 treatments. Sinking speeds were significantly slower for pteropods exposed to medium and high CO2 in comparison to the ambient treatment. Swimming behaviour showed less clear patterns of response to treatment and duration of exposure, but overall, swimming did not appear to be hindered under elevated CO2. Sinking is used by L. retroversa for predator evasion, and altered speeds and increased visibility could increase the susceptibility of pteropods to predation.
In situ detection of species relevant to the carbon cycle in seawater with submersible potentiometric probes
Published 22 November 2017 Science ClosedTags: chemistry, methods
We report on the development of a submersible probe for the simultaneous potentiometric detection of carbonate, calcium, and pH in seawater. All-solid-state electrodes incorporating nanomaterials provide an adequate response time (<10 s), stability (drifts of <0.9 mV h–1), reproducibility (calibration parameter deviation of <0.7%), and accuracy (deviation of <8% compared to reference techniques) for real-time monitoring of seawater using a flow system. The functioning of the deployable prototype was checked in an outdoor mesocosm and via long-term monitoring in Genoa Harbor. The electrodes worked properly for 3 weeks, and the system demonstrated the capability to autonomously operate with routines for repetitive measurements, data storage, and management. In situ profiles observed in Genoa Harbor and Arcachon Bay were validated using on site and ex situ techniques. The validation of in situ-detected carbonate is a challenge because both re-equilibration of the sample with atmospheric CO2 and the use of apparent thermodynamic constants for speciation calculations lead to some differences (<20% deviation). The submersible probe is a promising tool for obtaining rapid and trustworthy information about chemical levels in marine systems. Moreover, the fluidic approach allows for the integration of other ion sensors that may require sample pretreatment.
Reproduction of an azooxanthellate coral is unaffected by ocean acidification
Published 22 November 2017 Science ClosedTags: biological response, corals, field, Mediterranean, morphology, reproduction, vents
Anthropogenic carbon dioxide (CO2) emissions and consequent ocean acidification (OA) are projected to have extensive consequences on marine calcifying organisms, including corals. While the effects of OA on coral calcification are well documented, the response of reproduction is still poorly understood since no information are reported for temperate corals. Here we investigate for the first time the influence of OA on sexual reproduction of the temperate azooxanthellate solitary scleractinian Leptopsammia pruvoti transplanted along a natural pCO2 gradient at a Mediterranean CO2 vent. After 3 months, future projection of pH levels did not influence the germ cell production, gametogenesis and embryogenesis in this azooxanthellate coral. These findings suggest that reproductive potential may be quite tolerant to decreasing pH, with implications for ecosystem function and services in a changing ocean.
Continue reading ‘Reproduction of an azooxanthellate coral is unaffected by ocean acidification’
Extreme ocean acidification reduces the susceptibility of eastern oyster shells to a polydorid parasite
Published 22 November 2017 Science ClosedTags: annelids, biological response, laboratory, mollusks, morphology, performance
Ocean acidification poses a threat to marine organisms. While the physiological and behavioural effects of ocean acidification have received much attention, the effects of acidification on the susceptibility of farmed shellfish to parasitic infections are poorly understood. Here we describe the effects of moderate (pH 7.5) and extreme (pH 7.0) ocean acidification on the susceptibility of Crassostrea virginica shells to infection by a parasitic polydorid, Polydora websteri. Under laboratory conditions, shells were exposed to three pH treatments (7.0, 7.5 and 8.0) for 3- and 5-week periods. Treated shells were subsequently transferred to an oyster aquaculture site (which had recently reported an outbreak of P. websteri) for 50 days to test for effects of pH and exposure time on P. websteri recruitment to oyster shells. Results indicated that pH and exposure time did not affect the length, width or weight of the shells. Interestingly, P. websteri counts were significantly lower under extreme (pH 7.0; ~50% reduction), but not moderate (pH 7.5; ~20% reduction) acidification levels; exposure time had no effect. This study suggests that extreme levels – but not current and projected near-future levels – of acidification (∆pH ~1 unit) can reduce the susceptibility of eastern oyster shells to P. websteri infections.
Ocean acidification impacts primary and bacterial production in Antarctic coastal waters during austral summer
Published 21 November 2017 Science ClosedTags: abundance, Antarctic, biological response, BRcommunity, laboratory, multiple factors, nutrients, otherprocess, photosynthesis, phytoplankton, primary production, prokaryotes
- • Elevated CO2 decreased primary productivity and gross primary production.
- • Elevated CO2 decreased bacterial productivity but increased bacterial production.
- • Increased bacterial production was associated with reduced grazing pressure.
- • Elevated CO2 decreased net community production when nitrate was available.
- • Under nitrate limitation net community production responses to CO2 were suppressed.
Abstract
Polar waters may be highly impacted by ocean acidification (OA) due to increased solubility of CO2 at colder water temperatures. Three experiments examining the influence of OA on primary and bacterial production were conducted during austral summer at Davis Station, East Antarctica (68°35′ S, 77°58′ E). For each experiment, six minicosm tanks (650 L) were filled with 200 μm filtered coastal seawater containing natural communities of Antarctic marine microbes. Assemblages were incubated for 10 to 12 days at CO2 concentrations ranging from pre-industrial to post-2300. Primary and bacterial production rates were determined using NaH14CO3 and 14C-leucine, respectively. Net community production (NCP) was also determined using dissolved oxygen. In all experiments, maximum photosynthetic rates (Pmax, mg C mg chl a− 1 h− 1) decreased with elevated CO2, clearly reducing rates of total gross primary production (mg C L− 1 h− 1). Rates of cell-specific bacterial productivity (μg C cell− 1 h− 1) also decreased under elevated CO2, yet total bacterial production (μg C L− 1 h− 1) and cell abundances increased with CO2 over Days 0–4. Initial increases in bacterial production and abundance were associated with fewer heterotrophic nanoflagellates and therefore less grazing pressure. The main changes in primary and bacterial productivity generally occurred at CO2 concentrations > 2 × present day (> 780 ppm), with the same responses occurring regardless of seasonally changing environmental conditions and microbial assemblages. However, NCP varied both within and among experiments, largely due to changing nitrate + nitrite (NOx) availability. At NOx concentrations < 1.5 μM photosynthesis to respiration ratios showed that populations switched from net autotrophy to heterotrophy and CO2 responses were suppressed. Overall, OA may reduce production in Antarctic coastal waters, thereby reducing food availability to higher trophic levels and reducing draw-down of atmospheric CO2, thus forming a positive feedback to climate change. NOX limitation may suppress this OA response but cause a similar decline.
Native and exotic oysters in Brazil: comparative tolerance to hypercapnia
Published 21 November 2017 Science ClosedTags: biological response, laboratory, mollusks, physiology, South Atlantic
- • C. gigas and C. brasiliana showed differentiated biochemical response to hypercapnia.
- • Juveniles presented a more pronounced stress response than adults in both species.
- • Contrasting metabolic shifts were observed between both species to endure hypercapnia.
- • Antioxidant and metabolic responses were sufficient to prevent excessive LPO.
- Abstract
Environmental hypercapnia in shallow coastal marine ecosystems can be exacerbated by increasing levels of atmospheric CO2. In these ecosystems organisms are expected to become increasingly subjected to pCO2 levels several times higher than those inhabiting ocean waters (e.g.: 10,000 µatm), but still our current understanding on different species capacity to respond to such levels of hypercapnia is limited. Oysters are among the most important foundation species inhabiting these coastal ecosystems, although natural oyster banks are increasingly threatened worldwide. In the present study we studied the effects of hypercapnia on two important oyster species, the pacific oyster C. gigas and the mangrove oyster C. brasiliana, to bring new insights on different species response mechanisms towards three hypercapnic levels (ca. 1,000; 4,000; 10,000 µatm), by study of a set of biomarkers related to metabolic potential (electron transport system – ETS), antioxidant capacity (SOD, CAT, GSH), cellular damage (LPO) and energetic fitness (GLY), in two life stages (juvenile and adult) after 28 days of exposure.
Results showed marked differences between each species tolerance capacity to hypercapnia, with contrasting metabolic readjustment strategies (ETS), different antioxidant response capacities (SOD, CAT, GSH), which generally allowed to prevent increased cellular damage (LPO) and energetic impairment (GLY) in both species. Juveniles were more responsive to hypercapnia stress in both congeners, and are likely to be most sensitive to extreme hypercapnia in the environment. Juvenile C. gigas presented more pronounced biochemical alterations at intermediate hypercapnia (4,000 µatm) than C. brasiliana. Adult C. gigas showed biochemical alterations mostly in response to high hypercapnia (10,000 µatm), while adult C. brasiliana were less responsive to this environmental stressor, despite presenting decreased metabolic potential.
Our data bring new insights on the biochemical performance of two important oyster species, and suggest that the duration of extreme hypercapnia events in the ecosystem may pose increased challenges for these organisms as their tolerance capacity may be time limited.
Continue reading ‘Native and exotic oysters in Brazil: comparative tolerance to hypercapnia’
Individual and interactive effects of ocean acidification, global warming, and UV radiation on phytoplankton
Published 21 November 2017 Science ClosedTags: biological response, phytoplankton, review
Rising carbon dioxide (CO2) concentrations in the atmosphere result in increasing global temperatures and ocean warming (OW). Concomitantly, dissolution of anthropogenic CO2 declines seawater pH, resulting in ocean acidification (OA) and altering marine chemical environments. The marine biological carbon pump driven by marine photosynthesis plays an important role for oceanic carbon sinks. Therefore, how ocean climate changes affect the amount of carbon fixation by primary producers is closely related to future ocean carbon uptake. OA may upregulate metabolic pathways in phytoplankton, such as upregulating ß-oxidation and the tricarboxylic acid cycle, resulting in increased accumulation of toxic phenolic compounds. Ocean warming decreases global phytoplankton productivity; however, regionally, it may stimulate primary productivity and change phytoplankton community composition, due to different physical and chemical environmental requirements of species. It is still controversial how OA and OW interactively affect marine carbon fixation by photosynthetic organisms. OA impairs the process of calcification in calcifying phytoplankton and aggravate ultraviolet (UV)-induced harms to the cells. Increasing temperatures enhance the activity of cellular repair mechanisms, which mitigates UV-induced damage. The effects of OA, warming, enhanced exposure to UV-B as well as the interactions of these environmental stress factors on phytoplankton productivity and community composition, are discussed in this review.
Boron isotopic systematics in scleractinian corals and the role of pH up-regulation
Published 21 November 2017 Science ClosedTags: corals, methods, physiology, review
The boron isotopic composition (δ11B) of scleractinian corals has been used to track changes in seawater pH and more recently as a probe into the processes controlling bio-calcification. For corals that precipitate aragonite skeletons, up-regulation of pH appears to be a general characteristic, typically being ~0.3 to ~0.6 pH units higher than ambient seawater. The relationship between the pH of the corals calcifying-fluid (pHcf) and seawater pHT (total scale) is shown to be dependent on both physiological as well environmental factors. In laboratory experiments conducted on symbiont-bearing (zooxanthellate) corals under conditions of constant temperature and seawater pH, changes in the δ11B derived calcifying fluid pHcf is typically 1/3 to 1/2 of that of ambient seawater. Similar linear relationships are found for cold water corals that live in relatively stable, cold, deep-water environments but at significantly elevated levels of pHcf (~0.5–1 pH units above seawater), a likely response to the lower pH of their deep-sea environments. In contrast, zooxanthellae-bearing corals living in shallow-water reef environments that experience significant natural variations in temperature, light, nutrients and seawater pH, show different types of responses. For example, over seasonal time-scales Porites corals from the Great Barrier Reef (GBR) have a large range in pHcf of ~8.3 to ~8.5, significantly greater (~×2 to ~×3) than that of reef-water (pHT ~8.01 to ~8.08), and an order of magnitude greater than that expected from ‘static’ laboratory experiments. Strong physiological controls, but of a different character, are found in corals grown in a Free Ocean Carbon Enrichment Experiment (FOCE) conducted in situ within the Heron Island lagoon (GBR). These corals exhibit near constant pHcf values regardless of external changes in temperature and seawater pH. This pattern of strong physiologically controlled ‘pH–homeostasis’, with elevated but constant pHcf has been found despite large natural seasonal variations in the pH (±0.15 pH units) of the lagoon waters, as well as the even larger super-imposed decreases in seawater pH (~0.25 pH units) designed to simulate year 2100 conditions. In natural reef environments we thus find that the processes influencing the up-regulation of pHcf in symbiont-bearing corals are subject to strong physiological controls, behaviour that is not well simulated in the current generation of aquaria-based experiments with fixed seawater pH and temperature. Conversely, cold-water corals that lack symbionts and inhabit the relatively stable deep-sea environments hold the best prospects for providing reliable reconstructions of seawater pH. Clearly, further studies utilising the δ11B-pHcf proxy combined with other DIC/carbonate-ion proxies (e.g. B/Ca), but conducted under realistic ‘natural’ conditions, are required to elucidate the processes controlling coral bio-calcification and to better understand the vulnerability of scleractinian corals to anthropogenic driven warming and ocean acidification.
