For the latest marine science and other ocean news, subscribe to Ocean Update, Marine Science Review and our other free newsletters.

SeaWeb connects marine scientists to a global audience. Tell us about
your research at editor@seaweb.org so that we can highlight your work.

Contaminants and Pollution: Ocean Acidification

• Schiermeier, Q.  Earth's acid test.  Nature 471(7337): 154-156, 2011.  
  

   

• Lopez, I.R., Kalman, J., Vale, C., and Blasco, J.  Influence of sediment acidification on the bioaccumulation of metals in Ruditapes philippinarum.  Environmental Science and Pollution Research 17(9): 1519-1528, 2010.
  Read Abstract >>

  Background, aim and scope  The influence of pH (range 6.5-8.5) on the uptake of Zn, Cd, Pb, Cu, Ni, Cr, Hg, and As by juveniles of the clam Ruditapes philippinarum  was examined in order to understand whether variation in sediment pH has significant repercussions on metal bioaccumulation.  Materials and methods  Clams were exposed to sediments collected in three locations in the Gulf of Cadiz (Huelva, Guadalquivir and Bay of Cadiz) and to contaminated particles derived from an accidental mining spill in Spain.  Results  With a notable exception of metal Cd, the concentration of metals within clams significantly increased (p < 0.1) when sediment pH was lowered by one or two units. Moreover, the magnitude of this effect was dependent on the type of sediment contamination.  Discussion  Lower pH increases metal solubility and reduces or invert the metal sorption of metals to sediments. Increases in free metal ions in water favors metal uptake by clams, hence pH is an important factor controlling the mobility of these metals within sediments and their subsequent bioaccumulation within biota. Although sediment-water exchange of Cd can increase with acidification, this excess may be counterbalanced by the presence of ligands in seawater preventing the uptake by organism. Besides chlorines, Cd has also an affinity with carbonates and other ligands present in sea water. These Cd-carbonate complexes may reduce the bioavailable to organisms.  Conclusions  These results highlight the potential implications of sediment acidification, either due to the storage excess of organic matter or to the forced capture of CO₂, on the increasing metal availability to benthic organisms.  Recommendations and perspectives  This kind of studies should be increased to address the influence of acidification in the behavior, bioavailability, toxicity, and risk assessment of contaminants associated with sediments either above sub-seabed geological formations in marine environments or in high enriched by organic matter in estuarine areas. Recently, the capture of CO₂ in marine environments has been approved and started; it is necessary to address the potential impacts associated with leakages or other events occurring during the procedure of injection and storage of CO₂.

• Comeau, S., Gorsky, G., Alliouane, S., and Gattuso, J.P.  Larvae of the pteropod Cavolinia inflexa exposed to aragonite undersaturation are viable but shell-less.  Marine Biology 157(10): 2341-2345, 2010.   
  Read Abstract >>

  Larvae of the Mediterranean pteropod Cavolinia inflexa were maintained at controlled pH_T values of 8.1, 7.82 and 7.51, equivalent, respectively, to pCO₂ levels of 380, 857 and 1,713 µatm. At pH_T 7.82, larvae exhibited malformations and lower shell growth, compared to the control condition. At pH_T 7.51, the larvae did not make shells but were viable and showed a normal development. However, smaller shells or no shells will have both ecological (food web) and biogeochemical (export of carbon and carbonate) consequences. These results suggest that pteropod larvae, as well as the species dependent upon them or upon adults as a food resource, might be significantly impacted by ocean acidification.

• Parker, L.M., Ross, P.M., and O'Connor, W.A.  Comparing the effect of elevated pCO₂ and temperature on the fertilization and early development of two species of oysters.  Marine Biology 157(11): 2435-2452, 2010.
  Read Abstract >>

  This study compared the synergistic effects of elevated pCO₂ and temperature on the early life history stages of two ecologically and economically important oysters: the Sydney rock oyster, Saccostrea glomerata and the Pacific oyster, Crassostrea gigas. Gametes, embryos, larvae and spat were exposed to four pCO₂ (375, 600, 750, 1,000 µatm) and four temperature (18, 22, 26, 30 ºC) levels. At elevated pCO₂ and suboptimal temperatures, there was a reduction in the fertilization success of gametes, a reduction in the development of embryos and size of larvae and spat and an increase in abnormal morphology of larvae. These effects varied between species and fertilization treatments with S. glomerata having greater sensitivity than C. gigas. In the absence of adaptation, C. gigas may become the more dominant species along the south-eastern coast of Australia, recruiting into estuaries currently dominated by the native S. glomerata.

• Thomsen, J. and Melzner, F.  Moderate seawater acidification does not elicit long-term metabolic depression in the blue mussel Mytilus edulis.  Marine Biology 157(12): 2667-2676, 2010.
  Read Abstract >>

  Marine organisms are exposed to increasingly acidic oceans, as a result of equilibration of surface ocean water with rising atmospheric CO₂ concentrations. In this study, we examined the physiological response of Mytilus edulis from the Baltic Sea, grown for 2 months at 4 seawater pCO₂ levels (39, 113, 243 and 405 Pa/385, 1,120, 2,400 and 4,000 µatm). Shell and somatic growth, calcification, oxygen consumption and NH₄⁺ excretion rates were measured in order to test the hypothesis whether exposure to elevated seawater pCO₂ is causally related to metabolic depression. During the experimental period, mussel shell mass and shell-free dry mass (SFDM) increased at least by a factor of two and three, respectively. However, shell length and shell mass growth decreased linearly with increasing pCO₂ by 6-20 and 10-34%, while SFDM growth was not significantly affected by hypercapnia. We observed a parabolic change in routine metabolic rates with increasing pCO₂ and the highest rates (+60%) at 243 Pa. NH₄⁺ excretion rose linearly with increasing pCO₂. Decreased O:N ratios at the highest seawater pCO₂ indicate enhanced protein metabolism which may contribute to intracellular pH regulation. We suggest that reduced shell growth under severe acidification is not caused by (global) metabolic depression but is potentially due to synergistic effects of increased cellular energy demand and nitrogen loss.

• Ericson, J.A., Lamare, M.D., Morley, S.A., and Barker, M.F.  The response of two ecologically important Antarctic invertebrates (Sterechinus neumayeri and Parborlasia corrugatus) to reduced seawater pH: effects on fertilisation and embryonic development.  Marine Biology 157(12): 2689-2702, 2010.
  Read Abstract >>

  Ocean acidification, or the lowering of seawater pH, is caused by sequestration of atmospheric CO₂ into the oceans. This study investigated the effects of present-day pH 8.0, predicted ocean surface pH for the years 2100 and 2300 (pH 7.7 and pH 7.3, respectively) and an extreme pH (pH 7.0) on fertilisation and embryogenesis in the Antarctic nemertean worm  Parborlasia corrugatus and sea urchin Sterechinus neumayeri. Fertilisation success was not affected by pH in P. corrugatus across a range of sperm concentrations. Fertilisation success in S. neumayeri declined significantly in pH 7.0 and 7.3 seawater, but only at a low sperm concentration. Seawater pH had no effect on the rate of egg cleavage in S. neumayeri, or the proportion of abnormal embryos 1-day post-fertilisation. P. corrugatus embryogenesis was also relatively robust to pH changes, with a significant effect detected only when the seawater pH was decreased to 7.0. While fertilisation and early cell division were relatively robust, later development through to the gastrula was sensitive to pH. In S. neumayeri, an effect of pH on development was evident by the gastrula stage, while there were significantly more abnormal P. corrugatus embryos in pH 7.0 up to the blastula stage, and in pH 7.0 and pH 7.3 at the coeloblastula stage. Our results are similar to the observations on other marine invertebrate species where fertilisation and early embryonic development are generally robust to lowered seawater pH, while the older coeloblastula and gastrula stages are more responsive. We also found no evidence to suggest that Antarctic species are more adversely affected by lower seawater pH compared with the findings for non-Antarctic counterparts. We conclude that in the two species we examined, near-future decreases in pH (decreases of a parts per thousand 0.3-0.5 pH units) may not have a significant effect on fertilisation and early embryogenesis, while predicted longer term decreases (decreases of a parts per thousand 0.7-0.77 pH units) could reduce fertilisation success in S. neumayeri if sperm concentrations are low and may increase abnormalities in P. corrugatus during later embryogenesis.

• Cigliano, M., Gambi, M.C., Rodolfo-Metalpa, R., Patti, F.P., and Hall-Spencer, J.M.  Effects of ocean acidification on invertebrate settlement at volcanic CO₂ vents.  Marine Biology 157(11): 2489-2502, 2010.
  Read Abstract >>

  We present the first study of the effects of ocean acidification on settlement of benthic invertebrates and microfauna. Artificial collectors were placed for 1 month along pH gradients at CO₂ vents off Ischia (Tyrrhenian Sea, Italy). Seventy-nine taxa were identified from six main taxonomic groups (foraminiferans, nematodes, polychaetes, molluscs, crustaceans and chaetognaths). Calcareous foraminiferans, serpulid polychaetes, gastropods and bivalves showed highly significant reductions in recruitment to the collectors as pCO₂ rose from normal (336 - 341 ppm, pH 8.09 - 8.15) to high levels (886 - 5,148 ppm) causing acidified conditions near the vents (pH 7.08 - 7.79). Only the syllid polychaete Syllis prolifera had higher abundances at the most acidified station, although a wide range of polychaetes and small crustaceans was able to settle and survive under these conditions. A few taxa (Amphiglena mediterranea, Leptochelia dubia, Caprella acanthifera) were particularly abundant at stations acidified by intermediate amounts of CO₂ (pH 7.41 - 7.99). These results show that increased levels of CO₂ can profoundly affect the settlement of a wide range of benthic organisms.

• Richier, S., Fiorini, S., Kerros, M.E., von Dassow, P., and Gattuso, J.P.  Response of the calcifying coccolithophore Emiliania huxleyi to low pH/high pCO₂: from physiology to molecular level.  Marine Biology 158(3): 551-560, 2011.
  Read Abstract >>

  The emergence of ocean acidification as a significant threat to calcifying organisms in marine ecosystems creates a pressing need to understand the physiological and molecular mechanisms by which calcification is affected by environmental parameters. We report here, for the first time, changes in gene expression induced by variations in pH/pCO₂ in the widespread and abundant coccolithophore Emiliania huxleyi. Batch cultures were subjected to increased partial pressure of CO₂ (pCO₂; i.e. decreased pH), and the changes in expression of four functional gene classes directly or indirectly related to calcification were investigated. Increased pCO₂ did not affect the calcification rate and only carbonic anhydrase transcripts exhibited a significant down-regulation. Our observation that elevated pCO₂ induces only limited changes in the transcription of several transporters of calcium and bicarbonate gives new significant elements to understand cellular mechanisms underlying the early response of E. huxleyi to CO₂-driven ocean acidification.

• Parker, L.M., Ross, P.M., and O'Connor, W.A.  Populations of the Sydney rock oyster, Saccostrea glomerata, vary in response to ocean acidification.  Marine Biology 158(3): 689-697, 2011.
  Read Abstract >>

  Acidifying oceans are predicted to fundamentally alter marine ecosystems. Over the next century, acute studies suggest that the impacts of climate change on marine organisms and ecosystems may be catastrophic. To date, however, little is known about whether the response of marine organisms varies within a species and whether this provides a potential ''adaptive capacity''. Here, we show that selectively bred lines of the ecologically and economically important estuarine mollusc, the Sydney rock oyster Saccostrea glomerata, are more resilient to ocean acidification than the wild populations. When reared at elevated pCO₂, we found a 25% reduction in shell growth of the selectively bred population of the Sydney rock oyster, Saccostrea glomerata, compared to a 64% reduction in shell growth of wild populations. This study shows that there are significantly different sensitivities to ocean acidification even within the same species, providing preliminary evidence that selective breeding may be a solution for important aquaculture industries to overcome the future effects of ocean acidification.

• Marchant, H.K., Calosi, P., and Spicer, J.I.  Short-term exposure to hypercapnia does not compromise feeding, acid-base balance or respiration of Patella vulgata but surprisingly is accompanied by radula damage.  Journal of the Marine Biological Association of the United Kingdom 90(7): 1379-1384, 2010.
  Read Abstract >>

  The effect of short-term (5 days) exposure to CO₂-acidified seawater (year 2100 predicted values, ocean pH = 7.6) on key aspects of the function of the intertidal common limpet Patella vulgata (Gastropoda: Patellidae) was investigated. Changes in extracellular acid-base balance were almost completely compensated by an increase in bicarbonate ions. A concomitant increase in haemolymph Ca²⁺ and visible shell dissolution implicated passive shell dissolution as the bicarbonate source. Analysis of the radula using SEM revealed that individuals from the hypercapnic treatment showed an increase in the number of damaged teeth and the extent to which such teeth were damaged compared with controls. As radula teeth are composed mainly of chitin, acid dissolution seems unlikely, and so the proximate cause of damage is unknown. There was no hypercapnia-related change in metabolism (O₂ uptake) or feeding rate, also discounting the possibility that teeth damage was a result of a CO₂-related increase in grazing. We conclude that although the limpet appears to have the physiological capacity to maintain its extracellular acid-base balance, metabolism and feeding rate over a 5 days exposure to acidified seawater, radular damage somehow incurred during this time could still compromise feeding in the longer term, in turn decreasing the top-down ecosystem control that P. vulgata exerts over rocky shore environments.

• Findlay, H.S., Burrows, M.T., Kendall, M.A., Spicer, J.I., and Widdicombe, S.  Can ocean acidification affect population dynamics of the barnacle Semibalanus balanoides at its southern range edge?  Ecology 91(10): 2931-2940, 2010.
  Read Abstract >>

  The global ocean and atmosphere are warming. There is increasing evidence suggesting that, in addition to other environmental factors, climate change is affecting species distributions and local population dynamics. Additionally, as a consequence of the growing levels of atmospheric carbon dioxide (CO₂), the oceans are taking up increasing amounts of this CO₂, causing ocean pH to decrease (ocean acidification). The relative impacts of ocean acidification on population dynamics have yet to be investigated, despite many studies indicating that there will be at least a sublethal impact on many marine organisms, particularly key calcifying organisms. Using empirical data, we forced a barnacle (Semibalanus balanoides) population model to investigate the relative influence of sea surface temperature (SST) and ocean acidification on a population nearing the southern limit of its geographic distribution. Hindcast models were compared to observational data from Cellar Beach (southwestern United Kingdom). Results indicate that a declining pH trend (-0.0017 unit/yr), indicative of ocean acidification over the past 50 years, does not cause an observable impact on the population abundance relative to changes caused by fluctuations in temperature. Below the critical temperature (here T_crit = 13.1 ºC), pH has a more significant affect on population dynamics at this southern range edge. However, above this value, SST has the overriding influence. At lower SST, a decrease in pH (according to the National Bureau of Standards, pH_NBS) from 8.2 to 7.8 can significantly decrease the population abundance. The lethal impacts of ocean acidification observed in experiments on early life stages reduce cumulative survival by ~25%, which again will significantly alter the population level at this southern limit. Furthermore, forecast predictions from this model suggest that combined acidification and warming cause this local population to die out 10 years earlier than would occur if there was only global warming and no concomitant decrease in pH.

• Kroeker, K.J., Kordas, R.L., Crim, R.N., and Singh, G.G.  Meta-analysis reveals negative yet variable effects of ocean acidification on marine organisms.  Ecology Letters 13(11): 1419-1434, 2010.
  Open Access >>
  Read Abstract >>

  Ocean acidification is a pervasive stressor that could affect many marine organisms and cause profound ecological shifts. A variety of biological responses to ocean acidification have been measured across a range of taxa, but this information exists as case studies and has not been synthesized into meaningful comparisons amongst response variables and functional groups. We used meta-analytic techniques to explore the biological responses to ocean acidification, and found negative effects on survival, calcification, growth and reproduction. However, there was significant variation in the sensitivity of marine organisms. Calcifying organisms generally exhibited larger negative responses than non-calcifying organisms across numerous response variables, with the exception of crustaceans, which calcify but were not negatively affected. Calcification responses varied significantly amongst organisms using different mineral forms of calcium carbonate. Organisms using one of the more soluble forms of calcium carbonate (high-magnesium calcite) can be more resilient to ocean acidification than less soluble forms (calcite and aragonite). Additionally, there was variation in the sensitivities of different developmental stages, but this variation was dependent on the taxonomic group. Our analyses suggest that the biological effects of ocean acidification are generally large and negative, but the variation in sensitivity amongst organisms has important implications for ecosystem responses.

• Diaz-Pulido, G., Gouezo, M., Tilbrook, B., Dove, S., and Anthony, K.R.N.  High CO₂ enhances the competitive strength of seaweeds over corals.  Ecology Letters 14(2): 156-162, 2011.
  Open Access >>
  Read Abstract >>

  Space competition between corals and seaweeds is an important ecological process underlying coral-reef dynamics. Processes promoting seaweed growth and survival, such as herbivore overfishing and eutrophication, can lead to local reef degradation. Here, we present the case that increasing concentrations of atmospheric CO₂ may be an additional process driving a shift from corals to seaweeds on reefs. Coral (Acropora intermedia) mortality in contact with a common coral-reef seaweed (Lobophora papenfussii) increased two- to threefold between background CO₂ (400 ppm) and highest level projected for late 21st century (1140 ppm). The strong interaction between CO₂ and seaweeds on coral mortality was most likely attributable to a chemical competitive mechanism, as control corals with algal mimics showed no mortality. Our results suggest that coral (Acropora) reefs may become increasingly susceptible to seaweed proliferation under ocean acidification, and processes regulating algal abundance (e.g. herbivory) will play an increasingly important role in maintaining coral abundance.

• Fiorini, S., Gattuso, J.P., van Rijswijk, P., and Middelburg, J.  Coccolithophores lipid and carbon isotope composition and their variability related to changes in seawater carbonate chemistry.  Journal of Experimental Marine Biology and Ecology 394(1-2): 74-85, 2010.
  Read Abstract >>

  Growth rate, C:N ratio, phospholipid-derived fatty acids (PLEA) distribution and organic carbon isotope composition (∂¹³C) of both life stages of the Prymnesiophyceae Emiliania huxleyi (Lohmann), Calcidiscus leptoporus (Murray and Blackman) and Syracosphaera pulchra (Lohman) were analyzed. Cultures were grown at two different CO₂ partial pressures (pCO₂, 400 and 760 µatm) under nutrient-replete conditions. Growth rates (µ) increased at 760 µatm in all species. C:N ratios were unaffected by pCO₂ in C. leptoporus  and in the diploid stage of E. huxleyi; they significantly decreased in the haploid stage of E. huxleyi and in both life stages of S. pulchra. At 400 µatm, high similarity was found between the lipid composition of C. leptoporus and S. pulchra differing from that of E. huxleyi. The haploid and diploid life stages showed significant differences in mono- and polyunsaturated C18 fatty acids (MUFA and PUFA), which were more abundant in either stage depending on the species. Except for palmitoleic, vaccenic acids and docosa-hexaeonic acid (DHA). C. leptoporus and S. pulchra fatty acids were lower compared to those of E. huxleyi. Differences in ∂¹³C between particulate organic carbon (POC) and PLFA (Δ∂¹³C_lipid-POC) showed common trends at both pCO₂: palmitoleic, oleic acids and DHA were systematically depleted compared to total cell biomass, C18 PUFA were enriched while saturated fatty acids (SAFA) were enriched in C. leptoporus and S. pulchra and depleted in E. huxleyi. Elevated pCO₂ influenced PLFA abundance, ∂¹³C of lipids and POC in a highly species-specific way. Fatty acids were generally more depleted at 760 µatm than at 400 µatm but the effect was variable among PLEA classes. The relationship between coccolithophore isotopic and PLFA composition and CO₂ concentration are analyzed and consequent variations in the future web-chain related to changes in carbonate chemistry are discussed.

• Yoshimura, T., Nishioka, J., Suzuki, K., Hattori, H., Kiyosawa, H., and Watanabe, Y.W.  Impacts of elevated CO₂ on organic carbon dynamics in nutrient depleted Okhotsk Sea surface waters.  Journal of Experimental Marine Biology and Ecology 395(1-2): 191-198, 2010.
  Read Abstract >>

  Increasing CO₂ in seawater (i.e. ocean acidification) may have various and potentially adverse effects on phytoplankton dynamics and hence the organic carbon dynamics. We conducted a CO₂ manipulation experiment in the Sea of Okhotsk in summer 2006 to investigate the response of the organic carbon dynamics. During the 14-day incubation of nutrient depleted and 200 µatm in situ pCO₂ surface water with a natural plankton assemblage under 150, 280, 480, and 590 µatm pCO₂, the amount of net dissolved organic carbon accumulation was significantly lower at >480 µatm pCO₂ than at 150 µatm pCO₂, while differences in net particulate organic carbon accumulation between the treatments were small and did not show a clear relationship with the pCO₂. This is the first report to show a decreased net organic carbon production of natural plankton community under elevated pCO₂. Phytoplankton pigment analysis suggests that the relative contribution of fucoxanthin-containing phytoplankton such as diatoms to the phytoplankton biomass was lower at >280 µatm pCO₂ than at 150 µatm pCO₂. Different pCO₂ conditions may alter the organic carbon dynamics through changes in plankton processes. We conclude that the continuing increase in atmospheric CO₂ in a time scale from the last half century to the end of this century has potential to affect the carbon cycle in nutrient depleted subpolar surface waters.

• Range, P., Chícharo, M.A., Ben-Hamadou, R., Piló, D., Matias, D., Joaquim, S., Oliveira, A.P., and Chícharo, L.  Calcification, growth and mortality of juvenile clams Ruditapes decussatus under increased pCO₂ and reduced pH: Variable responses to ocean acidification at local scales?  Journal of Experimental Marine Biology and Ecology 396(2): 177-184, 2011.
  Open Access >>
  Read Abstract >>

  We investigated the effects of ocean acidification on juvenile clams Ruditapes decussatus (average shell length 10.24 mm) in a controlled CO₂ perturbation experiment. The carbonate chemistry of seawater was manipulated by diffusing pure CO₂, to attain two reduced pH levels (by -0.4 and -0.7 pH units), which were compared to unmanipulated seawater. After 75 days we found no differences among pH treatments in terms of net calcification, size or weight of the clams. The naturally elevated total alkalinity of local seawater probably contributed to buffer the effects of increased pCO₂ and reduced pH. Marine organisms may, therefore, show diverse responses to ocean acidification at local scales, particularly in coastal, estuarine and transitional waters, where the physical-chemical characteristics of seawater are most variable. Mortality was significantly reduced in the acidified treatments. This trend was probably related to the occurrence of spontaneous spawning events in the control and intermediate acidification treatments. Spawning, which was unexpected due to the small size of the clams, was not observed for the pH -0.7 treatment, suggesting that the increased survival under acidified conditions may have been associated with a delay in the reproductive cycle of the clams. Future research about the impacts of ocean acidification on marine biodiversity should be extended to other types of biological and ecological processes, apart from biological calcification.

• Anlauf, H., D'Croz, L., and O'Dea, A.  A corrosive concoction: The combined effects of ocean warming and acidification on the early growth of a stony coral are multiplicative.  Journal of Experimental Marine Biology and Ecology 397(1): 13-20, 2011.
  Read Abstract >>

  Survival of coral planulae, and the successful settlement and healthy growth of primary polyps are critical for the dispersal of scleractinian corals and hence the recovery of degraded coral reefs. It is therefore important to explore how the warmer and more acidic oceanic conditions predicted for the future could affect these processes. This study used controlled culture to investigate the effects of a 1 ºC increase in temperature and a 0.2-0.25 unit decrease in pH on the settlement and survival of planulae and the growth of primary polyps in the Tropical Eastern Pacific coral Porites panamensis. We found that primary polyp growth was reduced only marginally by more acidic seawater but the combined effect of high temperature and lowered pH caused a significant reduction in growth of primary polyps by almost a third. Elevated temperature was found to significantly reduce the amount of zooxanthellae in primary polyps, and when combined with lowered pH resulted in a significant reduction in biomass of primary polyps. However, survival and settlement of planula larvae were unaffected by increased temperature, lowered acidity or the combination of both. These results indicate that in future scenarios of increased temperature and oceanic acidity coral planulae will be able to disperse and settle successfully but primary polyp growth may be hampered. The recovery of reefs may therefore be impeded by global change even if local stressors are curbed and sufficient sources of planulae are available.

• Kim, J.M. et al.  Enhanced production of oceanic dimethylsulfide resulting from CO₂-induced grazing activity in a high CO₂ world.  Environmental Science and Technology 44(21): 8140-8143, 2010.
  Read Abstract >>

  Oceanic dimethylsulfide (DMS) released to the atmosphere affects the Earth's radiation budget through the production and growth of cloud condensation nuclei over the oceans. However, it is not yet known whether this negative climate feedback mechanism will intensify or weaken in oceans characterized by high CO₂ levels and warm temperatures. To investigate the effects of two emerging environmental threats (ocean acidification and warming) on marine DMS production, we performed a perturbation experiment in a coastal environment. Two sets of CO₂ and temperature conditions (a pCO₂ of ~900 ppmv at ambient temperature conditions, and a pCO₂ of ~900 ppmv at a temperature ~3 ºC warmer than ambient) significantly stimulated the grazing rate and the growth rate of heterotrophic dinoflagellates (ubiquitous marine microzooplankton). The increased grazing rate resulted in considerable DMS production. Our results indicate that increased grazing-induced DMS production may occur in high CO₂ oceans in the future.

• Wu, Y., Gao, K., and Riebesell, U.  CO₂-induced seawater acidification affects physiological performance of the marine diatom Phaeodactylum tricornutum.  Biogeosciences 7(9): 2915-2923, 2010.
  Open Access >>
  Read Abstract >>

  CO₂/pH perturbation experiments were carried out under two different pCO₂ levels (39.3 and 101.3 Pa) to evaluate effects of CO₂-induced ocean acidification on the marine diatom Phaeodactylum tricornutum. After acclimation (>20 generations) to ambient and elevated CO2 conditions (with corresponding pH values of 8.15 and 7.80, respectively), growth and photosynthetic carbon fixation rates of high CO₂ grown cells were enhanced by 5% and 12%, respectively, and dark respiration stimulated by 34% compared to cells grown at ambient CO₂. The half saturation constant (K_m) for carbon fixation (dissolved inorganic carbon, DIC) increased by 20% under the low pH and high CO₂ condition, reflecting a decreased affinity for HCO₃^- or/and CO₂ and down-regulated carbon concentrating mechanism (CCM). In the high CO₂ grown cells, the electron transport rate from photosystem II (PSII) was photoinhibited to a greater extent at high levels of photosynthetically active radiation, while non-photochemical quenching was reduced compared to low CO₂ grown cells. This was probably due to the down-regulation of CCM, which serves as a sink for excessive energy. The balance between these positive and negative effects on diatom productivity will be a key factor in determining the net effect of rising atmospheric CO₂ on ocean primary production.

• Provoost, P., van Heuven, S., Soetaert, K., Laane, R.W.P.M., and Middelburg, J.J.  Seasonal and long-term changes in pH in the Dutch coastal zone.  Biogeosciences 7(11): 3869-3878, 2010.
  Open Access >>
  Read Abstract >>

  Recent observations and modelling studies suggest that biogeochemical changes can mask atmospheric CO₂-induced pH decreases. Data collected by the Dutch monitoring authorities in different coastal systems (North Sea, Wadden Sea, Ems-Dollard, Eastern Scheldt and Scheldt estuary) since 1975 provide an excellent opportunity to test whether this is the case in the Dutch coastal zone. The time-series were analysed using Multi-Resolution Analysis (MRA) which resulted in the identification of system-dependent patterns on both seasonal and intra-annual time scales. The observed rates of pH change greatly exceed those expected from enhanced CO₂ uptake, thus suggesting that other biogeochemical processes, possibly related to changes in nutrient loading, can play a dominant role in ocean acidification.

• Thomsen, J., Gutowska, M.A., Saphörster, J., Heinemann, A., Trübenbach, K., Fietzke, J., Hiebenthal, C., Eisenhauer, A., Körtzinger, A., Wahl, M., and Melzner, F.  Calcifying invertebrates succeed in a naturally CO₂-rich coastal habitat but are threatened by high levels of future acidification.  Biogeosciences 7(11): 3879-3891, 2010.
  Open Access >>
  Read Abstract >>

  CO₂ emissions are leading to an acidification of the oceans. Predicting marine community vulnerability towards acidification is difficult, as adaptation processes cannot be accounted for in most experimental studies. Naturally CO₂ enriched sites thus can serve as valuable proxies for future changes in community structure. Here we describe a natural analogue site in the Western Baltic Sea. Seawater pCO₂ in Kiel Fjord is elevated for large parts of the year due to upwelling of CO₂ rich waters. Peak pCO₂ values of >230 Pa (>2300 µatm) and pH_NBS values of <7.5 are encountered during summer and autumn, average pCO₂ values are ~70 Pa (~700 µatm). In contrast to previously described naturally CO₂ enriched sites that have suggested a progressive displacement of calcifying auto- and heterotrophic species, the macrobenthic community in Kiel Fjord is dominated by calcifying invertebrates. We show that blue mussels from Kiel Fjord can maintain control rates of somatic and shell growth at a pCO₂ of 142 Pa (1400 µatm, pH_NBS = 7.7). Juvenile mussel recruitment peaks during the summer months, when high water pCO₂ values of ~100 Pa (~1000 µatm) prevail. Our findings indicate that calcifying keystone species may be able to cope with surface ocean pH_NBS values projected for the end of this century when food supply is sufficient. However, owing to non-linear synergistic effects of future acidification and upwelling of corrosive water, peak seawater pCO₂ in Kiel Fjord and many other productive estuarine habitats could increase to values >400 Pa (>4000 µatm). These changes will most likely affect calcification and recruitment, and increase external shell dissolution.

• Gangstø, R., Joos, F., and Gehlen, M.  Sensitivity of pelagic calcification to ocean acidification.  Biogeosciences 8(2): 433-458, 2011.
  Open Access >>  
  Read Abstract >>

  Ocean acidification might reduce the ability of calcifying plankton to produce and maintain their shells of calcite, or of aragonite, the more soluble form of CaCO₃. In addition to possibly large biological impacts, reduced CaCO₃ production corresponds to a negative feedback on atmospheric CO₂. In order to explore the sensitivity of the ocean carbon cycle to increasing concentrations of atmospheric CO₂, we use the new biogeochemical Bern3D/PISCES model. The model reproduces the large scale distributions of biogeochemical tracers. With a range of sensitivity studies, we explore the effect of (i) using different parameterizations of CaCO₃ production fitted to available laboratory and field experiments, of (ii) letting calcite and aragonite be produced by auto- and heterotrophic plankton groups, and of (iii) using carbon emissions from the range of the most recent IPCC Representative Concentration Pathways (RCP). Under a high-emission scenario, the CaCO₃ production of all the model versions decreases from ~1 PgC yr^-1 to between 0.36 and 0.82 Pg C yr^-1 by the year 2100. The changes in CaCO₃ production and dissolution resulting from ocean acidification provide only a small feedback on atmospheric CO₂ of -1 to -11 ppm by the year 2100, despite the wide range of parameterizations, model versions and scenarios included in our study. A potential upper limit of the CO₂ calcification/dissolution feedback of -30 ppm by the year 2100 is computed by setting calcification to zero after 2000 in a high 21st century emission scenario. The similarity of feedback estimates yielded by the model version with calcite produced by nanophytoplankton and the one with calcite, respectively aragonite produced by mesozooplankton suggests that expending biogeochemical models to calcifying zooplankton might not be needed to simulate biogeochemical impacts on the marine carbonate cycle. The changes in saturation state confirm previous studies indicating that future anthropogenic CO₂ emissions may lead to irreversible changes in Ω_A for several centuries. Furthermore, due to the long-term changes in the deep ocean, the ratio of open water CaCO₃ dissolution to production stabilizes by the year 2500 at a value that is 30-50% higher than at pre-industrial times when carbon emissions are set to zero after 2100.

• Logan, C.A.  A review of ocean acidification and America's response.  BioScience 60(10): 819-828, 2010.
  Read Abstract >>

  Ocean acidification is likely to have direct negative physiological consequences for many marine organisms, and cause indirect effects on marine ecosystems. Ocean acidification could also affect the oceans' current role as a net carbon sink by altering the oceanic calcium carbonate budget. Although ocean acidification and climate change are both caused by greenhouse gas emissions, ocean acidification is not climate change per se, and is often referred to as ''the other carbon dioxide (CO₂) problem.'' As the United States considers actions in response to climate change, it is critical to take into account not only the impact of CO₂ emissions on the climate but also their ramifications for ocean chemistry. The metrics that currently guide the climate change debate are dominated by strategies to reduce thermal impacts on the terrestrial environment. In this article, I examine the effects of ocean acidification and why they should help guide decisionmakers in setting CO₂ emissions goals.

• Kadar, E., Simmance, F., Martin, O., Voulvoulis, N., Widdicombe, S., Mitov, S., Lead, J.R., and Readman, J.W.  The influence of engineered Fe₂O₃ nanoparticles and soluble (FeCl₃) iron on the developmental toxicity caused by CO₂-induced seawater acidification.  Environmental Pollution 158(12): 3490-3497, 2010.
  Read Abstract >>

  An embryo development assay using a common test organism, the edible mussel (Mytilus galloprovincialis), exposed to both Fe₂O₃ nanoparticles and soluble FeCl₃ at 3 acidic pHs, has provided evidence for the following: (1) CO₂ enriched seawater adjusted to pH projections for carbon capture leakage scenarios (CCS) significantly impaired embryo development; (2) under natural pH conditions, no significant effect was detected following exposure of embryos to Fe, no matter if in nano- or soluble form: (3) at pH of natural seawater nano-Fe particles aggregate into large, polydisperse and porous particles, with no biological impact detected; (4) at pH 6 and 7, such aggregates may moderate the damage associated with CO₂ enrichment as indicated by an increased prevalence of normal D-shell larvae when nano-Fe was present in the seawater at pH 7, while soluble iron benefited embryo development at pH 6, and (5) the observed effects of iron on pH-induced development toxicity were concentration dependent.

• Munday, P.L., Dixson, D.L., McCormick, M.I., Meekan, M., Ferrari, M.C.O., and Chivers, D.P.  Replenishment of fish populations is threatened by ocean acidification.  Proceedings of the National Academy of Sciences [USA] 107(29): 12930-12934, 2010.
  Open Access >>
  Read Abstract >>

  There is increasing concern that ocean acidification, caused by the uptake of additional CO₂ at the ocean surface, could affect the functioning of marine ecosystems; however, the mechanisms by which population declines will occur have not been identified, especially for noncalcifying species such as fishes. Here, we use a combination of laboratory and field-based experiments to show that levels of dissolved CO₂ predicted to occur in the ocean this century alter the behavior of larval fish and dramatically decrease their survival during recruitment to adult populations. Altered behavior of larvae was detected at 700 ppm CO₂, with many individuals becoming attracted to the smell of predators. At 850 ppm CO₂, the ability to sense predators was completely impaired. Larvae exposed to elevated CO₂ were more active and exhibited riskier behavior in natural coral-reef habitat. As a result, they had 5-9 times higher mortality from predation than current-day controls, with mortality increasing with CO₂ concentration. Our results show that additional CO₂ absorbed into the ocean will reduce recruitment success and have far-reaching consequences for the sustainability of fish populations.

• Albright, R., Mason, B., Miller, M., and Langdon, C.  Ocean acidification compromises recruitment success of the threatened Caribbean coral Acropora palmata.  Proceedings of the National Academy of Sciences [USA] 107(47): 20400-20404, 2010.
  Open Access >>
  Read Abstract >>

  Ocean acidification (OA) refers to the ongoing decline in oceanic pH resulting from the uptake of atmospheric CO₂. Mounting experimental evidence suggests that OA will have negative consequences for a variety of marine organisms. Whereas the effect of OA on the calcification of adult reef corals is increasingly well documented, effects on early life history stages are largely unknown. Coral recruitment, which necessitates successful fertilization, larval settlement, and postsettlement growth and survivorship, is critical to the persistence and resilience of coral reefs. To determine whether OA threatens successful sexual recruitment of reef-building corals, we tested fertilization, settlement, and postsettlement growth of Acropora palmata at pCO₂ levels that represent average ambient conditions during coral spawning (~400 µatm) and the range of pCO2 increases that are expected to occur in this century [(~560 µatm (mid-CO₂) and (~800 µatm (high-CO₂)]. Fertilization, settlement, and growth were all negatively impacted by increasing pCO₂, and impairment of fertilization was exacerbated at lower sperm concentrations. The cumulative impact of OA on fertilization and settlement success is an estimated 52% and 73% reduction in the number of larval settlers on the reef under pCO₂ conditions projected for the middle and the end of this century, respectively. Additional declines of 39% (mid-CO₂) and 50% (high-CO₂) were observed in postsettlement linear extension rates relative to controls. These results suggest that OA has the potential to impact multiple, sequential early life history stages, thereby severely compromising sexual recruitment and the ability of coral reefs to recover from disturbance.

• Beman, J.M., Chow, C.E., King, A.L., Feng, Y.Y., Fuhrman, J.A., Andersson, A., Bates, N.R., Popp, B.N., and Hutchins, D.A.  Global declines in oceanic nitrification rates as a consequence of ocean acidification.  Proceedings of the National Academy of Sciences [USA] 108(1): 208-213, 2011.
  Read Abstract >>

  Ocean acidification produced by dissolution of anthropogenic carbon dioxide (CO₂) emissions in seawater has profound consequences for marine ecology and biogeochemistry. The oceans have absorbed one-third of CO₂ emissions over the past two centuries, altering ocean chemistry, reducing seawater pH, and affecting marine animals and phytoplankton in multiple ways. Microbially mediated ocean biogeochemical processes will be pivotal in determining how the earth system responds to global environmental change; however, how they may be altered by ocean acidification is largely unknown. We show here that microbial nitrification rates decreased in every instance when pH was experimentally reduced (by 0.05-0.14) at multiple locations in the Atlantic and Pacific Oceans. Nitrification is a central process in the nitrogen cycle that produces both the greenhouse gas nitrous oxide and oxidized forms of nitrogen used by phytoplankton and other microorganisms in the sea; at the Bermuda Atlantic Time Series and Hawaii Ocean Time-series sites, experimental acidification decreased ammonia oxidation rates by 38% and 36%. Ammonia oxidation rates were also strongly and inversely correlated with pH along a gradient produced in the oligotrophic Sargasso Sea (r² = 0.87, P < 0.05). Across all experiments, rates declined by 8-38% in low pH treatments, and the greatest absolute decrease occurred where rates were highest off the California coast. Collectively our results suggest that ocean acidification could reduce nitrification rates by 3-44% within the next few decades, affecting oceanic nitrous oxide production, reducing supplies of oxidized nitrogen in the upper layers of the ocean, and fundamentally altering nitrogen cycling in the sea.

• Midorikawa, T. et al.  Decreasing pH trend estimated from 25-yr time series of carbonate parameters in the western North Pacific.  Tellus B 62(5): 649-659, 2010.
  Open Access >>
  Read Abstract >>

  We estimated long-term trends of ocean acidification in surface waters in latitudinal zones from 3°N to 33°N along the repeat hydrographic line at 137°E in the western North Pacific Ocean. Estimates were based on the observational records of oceanic CO₂ partial pressure and related surface properties over the last two decades. The computed pH time series both for 25 yr in winter (late January-early February) and for 21 yr in summer (June-July) exhibited significant decreasing trends in the extensive subtropical to equatorial zones, with interannual variations that were larger in summer. The calculated rates of pH decrease ranged from 0.0015 to 0.0021 yr^-1 (average, 0.0018 ± 0.0002 yr^-1) in winter and from 0.0008 to 0.0019 yr^-1 (average, 0.0013 ± 0.0005 yr^-1) in summer. The thermodynamic effects of rising sea surface temperature (SST) accounted for up to 44% (average, 15%) of the trend of pH decrease in the subtropical region in winter, whereas a trend of decreasing SST slowed the pH decrease in the northern subtropical region (around 25°N) in summer. We used the results from recent trends to evaluate future possible thermodynamic changes in the upper ocean carbonate system.

• Dissanayake, A., Clough, R., Spicer, J.I., and Jones, M.B.  Effects of hypercapnia on acid-base balance and osmo-/iono-regulation in prawns (Decapoda: Palaemonidae).  Aquatic Biology 11(1): 27-36, 2010.
  Read Abstract >>

  Anthropogenic carbon dioxide-induced 'ocean acidification' is predicted to have major implications for marine organisms. As the oceans becomes increasingly hypercapnic (elevated CO₂) and seawater pH decreases, the ability of organisms to maintain extracellular pH homeostasis (acid-base balance) may be compromised. Acid-base regulation occurs by ionic transport, where hydrogen and bicarbonate ions (HCO₃^-) are exchanged for sodium and chloride, respectively (H⁺/Na⁺; HCO₃^-/Cl^-), as exemplified by decapod crustaceans. Palaemonid prawns, in particular, are efficient hypo-ionic/osmotic regulators in seawater. We demonstrate that hypercapnic exposure (0.3 kPa) results in short-term (5 to 14 d) extracellular acidosis in 2 efficient ionic/osmo-regulators (thus, acid-base regulators), i.e. Palaemon elegans and P. serratus. Complete hypercapnic compensation was observed in both species after 30 d exposure with no effect on osmotic capacity, but at the expense of extracellular acid-base alteration (alkalosis). Furthermore, the predominantly subtidal species P. serratus was observed to be as tolerant as the intertidal species P. elegans, although 2 differing mechanisms of ionic regulation may be at work, with P. elegans and P. serratus displaying lower and elevated haemolymph ion concentrations (i.e. sodium, chloride and calcium), respectively.

• Hofmann, M. and Schellnhuber, H.J.  Ocean acidification: a millennial challenge.  Energy and Environmental Science 3(12): 1883-1896, 2010.
  Open Access >>
  Read Abstract >>

  During recent decades, Earth system research has provided overwhelming evidence that climate change, with disastrous consequences, will result from unbridled anthropogenic emissions of greenhouse gases. It is well accepted among climate scientists that these emissions, especially of CO₂, may force the planet to warm by up to seven degrees C by the end of the century. During recent years, however, a second comparably dangerous consequence of steadily increasing atmospheric carbon dioxide levels has received growing attention, namely the acidification of the oceans. Here we discuss its potential effects on marine biogeochemistry and review the recent literature on this issue. Calcifying organisms such as corals, pteropods, coccolithophorides and foraminifera are among the species that will suffer most from unabated ocean acidification.

• Berge, T., Daugbjerg, N., Andersen, B.B., and Hansen, P.J.  Effect of lowered pH on marine phytoplankton growth rates.  Marine Ecology Progress Series 416: 79-91, 2010.
  Read Abstract >>

  Continued anthropogenic carbon emissions are expected to result in an increase in atmospheric CO₂ concentration to 700 ppm by the end of this century. This will cause a corresponding drop in the global average surface water pH of the oceans by ~0.4 units to ~7.8 and an increase in the CO₂ concentration of seawater. Ocean acidification may potentially both stimulate and reduce primary production by marine phytoplankton. Data are scarce on the response of marine phytoplankton growth rates to lowered pH/increased CO₂. Using the acid addition method to lower the seawater pH and manipulate the carbonate system, we determined in detail the lower pH limit for growth rates of 2 model species of common marine phytoplankton. We also tested whether growth and production rates of 6 other common species of phytoplankton were affected by ocean acidification (lowered to pH 7.0). The lower pH limits for growth of the dinoflagellate Heterocapsa triquetra and the cryptophyte Teleaulax amphioxeia were pH ~6.0 and 6.3, respectively. The growth rates of these 2 species were significantly reduced in the range of pH 6.4 to 6.5. Cell volume, growth, and production rates of the 6 other phytoplankton species were statistically similar in the pH range of ~7.0 to 8.5. Our results and literature reports on growth at lowered pH indicate that marine phytoplankton in general are resistant to climate change in terms of ocean acidification, and do not increase or decrease their growth rates according to ecological relevant ranges of pH and free CO₂. We speculate about whether common natural pH fluctuations in time and space from 7.0 to 9.0 make phytoplankton capable of tolerating near-future ocean acidification. However, due to the less fluctuating pH environment of oceanic regions compared to coastal regions, truly oceanic species may be more sensitive to lowered pH than coastal species.

• Walther, K., Anger, K., and Pörtner, H.O.  Effects of ocean acidification and warming on the larval development of the spider crab Hyas araneus from different latitudes (54º vs. 79ºN).  Marine Ecology Progress Series 417: 159-170, 2010.
  Read Abstract >>

  The combined effects of predicted ocean acidification and global warming on the larvae of the cold-eurythermal spider crab Hyas araneus L. were investigated in 2 populations: a southern-most around Helgoland (North Sea, 54ºN) and a northernmost at Svalbard (North Atlantic, 79ºN). Larvae were exposed at temperatures of 3, 9 and 15 ºC to present day normocapnia (380 ppm CO₂) and to CO₂ conditions predicted for the near or medium-term future (710 ppm by the year 2100, 3000 ppm by 2300 and beyond). Larval development time, growth and C/N ratio were studied in the larval stages Zoea I, II, and Megalopa. Permanent differences in instar duration between both populations were detected in all stages, likely as a result of evolutionary temperature adaptation. With the exception of Zoea II at 3 ºC and under all CO₂ conditions, development in all instars from Svalbard was delayed compared to those from Helgoland. Most prominently, development was much longer and fewer specimens morphosed to the first crab instar in the Megalopa from Svalbard than from Helgoland. Enhanced CO₂ levels (particularly 3000 ppm) extended the duration of larval development and reduced larval growth (measured as dry mass) and fitness (decreasing C/N ratio, a proxy of the lipid content). Such effects were strongest in the zoeal stages of Svalbard larvae, and during the Megalopa instar of Helgoland larvae. The high sensitivity of megalopae from the Svalbard population to warming and of those from Helgoland to enhanced CO₂ levels suggests that this larval instar is a physiologically sensitive bottleneck within the life cycle of H. araneus.

• Waldbusser, G.G., Bergschneider, H., and Green, M.A.  Size-dependent pH effect on calcification in post-larval hard clam Mercenaria spp.  Marine Ecology Progress Series 417: 171-182, 2010.
  Read Abstract >>

  Increasing atmospheric carbon dioxide threatens to decrease pH in the world's oceans. Coastal and estuarine calcifying organisms of significant ecological and economical importance are at risk; however, several biogeochemical processes drive pH in these habitats. In particular, coastal and estuarine sediments are frequently undersaturated with respect to calcium carbonate due to high rates of organic matter remineralization, even when overlying waters are saturated. As a result, the post-larval stages of infaunal marine bivalves must be able to deposit new shell material in conditions that are corrosive to shell. We measured calcification rates on the hard clam, Mercenaria spp., in 5 post-larval size classes (0.39, 0.56, 0.78, 0.98, and 2.90 mm shell height) using the alkalinity anomaly method. Acidity of experimental water was controlled by bubbling with air-CO₂ blends to obtain pH values of 8.02, 7.64, and 7.41, corresponding to pCO₂ values of 424, 1120, and 1950 µatm. These pH values are typical of those found in many near-shore terrigenous marine sediments. Our results show that calcification rate decreased with lower pH in all 5 size classes measured. We also found a significant effect of size on calcification rate, with the smaller post-larval sizes unable to overcome dissolution pressure. Increased calcification rate with size allowed the larger sizes to overcome dissolution pressure and deposit new shell material under corrosive conditions. Size dependency of pH effects on calcification is likely due to organogenesis and developmental shifts in shell mineralogy occurring through the post-larval stage. Furthermore, we found significantly different calcification rates between the 2 sources of hard clams we used for these experiments, most likely due to genotypic differences. Our findings confirm the susceptibility of the early life stages of this important bivalve to decreasing pH and reveal mechanisms behind the increased mortality in post-larval juvenile hard clams related to dissolution pressure, that has been found in previous studies.

• Beniash, E., Ivanina, A., Lieb, N.S., Kurochkin, I., and Sokolova, I.M.  Elevated level of carbon dioxide affects metabolism and shell formation in oysters Crassostrea virginica.  Marine Ecology Progress Series 419: 95-108, 2010.
  Read Abstract >>

  Estuarine organisms are exposed to periodic strong fluctuations in seawater pH driven by biological carbon dioxide (CO₂) production, which may in the future be further exacerbated by the ocean acidification associated with the global rise in CO₂. Calcium carbonate-producing marine species such as mollusks are expected to be vulnerable to acidification of estuarine waters, since elevated CO₂ concentration and lower pH lead to a decrease in the degree of saturation of water with respect to calcium carbonate, potentially affecting biomineralization. Our study demonstrates that the increase in CO₂ partial pressure (pCO₂) in seawater and associated decrease in pH within the environmentally relevant range for estuaries have negative effects on physiology, rates of shell deposition and mechanical properties of the shells of eastern oysters Crassostrea virginica (Gmelin). High CO₂ levels (pH ~7.5, pCO₂ ~3500 µatm) caused significant increases in juvenile mortality rates and inhibited both shell and soft-body growth compared to the control conditions (pH ~8.2, pCO₂ ~380 µatm). Furthermore, elevated CO₂ concentrations resulted in higher standard metabolic rates in oyster juveniles, likely due to the higher energy cost of homeostasis. The high CO₂ conditions also led to changes in the ultrastructure and mechanical properties of shells, including increased thickness of the calcite laths within the hypostracum and reduced hardness and fracture toughness of the shells, indicating that elevated CO₂ levels have negative effects on the biomineralization process. These data strongly suggest that the rise in CO₂ can impact physiology and biomineralization in marine calcifiers such as eastern oysters, threatening their survival and potentially leading to profound ecological and economic impacts in estuarine ecosystems.

• Munday, P.L., Gagliano, M., Donelson, J.M., Dixson, D.L., and Thorrold, S.R.  Ocean acidification does not affect the early life history development of a tropical marine fish.  Marine Ecology Progress Series 423: 211-221, 2011.
  Read Abstract >>

  Determining which marine species are sensitive to elevated CO₂ and reduced pH, and which species tolerate these changes, is critical for predicting the impacts of ocean acidification on marine biodiversity and ecosystem function. Although adult fish are thought to be relatively tolerant to higher levels of environmental CO₂, very little is known about the sensitivity of juvenile stages, which are usually much more vulnerable to environmental change. We tested the effects of elevated environmental CO₂ on the growth, survival, skeletal development and otolith (ear bone) calcification of a common coral reef fish, the spiny damselfish Acanthochromis polyacanthus. Newly hatched juveniles were reared for 3 wk at 4 different levels of PCO_2(seawater) spanning concentrations already experienced in near-reef waters (450 µatm CO₂) to those predicted to occur over the next 50 to 100 yr in the IPCC A2 emission scenario (600, 725, 850 µatm CO₂). Elevated PCO₂ had no effect on juvenile growth or survival. Similarly, there was no consistent variation in the size of 29 different skeletal elements that could be attributed to CO₂ treatments. Finally, otolith size, shape and symmetry (between left and right side of the body) were not affected by exposure to elevated PCO₂, despite the fact that otoliths are composed of aragonite. This is the first comprehensive assessment of the likely effects of ocean acidification on the early life history development of a marine fish. Our results suggest that juvenile A. polyacanthus are tolerant of moderate increases in environmental CO₂ and that further acidification of the ocean will not, in isolation, have a significant effect on the early life history development of this species, and perhaps other tropical reef fishes.

• Welladsen, H.M., Southgate, P.C., and Heimann, K.  The effects of exposure to near-future levels of ocean acidification on shell characteristics of Pinctada fucata (Bivalvia: Pteriidae).  Molluscan Research 30(3): 125-130, 2010.
  Open Access >>
  Read Abstract >>

  Atmospheric carbon dioxide concentrations have greatly increased since the beginning of the industrial age. This has led to a decline in global ocean pH by 0.1 units, and continued decline of 0.3-0.5 units is predicted by the end of 2100. Acidification of the ocean has led to decreased calcification rates and dissolution of calcareous structures in a range of marine species. Shells of the pearl oyster Pinctada fucata exposed to acidified seawater (pH 7.8 and pH 7.6) for 28 days were 25.9% and 26.8% weaker than controls (pH 8.1-8.2), respectively, but there was no reduction in the organic content of shells exposed to acidified conditions. Scanning electron microscopy analysis of the growing edge of nacre lining the shells of  P. fucata showed that shells exposed to acidified conditions (pH 7.6) showed signs of malformation and/or dissolution, when compared to controls. The reduction in shell strength and the possible nacre malformation could have broad impacts on the ecology of pearl oysters and consequences for the cultured pearl industry that relies on them.

• Reuter, K.E., Lotterhos, K.E., Crim, R.N., Thompson, C.A., and Harley, C.D.G.  Elevated pCO₂ increases sperm limitation and risk of polyspermy in the red sea urchin Strongylocentrotus franciscanus.  Global Change Biology 17(1): 163-171, 2011.
  Open Access >>
  Read Abstract >>

  Anthropogenic carbon dioxide (CO₂) emissions and the resultant acidification of surface ocean waters are predicted to have far-reaching consequences for biological processes in the marine environment. For example, because changes in pH and pCO2 can alter sperm performance, ocean acidification may be accompanied by reductions in the success of fertilization in marine broadcast spawners. Several studies have attempted to determine the effects of elevated pCO₂ on marine invertebrate fertilization success, albeit with differing results. These conflicts may stem from the use of inappropriate sperm-egg contact times and, in several cases, the lack of measurements over a range of sperm concentrations extending from sperm-limited conditions to polyspermy scenarios. In our study, we used biologically realistic sperm-egg contact times and a full range of sperm concentrations to assess the effect of elevated pCO2 on fertilization in the broadcast spawning sea urchin, Strongylocentrotus franciscanus. Fertilization experiments were carried out in seawater bubbled with CO₂ to 400 (control), 800, and 1800 ppm. Using a fertilization kinetics model, we estimate that elevated pCO₂ levels both increased sperm limitation and reduced the efficiency of fast blocks to polyspermy. Thus, elevated pCO₂ decreased the range of sperm concentrations over which high fertilization success was likely. Given the inherent difficulties in achieving high fertilization success in broadcast spawners, raised pCO₂ levels are likely to exacerbate low fertilization success in low-density populations or in areas with high water turbulence.

• Kiessling, W. and Simpson, C.  On the potential for ocean acidification to be a general cause of ancient reef crises.  Global Change Biology 17(1): 56-67, 2011.
  Open Access >>
  Read Abstract >>

  Anthropogenic rise in the carbon dioxide concentration in the atmosphere leads to global warming and acidification of the oceans. Ocean acidification (OA) is harmful to many organisms but especially to those that build massive skeletons of calcium carbonate, such as reef corals. Here, we test the recent suggestion that OA leads not only to declining calcification of reef corals and reduced growth rates of reefs but may also have been a trigger of ancient reef crises and mass extinctions in the sea. We analyse the fossil record of biogenic reefs and marine organisms to (1) assess the timing and intensity of ancient reef crises, (2) check which reef crises were concurrent with inferred pulses of carbon dioxide concentrations and (3) evaluate the correlation between reef crises and mass extinctions and their selectivity in terms of inferred physiological buffering. We conclude that four of five global metazoan reef crises in the last 500 Myr were probably at least partially governed by OA and rapid global warming. However, only two of the big five mass extinctions show geological evidence of OA.

• Sewell, M.A. and Hofmann, G.E.  Antarctic echinoids and climate change: a major impact on the brooding forms.  Global Change Biology 17(2): 734-744, 2011.
  Read Abstract >>

  Ocean acidification (OA) and the accompanying changes to carbonate concentrations are predicted to have especially negative impacts in the Southern Ocean where, as a result of colder temperatures, there will be shallowing of both the aragonite (ASH) and calcite saturation horizons (CSH). Echinoids are a dominant group of the Antarctic macrofauna which, because of their high-Mg calcite skeleton, are particularly susceptible to changes in the ASH. Using published information on the bathymetric distributions of Antarctic echinoids, we show that the majority of heavily calcified echinoids have their lower bathymetric limit above a depth of ca. 3000 m, approximately the current depth of the CSH. Echinoids whose depth range extends below 3000 m generally have thin, weakly calcified tests and include species from the Order Holasteroida, and the Families Cidaridae and Schizasteridae. Examination of the reproductive mode of Antarctic echinoids shows that brooding, where calcification of the young occurs in the same CaCO₃ environment as the mother, is primarily found at a depth above 3000 m. The predicted shallowing of the ASH and CSH under OA conditions is likely to negatively impact growth and reproduction of heavily calcified brooders in the Family Cidaridae, which may result in changes to bathymetric ranges, local population extinction, and associated losses in macrofaunal biodiversity. As with other calcified deep sea invertebrates, echinoids may be particularly vulnerable to the impacts of increased CO₂ and OA in the Southern Ocean.

• Cummings, V. et al.  Ocean acidification at high latitudes: Potential effects on functioning of the Antarctic bivalve Laternula elliptica.  PLoS ONE 6(1): art. e16069, 2011.
  Open Access >>
  Read Abstract >>

  Ocean acidification is a well recognised threat to marine ecosystems. High latitude regions are predicted to be particularly affected due to cold waters and naturally low carbonate saturation levels. This is of concern for organisms utilising calcium carbonate (CaCO₃) to generate shells or skeletons. Studies of potential effects of future levels of pCO₂ on high latitude calcifiers are at present limited, and there is little understanding of their potential to acclimate to these changes. We describe a laboratory experiment to compare physiological and metabolic responses of a key benthic bivalve, Laternula elliptica, at pCO₂ levels of their natural environment (430 µatm, pH 7.99; based on field measurements) with those predicted for 2100 (735 µatm, pH 7.78) and glacial levels (187 µatm, pH 8.32). Adult L. elliptica basal metabolism (oxygen consumption rates) and heat shock protein HSP70 gene expression levels increased in response both to lowering and elevation of pH. Expression of chitin synthase (CHS), a key enzyme involved in synthesis of bivalve shells, was significantly up-regulated in individuals at pH 7.78, indicating L. elliptica were working harder to calcify in seawater undersaturated in aragonite (Ω_Ar = 0.71), the CaCO₃ polymorph of which their shells are comprised. The different response variables were influenced by pH in differing ways, highlighting the importance of assessing a variety of factors to determine the likely impact of pH change. In combination, the results indicate a negative effect of ocean acidification on whole-organism functioning of L. elliptica over relatively short terms (weeks-months) that may be energetically difficult to maintain over longer time periods. Importantly, however, the observed changes in L. elliptica CHS gene expression provides evidence for biological control over the shell formation process, which may enable some degree of adaptation or acclimation to future ocean acidification scenarios.

• Nakamura, M., Ohki, S., Suzuki, A., and Sakai, K.  Coral larvae under ocean acidification: Survival, metabolism, and metamorphosis.  PLoS ONE 6(1): art. e14521, 2011.
  Open Access >>
  Read Abstract >>

  Ocean acidification may negatively impact the early life stages of some marine invertebrates including corals. Although reduced growth of juvenile corals in acidified seawater has been reported, coral larvae have been reported to demonstrate some level of tolerance to reduced pH. We hypothesize that the observed tolerance of coral larvae to low pH may be partly explained by reduced metabolic rates in acidified seawater because both calcifying and non-calcifying marine invertebrates could show metabolic depression under reduced pH in order to enhance their survival. In this study, after 3-d and 7-d exposure to three different pH levels (8.0, 7.6, and 7.3), we found that the oxygen consumption of Acropora digitifera larvae tended to be suppressed with reduced pH, although a statistically significant difference was not observed between pH conditions. Larval metamorphosis was also observed, confirming that successful recruitment is impaired when metamorphosis is disrupted, despite larval survival. Results also showed that the metamorphosis rate significantly decreased under acidified seawater conditions after both short (2 h) and long (7 d) term exposure. These results imply that acidified seawater impacts larval physiology, suggesting that suppressed metabolism and metamorphosis may alter the dispersal potential of larvae and subsequently reduce the resilience of coral communities in the near future as the ocean pH decreases.

• Jiang, L.-Q., Cai, W.-J., Feely, R.A., Wang, Y.C., Guo, X.H., Gledhill, D.K., Hu, X.P., Arzayus, F., Chen, F.Z., Hartmann, J., and Zhang, L.J.  Carbonate mineral saturation states along the US East Coast.  Limnology and Oceanography 55(6): 2424-2432, 2010.
  Read Abstract >>

  To assess the impact of ocean acidification on the carbonate chemistry of the shelf waters off the southeastern United States (South Atlantic Bight [SAB]), we measured carbonate mineral saturation states from January 2005 to May 2006. The findings reveal that aragonite (Ω_arag: 2.6-4.0) and calcite (Ω_cal: 4.1- 6.0) saturation states were considerably higher than those recently reported along the West Coast of North America. Different water mass age between the Atlantic and Pacific Oceans during global ocean circulation is the primary reason for the higher carbonate mineral saturation states in the SAB than along the West Coast. The contrasting water temperatures in the two coasts contribute to such differences. Both upwelling and freshwater discharge also play important roles in controlling saturation state. Carbonate mineral saturation in the surface water of the West Coast is strongly controlled by the upwelling of high-salinity, low-temperature, low-oxygen, and low-pH deep water. In comparison, saturation states in the surface water of the SAB coast are rarely affected by upwelling. Instead, they are strongly influenced by the input of low-saturation-state water from rivers. Continued increases of atmospheric CO2 under the Intergovernmental Panel on Climate Change B1 emission scenario will decrease the carbonate mineral saturation states by up to 40% by the end of this century, and aragonite will approach undersaturation near the coast.

• Liu, J.W., Weinbauer, M.G., Maier, C., Dai, M.H., and Gattuso, J.P.  Effect of ocean acidification on microbial diversity and on microbe-driven biogeochemistry and ecosystem functioning.  Aquatic Microbial Ecology 61(3): 291-305, 2010.
  Open Access >>
  Read Abstract >>

  The ocean absorbs about 25% of anthropogenic CO₂ emissions, which alters its chemistry. Among the changes of the carbonate system are an increase in the partial pressure of CO₂ (pCO₂) and a decline of pH; hence, the whole process is often referred to as 'ocean acidification'. Many microbial processes can be affected either directly or indirectly via a cascade of effects through the response of non-microbial groups and/or through changes in seawater chemistry. We briefly review the current understanding of the impact of ocean acidification on microbial diversity and processes, and highlight the gaps that need to be addressed in future research. The focus is on Bacteria, Archaea, viruses and protistan grazers but also includes total primary production of phytoplankton as well as species composition of eukaryotic phytoplankton. Some species and communities exhibit increased primary production at elevated pCO₂. In contrast to their heterocystous counterparts, nitrogen fixation by non-heterocystous cyanobacteria is stimulated by elevated pCO₂. The experimental data on the response of prokaryotic production to ocean acidification are not consistent. Very few other microbial processes have been investigated at environmentally relevant pH levels. The potential for microbes to adapt to ocean acidification, at either the species level by genetic change or at the community level through the replacement of sensitive species or groups by non- or less sensitive ones, is completely unknown. Consequently, the impact of ocean acidification on keystone species and microbial diversity needs to be elucidated. Most experiments used a short-term perturbation approach by using cultured organisms; few were conducted in mesocosms and none in situ. There is likely a lot to be learned from observations in areas naturally enriched with CO₂, such as vents, upwelling and near-shore areas.

• Pascal, P.Y., Fleeger, J.W., Galvez, F., and Carman, K.R.  The toxicological interaction between ocean acidity and metals in coastal meiobenthic copepods.  Marine Pollution Bulletin 60(12): 2201-2208, 2010.
  Read Abstract >>

  Increased atmospheric CO₂ concentrations are causing greater dissolution of CO₂ into seawater, and are ultimately responsible for today's ongoing ocean acidification. We manipulated seawater acidity by addition of HCl and by increasing CO₂ concentration and observed that two coastal harpacticoid copepods, Amphiascoides atopus and Schizopera knabeni were both more sensitive to increased acidity when generated by CO₂. The present study indicates that copepods living in environments more prone to hypercapnia, such as mudflats where S. knabeni lives, may be less sensitive to future acidification. Ocean acidification is also expected to alter the toxicity of waterborne metals by influencing their speciation in seawater. CO₂ enrichment did not affect the free-ion concentration of Cd but did increase the free-ion concentration of Cu. Antagonistic toxicities were observed between CO₂ with Cd, Cu and Cu free-ion in A. atopus. This interaction could be due to a competition for H⁺ and metals for binding sites.

• Moulin, L., Catarino, A.I., Claessens, T., and Dubois, P.  Effects of seawater acidification on early development of the intertidal sea urchin Paracentrotus lividus (Lamarck 1816).  Marine Pollution Bulletin 62(1): 48-54, 2011.
  Open Access >>
  Read Abstract >>

  The effect of pH ranging from 8.0 to 6.8 (total scale - pH_T) on fertilization, cleavage and larval development until pluteus stage was assessed in an intertidal temperate sea urchin. Gametes were obtained from adults collected in two contrasting tide pools, one showing a significant nocturnal pH decrease (lowest pH_T = 7.4) and another where pH was more stable (lowest pH_T = 7.8). The highest pH_T at which significant effects on fertilization and cleavage were recorded was 7.6. On the contrary, larval development was only affected below pH_T 7.4, a value equal or lower than that reported for several subtidal species. This suggests that sea urchins inhabiting stressful intertidal environments produce offspring that may better resist future ocean acidification. Moreover, at pH_T 7.4, the fertilization rate of gametes whose progenitors came from the tide pool with higher pH decrease was significantly higher, indicating a possible acclimatization or adaptation of gametes to pH stress.

• Moheimani, N.R. and Borowitzka, M.A.  Increased CO₂ and the effect of pH on growth and calcification of Pleurochrysis carterae and Emiliania huxleyi (Haptophyta) in semicontinuous cultures.  Applied Microbiology and Biotechnology 90(4): 1399-1407, 2011.
  Read Abstract >>

  The effects of changes in CO₂ and pH on biomass productivity and carbon uptake of Pleurochrysis carterae and Emiliania huxleyi in open raceway ponds and a plate photobioreactor were studied. The pH of P. carterae cultures increased during day and decreased at night, whereas the pH of E. huxleyi cultures showed no significant diurnal changes. P. carterae coccolith production occurs during the dark period, whereas in E. huxleyi, coccolith production is mainly during the day. Addition of CO₂ at constant pH (pH-stat) resulted in an increase in P. carterae biomass and coccolith productivity, while CO₂ addition lowered E. huxleyi biomass and coccolith production. Neither of these algae could grow at less than pH7.5. Species-specific diurnal pH and pCO₂ variations could be indicative of significant differences in carbon uptake between these two species. While E. huxleyi  has been suggested to be predominantly a bicarbonate user, our results indicate that P. carterae may be using CO₂ as the main C source for photosynthesis and calcification.

• Waldbusser, G.G., Voigt, E.P., Bergschneider, H., Green, M.A., and Newell, R.I.E.  Biocalcification in the eastern oyster (Crassostrea virginica) in relation to long-term trends in Chesapeake Bay pH.  Estuaries and Coasts 34(2): 221-231, 2011.
  Read Abstract >>

  Anthropogenic carbon dioxide (CO₂) emissions reduce pH of marine waters due to the absorption of atmospheric CO₂ and formation of carbonic acid. Estuarine waters are more susceptible to acidification because they are subject to multiple acid sources and are less buffered than marine waters. Consequently, estuarine shell forming species may experience acidification sooner than marine species although the tolerance of estuarine calcifiers to pH changes is poorly understood. We analyzed 23 years of Chesapeake Bay water quality monitoring data and found that daytime average pH significantly decreased across polyhaline waters although pH has not significantly changed across mesohaline waters. In some tributaries that once supported large oyster populations, pH is increasing. Current average conditions within some tributaries however correspond to values that we found in laboratory studies to reduce oyster biocalcification rates or resulted in net shell dissolution. Calcification rates of juvenile eastern oysters, Crassostrea virginica, were measured in laboratory studies in a three-way factorial design with 3 pH levels, two salinities, and two temperatures. Biocalcification declined significantly with a reduction of ~0.5 pH units and higher temperature and salinity mitigated the decrease in biocalcification.

• Aufdenkampe, A.K., Mayorga, E., Raymond, P.A., Melack, J.M., Doney, S.C., Alin, S.R., Aalto, R.E., and Yoo, K.  Riverine coupling of biogeochemical cycles between land, oceans, and atmosphere.  Frontiers in Ecology and the Environment 9(1): 53-60, 2011.
  Open Access >>
  Read Abstract >>

  Streams, rivers, lakes, and other inland waters are important agents in the coupling of biogeochemical cycles between continents, atmosphere, and oceans. The depiction of these roles in global-scale assessments of carbon (C) and other bioactive elements remains limited, yet recent findings suggest that C discharged to the oceans is only a fraction of that entering rivers from terrestrial ecosystems via soil respiration, leaching, chemical weathering, and physical erosion. Most of this C influx is returned to the atmosphere from inland waters as carbon dioxide (CO₂) or buried in sedimentary deposits within impoundments, lakes, floodplains, and other wetlands. Carbon and mineral cycles are coupled by both erosion deposition processes and chemical weathering, with the latter producing dissolved inorganic C and carbonate buffering capacity that strongly modulate downstream pH, biological production of calcium-carbonate shells, and CO₂ outgassing in rivers, estuaries, and coastal zones. Human activities substantially affect all of these processes.

• Joint, I., Doney, S.C., and Karl, D.M.  Will ocean acidification affect marine microbes?  ISME Journal 5(1): 1-7, 2011.
  Open Access >>
  Read Abstract >>

  The pH of the surface ocean is changing as a result of increases in atmospheric carbon dioxide (CO₂), and there are concerns about potential impacts of lower pH and associated alterations in seawater carbonate chemistry on the biogeochemical processes in the ocean. However, it is important to place these changes within the context of pH in the present-day ocean, which is not constant; it varies systematically with season, depth and along productivity gradients. Yet this natural variability in pH has rarely been considered in assessments of the effect of ocean acidification on marine microbes. Surface pH can change as a consequence of microbial utilization and production of carbon dioxide, and to a lesser extent other microbially mediated processes such as nitrification. Useful comparisons can be made with microbes in other aquatic environments that readily accommodate very large and rapid pH change. For example, in many freshwater lakes, pH changes that are orders of magnitude greater than those projected for the twenty second century oceans can occur over periods of hours. Marine and freshwater assemblages have always experienced variable pH conditions. Therefore, an appropriate null hypothesis may be, until evidence is obtained to the contrary, that major biogeochemical processes in the oceans other than calcification will not be fundamentally different under future higher CO₂/lower pH conditions.

• Meron, D., Atias, E., Kruh, L.I., Elifantz, H., Minz, D., Fine, M., and Banin, E.  The impact of reduced pH on the microbial community of the coral Acropora eurystoma.  ISME Journal 5(1): 51-60, 2011.
  Open Access >>
  Read Abstract >>

  Rising concentrations of atmospheric carbon dioxide are acidifying the world's oceans. Surface seawater pH is 0.1 units lower than pre-industrial values and is predicted to decrease by up to 0.4 units by the end of the century. This change in pH may result in changes in the physiology of ocean organisms, in particular, organisms that build their skeletons/shells from calcium carbonate, such as corals. This physiological change may also affect other members of the coral holobiont, for example, the microbial communities associated with the coral, which in turn may affect the coral physiology and health. In the present study, we examined changes in bacterial communities in the coral mucus, tissue and skeleton following exposure of the coral Acropora eurystoma to two different pH conditions: 7.3 and 8.2 (ambient seawater). The microbial community was different at the two pH values, as determined by denaturing gradient gel electrophoresis and 16S rRNA gene sequence analysis. Further analysis of the community in the corals maintained at the lower pH revealed an increase in bacteria associated with diseased and stressed corals, such as Vibrionaceae and Alteromonadaceae. In addition, an increase in the number of potential antibacterial activity was recorded among the bacteria isolated from the coral maintained at pH 7.3. Taken together, our findings highlight the impact that changes in the pH may have on the coral-associated bacterial community and their potential contribution to the coral host.

• Bechmann, R.K., Taban, I.C., Westerlund, S., Godal, B.F., Arnberg, M., Vingen, S., Ingvarsdottir, A., and Baussant, T.  Effects of ocean acidification on early life stages of shrimp (Pandalus borealis) and mussel (Mytilus edulis).  Journal of Toxicology and Environmental Health Part A 74(7-9): 424-438, 2011.
  Open Access >>
  Read Abstract >>

  Ocean acidification (OA) resulting from anthropogenic emissions of carbon dioxide (CO₂) has already lowered and is predicted to further lower surface ocean pH. There is a particular need to study effects of OA on organisms living in cold-water environments due to the higher solubility of CO₂ at lower temperatures. Mussel larvae (Mytilus edulis) and shrimp larvae (Pandalus borealis) were kept under an ocean acidification scenario predicted for the year 2100 (pH 7.6) and compared against identical batches of organisms held under the current oceanic pH of 8.1, which acted as a control. The temperature was held at a constant 10 ºC in the mussel experiment and at 5 ºC in the shrimp experiment. There was no marked effect on fertilization success, development time, or abnormality to the D-shell stage, or on feeding of mussel larvae in the low-pH (pH 7.6) treatment. Mytilus edulis larvae were still able to develop a shell in seawater undersaturated with respect to aragonite (a mineral form of CaCO₃), but the size of low-pH larvae was significantly smaller than in the control. After 2 mo of exposure the mussels were 28% smaller in the pH 7.6 treatment than in the control. The experiment with Pandalus borealis larvae ran from 1 through 35 days post hatch. Survival of shrimp larvae was not reduced after 5 wk of exposure to pH 7.6, but a significant delay in zoeal progression (development time) was observed.

• Kawaguchi, S., Kurihara, H., King, R., Hale, L., Berli, T., Robinson, J.P., Ishida, A., Wakita, M., Virtue, P., Nicol, S., and Ishimatsu, A.  Will krill fare well under Southern Ocean acidification?  Biology Letters 7(2): 288-291, 2011.
  Read Abstract >>

  Antarctic krill embryos and larvae were experimentally exposed to 380 (control), 1000 and 2000 µatm pCO₂ in order to assess the possible impact of ocean acidification on early development of krill. No significant effects were detected on embryonic development or larval behaviour at 1000 µatm pCO₂; however, at 2000 µatm pCO₂ development was disrupted before gastrulation in 90 per cent of embryos, and no larvae hatched successfully. Our model projections demonstrated that Southern Ocean sea water pCO₂ could rise up to 1400 µatm in krill's depth range under the IPCC IS92a scenario by the year 2100 (atmospheric pCO₂ 788 µatm). These results point out the urgent need for understanding the pCO₂-response relationship for krill developmental and later stages, in order to predict the possible fate of this key species in the Southern Ocean.

• Martin, S., Richier, S., Pedrotti, M.L., Dupont, S., Castejon, C., Gerakis, Y., Kerros, M.E., Oberhansli, F., Teyssie, J.L., Jeffree, R., and Gattuso, J.P.  Early development and molecular plasticity in the Mediterranean sea urchin Paracentrotus lividus exposed to CO₂-driven acidification.  Journal of Experimental Biology 214(8): 1357-1368, 2011.
  Read Abstract >>

  Ocean acidification is predicted to have significant effects on benthic calcifying invertebrates, in particular on their early developmental stages. Echinoderm larvae could be particularly vulnerable to decreased pH, with major consequences for adult populations. The objective of this study was to understand how ocean acidification would affect the initial life stages of the sea urchin Paracentrotus lividus, a common species that is widely distributed in the Mediterranean Sea and the NE Atlantic. The effects of decreased pH (elevated PCO₂) were investigated through physiological and molecular analyses on both embryonic and larval stages. Eggs and larvae were reared in Mediterranean seawater at six pH levels, i.e. pH_T 8.1, 7.9, 7.7, 7.5, 7.25 and 7.0. Fertilization success, survival, growth and calcification rates were monitored over a 3 day period. The expression of genes coding for key proteins involved in development and biomineralization was also monitored. Paracentrotus lividus appears to be extremely resistant to low pH, with no effect on fertilization success or larval survival. Larval growth was slowed when exposed to low pH but with no direct impact on relative larval morphology or calcification down to pH_T 7.25. Consequently, at a given time, larvae exposed to low pH were present at a normal but delayed larval stage. More surprisingly, candidate genes involved in development and biomineralization were upregulated by factors of up to 26 at low pH. Our results revealed plasticity at the gene expression level that allows a normal, but delayed, development under low pH conditions.

• Hu, M.Y.A., Tseng, Y.-C., Stumpp, M., Gutowska, M.A., Kiko, R., Lucassen, M., and Melzner, F.  Elevated seawater pCO₂ differentially affects branchial acid-base transporters over the course of development in the cephalopod Sepia officinalis.  American Journal of Physiology 300(5): R1100-R1114, 2011.
  Read Abstract >>

  The specific transporters involved in maintenance of blood pH homeostasis in cephalopod molluscs have not been identified to date. Using in situ hybridization and immuno histochemical methods, we demonstrate that Na⁺/K⁺-ATPase (soNKA), a V-type H⁺-ATPase (soV-HA), and Na⁺/HCO₃^- cotransporter (soNBC) are co-localized in NKA-rich cells in the gills of Sepia officinalis. mRNA expression patterns of these transporters and selected metabolic genes were examined in response to moderately elevated seawater pCO₂ (0.16 and 0.35 kPa) over a time-course of six weeks in different ontogenetic stages. The applied CO₂ concentrations are relevant for ocean acidification scenarios projected for the coming decades. We determined strong expression changes in late stage embryos and hatchlings, with one to three log2-fold reductions in soNKA, soNBCe, socCAII and COX. In contrast, no hypercapnia induced changes in mRNA expression were observed in juveniles during both short- and long-term exposure. However a transiently increased demand of ion regulatory demand was evident during the initial acclimation reaction to elevated seawater pCO₂. Gill Na⁺/K⁺-ATPase activity and protein concentration were increased by approximately 15% in during short (2-11 day), but not long term (42 day) exposure. Our findings support the hypothesis that the energy budget of adult cephalopods is not significantly compromised during long-term exposure to moderate environmental hypercapnia. However, the down regulation of ion-regulatory and metabolic genes in late stage embryos, taken together with a significant reduction in somatic growth, indicates that cephalopod early life stages are challenged by elevated seawater pCO₂.

Read past issues of Marine Science Review in the archives.