Seawater carbonate chemistry and calcification during incubation experiments with Mytilus edulis and Grassostrea gigas, 2006

Ocean acidification resulting from human emissions of carbon dioxide has already lowered and will further lower surface ocean pH. The consequent decrease in calcium carbonate saturation potentially threatens calcareous marine organisms. Here, we demonstrate that the calcification rates of the edible mussel (Mytilus edulis) and Pacific oyster (Crassostrea gigas) decline linearly with increasing pCO2. Mussel and oyster calcification may decrease by 25 and 10%, respectively, by the end of the century, following the IPCC IS92a scenario (?740 ppmv in 2100). Moreover, mussels dissolve at pCO2 values exceeding a threshold value of ?1800 ppmv. As these two species are important ecosystem engineers in coastal ecosystems and represent a large part of worldwide aquaculture production, the predicted decrease of calcification in response to ocean acidification will probably have an impact on coastal biodiversity and ecosystem functioning as well as potentially lead to significant economic loss.

Seawater carbonate chemistry and Pacific oyster (Crassostrea gigas) biological processes during experiments, 2011

Ocean acidification, due to anthropogenic CO2 absorption by the ocean, may have profound impacts on marine biota. Calcareous organisms are expected to be particularly sensitive due to the decreasing availability of carbonate ions driven by decreasing pH levels. Recently, some studies focused on the early life stages of mollusks that are supposedly more sensitive to environmental disturbances than adult stages. Although these studies have shown decreased growth rates and increased proportions of abnormal development under low pH conditions, they did not allow attribution to pH induced changes in physiology or changes due to a decrease in aragonite saturation state. This study aims to assess the impact of several carbonate-system perturbations on the growth of Pacific oyster (Crassostrea gigas) larvae during the first 3 days of development (until shelled D-veliger larvae). Seawater with five different chemistries was obtained by separately manipulating pH, total alkalinity and aragonite saturation state (calcium addition). Results showed that the developmental success and growth rates were not directly affected by changes in pH or aragonite saturation state but were highly correlated with the availability of carbonate ions. In contrast to previous studies, both developmental success into viable D-shaped larvae and growth rates were not significantly altered as long as carbonate ion concentrations were above aragonite saturation levels, but they strongly decreased below saturation levels. These results suggest that the mechanisms used by these organisms to regulate calcification rates are not efficient enough to compensate for the low availability of carbonate ions under corrosive conditions.

Seawater carbonate chemistry and processes during experiments with coccolithophores (Emiliania huxleyi and Gephyrocapsa oceanica), 2000

The formation of calcareous skeletons by marine planktonic organisms and their subsequent sinking to depth generates a continuous rain of calcium carbonate to the deep ocean and underlying sediments1. This is important in regulating marine carbon cycling and ocean-atmosphere CO2 exchange2. The present rise in atmospheric CO2 levels3 causes significant changes in surface ocean pH and carbonate chemistry4. Such changes have been shown to slow down calcification in corals and coralline macroalgae5,6, but the majority of marine calcification occurs in planktonic organisms. Here we report reduced calcite production at increased CO2 concentrations in monospecific cultures of two dominant marine calcifying phytoplankton species, the coccolithophorids Emiliania huxleyi and Gephyrocapsa oceanica . This was accompanied by an increased proportion of malformed coccoliths and incomplete coccospheres. Diminished calcification led to a reduction in the ratio of calcite precipitation to organic matter production. Similar results were obtained in incubations of natural plankton assemblages from the north Pacific ocean when exposed to experimentally elevated CO2 levels. We suggest that the progressive increase in atmospheric CO2 concentrations may therefore slow down the production of calcium carbonate in the surface ocean. As the process of calcification releases CO2 to the atmosphere, the response observed here could potentially act as a negative feedback on atmospheric CO2 levels.

Seawater carbonate chemistry and biological processes during experiments with four species of marine diatoms

The effect of pCO2 on carbon acquisition and intracellular assimilation was investigated in the three bloom-forming diatom species, Eucampia zodiacus (Ehrenberg), Skeletonema costatum (Greville) Cleve, Thalassionema nitzschioides (Grunow) Mereschkowsky and the non-bloom-forming Thalassiosira pseudonana (Hust.) Hasle and Heimdal. In vivo activities of carbonic anhydrase (CA), photosynthetic O2 evolution, CO2 and HCO3? uptake rates were measured by membrane-inlet mass spectrometry (MIMS) in cells acclimated to pCO2 levels of 370 and 800 ?atm. To investigate whether the cells operate a C4-like pathway, activities of ribulose-1,5-bisphosphate carboxylase (RubisCO) and phosphoenolpyruvate carboxylase (PEPC) were measured at the mentioned pCO2 levels and a lower pCO2 level of 50 ?atm. In the bloom-forming species, extracellular CA activities strongly increased with decreasing CO2 supply while constantly low activities were obtained for T. pseudonana. Half-saturation concentrations (K1/2) for photosynthetic O2 evolution decreased with decreasing CO2 supply in the two bloom-forming species S. costatum and T. nitzschioides, but not in T. pseudonana and E. zodiacus. With the exception of S. costatum, maximum rates (Vmax) of photosynthesis remained constant in all investigated diatom species. Independent of the pCO2 level, PEPC activities were significantly lower than those for RubisCO, averaging generally less than 3%. All examined diatom species operate highly efficient CCMs under ambient and high pCO2, but differ strongly in the degree of regulation of individual components of the CCM such as Ci uptake kinetics and extracellular CA activities. The present data do not suggest C4 metabolism in the investigated species.

Seawater carbonate chemistry and calcification in the tropical urchin Echinometra viridis in a laboratory experiment

Atmospheric carbon dioxide (pCO2) has risen from approximately 280 to 400 ppm since the Industrial Revolution, due mainly to the combustion of fossil fuels, deforestation, and cement production. It is predicted to reach as high as 900 ppm by the end of this century. Ocean acidification resulting from the release of anthropogenic CO2 has been shown to impair the ability of some marine calcifiers to build their shells and skeletons. Here, we present the results of ocean acidification experiments designed to assess the effects of an increase in atmospheric pCO2 from ca. 448 to 827 ppm on calcification rates of the tropical urchin Echinometra viridis. Experiments were conducted under the urchin's winter (20 °C) and summer (30 °C) water temperatures in order to identify seasonal differences in the urchin's response to ocean acidification. The experiments reveal that calcification rates decreased for urchins reared under elevated pCO2, with the decline being more pronounced under wintertime temperatures than under summertime temperatures. These results indicate that the urchin E. viridis will be negatively impacted by CO2-induced ocean acidification that is predicted to occur by the end of this century. These results also suggest that impact of CO2-induced ocean acidification on urchin calcification will be more severe in the winter and in cooler waters.

Seawater carbonate chemistry and growth, carbon acquisition, and species interaction of Antarctic phytoplankton species in a laboratory experiment

Despite the fact that ocean acidification is considered to be especially pronounced in the Southern Ocean, little is known about CO2-dependent physiological processes and the interactions of Antarctic phytoplankton key species. We therefore studied the effects of CO2 partial pressure (PCO2) (16.2, 39.5, and 101.3 Pa) on growth and photosynthetic carbon acquisition in the bloom-forming species Chaetoceros debilis, Pseudo-nitzschia subcurvata, Fragilariopsis kerguelensis, and Phaeocystis antarctica. Using membrane-inlet mass spectrometry, photosynthetic O2 evolution and inorganic carbon (Ci) fluxes were determined as a function of CO2 concentration. Only the growth of C. debilis was enhanced under high PCO2. Analysis of the carbon concentrating mechanism (CCM) revealed the operation of very efficient CCMs (i.e., high Ci affinities) in all species, but there were species-specific differences in CO2-dependent regulation of individual CCM components (i.e., CO2 and uptake kinetics, carbonic anhydrase activities). Gross CO2 uptake rates appear to increase with the cell surface area to volume ratios. Species competition experiments with C. debilis and P. subcurvata under different PCO2 levels confirmed the CO2-stimulated growth of C. debilis observed in monospecific incubations, also in the presence of P. subcurvata. Independent of PCO2, high initial cell abundances of P. subcurvata led to reduced growth rates of C. debilis. For a better understanding of future changes in phytoplankton communities, CO2-sensitive physiological processes need to be identified, but also species interactions must be taken into account because their interplay determines the success of a species.

Suspended paticulate matter and respiration experiments of Laternula elliptica in Potter Cove, King George Island, Western Antarctic Peninsula

Recent rapid changes of air temperature on the western side of the Antarctic Peninsula results in increased sediment discharge and ice scouring frequencies in coastal regions. These changes are bound to especially affect slow growing, sessile filter feeders such as the Antarctic bivalve, Laternula elliptica, a long-lived and abundant key species with circumpolar distribution. We investigated the effect of sedimentation and ice scouring on small/young and large/old individuals at two closely located stations, distinctly influenced by both types of disturbance. Small individuals dealt better with disturbance in terms of their respiratory response to sediment exposure, reburrowing ability, and survival after injury, compared to larger animals. At the more disturbed station L. elliptica population density was lower, but larger animals reburrowed faster after iceberg disturbance and reduced their metabolic rate under strong sediment coverage, compared to larger animals of the less disturbed station, indicating that an adaptation or learning response to both types of disturbance may be possible. Smaller individuals were not influenced. Laternula elliptica seems capable of coping with the rapidly changing environmental conditions. Due to a decrease in population density and mean population lifespan, L. elliptica could however lose its key role in the bentho-pelagic carbon flux in areas of high sediment deposition.

Seawater carbonate chemistry and sea urchin Paracentrotus lividus biological processes during experiments, 2011

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. pHT 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 pHT 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.

Seawater carbonate chemistry and processes during experiments with Emiliania huxleyi, 2008

Ocean acidification in response to rising atmospheric CO2 partial pressures is widely expected to reduce calcification by marine organisms. From the mid-Mesozoic, coccolithophores have been major calcium carbonate producers in the world's oceans, today accounting for about a third of the total marine CaCO3 production. Here, we present laboratory evidence that calcification and net primary production in the coccolithophore species Emiliania huxleyi are significantly increased by high CO2 partial pressures. Field evidence from the deep ocean is consistent with these laboratory conclusions, indicating that over the past 220 years there has been a 40% increase in average coccolith mass. Our findings show that coccolithophores are already responding and will probably continue to respond to rising atmospheric CO2 partial pressures, which has important implications for biogeochemical modeling of future oceans and climate.

Seawater carbonate chemistry, calcification and dissolution response, and skeletal mineralogy of benthic orhanisms during experiments, 2011

Increasing atmospheric pCO2 reduces the saturation state of seawater with respect to the aragonite, high-Mg calcite (Mg/Ca > 0.04), and low-Mg calcite (Mg/Ca < 0.04) minerals from which marine calcifiers build their shells and skeletons. Notably, these polymorphs of CaCO3 have different solubilities in seawater: aragonite is more soluble than pure calcite, and the solubility of calcite increases with its Mg-content. Although much recent progress has been made investigating the effects of CO2-induced ocean acidification on rates of biological calcification, considerable uncertainties remain regarding impacts on shell/skeletal polymorph mineralogy. To investigate this subject, eighteen species of marine calcifiers were reared for 60-days in seawater bubbled with air-CO2 mixtures of 409 ± 6, 606 ± 7, 903 ± 12, and 2856 ± 54 ppm pCO2, yielding aragonite saturation states of 2.5 ± 0.4, 2.0 ± 0.4, 1.5 ± 0.3, and 0.7 ± 0.2. Calcite/aragonite ratios within bimineralic calcifiers increased with increasing pCO2, but were invariant within monomineralic calcifiers. Calcite Mg/Ca ratios (Mg/CaC) also varied with atmospheric pCO2 for two of the five high-Mg-calcite-producing organisms, but not for the low-Mg-calcite-producing organisms. These results suggest that shell/skeletal mineralogy within some-but not all-marine calcifiers will change as atmospheric pCO2 continues rising as a result of fossil fuel combustion and deforestation. Paleoceanographic reconstructions of seawater Mg/Ca, temperature, and salinity from the Mg/CaC of well-preserved calcitic marine fossils may also be improved by accounting for the effects of paleo-atmospheric pCO2 on skeletal Mg-fractionation.

Seawater carbonate chemistry, and Lithophyllum sp. and Feldmannia spp. coverage and dry weight during experiments, 2009

Climate-driven change represents the cumulative effect of global through local-scale conditions, and understanding their manifestation at local scales can empower local management. Change in the dominance of habitats is often the product of local nutrient pollution that occurs at relatively local scales (i.e. catchment scale), a critical scale of management at which global impacts will manifest. We tested whether forecasted global-scale change [elevated carbon dioxide (CO2) and subsequent ocean acidification] and local stressors (elevated nutrients) can combine to accelerate the expansion of filamentous turfs at the expense of calcifying algae (kelp understorey). Our results not only support this model of future change, but also highlight the synergistic effects of future CO2 and nutrient concentrations on the abundance of turfs. These results suggest that global and local stressors need to be assessed in meaningful combinations so that the anticipated effects of climate change do not create the false impression that, however complex, climate change will produce smaller effects than reality. These findings empower local managers because they show that policies of reducing local stressors (e.g. nutrient pollution) can reduce the effects of global stressors not under their governance (e.g. ocean acidification). The connection between research and government policy provides an example whereby knowledge (and decision making) across local through global scales provides solutions to some of the most vexing challenges for attaining social goals of sustainability, biological conservation and economic development.

Seawater carbonate chemistry, larval settlement and growth rate during experiments with coral Porites astreoides, 2008

In response to the increases in pCO2 projected in the 21st century, adult coral growth and calcification are expected to decrease significantly. However, no published studies have investigated the effect of elevated pCO2 on earlier life history stages of corals. Porites astreoides larvae were collected from reefs in Key Largo, Florida, USA, settled and reared in controlled saturation state seawater. Three saturation states were obtained, using 1 M HCl additions, corresponding to present (380 ppm) and projected pCO2 scenarios for the years 2065 (560 ppm) and 2100 (720 ppm). The effect of saturation state on settlement and post-settlement growth was evaluated. Saturation state had no significant effect on percent settlement; however, skeletal extension rate was positively correlated with saturation state, with ~50% and 78% reductions in growth at the mid and high pCO2 treatments compared to controls, respectively.

Seawater carbonate chemistry and biological processes during experiments with postlarvae of barnacle of Semibalanus balanoides and Elminius modestus, 2010

Ocean acidification and global warming are occurring concomitantly, yet few studies have investigated how organisms will respond to increases in both temperature and CO2. Intertidal microcosms were used to examine growth, shell mineralogy and survival of two intertidal barnacle post-larvae, Semibalanus balanoides and Elminius modestus, at two temperatures (14 and 19°C) and two CO2 concentrations (380 and 1,000 ppm), fed with a mixed diatom-flagellate diet at 15,000 cells ml-1 with flow rate of 10 ml-1 min-1. Control growth rates, using operculum diameter, were 14 ± 8 µm day-1 and 6 ± 2 µm day-1 for S. balanoides and E. modestus, respectively. Subtle, but significant decreases in E. modestus growth rate were observed in high CO2 but there were no impacts on shell calcium content and survival by either elevated temperature or CO2. S. balanoides exhibited no clear alterations in growth rate but did show a large reduction in shell calcium content and survival under elevated temperature and CO2. These results suggest that a decrease by 0.4 pH(NBS) units alone would not be sufficient to directly impact the survival of barnacles during the first month post-settlement. However, in conjunction with a 4-5°C increase in temperature, it appears that significant changes to the biology of these organisms will ensue.

Seawater carbonate chemistry, pigments and biological processes during experiments with coralline alga Corallina sessilis

Previous studies have shown that increasing atmospheric CO2 concentrations affect calcification in some planktonic and macroalgal calcifiers due to the changed carbonate chemistry of seawater. However, little is known regarding how calcifying algae respond to solar UV radiation (UVR, UVA+UVB, 280-400 nm). UVR may act synergistically, antagonistically or independently with ocean acidification (high CO2/low pH of seawater) to affect their calcification processes. We cultured the articulated coralline alga Corallina sessilis Yendo at 380 ppmv (low) and 1000 ppmv (high) CO2 levels while exposing the alga to solar radiation treatments with or without UVR. The presence of UVR inhibited the growth, photosynthetic O2evolution and calcification rates by13%, 6% and 3% in the low and by 47%, 20% and 8% in the high CO2 concentrations, respectively, reflecting a synergistic effect of CO2 enrichment with UVR. UVR induced significant decline of pH in the CO2-enriched cultures. The contents of key photosynthetic pigments, chlorophyll a and phycobiliproteins decreased, while UV-absorptivity increased under the highpCO2/low pH condition. Nevertheless, UV-induced inhibition of photosynthesis increased when the ratio of particulate inorganic carbon/particulate organic carbon decreased under the influence of CO2-acidified seawater, suggesting that the calcified layer played a UV-protective role. Both UVA and UVB negatively impacted photosynthesis and calcification, but the inhibition caused by UVB was about 2.5-2.6 times that caused by UVA. The results imply that coralline algae suffer from more damage caused by UVB as they calcify less and less with progressing ocean acidification.

Seawater carbonate chemistry and biological processes of Amphisorus hemprichii, Amphisorus kudakajimensis and Calcarina gaudichaudii during experiments, 2011

Ocean acidification, which like global warming is an outcome of anthropogenic CO2emissions, severely impacts marine calcifying organisms, especially those living in coral reef ecosystems. However, knowledge about the responses of reef calcifiers to ocean acidification is quite limited, although coral responses are known to be generally negative. In a culture experiment with two algal symbiont-bearing, reef-dwelling foraminifers, Amphisorus kudakajimensis and Calcarina gaudichaudii, in seawater under five different pCO2 conditions, 245, 375, 588, 763 and 907 µatm, maintained with a precise pCO2-controlling technique, net calcification of A. kudakajimensis was reduced under higher pCO2, whereas calcification of C. gaudichaudii generally increased with increased pCO2. In another culture experiment conducted in seawater in which bicarbonate ion concentrations were varied under a constant carbonate ion concentration, calcification was not significantly different between treatments in Amphisorus hemprichii, a species closely related to A. kudakajimensis, or in C. gaudichaudii. From these results, we concluded that carbonate ion and CO2 were the carbonate species that most affected growth ofAmphisorus and Calcarina, respectively. The opposite responses of these two foraminifer genera probably reflect different sensitivities to these carbonate species, which may be due to their different symbiotic algae.