Impact of CO2-driven acidification on the development of the sea cucumber Apostichopus japonicus (Selenka) (Echinodermata: Holothuroidea)

We evaluated the impact of ocean acidification on the early development of sea cucumber Apostichopus japonicus. The effect of pH-levels (pH 8.04, 7.85, 7.70 and 7.42) were tested on post-fertilization success, developmental (stage duration) and growth rates. Post-fertilization success decreased linearly with pH leading to a 6% decrease at pH 7.42 as compared to pH 8.1. The impact of pH on developmental time was stage-dependent: (1) stage duration increased linearly with decreasing pH in early-auricularia stage; (2) decreased linearly with decreasing pH in the mid-auricularia stage; but (3) pH decline had no effect on the late-auricularia stage. At the end of the experiment, the size of doliolaria larvae linearly increased with decreasing pH. In conclusion, a 0.62 unit decrease in pH had relatively small effects on A. japonicus early life-history compared to other echinoderms, leading to a maximum of 6% decrease in post-fertilization success and subtle effects on growth and development.

Effects of ocean acidification on the photosynthetic performance, carbonic anhydrase activity and growth of the giant kelp Macrocystis pyrifera

Under ocean acidification (OA), the 200 % increase in CO2(aq) and the reduction of pH by 0.3-0.4 units are predicted to affect the carbon physiology and growth of macroalgae. Here we examined how the physiology of the giant kelp Macrocystis pyrifera is affected by elevated pCO2/low pH. Growth and photosynthetic rates, external and internal carbonic anhydrase (CA) activity, HCO3 (-) versus CO2 use were determined over a 7-day incubation at ambient pCO2 400 µatm/pH 8.00 and a future OA treatment of pCO2 1200 µatm/pH 7.59. Neither the photosynthetic nor growth rates were changed by elevated CO2 supply in the OA treatment. These results were explained by the greater use of HCO3 (-) compared to CO2 as an inorganic carbon (Ci) source to support photosynthesis. Macrocystis is a mixed HCO3 (-) and CO2 user that exhibits two effective mechanisms for HCO3 (-) utilization; as predicted for species that possess carbon-concentrating mechanisms (CCMs), photosynthesis was not substantially affected by elevated pCO2. The internal CA activity was also unaffected by OA, and it remained high and active throughout the experiment; this suggests that HCO3 (-) uptake via an anion exchange protein was not affected by OA. Our results suggest that photosynthetic Ci uptake and growth of Macrocystis will not be affected by elevated pCO2/low pH predicted for the future, but the combined effects with other environmental factors like temperature and nutrient availability could change the physiological response of Macrocystis to OA. Therefore, further studies will be important to elucidate how this species might respond to the global environmental change predicted for the ocean.

The effects of water acidification, temperature and salinity on the regenerative capacity of the polychaete Diopatra neapolitana

Changes in seawater pH, temperature and salinity are expected to occur in the near future, which can be a threat to aquatic systems, mainly for marine coastal areas, and their inhabiting species. Hence, the present study proposes to evaluate the effects of temperature shifts, pH decrease and salinity changes in the tissue's regenerative capacity of the polychaete Diopatra neapolitana. This study evidenced that D. neapolitana individuals exposed to lower pH exhibited a significantly lower capacity to regenerate their body, while with the increase of temperature individuals showed a higher capacity to regenerate their tissues. Furthermore, the present work demonstrated that individuals exposed to salinities 28 and 35 did not present significant differences between them, while salinities 21 and 42 negatively influenced the regenerative capacity of D. neapolitana. At the end of regeneration, comparing all conditions, high salinity (42) seemed to have a greater impact on the regenerative capacity of individuals than the other factors, since under this condition individuals took longer to completely regenerate. Overall, this study demonstrated that variations in abiotic factors can strongly affect D. neapolitana's performance.

Performance of the Arctic calanoid copepods Calanus glacialis and C. hyperboreus under elevated pCO2 and temperatures

The sensitivity of copepods to ocean acidification (OA) and warming may increase with time, however, studies >10 days and on synergistic effects are rare. We therefore incubated late copepodites and females of two dominant Arctic species, Calanus glacialis and Calanus hyperboreus, at 0 °C at 390 and 3000 µatm pCO2 for several months in fall/winter 2010. Respiration rates, body mass and mortality in both species and life stages did not change with pCO2. To detect synergistic effects, in 2011 C. hyperboreus females were kept at different pCO2 and temperatures (0, 5, 10 °C). Incubation at 10 °C induced sublethal stress, which might have overruled effects of pCO2. At 5 °C and 3000 µatm, body carbon was significantly lowest indicating a synergistic effect. The copepods, thus, can tolerate pCO2 predicted for a future ocean, but in combination with increasing temperatures they could be sensitive to OA.

Geographical variation in shell morphology of juvenile snails (Concholepas concholepas) along the physical-chemical gradient of the Chilean coast

Changes in phenotypic traits, such as mollusc shells, are indicative of variations in selective pressure along environmental gradients. Recently, increased sea surface temperature (SST) and ocean acidification (OA) due to increased levels of carbon dioxide in the seawater have been described as selective agents that may affect the biological processes underlying shell formation in calcifying marine organisms. The benthic snail Concholepas concholepas (Muricidae) is widely distributed along the Chilean coast, and so is naturally exposed to a strong physical-chemical latitudinal gradient. In this study, based on elliptical Fourier analysis, we assess changes in shell morphology (outlines analysis) in juvenile C. concholepas collected at northern (23°S), central (33°S) and southern (39°S) locations off the Chilean coast. Shell morphology of individuals collected in northern and central regions correspond to extreme morphotypes, which is in agreement with both the observed regional differences in the shell apex outlines, the high reclassification success of individuals (discriminant function analysis) collected in these regions, and the scaling relationship in shell weight variability among regions. However, these extreme morphotypes showed similar patterns of mineralization of calcium carbonate forms (calcite and aragonite). Geographical variability in shell shape of C. concholepas described by discriminant functions was partially explained by environmental variables (pCO2, SST). This suggests the influence of corrosive waters, such as upwelling and freshwaters penetrating into the coastal ocean, upon spatial variation in shell morphology. Changes in the proportion of calcium carbonate forms precipitated by C. concholepas across their shells and its susceptibility to corrosive coastal waters are discussed.

Effects of Ocean Acidification and Warming on Sperm Activity and Early Life Stages of the Mediterranean Mussel (Mytilus galloprovincialis)

Larval stages are among those most vulnerable to ocean acidification (OA). Projected atmospheric CO2 levels for the end of this century may lead to negative impacts on communities dominated by calcifying taxa with planktonic life stages. We exposed Mediterranean mussel (Mytilus galloprovincialis) sperm and early life stages to pHT levels of 8.0 (current pH) and 7.6 (2100 level) by manipulating pCO2 level (380 and 1000 ppm). Sperm activity was examined at ambient temperatures (16-17 °C) using individual males as replicates. We also assessed the effects of temperature (ambient and = 20 °C) and pH on larval size, survival, respiration and calcification of late trochophore/early D-veliger stages using a cross-factorial design. Increased pCO2 had a negative effect on the percentage of motile sperm (mean response ratio R= 71%) and sperm swimming speed (R= 74%), possibly indicating reduced fertilization capacity of sperm in low concentrations. Increased temperature had a more prominent effect on larval stages than pCO2, reducing performance (RSize = 90% and RSurvival = 70%) and increasing energy demand (RRespiration = 429%). We observed no significant interactions between pCO2 and temperature. Our results suggest that increasing temperature might have a larger impact on very early larval stages of M. galloprovincialis than OA at levels predicted for the end of the century.

Responses of the metabolism of the larvae of Pocillopora damicornis to ocean acidification and warming

Ocean acidification and warming are expected to threaten the persistence of tropical coral reef ecosystems. As coral reefs face multiple stressors, the distribution and abundance of corals will depend on the successful dispersal and settlement of coral larvae under changing environmental conditions. To explore this scenario, we used metabolic rate, at holobiont and molecular levels, as an index for assessing the physiological plasticity of Pocillopora damicornis larvae from this site to conditions of ocean acidity and warming. Larvae were incubated for 6 hours in seawater containing combinations of CO2 concentration (450 and 950 µatm) and temperature (28 and 30°C). Rates of larval oxygen consumption were higher at elevated temperatures. In contrast, high CO2 levels elicited depressed metabolic rates, especially for larvae released later in the spawning period. Rates of citrate synthase, a rate-limiting enzyme in aerobic metabolism, suggested a biochemical limit for increasing oxidative capacity in coral larvae in a warming, acidifying ocean. Biological responses were also compared between larvae released from adult colonies on the same day (cohorts). The metabolic physiology of Pocillopora damicornis larvae varied significantly by day of release. Additionally, we used environmental data collected on a reef in Moorea, French Polynesia to provide information about what adult corals and larvae may currently experience in the field. An autonomous pH sensor provided a continuous time series of pH on the natal fringing reef. In February/March, 2011, pH values averaged 8.075±0.023. Our results suggest that without adaptation or acclimatization, only a portion of naïve Pocillopora damicornis larvae may have suitable metabolic phenotypes for maintaining function and fitness in an end-of-the century ocean.

The effects of thermal and high-CO2 stresses on the metabolism and surrounding microenvironment of the coral Galaxea fascicularis

The effects of elevated temperature and high pCO2 on the metabolism of Galaxea fascicularis were studied with oxygen and pH microsensors. Photosynthesis and respiration rates were evaluated from the oxygen fluxes from and to the coral polyps. High-temperature alone lowered both photosynthetic and respiration rates. High pCO2 alone did not significantly affect either photosynthesis or respiration rates. Under a combination of high-temperature and high-CO2, the photosynthetic rate increased to values close to those of the controls. The same pH in the diffusion boundary layer was observed under light in both (400 and 750 ppm) CO2 treatments, but decreased significantly in the dark as a result of increased CO2. The ATP contents decreased with increasing temperature. The effects of temperature on the metabolism of corals were stronger than the effects of increased CO2. The effects of acidification were minimal without combined temperature stress. However, acidification combined with higher temperature may affect coral metabolism due to the amplification of diel variations in the microenvironment surrounding the coral and the decrease in ATP contents.

Combined metabolome and proteome analysis of the mantle tissue from Pacific oyster Crassostrea gigas exposed to elevated pCO2

Ocean acidification (OA) has been found to affect an array of normal physiological processes in mollusks, especially posing a significant threat to the fabrication process of mollusk shell. In the current study, the impact of exposure to elevated pCO2 condition was investigated in mantle tissue of Crassostrea gigas by an integrated metabolomic and proteomic approach. Analysis of metabolome and proteome revealed that elevated pCO2 could affect energy metabolism in oyster C. gigas, marked by differentially altered ATP, succinate, MDH, PEPCK and ALDH levels. Moreover, the up-regulated calponin-2, tropomyosins and myosin light chains indicated that elevated pCO2 probably caused disturbances in cytoskeleton structure in mantle tissue of oyster C. gigas. This work demonstrated that a combination of proteomics and metabolomics could provide important insights into the effects of OA at molecular levels.

Whole transcriptome analysis of the coral Acropora millepora reveals complex responses to CO2-driven acidification during the initiation of calcification

The impact of ocean acidification (OA) on coral calcification, a subject of intense current interest, is poorly understood in part because of the presence of symbionts in adult corals. Early life history stages of Acropora spp. provide an opportunity to study the effects of elevated CO(2) on coral calcification without the complication of symbiont metabolism. Therefore, we used the Illumina RNAseq approach to study the effects of acute exposure to elevated CO(2) on gene expression in primary polyps of Acropora millepora, using as reference a novel comprehensive transcriptome assembly developed for this study. Gene ontology analysis of this whole transcriptome data set indicated that CO(2) -driven acidification strongly suppressed metabolism but enhanced extracellular organic matrix synthesis, whereas targeted analyses revealed complex effects on genes implicated in calcification. Unexpectedly, expression of most ion transport proteins was unaffected, while many membrane-associated or secreted carbonic anhydrases were expressed at lower levels. The most dramatic effect of CO(2) -driven acidification, however, was on genes encoding candidate and known components of the skeletal organic matrix that controls CaCO(3) deposition. The skeletal organic matrix effects included elevated expression of adult-type galaxins and some secreted acidic proteins, but down-regulation of other galaxins, secreted acidic proteins, SCRiPs and other coral-specific genes, suggesting specialized roles for the members of these protein families and complex impacts of OA on mineral deposition. This study is the first exhaustive exploration of the transcriptomic response of a scleractinian coral to acidification and provides an unbiased perspective on its effects during the early stages of calcification.

Physiological response of the cold-water coral Desmophyllum dianthus to thermal stress and ocean acidification

Rising temperatures and ocean acidification driven by anthropogenic carbon emissions threaten both tropical and temperate corals. However, the synergistic effect of these stressors on coral physiology is still poorly understood, in particular for cold-water corals. This study assessed changes in key physiological parameters (calcification, respiration and ammonium excretion) of the widespread cold-water coral Desmophyllum dianthus maintained for 8 months at two temperatures (ambient 12 °C and elevated 15 °C) and two pCO2 conditions (ambient 390 ppm and elevated 750 ppm). At ambient temperatures no change in instantaneous calcification, respiration or ammonium excretion rates was observed at either pCO2 levels. Conversely, elevated temperature (15 °C) significantly reduced calcification rates, and combined elevated temperature and pCO2 significantly reduced respiration rates. Changes in the ratio of respired oxygen to excreted nitrogen (O:N), which provides information on the main sources of energy being metabolized, indicated a shift from mixed use of protein and carbohydrate/lipid as metabolic substrates under control conditions, to less efficient protein-dominated catabolism under both stressors. Overall, this study shows that the physiology of D. dianthus is more sensitive to thermal than pCO2 stress, and that the predicted combination of rising temperatures and ocean acidification in the coming decades may severely impact this cold-water coral species.

Incorporation of Mg and Sr in calcite of cultured benthic foraminifera (Heterostegina depressa and Ammonia tepida) and seawater carbonate chemistry, 2010

We investigated the effect of the calcium concentration in seawater and thereby the calcite saturation state (omega) on the magnesium and strontium incorporation into benthic foraminiferal calcite under laboratory conditions. For this purpose individuals of the shallow-water species Heterostegina depressa (precipitating high-Mg calcite, symbiont-bearing) and Ammonia tepida (low-Mg calcite, symbiont-barren) were cultured in media under a range of [Ca2+], but similar Mg/Ca ratios. Trace element/Ca ratios of newly formed calcite were analysed with Laser Ablation Inductively Coupled Plasma Mass Spectrometry (LA-ICP-MS) and normalized to the seawater elemental composition using the equation DTE=(TE/Cacalcite)/(TE/Caseawater). The culturing study shows that DMg of A. tepida significantly decreases with increasing omega at a gradient of -4.3x10-5 per omega unit. The DSr value of A. tepida does not change with omega, suggesting that fossil Sr/Ca in this species may be a potential tool to reconstruct past variations in seawater Sr/Ca. Conversely, DMg of H. depressa shows only a minor decrease with increasing omega, while DSr increases considerably with omega at a gradient of 0.009 per omega unit. The different responses to seawater chemistry of the two species may be explained by a difference in the calcification pathway that is, at the same time, responsible for the variation in the total Mg incorporation between the two species. Since the Mg/Ca ratio in H. depressa is 50-100 times higher than that of A. tepida, it is suggested that the latter exhibits a mechanism that decreases the Mg/Ca ratio of the calcification fluid, while the high-Mg calcite forming species may not have this physiological tool. If the dependency of Mg incorporation on seawater [Ca2+] is also valid for deep-sea benthic foraminifera typically used for paleostudies, the higher Ca concentrations in the past may potentially bias temperature reconstructions to a considerable degree. For instance, 25 Myr ago Mg/Ca ratios in A. tepida would have been 0.2 mmol/mol lower than today, due to the 1.5 times higher [Ca2+] of seawater, which in turn would lead to a temperature underestimation of more than 2 °C.