High pCO2 Treatment Research Articles

Within- and transgenerational stress legacy effects of ocean acidification on red abalone (Haliotis rufescens) growth and survival.

Understanding the mechanisms by which individual organisms respond and populations adapt to global climate change is a critical challenge. The role of plasticity and acclimation, within and across generations, may be essential given the pace of change. We investigated plasticity across generations and life stages in response to ocean acidification (OA), which poses a growing threat to both wild populations and the sustainable aquaculture of shellfish. Most studies of OA on shellfish focus on acute effects, and less is known regarding the longer term carryover effects that may manifest within or across generations. We assessed these longer term effects in red abalone (Haliotis rufescens) using a multi-generational split-brood experiment. We spawned adults raised in ambient conditions to create offspring that we then exposed to high pCO2 (1180 μatm; simulating OA) or low pCO2 (450 μatm; control or ambient conditions) during the first 3 months of life. We then allowed these animals to reach maturity in ambient common garden conditions for 4 years before returning the adults into high or low pCO2 treatments for 11 months and measuring growth and reproductive potential. Early-life exposure to OA in the F1 generation decreased adult growth rate even after 5 years especially when abalone were re-exposed to OA as adults. Adult but not early-life exposure to OA negatively impacted fecundity. We then exposed the F2 offspring to high or low pCO2 treatments for the first 3 months of life in a fully factorial, split-brood design. We found negative transgenerational effects of parental OA exposure on survival and growth of F2 offspring, in addition to significant direct effects of OA on F2 survival. These results show that the negative impacts of OA can last within and across generations, but that buffering against OA conditions at critical life-history windows can mitigate these effects.

Elevated pCO2 changes community structure and function by affecting phytoplankton group-specific mortality

The rise of atmospheric pCO2 has created a number of problems for marine ecosystem. In this study, we initially quantified the effects of elevated pCO2 on the group-specific mortality of phytoplankton in a natural community based on the results of mesocosm experiments. Diatoms dominated the phytoplankton community, and the concentration of chlorophyll a was significantly higher in the high-pCO2 treatment than the low-pCO2 treatment. Phytoplankton mortality (percentage of dead cells) decreased during the exponential growth phase. Although the mortality of dinoflagellates did not differ significantly between the two pCO2 treatments, that of diatoms was lower in the high-pCO2 treatment. Small diatoms dominated the diatom community. Although the mortality of large diatoms did not differ significantly between the two treatments, that of small diatoms was lower in the high-pCO2 treatment. These results suggested that elevated pCO2 might enhance dominance by small diatoms and thereby change the community structure of coastal ecosystems.

Impaired hatching exacerbates the high CO2 sensitivity of embryonic sand lance Ammodytes dubius

Rising oceanic partial pressure of CO2 (pCO2) could affect many traits in fish early life stages, but only few species to date have shown direct CO2-induced survival reductions. This might partly be because species from less CO2-variable, offshore environments in higher latitudes are currently underrepresented in the literature. We conducted new experimental work on northern sand lance Ammodytes dubius, a key forage fish on offshore Northwest Atlantic sand banks, which was recently suggested to be highly CO2-sensitive. In 2 complementary trials, we produced embryos from wild, Gulf of Maine spawners and reared them at several pCO2 levels (~400-2000 µatm) in combination with static (6, 7, 10°C) and dynamic (10→5°C) temperature treatments. Again, we consistently observed large, CO2-induced reductions in hatching success (-23% at 1000 µatm, -61% at ~2000 µatm), and the effects were temperature-independent. To distinguish pCO2 effects during development from potential impacts on hatching itself, some embryos were switched between high and control pCO2 treatments just prior to hatch. This indeed altered hatching patterns, consistent with the CO2-impaired hatching hypothesis. High CO2 also delayed the day of first hatch in one trial and peak hatch in the other, where later-hatched larvae were of similar size but with progressively less endogenous energy reserves. For context, we extracted seasonal pCO2 projections for Stellwagen Bank (Gulf of Maine) from regional ensemble simulations, which indicated a CO2-induced reduction in sand lance hatching success to 71% of contemporary levels by 2100. The species’ unusual CO2 sensitivity has large ecological and scientific ramifications that warrant future in-depth research.

Elevated pCO2 Impedes Succession of Phytoplankton Community From Diatoms to Dinoflagellates Along With Increased Abundance of Viruses and Bacteria

Eutrophic coastal regions are highly productive and greatly influenced by human activities. Primary production supporting the coastal ecosystems is supposed to be affected by progressive ocean acidification driven by increasing CO2 emissions. In order to investigate the effects of high pCO2 (HC) on eutrophic plankton community structure and ecological functions, we employed 9 mesocosms and carried out an experiment under ambient (∼410 ppmv) and future high (1000 ppmv) atmospheric pCO2 conditions, using in situ plankton community in Wuyuan Bay, East China Sea. Our results showed that HC along with natural seawater temperature rise significantly boosted biomass of diatoms with decreased abundance of dinoflagellates in the late stage of the experiment, demonstrating that HC repressed the succession from diatoms to dinoflagellates, a phenomenon observed during algal blooms in the East China Sea. HC did not significantly influence the primary production or biogenic silica contents of the phytoplankton assemblages. However, the HC treatments increased the abundance of viruses and heterotrophic bacteria, reflecting a refueling of nutrients for phytoplankton growth from virus-mediated cell lysis and bacterial degradation of organic matters. Conclusively, our results suggest that increasing CO2 concentrations can modulate plankton structure including the succession of phytoplankton community and the abundance of viruses and bacteria in eutrophic coastal waters, which may lead to altered biogeochemical cycles of carbon and nutrients.

Experimental assessment of the impacts of ocean acidification and urchin grazing on benthic kelp forest assemblages

Ocean acidification (OA) is likely to differentially affect the biology and physiology of calcifying and non-calcifying taxa, thereby potentially altering key ecological interactions (e.g., facilitation, competition, predation) in ways that are difficult to predict from single-species experiments. We used a two-factor experimental design to investigate how multispecies benthic assemblages in southern California kelp forests respond to OA and grazing by the purple sea urchin, Strongylocentrotus purpuratus. Settlement tiles accrued natural mixed assemblages of algae and invertebrates in a kelp forest off San Diego, CA for one year before being exposed to OA and grazing in a laboratory experiment for two months. Space occupying organisms were identified and pooled into six functional groups: calcified invertebrates, non-calcified invertebrates, calcified algae, fleshy algae, sediment, and bare space for subsequent analyses of community structure. Interestingly, communities that developed on separate tile racks were unique, despite being deployed close in space, and further changes in community structure in response to OA and grazing depended on this initial community state. On Rack 1, we found significant effects of both pCO2 and grazing with elevated pCO2 increasing cover of fleshy algae, but sea urchin grazers decreasing cover of fleshy algae. On Rack 2, we found a ~ 35% higher percent cover of sediment on tiles reared in ambient pCO2 but observed ~27% higher cover of bare space in the high pCO2 conditions. On Rack 3, we found an average of 45% lower percent cover of calcified sessile invertebrates at ambient pCO2 than in high pCO2 treatments on Rack 3. Net community calcification was 137% lower in elevated pCO2 treatments. Kelp sporophyte densities on tiles without urchins were 74% higher than on tiles with urchins and kelp densities were highest in the elevated pCO2 treatment. Urchin growth and grazing rates were 49% and 126% higher under ambient than high pCO2 conditions. This study highlights consistent negative impacts of OA on community processes such as calcification and grazing rates, even though impacts on community structure were highly context-dependent.

Effect of Ocean Acidification on Bacterial Metabolic Activity and Community Composition in Oligotrophic Oceans, Inferred From Short-Term Bioassays.

Increasing anthropogenic CO2 emissions in recent decades cause ocean acidification (OA), affecting carbon cycling in oceans by regulating eco-physiological processes of plankton. Heterotrophic bacteria play an important role in carbon cycling in oceans. However, the effect of OA on bacteria in oceans, especially in oligotrophic regions, was not well understood. In our study, the response of bacterial metabolic activity and community composition to OA was assessed by determining bacterial production, respiration, and community composition at the low-pCO2 (400 ppm) and high-pCO2 (800 ppm) treatments over the short term at two oligotrophic stations in the northern South China Sea. Bacterial production decreased significantly by 17.1–37.1 % in response to OA, since bacteria with high nucleic acid content preferentially were repressed by OA, which was less abundant under high-pCO2 treatment. Correspondingly, shifts in bacterial community composition occurred in response to OA, with a high fraction of the small-sized bacteria and high bacterial species diversity in a high-pCO2 scenario at K11. Bacterial respiration responded to OA differently at both stations, most likely attributed to different physiological responses of the bacterial community to OA. OA mitigated bacterial growth efficiency, and consequently, a larger fraction of DOC entering microbial loops was transferred to CO2.

Ocean acidification impacts on biomass and fatty acid composition of a post-bloom marine plankton community

A mesocosm approach was used to investigate the effects of ocean acidification (OA) on a natural plankton community in coastal waters off Norway by manipulating CO2 partial pressure (pCO2). Eight enclosures were deployed in the Raunefjord near Bergen. Treatment levels were ambient (~320 µatm) and elevated pCO2 (~2000 µatm), each in 4 replicate enclosures. The experiment lasted for 53 d in May-June 2015. To assess impacts of OA on the plankton community, phytoplankton and protozooplankton biomass and total seston fatty acid content were analyzed. In both treatments, the plankton community was dominated by the dinoflagellate Ceratium longipes. In the elevated pCO2 treatment, however, biomass of this species as well as that of other dinoflagellates was strongly negatively affected. At the end of the experiment, total dinoflagellate biomass was 4-fold higher in the control group than under elevated pCO2 conditions. In a size comparison of C. longipes, cell size in the high pCO2 treatment was significantly larger. The ratio of polyunsaturated fatty acids to saturated fatty acids of seston decreased at high pCO2. In particular, the concentration of docosahexaenoic acid (C 22:6n3c), essential for development and reproduction of metazoans, was less than half at high pCO2 compared to ambient pCO2. Thus, elevated pCO2 led to a deterioration in the quality and quantity of food in a natural plankton community, with potential consequences for the transfer of matter and energy to higher trophic levels

Differential gene expression patterns related to lipid metabolism in response to ocean acidification in larvae and juveniles of Atlantic cod

Elevated environmental carbon dioxide (pCO2) levels have been found to cause organ damage in the early life stages of different commercial fish species, including Atlantic cod (Gadus morhua). To illuminate the underlying mechanisms causing pathologies in the intestines, the kidney, the pancreas and the liver in response to elevated pCO2, we examined related gene expression patterns in Atlantic cod reared for two months under three different pCO2 regimes: 380 μatm (control), 1800 μatm (medium) and 4200 μatm (high). We extracted RNA from whole fish sampled during the larval (32 dph) and early juvenile stage (46 dph) for relative expression analysis of 18 different genes related to essential metabolic pathways. At 32 dph, larvae subjected to the medium treatment displayed an up-regulation of genes mainly associated with fatty acid and glycogen synthesis (GYS2, 6PGL, ACoA, CPTA1, FAS and PPAR1b). Larvae exposed to the high pCO2 treatment upregulated fewer but similar genes (6PGL, ACoA and PPAR1b,). These data suggest stress-induced alterations in the lipid and fatty acid metabolism and a disrupted lipid homeostasis in larvae, providing a mechanistic link to the findings of lipid droplet overload in the liver and organ pathologies. At 46 dph, no significant differences in gene expression were detected, confirming a higher resilience of juveniles in comparison to larvae when exposed to elevated pCO2 up to 4200 μatm.

The Biotechnological Potential of the Marine Diatom Skeletonema dohrnii to the Elevated Temperature and pCO2 Concentration.

Marine diatoms are promising candidates for biotechnological applications, since they contain high-value compounds, naturally. To facilitate the production of these compounds, stress conditions are often preferable; however, challenges remain with respect to maximizing a metabolic potential for the large-scale cultivation. Here, we sequenced the transcriptome of diatom Skeletonema dohrnii under the actual (21 °C, 400 ppm) and elevated (25 °C, 1000 ppm) temperature and pCO2 condition. Results indicated that cells grown at higher temperature and pCO2 showed increasing growth rate, pigment composition, and biochemical productivity as did the expression of chlorophyll, carotenoid and bioactive compound related genes or transcripts. Furthermore, performing de novo transcriptome, we identified 32,884 transcript clusters and found 10,974 of them were differentially expressed between these two conditions. Analyzing the functions of differentially expressed transcripts, we found many of them involved in core metabolic and biosynthesis pathways, including chlorophyll metabolism, carotenoid, phenylpropanoid, phenylalanine and tyrosine, and flavonoid biosynthesis was upregulated. Moreover, we here demonstrated that utilizing a unique bio-fixation ability, S. dohrnii is capable of suppressing central carbon metabolism to promote lipid productivity, fatty acid contents and other bioactive compounds under high temperature and pCO2 treatment. Our study suggests that this S. dohrnii species could be a potential candidate for wide-scale biotechnological applications under elevated temperature and CO2 conditions.

Parental environments alter DNA methylation in offspring of the purple sea urchin, Strongylocentrotus purpuratus

Phenotypic plasticity, within and across generations, is a strategy by which organisms can respond rapidly to environmental change. Epigenetic modifications, such as DNA methylation, have been proposed to be involved in phenotypic plasticity. We examined the potential for the environment to mediate both transgenerational and intragenerational plasticity in DNA methylation and phenotypes in early stages of the purple sea urchin, Strongylocentrotus purpuratus, an ecologically important herbivore in kelp forest ecosystems. This approach involved a controlled laboratory experiment where adult urchins were acclimated during gametogenesis to upwelling (~1300 μatm pCO2 & 13 °C) or non-upwelling (~650 μatm pCO2 & 17 °C) conditions that are representative of their kelp forest habitat. Progeny from these adults were raised in either high (~1050 μatm) or low (~450 μatm) pCO2 treatments and sampled at three developmental stages. Differences in condition experienced by mothers were associated with differentially methylated genes in the offspring. However, differences in developmental conditions corresponded to little observable effects on gene methylation in the progeny. Variation in gene body methylation across treatments was correlated with body size of the embryos and larvae, illustrating a potential link between transgenerational phenotypic plasticity and DNA methylation. Overall, our results suggest that epigenetic factors such as DNA methylation have the potential to contribute to phenotypic plasticity in a transgenerational framework, and further, that epigenetic processes may act as a mechanism of rapid response to environmental change.

Transgenerational effects in an ecological context: Conditioning of adult sea urchins to upwelling conditions alters maternal provisioning and progeny phenotype

Transgenerational plasticity occurs when the conditions experienced by the parental generation influence the phenotype of their progeny. This may in turn affect progeny performance and physiological tolerance, providing a means by which organisms cope with rapid environmental change. We conditioned adult purple sea urchins, Strongylocentrotus purpuratus, to combined pCO2 and temperature conditions reflective of in situ conditions of their natural habitat, the benthos in kelp forests of nearshore California, and then assessed the performance of their progeny raised under different pCO2 levels. Adults were conditioned during gametogenesis to treatments that reflected static non-upwelling (~650 μatm pCO2, ~17 °C) and upwelling (~1300 μatm pCO2, ~13 °C) conditions. Following approximately 4 months of conditioning, the adults were spawned and embryos were raised under low pCO2 (~450 μatm pCO2) or high pCO2 (~1050 μatm pCO2) treatments to determine if differential maternal conditioning impacted the progeny response to a single abiotic stressor: pCO2. We examined the size, protein content, and lipid content of eggs from both sets of conditioned female urchins. Offspring were sampled at four stages of early development: hatched blastula, gastrula, prism, and echinopluteus. This resulted in four sets of offspring: (1) progeny from non-upwelling-conditioned mothers raised under low pCO2, (2) progeny from non-upwelling-conditioned mothers raised under high pCO2, (3) progeny from upwelling-conditioned mothers raised under low pCO2, and (4) progeny from upwelling-conditioned mothers raised under high pCO2. We then assessed the effects of maternal conditioning along with the effects of developmental pCO2 levels on body size of the progeny. Our results showed that differential maternal conditioning had no impact on average egg size, although non-upwelling females produced eggs that were more variable in size. Maternal conditioning did not affect protein content but did have a modest impact on egg lipid content. Developing embryos whose mothers were conditioned to simulated upwelling conditions (~1300 μatm pCO2, ~13 °C) were greater in body size, although this effect was no longer evident at the echinopluteus larval stage. Although maternal conditioning affected offspring body size, the pCO2 levels under which the embryos were raised did not. Overall, this laboratory study provides insight into how transgenerational effects may function in nature. The impacts of parental environmental history on progeny phenotype during early development have important implications regarding recruitment success and population-level effects.

Ocean Acidification Regulates the Activity, Community Structure, and Functional Potential of Heterotrophic Bacterioplankton in an Oligotrophic Gyre

AbstractOcean acidification (OA), a consequence of increased global carbon dioxide (CO2) emissions, is considered a major threat to marine ecosystems. Its effects on bacterioplankton activity, diversity, and community composition have received considerable attention. However, the direct impact of OA on heterotrophic bacterioplankton is often masked by the significant response of phytoplankton due to the close coupling of heterotrophic bacterioplankton and autotrophs. Here we investigated the responses of a heterotrophic bacterioplankton assemblage to high pCO2 (790‐ppm) treatment in warm tropical western Pacific waters by conducting a microcosm experiment in dark for 12 days. Heterotrophic bacterioplankton abundance and production were enhanced by OA over the first 6 days of incubation, while the diversity and species richness were negatively affected. Bacterioplankton community composition in the high pCO2 treatment changed faster than that in the control. The molecular ecological network analysis showed that the elevated CO2 changed the overall connections among the bacterial community and resulted in a simple network under high CO2 condition. Species‐specific responses to OA were observed and could be attributed to the different life strategies and to the ability of a given species to adapt to environmental conditions. In addition, high‐throughput functional gene array analysis revealed that genes related to carbon and nitrogen cycling were positively affected by acidification. Together, our findings suggest that OA has direct effects on heterotrophic bacterioplankton in a low‐latitude warm ocean and may therefore affect global biogeochemical cycles.

Effect of elevated <i>p</i>CO<sub>2</sub> on trace gas production during an ocean acidification mesocosm experiment

Abstract. A mesocosm experiment was conducted in Wuyuan Bay (Xiamen), China, to investigate the effects of elevated pCO2 on the phytoplankton species Phaeodactylum tricornutum (P. tricornutum), Thalassiosira weissflogii (T. weissflogii) and Emiliania huxleyi (E. huxleyi) and their production ability of dimethylsulfide (DMS), dimethylsulfoniopropionate (DMSP), as well as four halocarbon compounds, bromodichloromethane (CHBrCl2), methyl bromide (CH3Br), dibromomethane (CH2Br2) and iodomethane (CH3I). Over a period of 5 weeks, P. tricornuntum outcompeted T. weissflogii and E. huxleyi, comprising more than 99 % of the final biomass. During the logarithmic growth phase (phase I), mean DMS concentration in high pCO2 mesocosms (1000 µatm) was 28 % lower than that in low pCO2 mesocosms (400 µatm). Elevated pCO2 led to a delay in DMSP-consuming bacteria concentrations attached to T. weissflogii and P. tricornutum and finally resulted in the delay of DMS concentration in the high pCO2 treatment. Unlike DMS, the elevated pCO2 did not affect DMSP production ability of T. weissflogii or P. tricornuntum throughout the 5-week culture. A positive relationship was detected between CH3I and T. weissflogii and P. tricornuntum during the experiment, and there was a 40 % reduction in mean CH3I concentration in the high pCO2 mesocosms. CHBrCl2, CH3Br, and CH2Br2 concentrations did not increase with elevated chlorophyll a (Chl a) concentrations compared with DMS(P) and CH3I, and there were no major peaks both in the high pCO2 or low pCO2 mesocosms. In addition, no effect of elevated pCO2 was identified for any of the three bromocarbons.

Nitrogen enrichment offsets direct negative effects of ocean acidification on a reef-building crustose coralline alga.

Ocean acidification (OA) and nutrient enrichment threaten the persistence of near shore ecosystems, yet little is known about their combined effects on marine organisms. Here, we show that a threefold increase in nitrogen concentrations, simulating enrichment due to coastal eutrophication or consumer excretions, offset the direct negative effects of near-future OA on calcification and photophysiology of the reef-building crustose coralline alga, Porolithon onkodes Projected near-future pCO2 levels (approx. 850 µatm) decreased calcification by 30% relative to ambient conditions. Conversely, nitrogen enrichment (nitrate + nitrite and ammonium) increased calcification by 90-130% in ambient and high pCO2 treatments, respectively. pCO2 and nitrogen enrichment interactively affected instantaneous photophysiology, with highest relative electron transport rates under high pCO2 and high nitrogen. Nitrogen enrichment alone increased concentrations of the photosynthetic pigments chlorophyll a, phycocyanin and phycoerythrin by approximately 80-450%, regardless of pCO2 These results demonstrate that nutrient enrichment can mediate direct organismal responses to OA. In natural systems, however, such direct benefits may be counteracted by simultaneous increases in negative indirect effects, such as heightened competition. Experiments exploring the effects of multiple stressors are increasingly becoming important for improving our ability to understand the ramifications of local and global change stressors in near shore ecosystems.

Shifting Balance of Protein Synthesis and Degradation Sets a Threshold for Larval Growth Under Environmental Stress.

Exogenous environmental factors alter growth rates, yet information remains scant on the biochemical mechanisms and energy trade-offs that underlie variability in the growth of marine invertebrates. Here we study the biochemical bases for differential growth and energy utilization (as adenosine triphosphate [ATP] equivalents) during larval growth of the bivalve Crassostrea gigas exposed to increasing levels of experimental ocean acidification (control, middle, and high pCO2, corresponding to ∼400, ∼800, and ∼1100 µatm, respectively). Elevated pCO2 hindered larval ability to accrete both shell and whole-body protein content. This negative impact was not due to an inability to synthesize protein per se, because size-specific rates of protein synthesis were upregulated at both middle and high pCO2 treatments by as much as 45% relative to control pCO2. Rather, protein degradation rates increased with increasing pCO2. At control pCO2, 89% of cellular energy (ATP equivalents) utilization was accounted for by just 2 processes in larvae, with protein synthesis accounting for 66% and sodium-potassium transport accounting for 23%. The energetic demand necessitated by elevated protein synthesis rates could be accommodated either by reallocating available energy from within the existing ATP pool or by increasing the production of total ATP. The former strategy was observed at middle pCO2, while the latter strategy was observed at high pCO2. Increased pCO2 also altered sodium-potassium transport, but with minimal impact on rates of ATP utilization relative to the impact observed for protein synthesis. Quantifying the actual energy costs and trade-offs for maintaining physiological homeostasis in response to stress will help to reveal the mechanisms of resilience thresholds to environmental change.

Ocean acidification effects on mesozooplankton community development: Results from a long-term mesocosm experiment.

Ocean acidification may affect zooplankton directly by decreasing in pH, as well as indirectly via trophic pathways, where changes in carbon availability or pH effects on primary producers may cascade up the food web thereby altering ecosystem functioning and community composition. Here, we present results from a mesocosm experiment carried out during 113 days in the Gullmar Fjord, Skagerrak coast of Sweden, studying plankton responses to predicted end-of-century pCO2 levels. We did not observe any pCO2 effect on the diversity of the mesozooplankton community, but a positive pCO2 effect on the total mesozooplankton abundance. Furthermore, we observed species-specific sensitivities to pCO2 in the two major groups in this experiment, copepods and hydromedusae. Also stage-specific pCO2 sensitivities were detected in copepods, with copepodites being the most responsive stage. Focusing on the most abundant species, Pseudocalanus acuspes, we observed that copepodites were significantly more abundant in the high-pCO2 treatment during most of the experiment, probably fuelled by phytoplankton community responses to high-pCO2 conditions. Physiological and reproductive output was analysed on P. acuspes females through two additional laboratory experiments, showing no pCO2 effect on females’ condition nor on egg hatching. Overall, our results suggest that the Gullmar Fjord mesozooplankton community structure is not expected to change much under realistic end-of-century OA scenarios as used here. However, the positive pCO2 effect detected on mesozooplankton abundance could potentially affect biomass transfer to higher trophic levels in the future.

Change in Emiliania huxleyi Virus Assemblage Diversity but Not in Host Genetic Composition during an Ocean Acidification Mesocosm Experiment

Effects of elevated pCO2 on Emiliania huxleyi genetic diversity and the viruses that infect E. huxleyi (EhVs) have been investigated in large volume enclosures in a Norwegian fjord. Triplicate enclosures were bubbled with air enriched with CO2 to 760 ppmv whilst the other three enclosures were bubbled with air at ambient pCO2; phytoplankton growth was initiated by the addition of nitrate and phosphate. E. huxleyi was the dominant coccolithophore in all enclosures, but no difference in genetic diversity, based on DGGE analysis using primers specific to the calcium binding protein gene (gpa) were detected in any of the treatments. Chlorophyll concentrations and primary production were lower in the three elevated pCO2 treatments than in the ambient treatments. However, although coccolithophores numbers were reduced in two of the high-pCO2 treatments; in the third, there was no suppression of coccolithophores numbers, which were very similar to the three ambient treatments. In contrast, there was considerable variation in genetic diversity in the EhVs, as determined by analysis of the major capsid protein (mcp) gene. EhV diversity was much lower in the high-pCO2 treatment enclosure that did not show inhibition of E. huxleyi growth. Since virus infection is generally implicated as a major factor in terminating phytoplankton blooms, it is suggested that no study of the effect of ocean acidification in phytoplankton can be complete if it does not include an assessment of viruses.

Effects of Enhanced pCO2and Temperature on Reproduction and Survival of the Copepod Calanus sinicus

We tested the combined effects of increased partial pressure of CO₂ (pCO₂) and temperature on the reproduction and survival of the copepod Calanus sinicus from Asan Bay, the Yellow Sea under laboratory conditions to understand the impact of acidification on copepods. Egg production rate, survival rate, and fecal pellet production of C. sinicus were not affected by 1305 ppm pCO₂ or with combined treatments of temperature and pCO₂, including 8℃ and 289 ppm pCO₂ (ambient), 8℃ and 753 ppm pCO₂ (high pCO₂), 12℃ and 289 ppm pCO₂ (high temperature), and 12℃ and 753 ppm pCO₂ (greenhouse), for 5 or 10 d of exposure. However, egg hatching success of C. sinicus decreased significantly in the greenhouse treatment compared with the ambient or the high pCO₂ treatments. These results suggest that a combined treatment (pCO₂ and temperature) affected egg viability more than a single treatment (pCO₂).

Ocean acidification effects on haploid and diploid Emiliania huxleyi strains: Why changes in cell size matter

The effects of ocean acidification (OA) on Emiliania huxleyi non-calcifying haploid strain CCMP 374 (s374) and calcifying diploid strain CCMP 2668 (s2668) were investigated in this study. Both E. huxleyi strains were cultured semi-continuously for ~20 generations under three pCO2 levels, one representing equilibrium with contemporary atmospheric pCO2 and two representing different OA scenarios projected for the end the century. During the course of the experiments, measurements were made for cell size in s374 and coccosphere size in strain s2668, cellular intrinsic growth rates, and the per cell (s374) and per coccosphere (s2668) concentrations of particulate organic carbon (POC) and nitrogen (PON), particulate inorganic carbon (PIC), chlorophyll a (chl a) and particulate dimethylsulfoniopropionate (DMSPp). In agreement with other studies, elevated pCO2 led to a small increase in POC and PON in the diploid strain, but not in the haploid strain. Although the PIC was static across pCO2 treatments in the diploid calcifier, PIC:POC was reduced under OA due to the disproportionate increase in POC. The concentration of E. huxleyi DMSPp cell−1 increased (s2668) or responded non-linearly (s374) to OA. Exposure to OA caused cell and coccosphere volumes to increase by 18% and 37% from the ambient to high pCO2 treatment in the haploid and diploid strain, respectively, despite equivalent cross-treatment growth rates. Therefore, when normalized to cell and coccosphere volume, small to negligible increases in cellular constituents under OA translated into decreased cellular and coccosphere densities (e.g. mass vol−1) of those same constituents. This produces seemingly contradictory cellular responses to OA depending on data normalization, and highlights the need to cautiously interpret OA experimental data when cell and coccosphere size is not reported. A consistent OA-induced increase in cell and coccosphere size has implications for E. huxleyi cellular physiology, ecology and trophic interactions, as cell size is a master characteristic that governs cellular rate processes, predator encounter rates, and predator ingestion efficiencies. Further, because POC and PON did not scale with volume increases, there is a dilution in the carbon and nitrogen concentration in E. huxleyi cells under OA. This result could have cascading effects on planktonic food webs as predator ingestion rates and growth efficiencies adjust.

CO2 leakage from carbon dioxide capture and storage (CCS) systems affects organic matter cycling in surface marine sediments

Carbon dioxide capture and storage (CCS), involving the injection of CO2 into the sub-seabed, is being promoted worldwide as a feasible option for reducing the anthropogenic CO2 emissions into the atmosphere. However, the effects on the marine ecosystems of potential CO2 leakages originating from these storage sites have only recently received scientific attention, and little information is available on the possible impacts of the resulting CO2-enriched seawater plumes on the surrounding benthic ecosystem. In the present study, we conducted a 20-weeks mesocosm experiment exposing coastal sediments to CO2-enriched seawater (at 5000 or 20,000 ppm), to test the effects on the microbial enzymatic activities responsible for the decomposition and turnover of the sedimentary organic matter in surface sediments down to 15 cm depth. Our results indicate that the exposure to high-CO2 concentrations reduced significantly the enzymatic activities in the top 5 cm of sediments, but had no effects on subsurface sediment horizons (from 5 to 15 cm depth). In the surface sediments, both 5000 and 20,000 ppm CO2 treatments determined a progressive decrease over time in the protein degradation (up to 80%). Conversely, the degradation rates of carbohydrates and organic phosphorous remained unaltered in the first 2 weeks, but decreased significantly (up to 50%) in the longer term when exposed at 20,000 ppm of CO2. Such effects were associated with a significant change in the composition of the biopolymeric carbon (due to the accumulation of proteins over time in sediments exposed to high-pCO2 treatments), and a significant decrease (∼20–50% at 5000 and 20,000 ppm respectively) in nitrogen regeneration. We conclude that in areas immediately surrounding an active and long-lasting leak of CO2 from CCS reservoirs, organic matter cycling would be significantly impacted in the surface sediment layers. The evidence of negligible impacts on the deeper sediments should be considered with caution and further investigated simulating the intrusion of CO2 from a subsurface source, as occurring during real CO2 leakages from CCS sites.