Ocean ecosystems are increasingly stressed by human-induced changes of their physical, chemical and biological environment. Among these changes, warming, acidification, deoxygenation and changes in primary productivity by marine phytoplankton can be considered as four of the major stressors of open ocean ecosystems. Due to rising atmospheric CO2 in the coming decades, these changes will be amplified. Here, we use the most recent simulations performed in the framework of the Coupled Model Intercomparison Project 5 to assess how these stressors may evolve over the course of the 21st century. The 10 Earth system models used here project similar trends in ocean warming, acidification, deoxygenation and reduced primary productivity for each of the IPCC’s representative concentration pathways (RCPs) over the 21st century. For the “business-as-usual” scenario RCP8.5, the model-mean changes in the 2090s (compared to the 1990s) for sea surface temperature, sea surface pH, global O2 content and integrated primary productivity amount to +2.73 (±0.72) °C, −0.33 (±0.003) pH unit, −3.45 (±0.44)% and −8.6 (±7.9)%, respectively. For the high mitigation scenario RCP2.6, corresponding changes are +0.71 (±0.45) °C, −0.07 (±0.001) pH unit, −1.81 (±0.31)% and −2.0 (±4.1)%, respectively, illustrating the effectiveness of extreme mitigation strategies. Although these stressors operate globally, they display distinct regional patterns and thus do not change coincidentally. Large decreases in O2 and in pH are simulated in global ocean intermediate and mode waters, whereas large reductions in primary production are simulated in the tropics and in the North Atlantic. Although temperature and pH projections are robust across models, the same does not hold for projections of subsurface O2 concentrations in the tropics and global and regional changes in net primary productivity. These high uncertainties in projections of primary productivity and subsurface oxygen prompt us to continue inter-model comparisons to understand these model differences, while calling for caution when using the CMIP5 models to force regional impact models.
Posts Tagged 'phytoplankton'
Multiple stressors of ocean ecosystems in the 21st century: projections with CMIP5 models (update)
Published 3 October 2013 Media coverage ClosedTags: biological response, chemistry, globalmodeling, modeling, multiple factors, oxygen, phytoplankton, primary production, temperature
Metabolism of a nitrogen-enriched coastal marine lagoon during the summertime
Published 11 September 2013 Science ClosedTags: algae, biogeochemistry, biological response, chemistry, field, light, multiple factors, North Atlantic, nutrients, oxygen, phanerogams, physiology, phytoplankton, primary production
We measured metabolism rates in a shallow, nitrogen-enriched coastal marine ecosystem on Cape Cod (MA, USA) during seven summers using an open-water diel oxygen method. We compared two basins, one directly receiving most of the nitrogen (N) load (“Snug Harbor”) and another further removed from the N load and better flushed (“Outer Harbor”). Both dissolved oxygen and pH varied greatly over the day, increasing in daylight and decreasing at night. The more N-enriched basin frequently went hypoxic during the night, and the pH in both basins was low (compared to standard seawater) when the oxygen levels were low, due to elevated carbon dioxide. Day-to-day variation in gross primary production (GPP) was high and linked in part to variation in light. Whole-ecosystem respiration tended to track this short-term variation in GPP, suggesting that respiration by the primary producers often dominated whole-system respiration. GPP was higher in the more N-loaded Snug Harbor. Seagrasses covered over 60 % of the area of the better-flushed, Outer Harbor throughout our study and were the major contributors to GPP there. Seagrasses covered 20 % of the area in Snug Harbor for the first 5 years of our study, and their contribution to GPP was relatively small. The seagrasses in Snug Harbor died off completely in the 6th year, but GPP remained high then and in the subsequent year. Overall, rates of phytoplankton GPP were relatively low, suggesting that benthic micro- and macro-algae may be the dominant primary producers in Snug Harbor in most years. Net ecosystem production in both Snug Harbor and the Outer Harbor was variable from year to year, showing net heterotrophy in some years and net autotrophy in others, with a trend towards increasing autotrophy over the 7 years reported here.
Continue reading ‘Metabolism of a nitrogen-enriched coastal marine lagoon during the summertime’
Climate change and ocean acidification impacts on lower trophic levels and the export of organic carbon to the deep ocean (update)
Published 9 September 2013 Science ClosedTags: biogeochemistry, biological response, calcification, chemistry, globalmodeling, modeling, multiple factors, phytoplankton, primary production, temperature, zooplankton
Most future projections forecast significant and ongoing climate change during the 21st century, but with the severity of impacts dependent on efforts to restrain or reorganise human activity to limit carbon dioxide (CO2) emissions. A major sink for atmospheric CO2, and a key source of biological resources, the World Ocean is widely anticipated to undergo profound physical and – via ocean acidification – chemical changes as direct and indirect results of these emissions. Given strong biophysical coupling, the marine biota is also expected to experience strong changes in response to this anthropogenic forcing. Here we examine the large-scale response of ocean biogeochemistry to climate and acidification impacts during the 21st century for Representative Concentration Pathways (RCPs) 2.6 and 8.5 using an intermediate complexity global ecosystem model, MEDUSA-2.0. The primary impact of future change lies in stratification-led declines in the availability of key nutrients in surface waters, which in turn leads to a global decrease (1990s vs. 2090s) in ocean productivity (−6.3%). This impact has knock-on consequences for the abundance of the low trophic level biogeochemical actors modelled by MEDUSA-2.0 (−5.8%), and these would be expected to similarly impact higher trophic level elements such as fisheries. Related impacts are found in the flux of organic material to seafloor communities (−40.7% at 1000 m), and in the volume of ocean suboxic zones (+12.5%). A sensitivity analysis removing an acidification feedback on calcification finds that change in this process significantly impacts benthic communities, suggesting that a~better understanding of the OA-sensitivity of calcifying organisms, and their role in ballasting sinking organic carbon, may significantly improve forecasting of these ecosystems. For all processes, there is geographical variability in change – for instance, productivity declines −21% in the Atlantic and increases +59% in the Arctic – and changes are much more pronounced under RCP 8.5 than the RCP 2.6 scenario.
Emiliania huxleyi increases calcification but not expression of calcification-related genes in long-term exposure to elevated temperature and pCO2
Published 29 August 2013 Science ClosedTags: adaptation, biological response, calcification, laboratory, molecular biology, multiple factors, phytoplankton, primary production, temperature
Increased atmospheric pCO2 is expected to render future oceans warmer and more acidic than they are at present. Calcifying organisms such as coccolithophores that fix and export carbon into the deep sea provide feedbacks to increasing atmospheric pCO2. Acclimation experiments suggest negative effects of warming and acidification on coccolithophore calcification, but the ability of these organisms to adapt to future environmental conditions is not well understood. Here, we tested the combined effect of pCO2 and temperature on the coccolithophore Emiliania huxleyi over more than 700 generations. Cells increased inorganic carbon content and calcification rate under warm and acidified conditions compared with ambient conditions, whereas organic carbon content and primary production did not show any change. In contrast to findings from short-term experiments, our results suggest that long-term acclimation or adaptation could change, or even reverse, negative calcification responses in E. huxleyi and its feedback to the global carbon cycle. Genome-wide profiles of gene expression using RNA-seq revealed that genes thought to be essential for calcification are not those that are most strongly differentially expressed under long-term exposure to future ocean conditions. Rather, differentially expressed genes observed here represent new targets to study responses to ocean acidification and warming.
Short- and long-term conditioning of a temperate marine diatom community to acidification and warming
Published 29 August 2013 Science ClosedTags: biological response, community composition, laboratory, multiple factors, phytoplankton, South Pacific, temperature
Ocean acidification and greenhouse warming will interactively influence competitive success of key phytoplankton groups such as diatoms, but how long-term responses to global change will affect community structure is unknown. We incubated a mixed natural diatom community from coastal New Zealand waters in a short-term (two-week) incubation experiment using a factorial matrix of warming and/or elevated pCO2 and measured effects on community structure. We then isolated the dominant diatoms in clonal cultures and conditioned them for 1 year under the same temperature and pCO2 conditions from which they were isolated, in order to allow for extended selection or acclimation by these abiotic environmental change factors in the absence of interspecific interactions. These conditioned isolates were then recombined into ‘artificial’ communities modelled after the original natural assemblage and allowed to compete under conditions identical to those in the short-term natural community experiment. In general, the resulting structure of both the unconditioned natural community and conditioned ‘artificial’ community experiments was similar, despite differences such as the loss of two species in the latter. pCO2 and temperature had both individual and interactive effects on community structure, but temperature was more influential, as warming significantly reduced species richness. In this case, our short-term manipulative experiment with a mixed natural assemblage spanning weeks served as a reasonable proxy to predict the effects of global change forcing on diatom community structure after the component species were conditioned in isolation over an extended timescale. Future studies will be required to assess whether or not this is also the case for other types of algal communities from other marine regimes.
Effects of carbon dioxide on biomass and species composition of a natural Baltic Sea spring bloom community
Published 28 August 2013 Science ClosedTags: abundance, Baltic, biological response, community composition, laboratory, phytoplankton
Carbon dioxide (CO2) emissions contribute to an increased mean temperature of the Earth and ocean acidification. The environmental changes give great concern for biodiversity and future environmental sustainability. Microalgae can possibly be used to recycle CO2 emissions and the biomass could be used for production of high value products like, healthy human food or biofuels. The aim of this study was to examine the effect of carbon dioxide on algae biomass production and species composition of a natural spring bloom community (NC) from the Baltic Sea. Spring blooms are dominated by diatoms which could be a good candidate for CO2 assimilation. The NC was exposed to CO2 gas and compared with NC without added CO2 sources (Air control). The NC was cultivated under controlled laboratory conditions with daily sampling for chlorophyll a and pH measurement. Species composition was investigated by microscope. Low pH reduced CO2 assimilation of the NC but was compensated for since no effect of CO2 could be seen on biomass production. Additionally CO2 had no effect on species composition indicating the species in the NC to be resistant to pH fluctuations. A clear shift in species composition could be seen over time. The diatoms dominated at experiment end confirming that they could potentially be used for algae cultivation to recycle CO2.
Effect of increased pCO2 on phytoplankton–virus interactions
Published 12 August 2013 Science ClosedTags: biological response, growth, laboratory, phytoplankton
Atmospheric carbon dioxide (CO2) has increased since the pre-industrial period and is predicted to continue to increase throughout the twenty-first century. The ocean is a sink for atmospheric CO2 and increased CO2 concentration will change the carbonate equilibrium of seawater and result in lower carbonate ion concentration and lower pH. This may affect the entire marine biota but in particular calcifying organisms. In this study we investigated the effect of increased CO2 on the virus host interaction of Emiliania huxleyi as a calcifying organism and of Phaeocystis poucheti as a non- calcifying organism. Both algae were grown in laboratory controlled conditions under past (280 ppmv), present (350 ppmv) and future (700 ppmv) CO2 concentrations with and without added virus. Increased CO2 had a negative effect on the growth rate of P. pouchetii, but not of E. huxleyi. No impact was found on viral lysis of P. pouchetii while increased burst size and slightly delayed lysis was observed for E. huxleyi with increased CO2. We conclude that this short time study could not confirm earlier reports and our hypothesis of a negative effect of high CO2 on E. huxleyi growth and E. huxleyi virus production.
Continue reading ‘Effect of increased pCO2 on phytoplankton–virus interactions’
Effect of ocean acidification on bacterial abundance, activity and diversity in the Ross Sea, Antarctica
Published 7 August 2013 Science ClosedTags: abundance, Antarctic, biological response, physiology, phytoplankton, prokaryotes
Three ocean acidification experiments were conducted on water from the same location in the Ross Sea, Southern Ocean, to ascertain how surface-water mixed populations, including the microbial community, would respond to changes in pH (pH 7.80 and 7.65). Bacterial extracellular enzymes, abundances, thymidine uptake rate, the diversity of the active fraction of the bacterial community and phytoplankton diversity were measured in response to changes in pH. Bacterial abundance increased at lower pH, and the active fraction of the bacteria decreased, concurrently becoming less diverse within 8 d. However, as the active fraction of the bacterial community evolved, changes in bacterial extracellular enzyme rates occurred, with phosphatase, β-glucosidase and lipase activity increasing up to 2-fold in the acidified incubations. These results suggest that carbohydrates and lipids may be hydrolysed faster with more rapid regeneration of nutrients at lower pH. The changes observed in our experiments indicate that the bacteria in the Ross Sea adapt quickly to lower pH but that bacterial diversity will be lost. However, this loss of diversity did not adversely affect bacterial activity and in fact enhanced their ability to break down carbohydrates and lipids and recycle phosphate. These changes will alter the rate of carbon and phosphate regeneration, potentially accelerating decomposition in surface waters and short-circuiting the biological pump.
Community interactions dampen acidification effects in a coastal plankton system
Published 29 July 2013 Science ClosedTags: abundance, Baltic, crustaceans, physiology, phytoplankton, reproduction, zooplankton
Changing seawater chemistry towards reduced pH as a result of increasing atmospheric carbon dioxide (CO2) is affecting oceanic organisms, particularly calcifying species. Responses of non-calcifying consumers are highly variable and mainly mediated through indirect ocean acidification effects induced by changing the biochemical content of their prey, as shown within single species and simple 2-trophic level systems. However, it can be expected that indirect CO2 impacts observed at the single species level are compensated at the ecosystem level by species richness and complex trophic interactions. A dampening of CO2-effects can be further expected for coastal communities adapted to strong natural fluctuations in pCO2, typical for productive coastal habitats. Here we show that a plankton community of the Kiel Fjord was tolerant to CO2 partial pressure (pCO2) levels projected for the end of this century (<1400 µatm), and only subtle differences were observed at the extremely high value of 4000 µatm. We found similar phyto- and microzooplankton biomass and copepod abundance and egg production across all CO2 treatment levels. Stoichiometric phytoplankton food quality was minimally different at the highest pCO2 treatment, but was far from being potentially limiting for copepods. These results are in contrast to studies that include only a single species, which observe strong indirect CO2 effects for herbivores and suggest limitations of biological responses at the level of organism to community. Although this coastal plankton community was highly tolerant to high fluctuations in pCO2, increase in hypoxia and CO2 uptake by the ocean can aggravate acidification and may lead to pH changes outside the range presently experienced by coastal organisms.
Continue reading ‘Community interactions dampen acidification effects in a coastal plankton system’
Pelagic community production and carbon-nutrient stoichiometry under variable ocean acidification in an Arctic fjord (update)
Published 18 July 2013 Science ClosedTags: Arctic, biogeochemistry, BRcommunity, field, mesocosms, phytoplankton, primary production, prokaryotes
Net community production (NCP) and carbon to nutrient uptake ratios were studied during a large-scale mesocosm experiment on ocean acidification in Kongsfjorden, western Svalbard, during June–July 2010. Nutrient depleted fjord water with natural plankton assemblages, enclosed in nine mesocosms of ~ 50 m3 in volume, was exposed to pCO2 levels ranging initially from 185 to 1420 μatm. NCP estimations are the cumulative change in dissolved inorganic carbon concentrations after accounting for gas exchange and total alkalinity variations. Stoichiometric coupling between inorganic carbon and nutrient net uptake is shown as a ratio of NCP to a cumulative change in inorganic nutrients. Phytoplankton growth was stimulated by nutrient addition half way through the experiment and three distinct peaks in chlorophyll a concentration were observed during the experiment. Accordingly, the experiment was divided in three phases. Cumulative NCP was similar in all mesocosms over the duration of the experiment. However, in phases I and II, NCP was higher and in phase III lower at elevated pCO2. Due to relatively low inorganic nutrient concentration in phase I, C : N and C : P uptake ratios were calculated only for the period after nutrient addition (phase II and phase III). For the total post-nutrient period (phase II + phase III) ratios were close to Redfield, however they were lower in phase II and higher in phase III. Variability of NCP, C : N and C : P uptake ratios in different phases reflects the effect of increasing CO2 on phytoplankton community composition and succession. The phytoplankton community was composed predominantly of haptophytes in phase I, prasinophytes, dinoflagellates, and cryptophytes in phase II, and haptophytes, prasinophytes, dinoflagellates and chlorophytes in phase III (Schulz et al., 2013). Increasing ambient inorganic carbon concentrations have also been shown to promote primary production and carbon assimilation. For this study, it is clear that the pelagic ecosystem response to increasing CO2 is more complex than that represented in previous work, e.g. Bellerby et al. (2008). Carbon and nutrient uptake representation in models should, where possible, be more focused on individual plankton functional types as applying a single stoichiometry to a biogeochemical model with regard to the effect of increasing pCO2 may not always be optimal. The phase variability in NCP and stoichiometry may be better understood if CO2 sensitivities of the plankton’s functional type biogeochemical uptake kinetics and trophic interactions are better constrained.
Arctic Ocean carbon biogeochemistry under climate change and ocean acidification
Published 8 July 2013 Science ClosedTags: Arctic, biogeochemistry, biological response, chemistry, field, mesocosms, modeling, multiple factors, phytoplankton, prokaryotes, regionalmodeling, temperature
Human-induced CO2 emissions to the atmosphere cause climate change and ocean acidification. The strongest indicators of climate change and ocean acidification are expected to be found in the Arctic Ocean (AO). The AO area is small compared to the world ocean, but the global influence of its carbon biogeochemical system with large spatial and temporal variability is considerable and complex. The AO carbon biogeochemical system is also expected to experience feedback in regard to climate change, and to influence the energy flow throughout the Arctic food web. This thesis investigates the carbon biogeochemical system in the AO: present variability; coupling with processes at the low trophic level; and response to future climate and CO2 scenarios. The study combines differing methodological approaches: (i) in-situ observations, (ii) field perturbation experiments, and (iii) ecosystem modeling. The thesis is based on four separate papers. Paper I describes the natural variability of particulate organic carbon and particulate organic nitrogen in a composition of seston and estimates the carbon to nitrogen (C:N) ratio in the AO seston. The paper is based on 3672 in-situ measurements gathered from sources both published and unpublished. The overall C:N ratio in seston was 7.4, which is significantly higher than the classical Redfield ratio of 6.6. A great regional variability in the seston C:N ratio was found. Paper II introduces the inorganic carbonate system around the Svalbard archipelago in the AO, at present and under future climate and CO2 scenarios. This paper is based on results from a coupled physical-biogeochemical ecosystem model forced by SRES A1B scenario, as well as on results of a CO2 perturbation study on the natural community conducted in an Arctic fjord. The results presented in this paper suggest that seawater pCO2 in the area around Svalbard at the end of the 21st century will be 300 μatm higher than at present in the Atlantic influenced region, and 400 μatm higher than at present in the Arctic influenced region. As a result, the waters in the Arctic-influenced region will be undersaturated with respect to aragonite, and waters in the Atlantic-influenced region will be close to the undersaturation state. The modeled summer decrease in seawater pCO2, and the increase in pH and aragonite saturation state are all steeper in the future. This was also observed during an experiment on ocean acidification in natural phytoplankton assemblage, which was perturbed with the projected high levels of seawater pCO2. Paper III is based on results from two model simulations, performed with the coupled physical-biogeochemical ecosystem model forced by SRES A1B scenario, parameterized with the constant C:N ratio and with the pCO2 sensitive C:N ratio. The paper demonstrates that more inorganic carbon could be fixed by autotrophs in the future surface Arctic waters if annual primary production increases in response to the pCO2 sensitive C:N ratio. As a result of higher primary production, and consequently higher export production in case of pCO2 sensitive C:N ratio, more carbon is released below the euphotic zone, which leads to lower pH and aragonite saturation states than in case with the constant C:N ratio. Paper IV is based on the results of the large-scale CO2 perturbation experiment, revealing enhanced carbon fixation by autotrophs at high levels of pCO2 when the phytoplankton assemblage was dominated by a smallsized phytoplankton group. The results of the paper suggest that net community production could enhance if small-sized phytoplankton thrives in the future Arctic Ocean.
The introduction to the thesis provides a comprehensive overview of the carbonate system and processes controlling it. The AO carbon biogeochemistry is introduced, with its uniqueness and importance for the earth climate system. The findings of the four papers are summarized and future prospects for carbon biogeochemistry research in the AO are discussed.
Continue reading ‘Arctic Ocean carbon biogeochemistry under climate change and ocean acidification’
Effect of pH on the morphology and viability of Scrippsiella trochoidea cysts in the hypoxic zone of a eutrophied area
Published 4 July 2013 Science ClosedTags: biological response, dissolution, field, laboratory, morphology, mortality, multiple factors, North Pacific, nutrients, oxygen, phytoplankton
To investigate the cause of morphological change of Scrippsiella trochoidea cysts and its ecological significance in the hypoxic zone of a eutrophied area, the effect of pH on the morphology and viability of S. trochoidea cysts was studied. In the acidification experiment, the dissolution of calcareous spines of S. trochoidea cysts was observed at less than pH 7.39, indicating that the morphological change of S. trochoidea cysts is caused by the low pH levels in acidic sediments of hypoxic zone. After being exposed to intense acidic environments, cysts of S. trochoidea without calcareous spines were able to germinate; however, they seem to be easily linked to degradation in the sediments. These results suggest that the survival of S. trochoidea cysts is being threatened by environmental conditions in the hypoxic zone of eutrophied area.
Effects of ocean acidification on phytoplankton in upwelling areas influenced by river discharges
Published 29 June 2013 Newsletters and reports , Science ClosedTags: biological response, chemistry, phytoplankton
Barbara Jacob is currently a post-doctoral associate at the Aquatic Ecosystem Functioning Lab (LAFE) under the sponsorship of Dr. Cristian A. Vargas at the Environmental Science Center EULA Chile (Universidad de Concepción), Chile. Her research is focused on understanding the effects of ocean acidification on natural phytoplankton communities as well as on key algal species (flagellates vs. diatom species).
About 48% of carbon dioxide released to the atmosphere in the last 200 years has been caused by man (Raven et al., 2005). The oceans have absorbed nearly half of the fossil-fuel carbon dioxide (CO2) emitted into the atmosphere since pre-industrial times. This capacity causes the reduction in seawater pH and carbonate saturation, a process known as “ocean acidification”. Studies of the effect of ocean acidification on phytoplankton suggest that increasing the concentration of CO2 may stimulate phytoplankton growth rate or efficiency of resource utilization and hence alter the species composition of phytoplankton communities. Recent studies have shown effects of ocean acidification increases the dissolved inorganic carbon consumption of a natural plankton community with rising CO2 (Riebesell et al., 2007). Stoichiometric changes in the C:N ratio of the primary production to high pCO2 levels may affect the availability of labile carbon that could be used by heterotrophic microbial community, in terms of their utilization of the mineral nutrients, which in turn, can limit the primary production due to the reduction of mineral nutrients.
Marine phytoplankton can adapt to ocean acidification
Published 29 June 2013 Newsletters and reports , Science ClosedTags: adaptation, biological response, phytoplankton
Kai Lohbeck is a PhD student in the BIOACID project at GEOMAR (Kiel, Germany). His interdisciplinary work combines biological oceanography and evolutionary biology to investigate the potential for evolutionary adaptation to ocean acidification in marine phytoplankton.
The uptake of fossil fuel-derived carbon dioxide by the surface ocean alters seawater carbonate chemistry and results in a drop in ocean pH (Caldeira and Wickett 2003). These changes, dubbed ocean acidification, have a severe impact on many marine organisms, especially those that build their cell walls, shells, scales or skeletons from calcium carbonate (Orr et al., 2005).
Coccolithophores, a group of planktonic microalgae that are among the most productive calcifying organisms in the sea (Westbroek et al., 1989), were found to be sensitive to ocean acidification with most studies showing a decline in growth and calcification rate at increased CO2 levels (Riebesell and Tortell 2011).
Continue reading ‘Marine phytoplankton can adapt to ocean acidification’
Effects of ocean acidification on iron availability to marine phytoplankton
Published 29 June 2013 Newsletters and reports , Science ClosedTags: biological response, chemistry, phytoplankton
Dalin Shi is currently a professor at the State Key Laboratory of Marine Environmental Science, Xiamen University, China. His research focuses on the biogeochemical cycling of trace metals in the ocean and their roles in the global carbon and nitrogen cycles.
About one-third of the anthropogenic carbon dioxide (CO2) released into the atmosphere dissolves in the ocean, increasing the partial pressure of CO2 (pCO2) and lowering the pH in surface water. These changes in seawater chemistry, commonly referred to as ocean acidification, will likely have significant effects on marine phytoplankton, which are responsible for about half of the contemporary global primary production (Field et al., 1998) and form the basis of all marine food webs.
Continue reading ‘Effects of ocean acidification on iron availability to marine phytoplankton’
Synergistic effects of elevated carbon dioxide and sodium hypochlorite on survival and impairment of three phytoplankton species
Published 21 June 2013 Science ClosedTags: biological response, laboratory, multiple factors, photosynthesis, phytoplankton, survival, toxicants
Sodium hypochlorite (NaOCl) is widely used to disinfect seawater in power plant cooling systems in order to reduce biofouling, and in ballast water treatment systems to prevent transport of exotic marine species. While the toxicity of NaOCl is expected to increase by ongoing ocean acidification, and many experimental studies have shown how algal calcification, photosynthesis and growth respond to ocean acidification, no studies have investigated the relationship between NaOCl toxicity and increased CO2. Therefore, we investigated whether the impacts of NaOCl on survival, chlorophyll a (Chl-a), and effective quantum yield in three marine phytoplankton belonging to different taxonomic classes are increased under high CO2 levels. Our results show that all biological parameters of the three species decreased under increasing NaOCl concentration, but increasing CO2 concentration alone (from 450 to 715 μatm) had no effect on any of these parameters in the organisms. However, due to the synergistic effects between NaOCl and CO2, the survival and Chl-a content in two of the species, Thalassiosira eccentrica and Heterosigma akashiwo, were significantly reduced under high CO2 when NaOCl was also elevated. The results show that combined exposure to high CO2 and NaOCl results in increasing toxicity of NaOCl in some marine phytoplankton. Consequently, greater caution with use of NaOCl will be required, as its use is widespread in coastal waters.
Effects of elevated pCO2 on the calcification and morphological characteristics of the coccolithophore Emiliania huxleyi : implications of ocean acidification
Published 21 June 2013 Science ClosedTags: biological response, calcification, growth, laboratory, morphology, phytoplankton
Increasing acidity in the oceans is a current cause for concern in populations of calcifying organisms. Reactions to increasing pCO2 by organisms are variable and unknown for many, including the small phytoplankton, coccolithophores. Strain CCMP2668 of the coccolithophore, Emiliania huxleyi, was grown in culture under three pCO2 treatments (~400 ppmv, ~750 ppmv, ~1000 ppmv) to understand the effects of increasing pCO2 on the calcification rate and morphological structure of the calcite coccoliths. Results indicated that cells held under control treatment conditions had a higher growth rate than the cells held under both the moderate and high pCO2 treatment conditions. However, no significant difference existed in the amount of particulate organic (POC) and inorganic carbon (PIC) among the control, moderate, and high treatments. Morphologically, after a visual inspection of scanning electron microscopy (SEM) images, an increase in the number of malformed coccoliths was observed in the enriched pCO2 (~15%) treatments in comparison to the control treatment (~3%). The discrepancy between the physiological and morphological results indicates that perhaps the physical structure of the coccolith is affected once exposed to a lower external pH, but that the process of producing the coccoliths remains unaffected by external pH. Variable responses by other species of coccolithophores, specifically other strains of Emiliania huxleyi, are common both in the geologic record and modern experiments. The results from the current experiment reiterate that effects of increasing pCO2 are likely to be strain and species specific, and adds to the knowledge by examining a strain not currently discussed in the literature. Coccolithophores are extremely important primary producers, in fact Emiliania huxleyi alone contributes 1-10% of total primary production, and bases for food webs. Therefore, despite the conflicting results to changing levels of pCO2, it is crucial to consider coccolithophores as a whole when developing political strategies to defend against changing atmospheric and seawater conditions.
Impact of CO2 and pH on the distribution and stable carbon isotopic composition of microbial biomarker lipids
Published 20 June 2013 Science ClosedTags: biological response, laboratory, methods, multiple factors, paleo, phytoplankton, prokaryotes
In addition to the more acknowledged consequences of climate change, such as global warming, the current human-induced increase of CO2 into the atmosphere is also responsible for a change in the chemical composition of seawater. Since 1750, the initiation of the industrial revolution, approximately 50% of the emitted anthropogenic CO2 is taken up by the oceans. These enhanced concentrations of aquatic CO2 is responsible for an increase of the seawater acidity and thus a decrease in pH, leading to ocean acidification. The impact of present-day ocean acidification on the development of future climate change is still not entirely understood. Of key importance, in this matter, is the role of primary producers within the global carbon cycle and underlying feedback mechanisms. Studying past periods of ocean acidification that are characterized by low pH and high atmospheric CO2 levels, are important in unravelling these issues. In this thesis the response of micro-organisms (algae, bacteria and archaea) to high CO2 and low pH levels has been investigated by studying the distribution patterns and the stable carbon isotopic composition of specific biomarkers in present day and past environments. This resulted in the development of a number of new and potentially promising proxies. The distribution of branched glycerol dialkyl glycerol tetraethers, expressed by the Cyclisation of Branched Tetraether (CBT) index, is now shown to record lake water pH and alkalinity and may therefore be suitable for reconstructing lake water chemistry. The strong dependence of stable carbon isotopic fractionation on aquatic CO2 concentrations in several algal species, as well as the application of algal biomarkers in reconstructions of past pCO2 levels during Eocene Thermal Maximum 2, suggests that specific biomarkers from various important phytoplankton groups can be used for the reconstruction of past pCO2 levels. Finally, the stable carbon isotopic composition of isoprenoid glycerol dialkyl glycerol tetraethers, derived from Thaumarchaeota, show great potential as a proxy for the reconstruction of stable carbon isotopic values of dissolved inorganic carbon and may be used as a new approach to constrain the negative carbon isotope excursions during hyperthermals, such as the Palaeocene-Eocene Thermal Maximum and Eocene Thermal Maximum 2. The studies presented in this thesis show that the distribution and stable carbon isotopic composition of certain lipid biomarkers add great value to assess direct changes in pH and atmospheric CO2 levels and thus contribute to our understanding of the effects of contemporary and past climate ocean acidification processes on the development of future climate change.
Ocean acidification reduces growth and calcification in a marine dinoflagellate
Published 18 June 2013 Science ClosedTags: biological response, calcification, growth, laboratory, methods, molecular biology, morphology, paleo, phytoplankton
Ocean acidification is considered a major threat to marine ecosystems and may particularly affect calcifying organisms such as corals, foraminifera and coccolithophores. Here we investigate the impact of elevated pCO2 and lowered pH on growth and calcification in the common calcareous dinoflagellate Thoracosphaera heimii. We observe a substantial reduction in growth rate, calcification and cyst stability of T. heimii under elevated pCO2. Furthermore, transcriptomic analyses reveal CO2 sensitive regulation of many genes, particularly those being associated to inorganic carbon acquisition and calcification. Stable carbon isotope fractionation for organic carbon production increased with increasing pCO2 whereas it decreased for calcification, which suggests interdependence between both processes. We also found a strong effect of pCO2 on the stable oxygen isotopic composition of calcite, in line with earlier observations concerning another T. heimii strain. The observed changes in stable oxygen and carbon isotope composition of T. heimii cysts may provide an ideal tool for reconstructing past seawater carbonate chemistry, and ultimately past pCO2. Although the function of calcification in T. heimii remains unresolved, this trait likely plays an important role in the ecological and evolutionary success of this species. Acting on calcification as well as growth, ocean acidification may therefore impose a great threat for T. heimii.
Continue reading ‘Ocean acidification reduces growth and calcification in a marine dinoflagellate’
Changes in coccolith calcification under stable atmospheric CO2
Published 16 June 2013 Science ClosedTags: biological response, morphology, North Atlantic, paleo, phytoplankton
Coccolith calcification is known to respond to ocean acidification in culture experiments as well as in present and past oceans. Previous studies basically focus on changes in coccolith weight due to increasing CO2 and the resulting changes in the carbonate system but pay little attention to the influence of other environmental factors. In order to untangle changes in coccolithophore calcification due to environmental factors such as temperature and/or productivity from changes caused by increasing pCO2 and carbonate ion concentration we here present a study on coccolith calcification from the Holocene North Atlantic Ocean. The pre-industrial Holocene with its predominantly stable carbonate system provides the conditions for such a comprehensive analysis. For a realistic analysis on changes in major components of Holocene coccolithophores, the family Noelaerhabdaceae was selected, which constitutes the main part of the assemblage in the North Atlantic. Records of average coccolith weights from three Holocene sediment cores along a North–South transect in the North Atlantic were analysed. During the Holocene mean weight (and therefore calcification) of Noelaerhabdaceae (E. huxleyi and Gephyrocapsa) coccoliths decreases at the Azores (Geofar KF 16) from around 7 to 5.5 pg, but increases at the Rockall Plateau (ODP Site 980) from around 6 to 8 pg and at the Vøring Plateau (MD08-3192) from 7 to 10.5 pg. This amplitude of average weight variability is within the range of glacial/interglacial changes that were interpreted to be an effect of decreasing carbonate ion concentration. By comparison with SEM assemblage counts, we show that weight changes are partly due to variations in the coccolithophore assemblage, but also an effect of a change in calcification and/or morphotype variability within single species. Our results indicate that there is no single key factor responsible for the observed changes in coccolith weight. A major increase in coccolith weight occurs during a slight decrease in carbonate ion concentration in the Late Holocene at the Rockall Plateau and Vøring Plateau. Here, more favourable productivity conditions apparently lead to an increase in coccolith weight, either due to the capability of coccolithophore species, especially E. huxleyi, to adapt to decreasing carbonate ion concentration, or due to a shift towards heavier calcifying morphotypes.
Continue reading ‘Changes in coccolith calcification under stable atmospheric CO2’
