Posts Tagged 'calcification'

Oyster biomineralisation under ocean acidification: from genes to shell

Biomineralisation is one of the key processes that is notably affected in marine calcifiers such as oysters under ocean acidification (OA). Understanding molecular changes in the biomineralisation process under OA and its heritability, therefore, is key to developing conservation strategies for protecting ecologically and economically important oyster species. To do this, in this study we have explicitly chosen the tissue involved in biomineralisation (mantle) of an estuarine commercial oyster species, Crassostrea hongkongensis. The primary aim of this study is to understand the influence of DNA methylation over gene expression of mantle tissue under decreased ~ pH 7.4, a proxy of OA, and to extrapolate if these molecular changes can be observed in the product of biomineralisation – the shell. We grew early juvenile C. hongkongensis, under decreased ~ pH 7.4 and control ~ pH 8.0 over 4.5 months and studied OA‐induced DNA methylation and gene expression patterns along with shell properties such as microstructure, crystal orientation and hardness.

The population of oysters used in this study was found to be moderately resilient to OA at the end of the experiment. The expression of key biomineralisation related genes such as carbonic anhydrase and alkaline phosphatase remained unaffected, thus, mechanical properties of the shell (shell growth rate, hardness and crystal orientation) were also maintained without any significant difference between control and OA conditions with signs of severe dissolution. In addition, this study makes three major conclusions: 1) higher expression of Ca2+ binding/signalling related genes in the mantle play a key role in maintaining biomineralisation under OA, 2) DNA methylation changes occur in response to OA, however, these methylation changes do not directly control gene expression, 3) OA would be more of a ‘dissolution problem’ rather than a ‘biomineralisation problem’ for resilient species that maintain calcification rate with normal shell growth and mechanical properties.

Continue reading ‘Oyster biomineralisation under ocean acidification: from genes to shell’

Geographical variation in phenotypic plasticity of intertidal sister limpet’s species under ocean acidification scenarios

Ocean Acidification (OA) can have pervasive effects in calcifying marine organisms, and a better understanding of how different populations respond at the physiological and evolutionary level could help to model the impacts of global change in marine ecosystems. Due to its natural geography and oceanographic processes, the Chilean coast provides a natural laboratory where benthic organisms are frequently exposed to diverse projected OA scenarios. The goal of this study was to assess whether a population of mollusks thriving in a more variable environment (Talcaruca) would present higher phenotypic plasticity in physiological and morphological traits in response to different pCO2 when compared to a population of the same species from a more stable environment (Los Molles). To achieve this, two benthic limpets (Scurria zebrina and Scurria viridula) inhabiting these two contrasting localities were exposed to ocean acidification experimental conditions representing the current pCO2 in the Chilean coast (500 μatm) and the levels predicted for the year 2100 in upwelling zones (1500 (μatm). Our results show that the responses to OA are species-specific, even in this related species. Interestingly, S. viridula showed better performance under OA than S. zebrina (i.e., similar sizes and carbonate content in individuals from both populations; lower effects of acidification on the growth rate combined with a reduction of metabolism at higher pCO2). Remarkably, these characteristics could explain this species’ success in overstepping the biogeographical break in the area of Talcaruca, which S. zebrina cannot achieve. Besides, the results show that the habitat factor has a strong influence on some traits. For instance, individuals from Talcaruca presented a higher growth rate plasticity index and lower shell dissolution rates in acidified conditions than those from Los Molles. These results show that limpets from the variable environment tend to display higher plasticity, buffering the physiological effects of OA compared with limpets from the more stable environment. Taken together, these findings highlight the key role of geographic variation in phenotypic plasticity to determine the vulnerability of calcifying organisms to future scenarios of OA.

Continue reading ‘Geographical variation in phenotypic plasticity of intertidal sister limpet’s species under ocean acidification scenarios’

Factors controlling coral skeletal U/Ca ratios with implications for their use as a proxy for past ocean conditions

Seawater temperature, salinity and carbonate chemistry have been shown to influence the uranium/calcium (U/Ca) ratios of scleractinian coral skeletons. This apparent sensitivity of U/Ca to multiple environmental parameters calls into question whether there is one environmental variable that most strongly controls coral U/Ca, and whether U/Ca can be straightforwardly applied as a paleoenvironmental proxy due to the tendency of environmental variables to covary in space and time. In this study, uranium concentration data from an existing compilation of tropical scleractinian coral U-series measurements is paired with environmental data from the World Ocean Atlas (WOA) and the Global Ocean Data Analysis Project (GLODAP) to examine the sensitivity of coral skeletal U/Ca to multiple seawater properties including temperature, salinity, pH, and saturation state. First, univariate linear regressions and multiple linear regressions were used to compare relationships between uranium and environmental parameters in the dataset with relationships observed in previous studies. Next, principal component analysis and regularized regression were used to identify the most likely predictors of coral U/Ca in order to create a multiple linear regression model. Results indicate that pH,  Ω, alkalinity, and temperature are all significant predictors of uranium concentrations in coral. The magnitude and strength of relationships between U/Ca and environmental variables also differ across different genera. Seawater properties with strong correlations and small ranges make interpretation of these results difficult. However, results of these analyses indicate that U/Ca is dependent on multiple environmental parameters and that previously developed univariate regressions may be insufficient to characterize the full range of variables that influence coral [238U].

Continue reading ‘Factors controlling coral skeletal U/Ca ratios with implications for their use as a proxy for past ocean conditions’

Effects of ocean acidification on carbon and nitrogen fixation in the hermatypic coral Galaxea fascicularis

The supply of metabolites from symbionts to scleractinian corals is crucial to coral health. Members of the Symbiodiniaceae can enhance coral calcification by providing photosynthetically fixed carbon (PFC) and energy, whereas dinitrogen (N2)-fixing bacteria can provide additional nutrients such as diazotrophically-derived nitrogen (DDN) that sustain coral productivity especially when alternative external nitrogen sources are scarce. How these mutualistic associations benefit corals in the future acidifying ocean is not well understood. In this study, we investigated the possible effects of ocean acidification (OA; pHs 7.7 and 7.4 vs. 8.1) on calcification in the hermatypic coral Galaxea fascicularis with respect to PFC and DDN assimilation. Our measurements based on isotopic tracing showed no significant differences in the assimilation of PFC among different pH treatments, but the assimilation of DDN decreased significantly after 28 days of stress at pH 7.4. The decreased DDN assimilation suggests a nitrogenous nutrient deficiency in the coral holotiont, potentially leading to reduced coral calcification and resilience to bleaching and other stressful events. This contrasting impact of OA on carbon and N flux demonstrates the flexibility of G. fascicularis in coping with OA, apparently by sustaining a largely undamaged photosystem at the expense of N2 fixation machinery, which competes with coral calcification for energy from photosynthesis. These findings shed new light on the critically important but more vulnerable N cycling in hospite, and on the trade-off between coral hosts and symbionts in response to future climate change.

Continue reading ‘Effects of ocean acidification on carbon and nitrogen fixation in the hermatypic coral Galaxea fascicularis’

Effects of ocean acidification on bleaching, survival, and calcification of Porites porites and P. astreoides in Cartagena, Colombia

Estimations of the ocean acidification-OA effects on marine environments indicate that coral reefs’ structure will collapse. This study aimed to determine the effects of OA, and its associated carbon chemistry in the sea water, on corals near the Colombian Caribbean city of Cartagena, taking as model organisms of the species Porites astreoides and P. porites. For each species, the effect of OA on bleaching, survival, and calcification was determined using artificial systems with pH of 7.879 ± 0.004 and 7.789 ± 0.007. The results showed that under the first pH, the bleaching of P. astreoides increased by 24.92% and its survival decreased by 80.56%, while at lowest pH, bleaching increased in 32.78% and survival decreased by 87.5%. In the case of P. porites, at first pH bleaching increased by 29.42% and survival decreased by 30.56% and at the lowest, bleaching increased in 37.32% and survival decreased by 13.39%. In both species, calcification was reduced in more than 90% at 7.879 ± 0.004 and their skeleton began to dissolve at 7.789 ± 0.007. This study represents the first effort to determine OA effects on Colombian Caribbean’s marine biota.

Continue reading ‘Effects of ocean acidification on bleaching, survival, and calcification of Porites porites and P. astreoides in Cartagena, Colombia’

An intertidal life: combined effects of acidification and winter heatwaves on a coralline alga (Ellisolandia elongata) and its associated invertebrate community


  • Coralline alga create a microhabitat with mitigating effect on ocean acidification
  • Temperature is the major driver of changes in the invertebrate reef community
  • Winter heatwaves and acidified conditions alter invertebrates community structure
  • Algal reef communities become dominated by opportunistic taxa


In coastal marine ecosystems coralline algae often create biogenic reefs. These calcareous algal reefs affect their associated invertebrate communities via diurnal oscillations in photosynthesis, respiration and calcification processes. Little is known about how these biogenic reefs function and how they will be affected by climate change. We investigated the winter response of a Mediterranean intertidal biogenic reef, Ellisolandia elongate exposed in the laboratory to reduced pH conditions (i.e. ambient pH – 0.3, RCP 8.5) together with an extreme heatwave event (+1.4°C for 15 days). Response variables considered both the algal physiology (calcification and photosynthetic rates) and community structure of the associated invertebrates (at taxonomic and functional level). The combination of a reduced pH with a heatwave event caused Ellisolandia elongata to significantly increase photosynthetic activity. The high variability of calcification that occurred during simulated night time conditions, indicates that there is not a simple, linear relationship between these two and may indicate that it will resilient to future conditions of climate change.

In contrast, the associated fauna were particularly negatively affected by the heatwave event, which impoverished the communities as opportunistic taxa became dominant. Local increases in oxygen and pH driven by the algae can buffer the microhabitat in the algal fronds, thus favouring the survival of small invertebrates.

Continue reading ‘An intertidal life: combined effects of acidification and winter heatwaves on a coralline alga (Ellisolandia elongata) and its associated invertebrate community’

Effects of extra feeding combined with ocean acidification and increased temperature on the carbon isotope values (δ13C) in the mussel shell


  • Ocean acidification, OA, increased metabolic carbon uptake in mussel shell calcite.
  • Additive effects of increased temperature and extra feeding on carbon uptake.
  • Mussels alter their biomineralisation pathways relating to food carbon uptake.
  • Metabolic carbon uptake is 7–11% higher in the shell aragonite compared to calcite.
  • Molluscs with different composites may alter biomineralisation under OA.


Ocean acidification (OA) and global warming present future challenges for shell producing organisms such as mussels through reduction in the carbonate available to produce shells in these and other valuable aquaculture species. Molluscs control their shell growth through biomineralisation, but the response of the mechanisms behind biomineralisation to OA conditions are relatively unknown. It is unclear how much carbon is taken into the shell from the environment compared to the uptake through the food source. Shell production is energetically costly to molluscs and metabolic processes and energetic partitioning may affect their ability to perform the underlying mechanisms of biomineralisation under OA. It is possible that additional food consumption might alleviate some impacts caused by acidification. We assessed the ability of extra feeding to alter the impacts of OA and increased temperatures on adult Mytilus edulis. Carbon isotopes (δ13C) were used to examine the change in biomineralisation pathway in mussels. OA did not alter the δ13C directly in separate analyses of the shell calcite and aragonite layers, mantle tissue and extrapallial fluid. However, ambient treatments with increased temperatures altered the mussel biomineralisation pathway in the shell calcite using CO32− instead of HCO3 as the main source of carbon. The proportion of metabolic carbon uptake into the mussel shell calcite layer increased under OA, with additive effects when exposed to increased temperatures and extra feeding. The proportion of metabolic carbon uptake is higher (7%–11%) in the shell aragonite layer compared to calcite, under ambient treatments. OA initially reduced the metabolic carbon uptake into the shell aragonite, but after a period of 4-months with extra feeding, the mussels were able to adjust their metabolic carbon uptake to a level experienced under ambient treatments. This indicates that an abundance of food resources may enable changes in mussel biomineralisation pathways to compensate for any decrease in seawater inorganic carbon associated with OA. The impact of OA on phytoplankton varies from species to species, changing the structure of the community which could provide sufficient food resources to maintain metabolic carbon uptake for mussel shell growth. This study of δ13C isotopic values has identified changes in biomineralisation pathway relating to the mussel metabolic carbon uptake from their food source, with varying results for the aragonite and calcite shell polymorphs. The implications of these findings suggest that some bivalve species with different shell composites may cope better under OA than others, demanding further study into species-specific biomineralisation pathways.

Continue reading ‘Effects of extra feeding combined with ocean acidification and increased temperature on the carbon isotope values (δ13C) in the mussel shell’

Microalgal photosynthesis induces alkalization of aquatic environment as a result of H+ uptake independently from CO2 concentration – new perspectives for environmental applications


  • Microalgae photosynthesis induces strongly H+ uptake reversing ocean acidification.
  • Water alkalization through algal H+ uptake is independent from CO2 concentration.
  • New management approaches for reversing ocean acidification using algal H+ uptake.
  • Algal H+ uptake depends on essential nutrients, cell density and light intensity.
  • Acidification of aquatic environment induces microalgal photosynthesis and growth.


The photosynthetic process in microalgae and the extracellular proton environment interact with each other. The photosynthetic process in microalgae induces a pH increase in the aquatic environment as a result of cellular protons uptake rather than as an effect of CO2 consumption. The photosynthetic water photolysis and the reduction/oxidation cycle of the plastoquinone pool provide lumen with protons. Weak bases act as “permeant buffers” in lumen during the photosynthetic procedure, converting the ΔpH to Δψ. This is possibly the main reason for continuous light-driven proton uptake from the aquatic environment through cytosol and stroma, into the lumen. The proton uptake rate and, therefore, the microalgal growth is proportional to the light intensity, cell concentration, and extracellular proton concentration. The low pH in microalgae cultures, without limitation factors related to light and nutrients, strongly induces photosynthesis (and proton uptake) and, consequently, growth. In contrast, the mitochondrial respiratory process, in the absence of photosynthetic activity, does not substantially alter the culture pH. Only after intensification of the respiratory process, using exogenous glucose supply leads to significantly reduced pH values in the culture medium, almost exclusively through proton output. Enhanced dissolution of atmospheric CO2 in water causes the phenomenon of ocean acidification, which prevents the process of calcification, a significant process for numerous phytoplankton and zooplankton organisms, as well for corals. The proposed interaction between microalgal photosynthetic activity and proton concentration in the aquatic environment, independently from the CO2 concentration, paves the way for new innovative management strategies for reversing the ocean acidification.

Continue reading ‘Microalgal photosynthesis induces alkalization of aquatic environment as a result of H+ uptake independently from CO2 concentration – new perspectives for environmental applications’

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 urchinStrongylocentrotus 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.

Continue reading ‘Experimental assessment of the impacts of ocean acidification and urchin grazing on benthic kelp forest assemblages’

Diurnally fluctuating pCO2 enhances growth of a coastal strain of Emiliania huxleyi under future-projected ocean acidification conditions

The carbonate chemistry in coastal waters is more variable compared with that of open oceans, both in magnitude and time scale of its fluctuations. However, knowledge of the responses of coastal phytoplankton to dynamic changes in pH/pCO2 has been scarcely documented. Hence, we investigated the physiological performance of a coastal isolate of the coccolithophore Emiliania huxleyi (PML B92/11) under fluctuating and stable pCO2 regimes (steady ambient pCO2, 400 μatm; steady elevated pCO2, 1200 μatm; diurnally fluctuating elevated pCO2, 600–1800 μatm). Elevated pCO2 inhibited the calcification rate in both the steady and fluctuating regimes. However, higher specific growth rates and lower ratios of calcification to photosynthesis were detected in the cells grown under diurnally fluctuating elevated pCO2 conditions. The fluctuating pCO2 regime alleviated the negative effects of elevated pCO2 on effective photochemical quantum yield and relative photosynthetic electron transport rate compared with the steady elevated pCO2 treatment. Our results suggest that growth of E. huxleyi could benefit from diel fluctuations of pH/pCO2 under future-projected ocean acidification, but its calcification was reduced by the fluctuation and the increased concentration of CO2, reflecting a necessity to consider the influences of dynamic pH fluctuations on coastal carbon cycles associated with ocean global changes.

Continue reading ‘Diurnally fluctuating pCO2 enhances growth of a coastal strain of Emiliania huxleyi under future-projected ocean acidification conditions’

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Ocean acidification in the IPCC AR5 WG II

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