Posts Tagged 'calcification'

Resilience of the temperate coral Oculina arbuscula to ocean acidification extends to the physiological level

Both juvenile and adult life stages of the temperate scleractinian coral Oculina arbuscula are resilient to the effects of moderate ocean acidification (OA) in contrast to many tropical corals in which growth and calcification rates are suppressed. Here, potential mechanisms of resilience to OA related to photosynthetic physiology and inorganic carbon processing were studied in adult O. arbuscula colonies. After exposing colonies to ambient and elevated carbon dioxide (CO2) treatments for 7 weeks, photosynthetic performance was characterized using photosynthesis versus irradiance experiments, chlorophyll fluorescence kinetics, and algal pigment content. Inorganic carbon-processing capabilities were assessed by measurement of internal and external carbonic anhydrase activity of the coral host, internal carbonic anhydrase activity of symbiotic algae, and the reliance of photosynthesis on external carbonic anhydrase. Photosynthetic physiology was unaffected by OA ruling out the possibility that resilience was mediated by increased photosynthetic energy supply. Carbonic anhydrase activities were maintained at elevated CO2 suggesting no major rearrangements of the inorganic carbon-processing machinery, but this could be a sign of resilience since tropical corals often down-regulate carbonic anhydrases at high CO2. The general lack of effect of ocean acidification on these physiological traits suggests other characteristics, such as maintenance of calcifying fluid pH and ability to acquire energy from heterotrophy, may be more important for the resilience of O. arbuscula to OA.

Continue reading ‘Resilience of the temperate coral Oculina arbuscula to ocean acidification extends to the physiological level’

Estuarine conditions more than pH modulate the physiological flexibility of mussel Perumytilus purpuratus populations

Highlights

  • Living under estuarine conditions causes physiological stress.
  • Estuarine conditions more than pH modulated the mussel performance and phenotypic plasticity.
  • Environmental variability of the habitat determines the phenotypic plasticity.
  • Environmental conditions of native habitats define the sensibility to climate change stressors.

Abstract

Coasts and their marine biota are exposed to major environmental heterogeneity as a consequence of natural drivers and anthropogenic stressors. Here, individuals of the mussel Perumytilus purpuratus from two different geographical populations exposed to contrasting environmental conditions (i.e. estuarine versus open coastal conditions) were used in a reciprocal transplant and a laboratory experiment in order to differential levels of local adaptation to their native sites, and sensibility to ocean acidification. After characterizing environmentally the two study sites, a set of life-history traits, as well as an estimated of the level of phenotypic plasticity were determined for both mussel populations. From the reciprocal transplant experiment, we observed that mussels originally coming from the estuarine habitat exhibited a distinctive performance pattern usually associated to physiological stress (i.e. higher metabolic rates, lower calcification and growth rates) leading also to important physiological trade-offs, and higher levels of phenotypic plasticity. Alternatively, mussels originating from the open coastal site showed lower physiological phenotypic plasticity suggesting a high grade of local adaptation. Contrary to expected, both populations responded very similar to lower pH conditions (i.e. increased metabolic rates with no important effects on growth and calcification, and lower physiological phenotypic plasticity). The study results indicated that overall estuarine conditions more than isolated pH would be modulating the performance and the level of phenotypic plasticity of the different P. purpuratus geographical populations studied. Our study also emphasizes the necessity of characterizing phenotypic plasticity under multiple-driver environments in order to cast more accurate predictions about the susceptibility of marine biota to future climate stressors such as the ocean acidification.

Continue reading ‘Estuarine conditions more than pH modulate the physiological flexibility of mussel Perumytilus purpuratus populations’

Predicting potential impacts of ocean acidification on marine calcifiers from the Southern Ocean

Understanding the vulnerability of marine calcifiers to ocean acidification is a critical issue, especially in the Southern Ocean (SO), which is likely to be the one of the first, and most severely affected regions. Since the industrial revolution, ~30% of anthropogenic CO2 has been absorbed by the oceans. Seawater pH levels have already decreased by 0.1 and are predicted to decline by ~ 0.3 by the year 2100. This process, known as ocean acidification (OA), is shallowing the saturation horizon, which is the depth below which calcium carbonate (CaCO3) dissolves, likely increasing the vulnerability of many marine calcifiers to dissolution. The negative impact of OA may be seen first in species depositing more soluble CaCO3 mineral phases such as aragonite and high-Mg calcite (HMC). These negative effects may become even exacerbated by increasing sea temperatures. Here we combine a review and a quantitative meta-analysis to provide an overview of the current state of knowledge about skeletal mineralogy of major taxonomic groups of SO marine calcifiers and to make predictions about how OA might affect different taxa. We consider their geographic range, skeletal mineralogy, biological traits and potential strategies to overcome OA. The meta-analysis of studies investigating the effects of the OA on a range of biological responses such as shell state, development and growth rate shows response variation depending on mineralogical composition. Species-specific responses due to mineralogical composition suggest taxa with calcitic, aragonitic and HMC skeletons may be more vulnerable to the expected carbonate chemistry alterations, and low magnesium calcite (LMC) species may be mostly resilient. Environmental and biological control on the calcification process and/or Mg content in calcite, biological traits and physiological processes are also expected to influence species specific responses.

Continue reading ‘Predicting potential impacts of ocean acidification on marine calcifiers from the Southern Ocean’

Decoupling salinity and carbonate chemistry: low calcium ion concentration rather than salinity limits calcification in Baltic Sea mussels

The Baltic Sea has a salinity gradient decreasing from fully marine (> 25) in the West to below 7 in the Central Baltic Proper. Reef forming mytilid mussels exhibit decreasing growth when salinity < 11, however the mechanisms underlying reduced calcification rates in dilute seawater are not fully understood. In fact, both [HCO3] and [Ca2+] also decrease with salinity, challenging calcifying organisms through CaCO3 undersaturation (Ω ≤ 1) and unfavourable ratios of calcification substrate (Ca2+ and HCO3) to inhibitor (H+). In this study we assessed the impact of isolated individual factors (salinity, [Ca2+], [HCO3] and pH) on calcification and growth of mytilid mussel populations along the Baltic salinity gradient. Laboratory experiments rearing juvenile Baltic Mytilus at a range of salinities (6, 11 and 16), HCO3 concentrations (300–2100 µmol kg−1) and Ca2+ concentrations (0.5–4 mmol kg−1) were coupled with field monitoring in three Baltic mussel reefs. Results reveal that as individual factors, low [HCO3], pH and salinity cannot explain low calcification rates in the Baltic Sea. Calcification rates are impeded when Ωaragonite ≤ 1 or the substrate inhibitor ratio ≤ 0.7, primarily due to [Ca2+] limitation which corresponds to a salinity of ca. 11. Increased food availability may be able to mask these negative impacts, but not when seawater conditions are permanently adverse, as observed in two Baltic reefs at salinities < 11. Future climatic models predict rapid desalination of the southwest and Central Baltic and potentially a reduction in [Ca2+] which may lead to a westward distribution shift of marine calcifiers. It is therefore vital to understand the mechanisms by which the ionic composition of seawater impacts bivalve calcification for better predicting the future of benthic Baltic ecosystems.

Continue reading ‘Decoupling salinity and carbonate chemistry: low calcium ion concentration rather than salinity limits calcification in Baltic Sea mussels’

Irradiance, photosynthesis and elevated pCO2 effects on net calcification in tropical reef macroalgae

Highlights

  • Most species from high-light environments are not able to calcifying under OA at night
  • Low-light species may be more susceptible to OA compared to high-light
  • Some species exhibit light-triggered calcification independent of photosystem II
  • Photosystem II independent calcification not sustained under OA

Abstract


Calcifying tropical macroalgae produce sediment, build three-dimensional habitats, and provide substrate for invertebrate larvae on reefs. Thus, lower calcification rates under declining pH and increasing ocean pCO2, or ocean acidification, is a concern. In the present study, calcification rates were examined experimentally under predicted end-of-the-century seawater pCO2 (1116 μatm) and pH (7.67) compared to ambient controls (pCO2 409 μatm; pH 8.04). Nine reef macroalgae with diverse calcification locations, calcium carbonate structure, photophysiology, and site-specific irradiance were examined under light and dark conditions. Species included five from a high light patch reef on the Florida Keys Reef Tract (FKRT) and four species from low light reef walls on Little Cayman Island (LCI). Experiments on FKRT and LCI species were conducted at 500 and 50 μmol photons m−2 s−1 in situ irradiance, respectively. Calcification rates independent of photosystem-II (PSII) were also investigated for FKRT species. The most consistent negative effect of elevated pCO2 on calcification rates in the tropical macroalgae examined occurred in the dark. Most species (89%) had net calcification rates of zero or net dissolution in the dark at low pH. Species from the FKRT that sustained positive net calcification rates in the light at low pH also maintained ~30% of their net calcification rates without PSII at ambient pH. However, calcification rates in the light independent of PSII were not sustained at low pH. Regardless of these low pH effects, most FKRT species daily net calcification rates, integrating light/dark rates over a 24h period, were not significantly different between low and ambient pH. This was due to a 10-fold lower dark, compared to light, calcification rate, and a strong correspondence between calcification and photosynthetic rates. Interestingly, low-light species sustained calcification rates on par with high-light species without high rates of photosynthesis. Low-light species’ morphology and physiology that promote high calcification rates at ambient pH, may increase their vulnerability to low pH. Our data indicate that the negative effect of elevated pCO2 and low pH on tropical macroalgae at the organismal level is their impact on dark net calcification, probably enhanced dissolution. However, elevated pCO2 and low pH effects on macroalgae daily calcification rates are greatest in species with lower net calcification rates in the light. Thus, macroalgae able to maintain high calcification rates in the light (high and low irradiance) at low pH, and/or sustain strong biotic control with high [H+] in the bulk seawater, are expected to dominate under global change.

Continue reading ‘Irradiance, photosynthesis and elevated pCO2 effects on net calcification in tropical reef macroalgae’

From particle attachment to space-filling coral skeletons

Reef-building corals and their aragonite (CaCO3) skeletons support entire reef ecosystems, yet their formation mechanism is poorly understood. Here we used synchrotron spectromicroscopy to observe the nanoscale mineralogy of fresh, forming skeletons from six species spanning all reef-forming coral morphologies: Branching, encrusting, massive, and table. In all species, hydrated and anhydrous amorphous calcium carbonate nanoparticles were precursors for skeletal growth, as previously observed in a single species. The amorphous precursors here were observed in tissue, between tissue and skeleton, and at growth fronts of the skeleton, within a low-density nano- or microporous layer varying in thickness from 7 to 20 µm. Brunauer-Emmett-Teller measurements, however, indicated that the mature skeletons at the microscale were space-filling, comparable to single crystals of geologic aragonite. Nanoparticles alone can never fill space completely, thus ion-by-ion filling must be invoked to fill interstitial pores. Such ion-by-ion diffusion and attachment may occur from the supersaturated calcifying fluid known to exist in corals, or from a dense liquid precursor, observed in synthetic systems but never in biogenic ones. Concomitant particle attachment and ion-by-ion filling was previously observed in synthetic calcite rhombohedra, but never in aragonite pseudohexagonal prisms, synthetic or biogenic, as observed here. Models for biomineral growth, isotope incorporation, and coral skeletons’ resilience to ocean warming and acidification must take into account the dual formation mechanism, including particle attachment and ion-by-ion space filling.

Continue reading ‘From particle attachment to space-filling coral skeletons’

The combined effects of ocean acidification and warming on a habitat-forming shell-crushing predatory crab

Highlights

  • We measured and compared traits at the cellular and organismal levels
  • Ocean warming and acidification affected crabs’ traits
  • Ocean warming increased the HSP70 levels
  • Crabs’ pinching strength was reduced by ocean acidification
  • Crabs’ self-righting speed was reduced by ocean warming and acidification

Abstract

In mid rocky intertidal habitats the mussel Perumytilus purpurarus monopolizes the substratum to the detriment of many other species. However, the consumption of mussels by the shell-crushing crab Acanthocyclus hassleri creates within the mussel beds space and habitat for several other species. This crab uses its disproportionately large claw to crush its shelled prey and plays an important role in maintaining species biodiversity. This study evaluated the consequences of projected near-future ocean acidification (OA) and warming (OW) on traits of A. hassleri linked with their predatory performance. Individual A. hassleri were maintained for 10-16 weeks under contrasting pCO2 (~500 and 1400 μatm) and temperature (~15 and 20 °C) levels. We compared traits at the organismal (oxygen consumption rate, survival, calcification rate, feeding rates, crusher claw pinching strength, self-righting speed, sarcomere length of the crusher claw muscles) and cellular (nutritional status ATP provisioning capacity through citrate synthase activity, expression of HSP70) level. Survival, calcification rate and sarcomere length were not affected by OA and OW. However, OW increased significantly feeding and oxygen consumption. Pinching strength was reduced by OA; meanwhile self-righting was increased by OA and OW. At 20 °C, carbohydrate content was reduced significantly by OA. Regardless of temperature, a significant reduction in energy reserves in terms of protein content by OA was found. The ATP provisioning capacity was significantly affected by the interaction between temperature and pCO2 and was highest at 15 °C and present day pCO2 levels. The HSP70 levels of crabs exposed to OW were higher than in the control crabs. We conclude that OA and OW might affect the amount and size of prey consumed by this crab. Therefore, by reducing the crab feeding performance these stressors might pose limits on their role in generating microhabitat for other rocky intertidal species inhabiting within mussel beds.

Continue reading ‘The combined effects of ocean acidification and warming on a habitat-forming shell-crushing predatory crab’

Coral-macroalgal competition under ocean warming and acidification

Highlights

  • Study investigates a common coral-macroalgal interaction under a low end emission scenario.
  • Light calcification is negatively influenced by an interaction of macroalgal contact and scenario.
  • Protein content, zooxanthellae density and Chlorophyll a were enhanced under scenario conditions.
  • Negative impacts of macroalgae on corals were observed, but not enhanced by scenario conditions.
  • More research on the impacts of climate change on the dynamics of coral-algal interactions is needed.

Abstract

Competition between corals and macroalgae is frequently observed on reefs with the outcome of these interactions affecting the relative abundance of reef organisms and therefore reef health. Anthropogenic activities have resulted in increased atmospheric CO2 levels and a subsequent rise in ocean temperatures. In addition to increasing water temperature, elevated CO2 levels are leading to a decrease in oceanic pH (ocean acidification). These two changes have the potential to alter ecological processes within the oceans, including the outcome of competitive coral-macroalgal interactions. In our study, we explored the combined effect of temperature increase and ocean acidification on the competition between the coral Porites lobata and on the Great Barrier Reef abundant macroalga Chlorodesmis fastigiata. A temperature increase of +1 °C above present temperatures and CO2 increase of +85 ppm were used to simulate a low end emission scenario for the mid- to late 21st century, according to the Representative Concentration Pathway 2.6 (RCP2.6). Our results revealed that the net photosynthesis of P. lobata decreased when it was in contact with C. fastigiata under ambient conditions, and that dark respiration increased under RCP2.6 conditions. The Photosynthesis to Respiration (P:R) ratios of corals as they interacted with macroalgal competitors were not significantly different between scenarios. Dark calcification rates of corals under RCP2.6 conditions, however, were negative and significantly decreased compared to ambient conditions. Light calcification rates were negatively affected by the interaction of macroalgal contact in the RCP2.6 scenario, compared to algal mimics and to coral under ambient conditions. Chlorophyll a, and protein content increased in the RCP2.6 scenario, but were not influenced by contact with the macroalga. We conclude that the coral host was negatively affected by RCP2.6 conditions, whereas the productivity of its symbionts (zooxanthellae) was enhanced. While a negative effect of the macroalga (C. fastigiata) on the coral (P. lobata) was observed for the P:R ratio under control conditions, it was not enhanced under RCP2.6 conditions.

Continue reading ‘Coral-macroalgal competition under ocean warming and acidification’

Experimental techniques to assess coral physiology in situ: current approaches and novel insights

Coral reefs are declining worldwide due to global changes in the marine environment. The increasing frequency and severity of massive bleaching events in the tropics are highlighting the need to better understand the stages of coral physiological responses to extreme conditions. Moreover, like many other coastal regions, coral reef ecosystems are facing additional localized anthropogenic issues such as nutrient loading, increased turbidity, and coastal development. The changes in coral metabolism under local or global stress conditions is studied largely through laboratory manipulation and field observations. Different strategies have been developed to measure the health status of a damaged reef, ranging from the resolution of individual polyps to an entire coral community, but techniques for measuring coral physiology in situ are not yet widely implemented. For instance, while there are many studies of the coral holobiont response in single or limited-number multiple stressor experiments, they provide only partial insights to metabolic performance under more complex temporally and spatially variable natural conditions. Here, we discuss the current status of coral reefs and their global and local stressors in the context of current experimental techniques that measure core processes in coral metabolism (respiration, photosynthesis, and biocalcification) and their role in indicating the health status of colonies and communities. The state of the art of in situ techniques for experimental and monitoring purposes is explored. We highlight the need to improve the capability of in situ studies in order to better understand the resilience and stress response of corals under multiple global and local scale stressors.

Continue reading ‘Experimental techniques to assess coral physiology in situ: current approaches and novel insights’

Differential sensitivity of a symbiont‐bearing foraminifer to seawater carbonate chemistry in a decoupled DIC‐pH experiment

Larger benthic foraminifera (LBF) are unicellular eukaryotic calcifying organisms and an important component of tropical and subtropical modern and ancient oceanic ecosystems. They are major calcium carbonate producers and important contributors to primary production due to the photosynthetic activity of their symbiotic algae. Studies investigating the response of LBF to seawater carbonate chemistry changes are therefore essential for understanding the impact of climate changes and ocean acidification (OA) on shallow marine ecosystems. In this study, calcification, respiration, and photosynthesis of the widespread diatom‐bearing LBF Operculina ammonoides were measured in laboratory experiments that included manipulation of carbonate chemistry parameters. pH was altered while keeping dissolved inorganic carbon (DIC) constant, and DIC was altered while keeping pH constant. The results show clear vulnerability of O. ammonoides to low pH and CO32− under constant DIC conditions, and no increased photosynthesis or calcification under high DIC concentrations. Our results call into question previous hypotheses, suggesting that mechanisms such as the degree of cellular control on calcification site pH/DIC and/or enhanced symbiont photosynthesis in response to OA may render the hyaline (perforate and calcitic‐radial) LBF to be less responsive to OA than porcelaneous LBF. In addition, manipulating DIC did not affect calcification when pH was close to present seawater levels in a model encompassing the total population size range. In contrast, larger individuals (>1,200 μm, >1 mg) were sensitive to changes in DIC, a phenomenon we attribute to their physiological requirement to concentrate large quantities of DIC for their calcification process.

Continue reading ‘Differential sensitivity of a symbiont‐bearing foraminifer to seawater carbonate chemistry in a decoupled DIC‐pH experiment’

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