Posts Tagged 'respiration'

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’

Eat, breathe, repeat: physiological responses of the mussel Mytilus galloprovincialis to Diclofenac and ocean acidification

Combined effects of the nonsteroidal anti-inflammatory drug diclofenac and lowered seawater pH were assessed on the physiological responses of the mussel Mytilus galloprovincialis. Bivalves were exposed for 1 week to natural pH (8.1) and two reduced pH values (pH −0.4 units and pH −0.7 units), as predicted under a climate change scenario. After the first week, exposure continued for additional 2 weeks, both in the absence and in the presence of environmentally relevant concentrations of diclofenac (0.05 and 0.5 µg/L). Clearance rate, respiration rate, and excretion rate were measured after 7 days of exposure to pH only and after 14 (T1) and 21 (T2) days of exposure to the various pH*diclofenac combinations. At all sampling times, pH significantly affected all the biological parameters considered, whereas diclofenac generally exhibited a significant influence only at T2. Overall, results demonstrated that the physiological performance of M. galloprovincialis was strongly influenced by the experimental conditions tested, in particular by the interaction between the two stressors after 21 days of exposure. Further studies are needed to assess the combined effects of climate changes and emerging contaminants on bivalve physiology during different life stages, especially reproduction.

Continue reading ‘Eat, breathe, repeat: physiological responses of the mussel Mytilus galloprovincialis to Diclofenac and ocean acidification’

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’

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’

Photophysiological responses of the marine macroalga Gracilariopsis lemaneiformis to ocean acidification and warming

Highlights

  • Warming counteracted the negative effects of OA on growth and pigmentations.
  • OA synergy with warming showed down regulated CCMs.
  • OA synergy with warming decrease tissue C but increase tissue N per biomass.

Abstract

To study the combined effects of ocean acidification (OA) and warming on the growth and photosynthetic performance of the economically important marine macroalga Gracilariopsis lemaneiformis, thalli were grown under ambient low CO2 (390 μatm, LC) and elevated high CO2 (1000 μatm, HC) conditions with culture temperatures of 20 °C and 24 °C. Based on the evaluation of growth and photosynthetic responses to light and dissolved inorganic carbon (DIC), HC decreased the growth rate and phycoerythrin (PE) and phycocyanin (PC) levels but increased contents of UV-absorbing compounds (UVACs) in G. lemaneiformis at 20 °C, and high temperature counteracted these effects. Photosynthetic responses such as chlorophyll fluorescence parameters (maximum relative electron transport rate, rETRmax; light use efficiency, α; saturation light intensity, Ik; maximum quantum yield, FV/FM; effective quantum yield, Y(II) and non-photochemical quenching, NPQ) were not different among the treatments. However, increased oxygen evolution (Pn) and dark respiration (Rd) rates were observed at 20 °C in the HC treatment. No significant effects of HC on apparent carboxylation efficiency (ACE), maximum oxygen evolution rate (Vmax) and DIC affinity for oxygen evolution (K1/2DIC) were found, and HC synergy with high temperature increased K1/2DIC. A lower C/N ratio with decreased tissue carbon but increased nitrogen was observed under HC and high-temperature treatment. Our results indicate that high temperature may counteract the negative effects of OA on the growth and pigment characteristics of G. lemaneiformis and improve food quality, as evidenced by enhanced N per biomass.

Continue reading ‘Photophysiological responses of the marine macroalga Gracilariopsis lemaneiformis to ocean acidification and warming’

Coastal ocean acidification: dynamics and potential to affect marine mollusks

Coastal marine ecosystems are both ecologically and economically productive, and as human coastal populations expand, these critical habitats have become subject to a suite of anthropogenic stressors. During the past century, the progressive rise in levels of atmospheric carbon dioxide (CO2) entering world oceans has decreased ocean pH and caused ocean acidification. An additional and often overlooked cause of acidification in coastal zones is the production of CO2 via microbial degradation of organic matter. Nutrient loading in coastal ecosystems facilitates enhanced algal productivity and the subsequent decomposition of this algal biomass reduces oxygen levels and can promote hypoxia. The precise temporal and spatial dynamics of acidification and hypoxia as well as their potential effects on resource bivalves are not well described in most coastal waters. Here, to evaluate the status of aquatic acidification in coastal systems, I examine the seasonal, diel, and high-resolution spatiotemporal dynamics of carbonate chemistry and dissolved oxygen (DO) over a six year period in multiple northeast US estuaries and across multiple coastal habitats that host keystone marine species while concurrently quantifying the growth and survival of multiple early life stage suspension feeding bivalves. To assess the potential for acidification in eutrophic estuaries, the levels of DO, pH, the partial pressure of carbon dioxide (pCO2), and the saturation state of aragonite (ΩAr) were iv horizontally and vertically assessed during the onset, peak, and demise of low oxygen conditions in systems across the northeast US including Narragansett Bay (RI), Long Island Sound (CTNY), Jamaica Bay (NY), and Hempstead Bay (NY). Hypoxic waters and/or regions in close proximity to sewage discharge had extremely high levels of pCO2, (> 3,000 µatm), acidic pH (< 7.0), and were undersaturated with respect to aragonite (ΩAr < 1). The close spatial and temporal correspondence between DO and pH and the occurrence of extremes in these conditions in regions with the most intense nutrient loading indicated that they were driven primarily by enhanced microbial respiration relative to physical exchange processes. Next, I quantified the temporal and spatial dynamics of DO, carbonate chemistry, and net ecosystem metabolism (NEM) from spring through fall in multiple, distinct, temperate estuarine habitats: seagrass meadows, salt marshes, an open water estuary, and a shallow water habitat dominated by benthic macroalgae. All habitats displayed clear diurnal patterns of pH and DO, with minimums observed during early morning and maximums observed in the afternoon where diel ranges in pH and DO varied by site. NEM across habitats ranged from net autotrophic (macroalgae and seagrass) to metabolically balanced (open water) and net heterotrophic (salt marsh). Each habitat examined exhibited distinct buffering capacities that varied seasonally and were modulated by adjacent biological activity and variations in total alkalinity (TA) and dissolved inorganic carbon (DIC). I utilized continuous monitoring devices to characterize the diurnal dynamics of DO and carbonate chemistry from spring through fall across two, temperate eutrophic estuaries, western Long Island Sound and Jamaica Bay, NY. Vertical dynamics were resolved using an underway towing profiler and an automated stationary profiling unit. During the study, high rates of respiration in surface and bottom waters (> -0.2 mg O2 L -1 h -1 ) were observed where ephemeral surface water algal blooms caused brief periods of basification and supersaturation of DO that v were succeeded by periods of acidification and hypoxia. Diurnal vertical profiles demonstrated that oxic surface waters saturated with respect to calcium carbonate (aragonite) during the day transitioned to being unsaturated and hypoxic at night. Evidence is presented that, beyond respiration, nitrification of surface water strongly influenced by sewage discharge and oxidation processes in sediments can also contribute to acidification in these estuaries. Finally, the growth and survival of three bivalve species (Argopecten irradians, Crassostrea virginica, Mytilus edulis) were examined in an in-situ CO2 enrichment system deployed in a seagrass meadow and an open water estuary, and across a natural eutrophication gradient in Jamaica Bay, NY. In the seagrass meadow, the growth and survival of C. virginica and A. irradians significantly declined during the late summer in response to CO2 gas injection. During the open water CO2 enrichment experiment, all three species of bivalves exhibited depressed growth within the acidified chambers with no significant difference in mortality between treatments. In Jamaica Bay, dense phytoplankton blooms in the early summer decreased CO2 and increased DO creating spatial refuges for bivalves where growth rates were enhanced, but by the late summer, trends reversed as bivalve growth was depressed at these same locations due to the onset of acidification and hypoxia. Collectively, this dissertation has identified coastal ocean acidification as a symptom of eutrophication that can threaten marine bivalve populations.

Continue reading ‘Coastal ocean acidification: dynamics and potential to affect marine mollusks’

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’

Effects of warming and CO2 enrichment on O2 consumption, porewater oxygenation and pH of subtidal silt sediment

We investigated the effects of seawater warming and CO2 enrichment on the microbial community metabolism (using O2 consumption as a proxy) in subtidal silt sediment. Intact sediment cores, without large dwelling infauna, were incubated for 24 days at 12 (in situ) and 18 °C to confirm the expected temperature response. We then enriched the seawater overlying a subset of cold and warm-incubated cores with CO2 (+ ΔpCO2: 253–396 µatm) for 16 days and measured the metabolic response. Warming increased the depth-integrated volume-specific O2 consumption (Rvol), the maximum in the volume-specific O2 consumption at the bottom of the oxic zone (Rvol,bmax) and the volume-specific net O2 production (Pn,vol), and decreased the O2 penetration depth (O2-pd) and the depth of Rvol,bmax (depthbmax). Benthic photosynthesis oscillated the pH in the upper 2 mm of the sediment. CO2 enrichment of the warm seawater did not alter this oscillation but shifted the pH profile towards acidity; the effect was greatest at the surface and decreased to a depth of 12 mm. Confoundment rendered the CO2 treatment of the cold seawater inconclusive. In warm seawater, we found no statistically clear effect of CO2 enrichment on RvolRvol,bmaxPn,vol, O2-pd, or depthbmax and therefore suspect that this perturbation did not alter the microbial community metabolism. This confirms the conclusion from experiments with other, contrasting types of sediment.

Continue reading ‘Effects of warming and CO2 enrichment on O2 consumption, porewater oxygenation and pH of subtidal silt sediment’

Energetic response of Atlantic surfclam Spisula solidissima to ocean acidification

Highlights

  • Surfclam energy budget is decreased by high ρCO2 concentration.
  • High ρCO2 concentration affects negatively surfclam clearance rate.
  • Surfclams adopt different metabolic strategies facing ocean acidification.
  • Metabolic loss rises after a moderate ρCO2 concentration increase.

Abstract

In this study, we assessed the Atlantic surfclam (Spisula solidissima) energy budget under different ocean acidification conditions (OA). During 12 weeks, 126 individuals were maintained at three different ρCO2 concentrations. Every two weeks, individuals were sampled for physiological measurements and scope for growth (SFG). In the high ρCO2 treatment, clearance rate decreased and excretion rate increased relative to the low ρCO2 treatment, resulting in reduced SFG. Moreover, oxygen:nitrogen (O:N) excretion ratio dropped, suggesting that a switch in metabolic strategy occurred. The medium ρCO2 treatment had no significant effects upon SFG; however, metabolic loss increased, suggesting a rise in energy expenditure. In addition, a significant increase in food selection efficiency was observed in the medium treatment, which could be a compensatory reaction to the metabolic over-costs. Results showed that surfclams are particularly sensitive to OA; however, the different compensatory mechanisms observed indicate that they are capable of some temporary resilience.

Continue reading ‘Energetic response of Atlantic surfclam Spisula solidissima to ocean acidification’

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