Effect of reduced pH on physiology and shell integrity of juvenile Haliotis iris (paua) from New Zealand.
ABSTRACT: The New Zealand pāua or black footed abalone, Haliotis iris, is one of many mollusc species at potential risk from ocean acidification and warming. To investigate possible impacts, juvenile pāua (~24 mm shell length) were grown for 4 months in seawater pH/pCO2 conditions projected for 2100. End of century seawater projections (pHT 7.66/pCO2 ~1,000 μatm) were contrasted with local ambient conditions (pHT 8.00/pCO2 ~400 μatm) at two typical temperatures (13 and 15 °C). We used a combination of methods (morphometric, scanning electron microscopy, X-ray diffraction) to investigate effects on juvenile survival and growth, as well as shell mineralogy and integrity. Lowered pH did not affect survival, growth rate or condition, but animals grew significantly faster at the higher temperature. Juvenile pāua were able to biomineralise their inner nacreous aragonite layer and their outer prismatic calcite layer under end-of-century pH conditions, at both temperatures, and carbonate composition was not affected. There was some thickening of the nacre layer in the newly deposited shell with reduced pH and also at the higher temperature. Most obvious was post-depositional alteration of the shell under lowered pH: the prismatic calcite layer was thinner, and there was greater etching of the external shell surface; this dissolution was greater at the higher temperature. These results demonstrate the importance of even a small (2 °C) difference in temperature on growth and shell characteristics, and on modifying the effects at lowered pH. Projected CO2-related changes may affect shell quality of this iconic New Zealand mollusc through etching (dissolution) and thinning, with potential implications for resilience to physical stresses such as predation and wave action.
Project description:The rising anthropogenic atmospheric CO2 results in the reduction of seawater pH, namely ocean acidification (OA). In East China Sea, the largest coastal hypoxic zone was observed in the world. This region is also strongly impacted by ocean acidification as receiving much nutrient from Changjiang and Qiantangjiang, and organisms can experience great short-term natural variability of DO and pH in this area. In order to evaluate the defense responses of marine mussels under this scenario, the thick shell mussel Mytilus coruscus were exposed to three pH/pCO2 levels (7.3/2800 μatm, 7.7/1020 μatm, 8.1/376 μatm) at two dissolved oxygen concentrations (DO, 2.0, 6.0 mg L-1) for 72 h. Results showed that byssus thread parameters, such as the number, diameter, attachment strength and plaque area were reduced by low DO, and shell-closing strength was significantly weaker under both hypoxia and low pH conditions. Expression patterns of genes related to mussel byssus protein (MBP) were affected by hypoxia. Generally, hypoxia reduced MBP1 and MBP7 expressions, but increased MBP13 expression. In conclusion, both hypoxia and low pH induced negative effects on mussel defense responses, with hypoxia being the main driver of change. In addition, significant interactive effects between pH and DO were observed on shell-closing strength. Therefore, the adverse effects induced by hypoxia on the defense of mussels may be aggravated by low pH in the natural environments.
Project description:Shallow water provides important habitat for many species, but also exposes these organisms to daily fluctuations in dissolved oxygen (DO) and pH caused by cycles in the balance between photosynthesis and respiration that can contribute to repeated, brief periods of hypoxia and low pH (caused by elevated pCO2). The amplitude of these cycles, and the severity and duration of hypoxia and hypercapnia that result, can be increased by eutrophication, and are predicted to worsen with climate change. We conducted laboratory experiments to test the effects of both diel-cycling and constant low DO and pH (elevated pCO2) on growth of the juvenile eastern oyster (Crassostrea virginica), an economically and ecologically important estuarine species. Severe diel-cycling hypoxia (to 0.5 mg O2 L-1) reduced shell growth in juvenile oysters, as did constant hypoxia (1.2 and 2.0 mg O2 L-1), although effects varied among experiments, oyster ages, and exposure durations. Diel-cycling pH reduced growth only in experiments in which calcite saturation state cycled to ?0.10 and only during the initial weeks of these experiments. In other cases, cycling pH sometimes led to increased growth rates. Comparisons of treatment effects across multiple weeks of exposure, and during a longer post-experiment field deployment, indicated that juvenile oysters can acclimate to, and in some cases compensate for initial reductions in growth. As a result, some ecosystem services dependent on juvenile oyster growth rates may be preserved even under severe cycling hypoxia and pH.
Project description:Ocean acidification is altering the oceanic carbonate saturation state and threatening the survival of marine calcifying organisms. Production of their calcium carbonate exoskeletons is dependent not only on the environmental seawater carbonate chemistry but also the ability to produce biominerals through proteins. We present shell growth and structural responses by the economically important marine calcifier Mytilus edulis to ocean acidification scenarios (380, 550, 750, 1000?µatm pCO2). After six months of incubation at 750?µatm pCO2, reduced carbonic anhydrase protein activity and shell growth occurs in M. edulis. Beyond that, at 1000?µatm pCO2, biomineralisation continued but with compensated metabolism of proteins and increased calcite growth. Mussel growth occurs at a cost to the structural integrity of the shell due to structural disorientation of calcite crystals. This loss of structural integrity could impact mussel shell strength and reduce protection from predators and changing environments.
Project description:Key calcifying reef taxa are currently threatened by thermal stress associated with elevated sea surface temperatures (SST) and reduced calcification linked to ocean acidification (OA). Here we undertook an 8 week experimental exposure to near-future climate change conditions and explored the microbiome response of the corals Acropora millepora and Seriatopora hystrix, the crustose coralline algae Hydrolithon onkodes, the foraminifera Marginopora vertebralis and Heterostegina depressa and the sea urchin Echinometra sp. Microbial communities of all taxa were tolerant of elevated pCO2/reduced pH, exhibiting stable microbial communities between pH 8.1 (pCO2 479-499 μatm) and pH 7.9 (pCO2 738-835 μatm). In contrast, microbial communities of the CCA and foraminifera were sensitive to elevated seawater temperature, with a significant microbial shift involving loss of specific taxa and appearance of novel microbial groups occurring between 28 and 31 °C. An interactive effect between stressors was also identified, with distinct communities developing under different pCO2 conditions only evident at 31 °C. Microbiome analysis of key calcifying coral reef species under near-future climate conditions highlights the importance of assessing impacts from both increased SST and OA, as combinations of these global stressors can amplify microbial shifts which may have concomitant impacts for coral reef structure and function.
Project description:While acute stressors can be detrimental, environmental stress conditioning can improve performance. To test the hypothesis that physiological status is altered by stress conditioning, we subjected juvenile Pacific geoduck, Panopea generosa, to repeated exposures of elevated pCO2 in a commercial hatchery setting followed by a period in ambient common garden. Respiration rate and shell length were measured for juvenile geoduck periodically throughout short-term repeated reciprocal exposure periods in ambient (~550 ?atm) or elevated (~2400 ?atm) pCO2 treatments and in common, ambient conditions, 5 months after exposure. Short-term exposure periods comprised an initial 10-day exposure followed by 14 days in ambient before a secondary 6-day reciprocal exposure. The initial exposure to elevated pCO2 significantly reduced respiration rate by 25% relative to ambient conditions, but no effect on shell growth was detected. Following 14 days in common garden, ambient conditions, reciprocal exposure to elevated or ambient pCO2 did not alter juvenile respiration rates, indicating ability for metabolic recovery under subsequent conditions. Shell growth was negatively affected during the reciprocal treatment in both exposure histories; however, clams exposed to the initial elevated pCO2 showed compensatory growth with 5.8% greater shell length (on average between the two secondary exposures) after 5 months in ambient conditions. Additionally, clams exposed to the secondary elevated pCO2 showed 52.4% increase in respiration rate after 5 months in ambient conditions. Early exposure to low pH appears to trigger carryover effects suggesting bioenergetic re-allocation facilitates growth compensation. Life stage-specific exposures to stress can determine when it may be especially detrimental, or advantageous, to apply stress conditioning for commercial production of this long-lived burrowing clam.
Project description:Anthropogenic climate change exposes marine organisms to CO2 induced ocean acidification (OA). Marine animals may make physiological and behavioral adaptations to cope with OA. Elevated pCO2 may affect metabolism, feeding, and energy partition of marine crabs, and thereby affect their predator-prey dynamics with mussels. Therefore, we examined the effects of simulated future elevated pCO2 on feeding behavior and energy metabolism of the brown crab Cancer pagurus. Following 54 days of pre-acclimation to control CO2 levels (360 μatm) at 11°C, crabs were exposed to consecutively increased oceanic CO2 levels (2 weeks for 1200 and 2300 μatm, respectively) and subsequently returned to control CO2 level (390 μatm) for 2 weeks in order to study their potential to acclimate elevated pCO2 and recovery performance. Standard metabolic rate (SMR), specific dynamic action (SDA) and feeding behavior of the crabs were investigated during each experimental period. Compared to the initial control CO2 conditions, the SMRs of CO2 exposed crabs were not significantly increased, but increased significantly when the crabs were returned to normal CO2 levels. Conversely, SDA was significantly reduced under high CO2 and did not return to control levels during recovery. Under high CO2, crabs fed on smaller sized mussels than under control CO2; food consumption rates were reduced; foraging parameters such as searching time, time to break the prey, eating time, and handling time were all significantly longer than under control CO2, and prey profitability was significantly lower than that under control conditions. Again, a two-week recovery period was not sufficient for feeding behavior to return to control values. PCA results revealed a positive relationship between feeding/SDA and pH, but negative relationships between the length of foraging periods and pH. In conclusion, elevated pCO2 caused crab metabolic rate to increase at the expense of SDA. Elevated pCO2 affected feeding performance negatively and prolonged foraging periods. These results are discussed in the context of how elevated pCO2 may impair the competitiveness of brown crabs in benthic communities.
Project description:Euphausia superba (Antarctic krill) is a keystone species in the Southern Ocean, but little is known about how it will respond to climate change. Ocean acidification, caused by sequestration of carbon dioxide into ocean surface waters (pCO2), alters the lipid biochemistry of some organisms. This can have cascading effects up the food chain. In a year-long laboratory experiment adult krill were exposed to ambient seawater pCO2 levels (400 μatm), elevated pCO2 levels mimicking near-future ocean acidification (1000, 1500 and 2000 μatm) and an extreme pCO2 level (4000 μatm). Total lipid mass (mg g-1 DM) of krill was unaffected by near-future pCO2. Fatty acid composition (%) and fatty acid ratios associated with immune responses and cell membrane fluidity were also unaffected by near-future pCO2, apart from an increase in 18:3n-3/18:2n-6 ratios in krill in 1500 μatm pCO2 in winter and spring. Extreme pCO2 had no effect on krill lipid biochemistry during summer. During winter and spring, krill in extreme pCO2 had elevated levels of 18:2n-6 (up to 1.2% increase), 20:4n-6 (up to 0.8% increase), lower 18:3n-3/18:2n-6 and 20:5n-3/20:4n-6 ratios, and showed evidence of increased membrane fluidity (up to three-fold increase in phospholipid/sterol ratios). These results indicate that the lipid biochemistry of adult krill is robust to near-future ocean acidification.
Project description:Anthropogenic CO2 is a major driver of current environmental change in most ecosystems1, and the related ocean acidification (OA) is threatening marine biota2. With increasing pCO2, calcification rates of several species decrease3, although cases of up-regulation are observed4. Here, we show that biological control over mineralization relates to species abundance along a natural pH gradient. As pCO2 increased, the mineralogy of a scleractinian coral (Balanophyllia europaea) and a mollusc (Vermetus triqueter) did not change. In contrast, two calcifying algae (Padina pavonica and Acetabularia acetabulum) reduced and changed mineralization with increasing pCO2, from aragonite to the less soluble calcium sulphates and whewellite, respectively. As pCO2 increased, the coral and mollusc abundance was severely reduced, with both species disappearing at pH < 7.8. Conversely, the two calcifying and a non-calcifying algae (Lobophora variegata) showed less severe or no reductions with increasing pCO2, and were all found at the lowest pH site. The mineralization response to decreasing pH suggests a link with the degree of control over the biomineralization process by the organism, as only species with lower control managed to thrive in the lowest pH.
Project description:The indirect effects of changing climate in modulating trophic interactions can be as important as the direct effects of climate stressors on consumers. The success of the herbivorous juvenile stage of the crown-of-thorns starfish (COTS), Acanthaster planci, may be affected by the impacts of ocean conditions on its crustose coralline algal (CCA) food. To partition the direct effects of near future ocean acidification on juvenile COTS and indirect effects through changes in their CCA food, COTS were grown in three pHT levels (7.9, 7.8, 7.6) and fed CCA grown at similar pH levels. Consumption of CCA by COTS was bolstered when the COTS were grown in low pH and when they were fed CCA grown in low pH regardless of the pH in which the COTS were reared. COTS fed CCA grown at pH 7.6 grew fastest, but the pH/pCO2 that the COTS were reared in had no direct effect on growth. Ocean acidification conditions decreased the C : N ratio and carbonate levels in the CCA. Bolstered growth in COTS may be driven by enhanced palatability, increased nutritive state and reduced defences of their CCA food. These results indicate that near future acidification will increase the success of early juvenile COTS and boost recruitment into the coral-eating life stage.
Project description:Ocean acidification (OA) and the resultant changing carbonate saturation states is threatening the formation of calcium carbonate shells and exoskeletons of marine organisms. The production of biominerals in such organisms relies on the availability of carbonate and the ability of the organism to biomineralize in changing environments. To understand how biomineralizers will respond to OA the common blue mussel, Mytilus edulis, was cultured at projected levels of pCO2 (380, 550, 750, 1000 µatm) and increased temperatures (ambient, ambient plus 2°C). Nanoindentation (a single mussel shell) and microhardness testing were used to assess the material properties of the shells. Young's modulus (E), hardness (H) and toughness (KIC) were measured in mussel shells grown in multiple stressor conditions. OA caused mussels to produce shell calcite that is stiffer (higher modulus of elasticity) and harder than shells grown in control conditions. The outer shell (calcite) is more brittle in OA conditions while the inner shell (aragonite) is softer and less stiff in shells grown under OA conditions. Combining increasing ocean pCO2 and temperatures as projected for future global ocean appears to reduce the impact of increasing pCO2 on the material properties of the mussel shell. OA may cause changes in shell material properties that could prove problematic under predation scenarios for the mussels; however, this may be partially mitigated by increasing temperature.