Posts Tagged 'mortality'

Paradise lost: end‐of‐century warming and acidification under business‐as‐usual emissions have severe consequences for symbiotic corals

Despite recent efforts to curtail greenhouse gas emissions, current global emission trajectories are still following the business‐as‐usual RCP8.5 emission pathway. The resulting ocean warming and acidification have transformative impacts on coral reef ecosystems, detrimentally affecting coral physiology and health, and these impacts are predicted to worsen in the near future. In this study, we kept fragments of the symbiotic corals Acropora intermedia (thermally sensitive) and Porites lobata (thermally tolerant) for 7 weeks under an orthogonal design of predicted end‐of‐century RCP8.5 conditions for temperature and pCO2 (3.5 °C and 570 ppm above present‐day respectively) to unravel how temperature and acidification, individually or interactively, influence metabolic and physiological performance. Our results pinpoint thermal stress as the dominant driver of deteriorating health in both species because of its propensity to destabilize coral‐dinoflagellate symbiosis (bleaching). Acidification had no influence on metabolism but had a significant negative effect on skeleton growth, particularly when photosynthesis was absent such as in bleached corals or under dark conditions. Total loss of photosynthesis after bleaching caused an exhaustion of protein and lipid stores and collapse of calcification that ultimately led to A. intermedia mortality. Despite complete loss of symbionts from its tissue, P. lobata maintained small amounts of photosynthesis and experienced a weaker decline in lipid and protein reserves that presumably contributed to higher survival of this species. Our results indicate that ocean warming and acidification under business‐as‐usual CO2 emission scenarios will likely extirpate thermally‐sensitive coral species before the end of the century, while slowing the recovery of more thermally‐tolerant species from increasingly severe mass coral bleaching and mortality. This could ultimately lead to the gradual disappearance of tropical coral reefs globally, and a shift on surviving reefs to only the most resilient coral species.

Continue reading ‘Paradise lost: end‐of‐century warming and acidification under business‐as‐usual emissions have severe consequences for symbiotic corals’

Intra-specific variation of ocean acidification effects in marine mussels and oysters: integrative physiological studies on tissue and organism responses

Uptake of increasing anthropogenic CO2 emissions by ocean surface waters is causing an increase of seawater PCO2 accompanied by a decrease of seawater pH and carbonate ion concentrations. This process, termed ocean acidification (OA), is predicted to negatively affect many marine organisms with likely consequences for marine ecosystems and the services they provide. Calcifying mussels and oysters, and particularly their early life stages, are predicted to be among the most OA sensitive taxa, as OA interferes with the calcification process. In addition, mussels and oysters possess a relatively low ability to compensate for CO2 induced disturbances in extracellular body fluid pH with potential physiological downstream effects such as elevated metabolic maintenance costs. As mussels and oysters are key habitat forming organisms in many highly productive temperate coastal communities, negative OA effects may translate into deleterious effects at an ecosystem scale. In particular, the relative long generation time of most marine bivalves raises the concern that the rapid rate at which OA occurs may outpace species’ ability to genetically adapt, leaving pre-existing genetic variation as a potential key to species resilience under OA. Against this backdrop, this thesis contributes to the understanding of physiological mechanisms that underpin and define the OA vulnerability of ecologically and economically important mussels and oysters. Thereby, emphasis was placed on investigating intra-specific variance as a proxy for potential adaptive capacities. Kiel Fjord is located in the Western Baltic Sea and is characterised by strong seasonal and diurnal fluctuations in seawater PCO2. These fluctuations are caused by upwelling events of acidified bottom waters with peak PCO2 values (>2300 μatm) that are already by far exceeding those projected for open ocean surface waters by the end of this century. Despite these unfavourable conditions, blue mussels (Mytilus edulis) dominate the benthic community, which makes this population particularly interesting in the context of metabolic adaptation to OA. Consequently, a long-term multi-generation CO2 acclimation experiment with different family lines of M. edulis from Kiel Fjord formed the first part of this thesis. Offspring of 16 different family lines were transferred to three different PCO2 conditions, representing present and predicted PCO2 levels in Kiel Fjord (700 μatm (control), 1120 μatm (intermediate) and 2400 μatm (high)). Larval survival rates were substantially different between family lines at the highest PCO2 level. Based on these differences, families were classified as either ‘tolerant’ (i.e. successful settlement at all PCO2 levels) or ‘sensitive’ (i.e. successful settlement only at control and intermediate PCO2 level). Subsequently, the offspring were raised for over one year at respective PCO2 levels, followed by measurements of physiological parameters at the whole-animal, tissue (gill and outer mantle) and biochemical level (key metabolic enzymes). The results revealed that routine metabolic rates (RMR) and summed tissue respiration were increased in tolerant families at intermediate PCO2, indicating elevated homeostatic costs. However, this higher energy demand at the intermediate PCO2 level was not accompanied by a simultaneous increase in energy assimilation (i.e. clearance rates (CR)), indicating an incipient imbalance in energy demand and supply. Consequently, RMRs at the highest PCO2 were not different to control RMRs but associated with reduced CRs, which correlated with a lower gill metabolic scope, reduced gill mitochondrial capacities (lower capacities for citrate synthase (CS) and cytochrome c oxidase (COX)) as well as an increased capacity for anaerobic energy production (lower ratio of pyruvate kinase to phospoenolpyruvate carboxykinase). In conjunction with a lower COX to CS ratio observed in outer mantle tissue, this suggested a CO2-induced shift of metabolic pathways in tolerant families at the highest PCO2 level. By contrast, sensitive families had an unchanged RMR, tissue respiration and CR at the intermediate CO2. However, a higher control RMR in sensitive than tolerant families at similar CR suggested a lower, CO2 independent metabolic efficiency in sensitive families. This was also reflected in their lower gill mitochondrial scope at control conditions compared to tolerant families. These findings suggested that sensitive families lack the metabolic scope to cover OA induced higher maintenance costs and have to rely on energy reallocation and thus, energy trade-offs which may also have prevented survival at the highest experimental PCO2 level. Accordingly, investigations of 3-hydroxyacyl-CoA dehydrogenase (HADH) capacities, which catalyses a key step in lipid oxidation, suggested an increased reliance on lipids as metabolic fuel in sensitive families at elevated PCO2. If this was also prevalent during the larval phase, a quicker depletion of lipid reserves before completion of metamorphosis may have contributed to the higher larval mortality at the highest PCO2 treatment in sensitive compared to tolerant mussels. The second part of the thesis aimed to clarify whether a higher OA tolerance in Sydney rock oysters (Saccostrea glomerata) is directly correlated with an increased capacity to compensate for CO2 induced extracellular acid-base disturbances, and whether such a capacity is driven by higher metabolic and ion-regulatory costs at the tissue level. Earlier studies focusing on two different populations of Sydney rock oysters demonstrated that oysters that were selectively bred for increased growth and disease resistance (‘selected oysters’) have a higher CO2 resilience compared to the wild population (‘wild oysters’). To unravel the underlying physiological mechanisms, oysters of both populations were acclimated at control and elevated PCO2 (1100 μatm) levels for seven weeks, followed by determinations of extracellular acidbase parameters (pHe, PeCO2, [HCO3 -]e), tissue respiration and indirect determination of energy demands of major ion regulatory transport proteins. Indeed, at elevated PCO2, wild oysters had a lower pHe and an increased PeCO2 whereas extracellular acid-base status of selected oysters remained unaffected. However, differing pHe values between oyster types were not driven by elevated metabolic costs of major ion regulators at tissue level. Selected oysters rather exhibited an increased systemic capacity to eliminate metabolic CO2, which likely came through higher and energetically more efficient filtration rates and associated facilitation of gas exchange, suggesting that effective filtration and CO2 resilience might be positively correlated traits in oysters. In conclusion, the findings of this thesis contribute to the growing evidence that ongoing OA will likely impair the physiology of marine mussels and oysters with potentially associated downstream consequences for the respective ecosystems. However, the results also suggest adaptive capacities in both species studied. The higher CO2 resilience of selected Sydney rock oysters was expressed within the – in evolutionary terms – rapid time span of only a few generations of selective breeding, which indicates that rapid adaptation to OA may be possible in marine bivalves. The observed intra-specific variation of OA responses in blue mussels suggests standing genetic variation within this population, which is likely to be key for the persistence of populations under rapidly occurring OA. However, as global change is not limited to OA, future research will have to reassess potential resilience traits and adaptive capacities to OA when combined with changes in other environmental drivers.

Continue reading ‘Intra-specific variation of ocean acidification effects in marine mussels and oysters: integrative physiological studies on tissue and organism responses’

Paths to growth: exploring the effects of reduced pH and increased temperature on a fisheries-important prawn

Crustaceans are relatively understudied in regards to their vulnerability to the changing ocean conditions of ocean acidification and ocean warming. Although they are generally considered less vulnerable to reduced pH and increased temperature than other calcifying groups, studies have found potential effects on their growth, energy storage, and prey detection. In this study, we examined the vulnerability of the ridgeback prawn, Sicyonia ingentis, which is a commercially important species along the West coast of the United States. Prawn were exposed to reduced pH (7.50 ± 0.02; pCO₂ = 1475 ± 25 µatm) and increased temperature (16.2 ± 0.7°C) conditions in a full factorial design for twelve weeks. Prawns were monitored for survival and growth throughout the experiment. At the end of the experiment, their prey detection was analyzed via antennular flicking rates, and they were dissected for Gonadosomatic Index (GSI) and Hepatosomatic Index (HSI) measurements, which are indicators of gonad development, energy storage, and the trade-off between the two. No significant effect of treatment was found for antennular flicking, GSI, or HSI. The second molt increment was significantly less in the reduced pH/increased temperature treatment in comparison to the control (ANOVA: F3,18 = 3.36, p = 0.04), but growth over the experiment did not differ among treatments. Survival was significantly lower in the reduced pH/increased temperature treatment. S. ingentis is robust to a pH below its natural range, but the synergistic effects of reduced pH and increased temperature have a significant impact on mortality.

Continue reading ‘Paths to growth: exploring the effects of reduced pH and increased temperature on a fisheries-important prawn’

Effects of elevated CO2 on survival, growth, digestive enzymes and glucose concentration of white leg shrimp (Litopenaeus vannamei Boone, 1931) from postlarvae 15 to juvenile stage (in Vietnamese)

This study was carried out to determine the effects of CO2 on survival, growth, digestive enzyme activity and glucose concentration of white leg shrimp from 15-day postlarvae to juvenile stage. The study was designed using a completely randomized with 4-CO2 treatments including 2.32, 7.81, 19.0 and 45.6 mg/L equal to pH of 8.1, 7.6, 7.2 and 6.8, respectively. Postlarvae of 0.019 g and 1.20 cm length were stocked at the density of 100 ind./200-L tank. After 45 days, the survival rate of shrimp in control treatment (2.32 mg/L CO2 or pH=8.1) was 70.0%, and the lowest survival rate occurred in the CO2 treatment of 45.6 mg/L (28.3%). The lowest final individual weight and length in CO2 concentration of 45.6 mg/L were 1.09 g and 4.69 cm. The lowest enzyme activities were in CO2 treatment of 45.6 mg/L. Glucose concentration was highest in 37.5 mg/100 mL. The high CO2 concentration will adversely affect growth, survival rate, reduce some digestive enzymes and increase glucose concentration in hemolymph of white leg shrimp.

Continue reading ‘Effects of elevated CO2 on survival, growth, digestive enzymes and glucose concentration of white leg shrimp (Litopenaeus vannamei Boone, 1931) from postlarvae 15 to juvenile stage (in Vietnamese)’

Effects of coastal acidification on North Atlantic bivalves: interpreting laboratory responses in the context of in situ populations

Experimental exposure of early life stage bivalves has documented negative effects of elevated pCO2 on survival and growth, but the population consequences of these effects are unknown. We substituted laboratory responses into baseline population models of northern quahog Mercenaria mercenaria and bay scallop Argopecten irradians. The models were constructed using inverse demography with time series of size-structured field data from New York, USA, whereas the stress-response relationships were developed using data from published laboratory studies. We used stochastic projections and diffusion approximations of extinction probability to estimate cumulative risk of 50% population decline during 5 yr projections at pCO2 levels of 400, 800, and 1200 µatm. Although the A. irradians field population exhibited higher growth (12% yr-1) than the declining M. mercenaria population (-8% yr-1), cumulative risk was higher due to variance in the stochastic growth rate estimate (log λs = -0.02, σ2 = 0.24). This 5 yr risk increased from 56% at 400 µatm to 99 and >99% at 800 and 1200 µatm, respectively. For M. mercenaria (log λs = -0.09, σ2 = 0.01), 5 yr risk was 25, 79, and 97% at 400, 800, and 1200 µatm, respectively. These estimates could be improved with detailed consideration of harvest, disease, restocking, compensatory responses, and interactions between these and other effects. However, results clearly indicate that early life stage responses to plausible levels of pCO2 enrichment have the potential to cause significant increases in risk to these marine bivalve populations.

Continue reading ‘Effects of coastal acidification on North Atlantic bivalves: interpreting laboratory responses in the context of in situ populations’

Experimental acidification increases susceptibility of Mercenaria mercenaria to infection by Vibrio species

Highlights

• Clams in high pCO2/low pH were more susceptible to infection by pathogenic Vibrios.

• Growth and abundance of Vibrio spp. were greater under high pCO2/low pH.

• Clams reared under high pCO2/low pH seemed to have a broad tolerance range for pH.

• Long-term effect of acidification and susceptibility to vibriosis is understudied.

Abstract

Ocean acidification alters seawater carbonate chemistry, which can have detrimental impacts for calcifying organisms such as bivalves. This study investigated the physiological cost of resilience to acidification in Mercenaria mercenaria, with a focus on overall immune performance following exposure to Vibrio spp. Larval and juvenile clams reared in seawater with high pCO2 (∼1200 ppm) displayed an enhanced susceptibility to bacterial pathogens. Higher susceptibility to infection in clams grown under acidified conditions was derived from a lower immunity to infection more so than an increase in growth of bacteria under high pCO2. A reciprocal transplant of juvenile clams demonstrated the highest mortality amongst animals transplanted from low pCO2/high pH to high pCO2/low pH conditions and then exposed to bacterial pathogens. Collectively, these results suggest that increased pCO2 will result in immunocompromised larvae and juveniles, which could have complex and pernicious effects on hard clam populations.

Continue reading ‘Experimental acidification increases susceptibility of Mercenaria mercenaria to infection by Vibrio species’

Negative effects of diurnal changes in acidification and hypoxia on early-life stage estuarine fishes

Estuaries serve as important nursery habitats for various species of early-life stage fish, but can experience cooccurring acidification and hypoxia that can vary diurnally in intensity. This study examines the effects of acidification (pH 7.2–7.4) and hypoxia (dissolved oxygen (DO) ~ 2–4 mg L−1) as individual and combined stressors on four fitness metrics for three species of forage fish endemic to the U.S. East Coast: Menidia menidia, Menidia beryllina, and Cyprinodon variegatus. Additionally, the impacts of various durations of exposure to these two stressors was also assessed to explore the sensitivity threshold for larval fishes under environmentally-representative conditions. C. variegatus was resistant to chronic low pH, while M. menidia and M. beryllina experienced significantly reduced survival and hatch time, respectively. Exposure to hypoxia resulted in reduced hatch success of both Menidia species, as well as diminished survival of M. beryllina larvae. Diurnal exposure to low pH and low DO for 4 or 8 h did not alter survival of M. beryllina, although 8 or 12 h of daily exposure through the 10 days posthatch significantly depressed larval size. In contrast, M. menidia experienced significant declines in survival for all intervals of diel cycling hypoxia and acidification (4–12 h). Exposure to 12-h diurnal hypoxia generally elicited negative effects equal to, or of greater severity, than chronic exposure to low DO at the same levels despite significantly higher mean DO exposure concentrations. This evidences a substantial biological cost to adapting to changing DO levels, and implicates diurnal cycling of DO as a significant threat to fish larvae in estuaries. Larval responses to hypoxia, and to a lesser extent acidification, in this study on both continuous and diurnal timescales indicate that estuarine conditions throughout the spawning and postspawn periods could adversely affect stocks of these fish, with diverse implications for the remainder of the food web.

Continue reading ‘Negative effects of diurnal changes in acidification and hypoxia on early-life stage estuarine fishes’


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Ocean acidification in the IPCC AR5 WG II

OUP book