Effects of ocean acidification on respiration, growth and C:N ratio of arctic Hyas araneus larvae

Early life stages of marine crustaceans respond sensitively to elevated seawater PCO2. However, the underlying physiological mechanisms have not been studied well. We therefore investigated the effects of elevated seawater PCO2 on oxygen consumption, dry weight, elemental composition, median developmental time (MDT) and mortality in zoea I larvae of the spider crab Hyas araneus (Svalbard 79°N/11°E; collection, May 2009; hatch, December 2009). At the time of moulting, oxygen consumption rate had reached a steady state level under control conditions. In contrast, elevated seawater PCO2 caused the metabolic rate to rise continuously leading to a maximum 1.5-fold increase beyond control level a few days before moulting into the second stage (zoea II), followed by a pronounced decrease. Dry weight of larvae reared under high CO2 conditions was lower than in control larvae at the beginning of the moult cycle, yet this difference had disappeared at the time of moulting. MDT of zoea I varied between 45 ± 1 days under control conditions and 42 ± 2 days under the highest seawater CO2 concentration. The present study indicates that larval development under elevated seawater PCO2 levels results in higher metabolic costs during premoulting events in zoea I. However, H. araneus zoea I larvae seem to be able to compensate for higher metabolic costs as larval MDT and survival was not affected by elevated PCO2 levels.

Data compilation of respiration, feeding, and growth rates of marine pelagic organisms

The metabolic rate of organisms may either be viewed as a basic property from which other vital rates and many ecological patterns emerge and that follows a universal allometric mass scaling law; or it may be considered a property of the organism that emerges as a result of the organism's adaptation to the environment, with consequently less universal mass scaling properties. Data on body mass, maximum ingestion and clearance rates, respiration rates and maximum growth rates of animals living in the ocean epipelagic were compiled from the literature, mainly from original papers but also from previous compilations by other authors. Data were read from tables or digitized from graphs. Only measurements made on individuals of know size, or groups of individuals of similar and known size were included. We show that clearance and respiration rates have life-form-dependent allometries that have similar scaling but different elevations, such that the mass-specific rates converge on a rather narrow size-independent range. In contrast, ingestion and growth rates follow a near-universal taxa-independent ~3/4 mass scaling power law. We argue that the declining mass-specific clearance rates with size within taxa is related to the inherent decrease in feeding efficiency of any particular feeding mode. The transitions between feeding mode and simultaneous transitions in clearance and respiration rates may then represent adaptations to the food environment and be the result of the optimization of tradeoffs that allow sufficient feeding and growth rates to balance mortality.

European sea bass, Dicentrarchus labrax, in a changing ocean

Ocean acidification, caused by rising concentrations of carbon dioxide (CO2), is widely considered to be a major global threat to marine ecosystems. To investigate the potential effects of ocean acidification on the early life stages of a commercially important fish species, European sea bass (Dicentrarchus labrax), 12 000 larvae were incubated from hatch through metamorphosis under a matrix of two temperatures (17 and 19 °C) and two seawater pCO2 levels (ambient and 1,000 µatm) and sampled regularly for 42 days. Calculated daily mortality was significantly affected by both temperature and pCO2, with both increased temperature and elevated pCO2 associated with lower daily mortality and a significant interaction between these two factors. There was no significant pCO2 effect noted on larval morphology during this period but larvae raised at 19 °C possessed significantly larger eyes and lower carbon:nitrogen ratios at the end of the study compared to those raised under 17 °C. Similarly, when the incubation was continued to post-metamorphic (juvenile) animals (day 67-69), fish raised under a combination of 19 °C and 1000 µatm pCO2 were significantly heavier. However, juvenile D. labrax raised under this combination of 19 °C and 1000 µatm pCO2 also exhibited lower aerobic scopes than those incubated at 19 °C and ambient pCO2. Most studies investigating the effects of near-future oceanic conditions on the early life stages of marine fish have used incubations of relatively short durations and suggested that these animals are resilient to ocean acidification. Whilst the increased survival and growth observed in this study supports this view, we conclude that more work is required to investigate whether the differences in juvenile physiology observed in this study manifest as negative impacts in adult fish.

Responses of the metabolism of the larvae of Pocillopora damicornis to ocean acidification and warming

Ocean acidification and warming are expected to threaten the persistence of tropical coral reef ecosystems. As coral reefs face multiple stressors, the distribution and abundance of corals will depend on the successful dispersal and settlement of coral larvae under changing environmental conditions. To explore this scenario, we used metabolic rate, at holobiont and molecular levels, as an index for assessing the physiological plasticity of Pocillopora damicornis larvae from this site to conditions of ocean acidity and warming. Larvae were incubated for 6 hours in seawater containing combinations of CO2 concentration (450 and 950 µatm) and temperature (28 and 30°C). Rates of larval oxygen consumption were higher at elevated temperatures. In contrast, high CO2 levels elicited depressed metabolic rates, especially for larvae released later in the spawning period. Rates of citrate synthase, a rate-limiting enzyme in aerobic metabolism, suggested a biochemical limit for increasing oxidative capacity in coral larvae in a warming, acidifying ocean. Biological responses were also compared between larvae released from adult colonies on the same day (cohorts). The metabolic physiology of Pocillopora damicornis larvae varied significantly by day of release. Additionally, we used environmental data collected on a reef in Moorea, French Polynesia to provide information about what adult corals and larvae may currently experience in the field. An autonomous pH sensor provided a continuous time series of pH on the natal fringing reef. In February/March, 2011, pH values averaged 8.075±0.023. Our results suggest that without adaptation or acclimatization, only a portion of naïve Pocillopora damicornis larvae may have suitable metabolic phenotypes for maintaining function and fitness in an end-of-the century ocean.

Seawater carbonate chemistry, respiration, maximum photochemical efficiency and mortality of brooded larvae of Pocillopora//damicornis in a laboratory experiment

To evaluate the effects of temperature and pCO2 on coral larvae, brooded larvae of Pocillopora damicornis from Nanwan Bay, Taiwan (21°56.179' N, 120°44.85' E), were exposed to ambient (419-470 µatm) and high (604-742 µatm) pCO2 at ~25 and ~29 °C in two experiments conducted in March 2010 and March 2012. Larvae were sampled from four consecutive lunar days (LD) synchronized with spawning following the new moon, incubated in treatments for 24 h, and measured for respiration, maximum photochemical efficiency of PSII (F v/F m), and mortality. The most striking outcome was a strong effect of time (i.e., LD) on larvae performance: respiration was affected by an LD × temperature interaction in 2010 and 2012, as well as an LD × pCO2 × temperature interaction in 2012; F v/F m was affected by LD in 2010 (but not 2012); and mortality was affected by an LD × pCO2 interaction in 2010, and an LD × temperature interaction in 2012. There were no main effects of pCO2 in 2010, but in 2012, high pCO2 depressed metabolic rate and reduced mortality. Therefore, differences in larval performance depended on day of release and resulted in varying susceptibility to future predicted environmental conditions. These results underscore the importance of considering larval brood variation across days when designing experiments. Subtle differences in experimental outcomes between years suggest that transgenerational plasticity in combination with unique histories of exposure to physical conditions can modulate the response of brooded coral larvae to climate change and ocean acidification.

Mixed effects of elevated pCO2 on fertilisation, larval and juvenile development and adult responses in the mobile subtidal scallop Mimachlamys asperrima (Lamarck, 1819)

Ocean acidification is predicted to have severe consequences for calcifying marine organisms especially molluscs. Recent studies, however, have found that molluscs in marine environments with naturally elevated or fluctuating CO2 or with an active, high metabolic rate lifestyle may have a capacity to acclimate and be resilient to exposures of elevated environmental pCO2. The aim of this study was to determine the effects of near future concentrations of elevated pCO2 on the larval and adult stages of the mobile doughboy scallop, Mimachlamys asperrima from a subtidal and stable physio-chemical environment. It was found that fertilisation and the shell length of early larval stages of M. asperrima decreased as pCO2 increased, however, there were less pronounced effects of elevated pCO2 on the shell length of later larval stages, with high pCO2 enhancing growth in some instances. Byssal attachment and condition index of adult M. asperrima decreased with elevated pCO2, while in contrast there was no effect on standard metabolic rate or pHe. The responses of larval and adult M. asperrima to elevated pCO2 measured in this study were more moderate than responses previously reported for intertidal oysters and mussels. Even this more moderate set of responses are still likely to reduce the abundance of M. asperrima and potentially other scallop species in the world's oceans at predicted future pCO2 levels.

Parental effects improve escape performance of juvenile reef fish in a high-CO2 world

Rising CO2 levels in the oceans are predicted to have serious consequences for many marine taxa. Recent studies suggest that non-genetic parental effects may reduce the impact of high CO2 on the growth, survival and routine metabolic rate of marine fishes, but whether the parental environment mitigates behavioural and sensory impairment associated with high CO2 remains unknown. Here, we tested the acute effects of elevated CO2 on the escape responses of juvenile fish and whether such effects were altered by exposure of parents to increased CO2 (transgenerational acclimation). Elevated CO2 negatively affected the reactivity and locomotor performance of juvenile fish, but parental exposure to high CO2 reduced the effects in some traits, indicating the potential for acclimation of behavioural impairment across generations. However, acclimation was not complete in some traits, and absent in others, suggesting that transgenerational acclimation does not completely compensate the effects of high CO2 on escape responses.

Elevated pCO2 causes developmental delay in early larval Pacific oysters, Crassostrea gigas

Increasing atmospheric CO2 equilibrates with surface seawater, elevating the concentration of aqueous hydrogen ions. This process, ocean acidification, is a future and contemporary concern for aquatic organisms, causing failures in Pacific oyster (Crassostrea gigas) aquaculture. This experiment determines the effect of elevated pCO2 on the early development of C. gigas larvae from a wild Pacific Northwest population. Adults were collected from Friday Harbor, Washington, USA (48°31.7' N, 12°1.1' W) and spawned in July 2011. Larvae were exposed to Ambient (400 µatm CO2), MidCO2 (700 µatm), or HighCO2 (1,000 µatm). After 24 h, a greater proportion of larvae in the HighCO2 treatment were calcified as compared to Ambient. This unexpected observation is attributed to increased metabolic rate coupled with sufficient energy resources. Oyster larvae raised at HighCO2 showed evidence of a developmental delay by 3 days post-fertilization, which resulted in smaller larvae that were less calcified.

Populations of Pacific Oysters Crassostrea gigas Respond Variably to Elevated CO2 and Predation by Morula marginalba

Ocean acidification is anticipated to decrease calcification and increase dissolution of shelled molluscs. Molluscs with thinner and weaker shells may be more susceptible to predation, but not all studies have measured negative responses of molluscs to elevated pCO2. Recent studies measuring the response of molluscs have found greater variability at the population level than first expected. Here we investigate the impact of acidification on the predatory whelk Morula marginalba and genetically distinct subpopulations of the Pacific oyster Crassostrea gigas. Whelks and eight family lines of C. gigas were separately exposed to ambient (385 ppm) and elevated (1000 ppm) pCO2 for 6 weeks. Following this period, individuals of M. marginalba were transferred into tanks with oysters at ambient and elevated pCO2 for 17 days. The increase in shell height of the oysters was on average 63% less at elevated compared to ambient pCO2. There were differences in shell compression strength, thickness, and mass among family lines of C. gigas, with sometimes an interaction between pCO2 and family line. Against expectations, this study found increased shell strength in the prey and reduced shell strength in the predator at elevated compared to ambient pCO2. After 10 days, the whelks consumed significantly more oysters regardless of whether C. gigas had been exposed to ambient or elevated CO2, but this was not dependent on the family line and the effect was not significant after 17 days. Our study found an increase in predation after exposure of the predator to predicted near-future levels of estuarine pCO2.

Environmental assay on the effect of poultry manure application on soil organisms in agroecosystems

This paper reports the effects produced on the organisms of the soil (plants, invertebrates and microorganisms), after the application of two types of poultry manure (sawdust and straw bed) on an agricultural land. The test was made using a terrestrial microcosm, Multi-Species Soil System (MS3) developed in INIA. There was no difference in the germination for any of the three species of plants considered in the study. The biomass was increased in the wheat (Triticum aestivum) coming from ground treated with both kinds of poultry manure. Oilseed rape (Brasica rapa) was not affected and regarding vetch (Vicia sativa) only straw poultry manure showed significant difference. For length only Vicia sativa was affected showing a reduction when straw was exposed to poultry manure. When the effect on invertebrates was studied, we observed a reduction in the number of worms during the test, especially from the ground control (13.7%), higher than in the ground with sawdust poultry manure (6.7%), whereas in the ground with straw poultry manure, there was no reduction. The biomass was affected and at the end of the test it was observed that while the reduction of worms in the ground control was about 48%, the number of those that were in the ground with sawdust poultry manure or straw poultry manure decreased by 41% and 22% respectively. Finally, the effects on microorganisms showed that the enzymatic activities: dehydrogenase (DH) and phosphatase and basal respiration rate increased at the beginning of the test, and the differences were statistically significant compared with the values of the control group. During the test, all these parameters decreased (except DH activities) but they were always higher than in the ground control. This is why it is possible to deduce that the contribution of poultry manure caused an improvement in the conditions of fertilization and also for the soil.

Microvascular and tissue oxygen gradients in the rat mesentery

One of the most important functions of the blood circulation is O2 delivery to the tissue. This process occurs primarily in microvessels that also regulate blood flow and are the site of many metabolic processes that require O2. We measured the intraluminal and perivascular pO2 in rat mesenteric arterioles in vivo by using noninvasive phosphorescence quenching microscopy. From these measurements, we calculated the rate at which O2 diffuses out of microvessels from the blood. The rate of O2 efflux and the O2 gradients found in the immediate vicinity of arterioles indicate the presence of a large O2 sink at the interface between blood and tissue, a region that includes smooth muscle and endothelium. Mass balance analyses show that the loss of O2 from the arterioles in this vascular bed primarily is caused by O2 consumption in the microvascular wall. The high metabolic rate of the vessel wall relative to parenchymal tissue in the rat mesentery suggests that in addition to serving as a conduit for the delivery of O2 the microvasculature has other functions that require a significant amount of O2.

Torpor in mice is induced by both leptin-dependent and -independent mechanisms

We tested the effect of chronic leptin treatment on fasting-induced torpor in leptin-deficient A-ZIP/F-1 and ob/ob mice. A-ZIP/F-1 mice have virtually no white adipose tissue and low leptin levels, whereas ob/ob mice have an abundance of fat but no leptin. These two models allowed us to examine the roles of adipose tissue and leptin in the regulation of entry into torpor. Torpor is a short-term hibernation-like state that allows conservation of metabolic fuels. We first characterized the A-ZIP/F-1 animals, which have a 10-fold reduction in total body triglyceride stores. Upon fasting, A-ZIP/F-1 mice develop a lower metabolic rate and decreased plasma glucose, insulin, and triglyceride levels, with no increase in free fatty acids or β-hydroxybutyrate. Unlike control mice, by 24 hr of fasting, they have nearly exhausted their triglycerides and are catabolizing protein. To conserve energy supplies during fasting, A-ZIP/F-1 (but not control) mice entered deep torpor, with a minimum core body temperature of 24°C, 2°C above ambient. In ob/ob mice, fasting-induced torpor was completely reversed by leptin treatment. In contrast, neither leptin nor thyroid hormone prevented torpor in A-ZIP/F-1 mice. These data suggest that there are at least two signals for entry into torpor in mice, a low leptin level and another signal that is independent of leptin and thyroid hormone levels. Studying rodent torpor provides insight into human torpor-like states such as near drowning in cold water and induced hypothermia for surgery.

Integrated control of appetite and fat metabolism by the leptin-proopiomelanocortin pathway

Leptin deficiency results in a complex obesity phenotype comprising both hyperphagia and lowered metabolism. The hyperphagia results, at least in part, from the absence of induction by leptin of melanocyte stimulating hormone (MSH) secretion in the hypothalamus; the MSH normally then binds to melanocortin-4 receptor expressing neurons and inhibits food intake. The basis for the reduced metabolic rate has been unknown. Here we show that leptin administered to leptin-deficient (ob/ob) mice results in a large increase in peripheral MSH levels; further, peripheral administration of an MSH analogue results in a reversal of their abnormally low metabolic rate, in an acceleration of weight loss during a fast, in partial restoration of thermoregulation in a cold challenge, and in inducing serum free fatty acid levels. These results support an important peripheral role for MSH in the integration of metabolism with appetite in response to perceived fat stores indicated by leptin levels.

Medial prefrontal cortex and self-referential mental activity: Relation to a default mode of brain function

Medial prefrontal cortex (MPFC) is among those brain regions having the highest baseline metabolic activity at rest and one that exhibits decreases from this baseline across a wide variety of goal-directed behaviors in functional imaging studies. This high metabolic rate and this behavior suggest the existence of an organized mode of default brain function, elements of which may be either attenuated or enhanced. Extant data suggest that these MPFC regions may contribute to the neural instantiation of aspects of the multifaceted “self.” We explore this important concept by targeting and manipulating elements of MPFC default state activity. In this functional magnetic resonance imaging (fMRI) study, subjects made two judgments, one self-referential, the other not, in response to affectively normed pictures: pleasant vs. unpleasant (an internally cued condition, ICC) and indoors vs. outdoors (an externally cued condition, ECC). The ICC was preferentially associated with activity increases along the dorsal MPFC. These increases were accompanied by decreases in both active task conditions in ventral MPFC. These results support the view that dorsal and ventral MPFC are differentially influenced by attentiondemanding tasks and explicitly self-referential tasks. The presence of self-referential mental activity appears to be associated with increases from the baseline in dorsal MPFC. Reductions in ventral MPFC occurred consistent with the fact that attention-demanding tasks attenuate emotional processing. We posit that both self-referential mental activity and emotional processing represent elements of the default state as represented by activity in MPFC. We suggest that a useful way to explore the neurobiology of the self is to explore the nature of default state activity.

Blood flow and oxygen delivery to human brain during functional activity: Theoretical modeling and experimental data

Coupling of cerebral blood flow (CBF) and cerebral metabolic rate for oxygen (CMRO2) in physiologically activated brain states remains the subject of debates. Recently it was suggested that CBF is tightly coupled to oxidative metabolism in a nonlinear fashion. As part of this hypothesis, mathematical models of oxygen delivery to the brain have been described in which disproportionately large increases in CBF are necessary to sustain even small increases in CMRO2 during activation. We have explored the coupling of CBF and oxygen delivery by using two complementary methods. First, a more complex mathematical model was tested that differs from those recently described in that no assumptions were made regarding tissue oxygen level. Second, [15O] water CBF positron emission tomography (PET) studies in nine healthy subjects were conducted during states of visual activation and hypoxia to examine the relationship of CBF and oxygen delivery. In contrast to previous reports, our model showed adequate tissue levels of oxygen could be maintained without the need for increased CBF or oxygen delivery. Similarly, the PET studies demonstrated that the regional increase in CBF during visual activation was not affected by hypoxia. These findings strongly indicate that the increase in CBF associated with physiological activation is regulated by factors other than local requirements in oxygen.