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The large radiation of terrestrial isopods (suborder Oniscidea) includes several families that are represented primarily in marine-littoral or riparian habitats. Among these are members of Ligiidae and Tylidae as well as several basal families within the section Crinocheta. Structural and physiological evidence supports a marine-littoral ancestry of the Oniscidea. We examined aerial and aquatic respiration (measured as VCO2) in six species of marine-littoral Oniscidea representing five families, as well as one riparian and one endogean species. Complimentary data were collected for immersion tolerance and whole-animal permeability in air, and structural specialization of the respiratory pleopods was examined using SEM. Ligia occidentalis Dana, 1853 (marine, littoral) and Ligidium lapetum Mulaik & Mulaik, 1942 (riparian) showed similar VCO2 in air and water. VCO2 in air for the other species was significantly higher than in water. Compared across species, aerial VCO2 scaled with mass in accordance with Kleiber’s law (β = 0.774) while aquatic VCO2 increased in approximate proportion to mass (β = 0.957). At least some specimens of the six marine-littoral species survived over 24 h immersion. Ligidium lapetum and the endogean trichoniscid Brackenridgia heroldi (Arcangeli, 1932) also tolerated prolonged immersion in freshwater but did not survive beyond 5–6 h, probably due to limited capacity for hyper-regulation. The upper shore sand-burrowers, Tylos punctatus Holmes & Gay, 1909 and Alloniscus perconvexus Dana, 1856 had the lowest permeability among the study species and are the only representatives with elaborated pleopodal respiratory fields (Alloniscus) and lungs (Tylos). The ventral lung spiracles of T. punctatus are surrounded by an extensive cuticle meshwork and we propose that this functions as a plastron field to enhance aquatic gas exchange. Collectively, the results show that littoral species tolerate significant periods of immersion, allowing them to withstand habitat inundation during spring high tides, storm swells and, in riparian species, rainstorms and snowmelt.

How aquatic primary productivity influences the carbon (C) sequestering capacity of wetlands is uncertain. We evaluated the magnitude and variability in aquatic C dynamics and compared them to net ecosystem CO2 exchange (NEE) and ecosystem respiration (Reco) rates within calcareous freshwater wetlands in Everglades National Park. We continuously recorded 30-min measurements of dissolved oxygen (DO), water level, water temperature (Twater), and photosynthetically active radiation (PAR). These measurements were coupled with ecosystem CO2 fluxes over 5 years (2012–2016) in a long-hydroperiod peat-rich, freshwater marsh and a short-hydroperiod, freshwater marl prairie. Daily net aquatic primary productivity (NAPP) rates indicated both wetlands were generally net heterotrophic. Gross aquatic primary productivity (GAPP) ranged from 0 to − 6.3 g C m−2 day−1 and aquatic respiration (RAq) from 0 to 6.13 g C m−2 day−1. Nonlinear interactions between water level, Twater, and GAPP and RAq resulted in high variability in NAPP that contributed to NEE. Net aquatic primary productivity accounted for 4–5% of the deviance explained in NEE rates. With respect to the flux magnitude, daily NAPP was a greater proportion of daily NEE at the long-hydroperiod site (mean = 95%) compared to the short-hydroperiod site (mean = 64%). Although we have confirmed the significant contribution of NAPP to NEE in both long- and short-hydroperiod freshwater wetlands, the decoupling of the aquatic and ecosystem fluxes could largely depend on emergent vegetation, the carbonate cycle, and the lateral C flux.

Different erosion processes deliver large amounts of terrestrial soil organic carbon (SOC) to rivers. Mounting evidence indicates that a significant fraction of this SOC, which displays a wide range of ages, is rapidly decomposed after entering the river system. The mechanisms explaining this rapid decomposition of previously stable SOC still remain unclear. In this study, we investigated the relative importance of two mechanisms that possibly control SOC decomposition rates in aquatic systems: (i) in the river water SOC is exposed to the aquatic microbial community which is able to metabolize SOC much more quickly than the soil microbial community and (ii) SOC decomposition in rivers is facilitated due to the hydrodynamic disturbance of suspended sediment particles. We performed different series of short-term (168 h) incubations quantifying the rates of SOC decomposition in an aquatic system under controlled conditions. Organic carbon decomposition was measured continuously through monitoring dissolved O2 (DO) concentration using a fiber-optic sensor (FireStingO2, PyroScience). Under both shaking and standing conditions, we found a significant difference in decomposition rate between SOC with aquatic microbial organisms added (SOC + AMO) and without aquatic microbial organisms (SOC − AMO). The presence of an aquatic microbial community enhanced the SOC decomposition process by 70 %–128 % depending on the soil type and shaking–standing conditions. While some recent studies suggested that aquatic respiration rates may have been substantially underestimated by performing measurement under stationary conditions, our results indicate that the effect of hydrodynamic disturbance is relatively minor, under the temperature conditions, for the soil type, and for the suspended matter concentration range used in our experiments. We propose a simple conceptual model explaining these contrasting results.

Bergmann's rule is the propensity for species-mean body size to decrease with increasing temperature. Temperature-dependent oxygen limitation has been hypothesized to help drive temperature-size relationships among ectotherms, including Bergmann's rule, where organisms reduce body size under warm oxygen-limited conditions, thereby maintaining aerobic scope. Temperature-dependent oxygen limitation should be most pronounced among aquatic ectotherms that cannot breathe aerially, as oxygen solubility in water decreases with increasing temperature. We use phylogenetically explicit analyses to show that species-mean adult size of aquatic salamanders with branchial or cutaneous oxygen uptake becomes small in warm environments and large in cool environments, whereas body size of aquatic species with lungs (i.e., that respire aerially), as well as size of semiaquatic and terrestrial species do not decrease with temperature. We argue that oxygen limitation drives the evolution of small size in warm aquatic environments for species with aquatic respiration. More broadly, the stronger decline in size with temperature observed in aquatic versus terrestrial salamander species mirrors the relatively strong plastic declines in size observed previously among aquatic versus terrestrial invertebrates, suggesting that temperature-dependent oxygen availability can help drive patterns of plasticity, micro- and macroevolution.

When water bodies with unique biogeochemical constituents mix together there is potential for diverse responses by aquatic microbial communities and associated ecosystem functions. Here we evaluate bulk respiration under varying mixtures of turbid Amazon River water and two lowland tributaries-the Tapajos and Xingu rivers-based on O-2 drawdown in dark rotating incubation chambers. Experiments containing 5, 17, 33, and 50% tributary water mixed with Amazon River water were performed for the Tapajos and Xingu rivers at three different rotation velocities (0, 0.22, and 0.66 m s(-1)) during the falling water period. Pseudo first order reaction coefficients (k'), a measure of respiration potential, ranged from -0.15 to -1.10 d(-1), corresponding to respiration rates from 1.0 to 8.1 mg O-2 L d(-1). k'-values consistently increased with the rate of chamber rotation, and also was generally higher in the tributary-mainstem mixtures compared to pure endmembers. For both the Tapajos and Xingu rivers, the 17% mixture of tributary water yielded maximal k'-values, which were up to 2.9 and 2.2 times greater than in the tributary endmembers, respectively. The 50% mixtures, on the other hand, did not result in large increases in k'. We hypothesize that enhanced respiration potential after mixing unique water is driven, in part, by microbial priming effects that have been previously identified on a molecular level for these rivers. The results of this study suggest that there may be an optimal mixture for priming effects to occur in terms of the relative abundance of "priming" and "primed" substrates.

Radiocarbon ( 14 C) is a key tracer for detecting the mobilization of previously stored terrestrial organic carbon (C) into aquatic systems. Old C (>1,000 years BP) may be “masked” by postbomb C (fixed from the atmosphere post-1950 CE), potentially rendering bulk aquatic dissolved organic C (DOC) 14 C measurements insensitive to old C. We collected DOC with a modern 14 C signature from a temperate Scottish peatland stream and decomposed it to produce CO 2 under simulated natural conditions over 140 days. We measured the 14 C of both DOC and CO 2 at seven time points and found that while DOC remained close to modern in age, the resultant CO 2 progressively increased in age up to 2,356 ± 767 years BP. The results of this experiment demonstrate that the bulk DO 14 C pool can hide the presence of old C within peatland stream DOC export, demonstrating that bulk DO 14 C measurements can be an insensitive indicator of peatland disturbance. Our experiment also demonstrates that this old C component is biologically and photochemically available for conversion to the greenhouse gas CO 2 , and as such, bulk DO 14 C measurements do not reflect the 14 C signature of the labile organic C pool exported by inland water systems more broadly. Moreover, our experiment suggests that old C may be an important component of CO 2 emissions to the atmosphere from peatland aquatic systems, with implications for tracing and modeling interactions between the hydrological and terrestrial C cycles.

Agricultural crops play an important role in the global carbon and water cycle. Global climate change scenarios predict enhanced water scarcity and altered precipitation pattern in many parts of the world. Hence, a mechanistic understanding of water fluxes, productivity and water use efficiency of cultivated crops is of major importance, i.e. to adapt management practices. We compared water and carbon fluxes of paddy and rainfed rice by canopy scale gas exchange measurements, crop growth, daily evapotranspiration, transpiration and carbon flux modeling. Throughout a monsoon rice growing season, soil evaporation in paddy rice contributed strongly to evapotranspiration (96.6% to 43.3% from initial growth to fully developed canopy and amounted to 57.9% of total water losses over the growing seasons. Evaporation of rainfed rice was significantly lower (by 65% on average) particularly before canopy closure. Water use efficiency (WUE) was significantly higher in rainfed rice both from an agronomic (WUEagro, i.e. grain yield per evapotranspiration) and ecosystem (WUEeco, i.e. gross primary production per evapotranspiration) perspective. However, our results also show that higher WUE in rainfed rice comes at the expense of higher respiration losses compared to paddy rice (26% higher on average). Hence, suggestions on water management depend on the regional water availability (i.e. Mediterranean vs. Monsoon climate) and the balance between higher respiratory losses versus a potential reduction in CH4 and other greenhouse gas emissions. Our results suggest that a shift from rainfed/unsaturated soil to waterlogged paddy conditions after closure of the rice canopy might be a good compromise towards a sustainable use of water while preserving grain yield, particularly for water-limited production areas.

Freshwater fish may be exposed to high levels of carbon dioxide (CO2) because of several actions, including anesthesia and high levels of aquatic respiration and potentially as the result of using high-CO2 plumes as a barrier to the movements of invasive fishes. Metabolic phenotype can potentially drive how freshwater fish respond to high CO2. We therefore quantified how tolerance (measured using time to equilibrium loss [ELT]) was driven by metabolic phenotype in a cosmopolitan freshwater fish species, Micropterus salmoides. ELT was repeatable, with 60% of the variance across trials attributable to individual differences. For each fish, standard metabolic rate and maximum metabolic rate were measured using respirometers and time to exhaustion after a chase test was recorded. Fish with high anaerobic performance were less tolerant to elevated CO2, potentially as a result of preexisting metabolic acidosis. Standard metabolic rate and aerobic scope did not predict ELT. Our findings define which fish may be more vulnerable to high CO2, a potential mechanism for this tolerance, and show that tolerance to high CO2 may be acted on by natural selection. Should freshwater ecosystems become elevated in CO2, by either natural means or anthropogenic means, it is possible that there is potential for heritable selection of CO2 tolerance, evidenced by the fact that ELT was found to be repeatable. "The study was supported by Illinois Department of Natural Resources (CAFWS-93) and the US Geological Survey, through funds provided to C.D.S. by the Great Lakes Restoration Initiative (G14AC00119)." https://www.journals.uchicago.edu/doi/abs/10.1086/693376

Fishes with bimodal respiration differ in the extent of their reliance on air breathing to support aerobic metabolism, which is reflected in their lifestyles and ecologies. Many freshwater species undertake seasonal and reproductive migrations that presumably involve sustained aerobic exercise. In the six species studied to date, aerobic exercise in swim flumes stimulated air-breathing behaviour, and there is evidence that surfacing frequency and oxygen uptake from air show an exponential increase with increasing swimming speed. In some species, this was associated with an increase in the proportion of aerobic metabolism met by aerial respiration, while in others the proportion remained relatively constant. The ecological significance of anaerobic swimming activities, such as sprinting and fast-start manoeuvres during predator-prey interactions, has been little studied in air-breathing fishes. Some species practise air breathing during recovery itself, while others prefer to increase aquatic respiration, possibly to promote branchial ion exchange to restore acid-base balance, and to remain quiescent and avoid being visible to predators. Overall, the diversity of air-breathing fishes is reflected in their swimming physiology as well, and further research is needed to increase the understanding of the differences and the mechanisms through which air breathing is controlled and used during exercise.

Several taxonomically disparate groups of fishes have evolved the ability to extract oxygen from the air with elements of their gut. Despite perceived difficulties with balancing digestive and respiratory function, gut air breathing (GAB) has evolved multiple times in fishes and several GAB families are among the most successful fish families in terms of species numbers. When gut segments evolve into an air-breathing organ (ABO), there is generally a specialized region for exchange of gases where the gut wall has diminished, vascularization has increased, capillaries have penetrated into the luminal epithelium and surfactant is produced. This specialized region is generally separated from digestive portions of the gut by sphincters. GAB fishes tend to be facultative air breathers that use air breathing to supplement aquatic respiration in hypoxic waters. Some hindgut breathers may be continuous, but not obligate air breathers (obligate air breathers drown if denied access to air). Gut ABOs are generally used only for oxygen uptake; CO2 elimination seems to occur via the gills and skin in all GAB fishes studied. Aerial ventilation in GAB fishes is driven primarily by oxygen partial pressure of the water (PO2) and possibly also by metabolic demand. The effect of aerial ventilation on branchial ventilation and the cardiovascular system is complex and generalizations across taxa or ABO type are not currently possible. Blood from GAB fishes generally has a low blood oxygen partial pressure that half saturates haemoglobin (p50) with a very low erythrocytic nucleoside triphosphate concentration [NTP]. GAB behaviour in nature depends on the social and ecological context of the animal as well as on physiological factors.

The Canterbury mudfish Neochanna burrowsius was found to be a pseudo-aestivating galaxiid with a low metabolic rate and significant cutaneous oxygen uptake (c. 43%) in both air and water. Another galaxiid, inanga Galaxias maculatus, had a higher metabolic rate in both media but the proportion of oxygen uptake met by cutaneous respiration rose significantly from 38 to 63% when the fish were exposed to air. Besides its important role in oxygen uptake, the skin of both species also contributed significantly to excretion of carbon dioxide in air, indicating the critical role of the integument as a respiratory tissue. In air, G. maculatus may increase cutaneous gas exchange to meet metabolic demands owing to the reduced utility of the gills, but as emersed G. maculatus were only able to maintain metabolic rates at c. 67% of that measured in water, this strategy probably only permits short-term survival. By contrast, the low and unchanging metabolic rate in water and air in N. burrowsius is a feature that may facilitate tolerance of long periods of emersion in the desiccating environments they inhabit.

Large changes in oxygen availability in aquatic environments, ranging from anoxia through to hyperoxia, can lead to corresponding wide variation in the production of reactive oxygen species (ROS) by animals with aquatic respiration. Therefore, animals living in marine, estuarine and freshwater environments have developed efficient antioxidant defenses to minimize oxidative stress and to regulate the cellular actions of ROS. Changes in oxygen levels may lead to bursts of ROS generation that can be particularly harmful. This situation is commonly experienced by aquatic animals during abrupt transitions from periods of hypoxia/anoxia back to oxygenated conditions (e.g. intertidal cycles). The strategies developed differ significantly among aquatic species and are (i) improvement of their endogenous antioxidant system under hyperoxia (that leads to increased ROS formation) or other similar ROS-related stresses, (ii) increase in antioxidant levels when displaying higher metabolic rates, (iii) presence of constitutively high levels of antioxidants, that attenuates oxidative stress derived from fluctuations in oxygen availability, or (iv) increase in the activity of antioxidant enzymes (and/or the levels of their mRNAs) during hypometabolic states associated with anoxia/hypoxia. This enhancement of the antioxidant system - coined over a decade ago as "preparation for oxidative stress" - controls the possible harmful effects of increased ROS formation during hypoxia/reoxygenation. The present article proposes a novel explanation for the biochemical and molecular mechanisms involved in this phenomenon that could be triggered by hypoxia-induced ROS formation. We also discuss the connections among oxygen sensing, oxidative damage and regulation of the endogenous antioxidant defense apparatus in animals adapted to many natural or man-made challenges of the aquatic environment.

The air-breathing striped snakehead Channa striata is an important fish in Asian aquaculture with high market value. C. striata is typically cultured in simple mud ponds, where it is frequently exposed to severe hypoxia throughout the growth cycle. Here, the partitioning of oxygen uptake during digestion, and the size of the postprandial metabolism (specific dynamic action or SDA), were studied in hypoxic and normoxic snakehead (30 and 150 mm Hg, respectively). The ventilatory response to hypoxia was investigated separately. When fish were fed 5% of their body mass as fish fillet, total MO 2 increased to 2–2.5 times above the standard metabolic rate. Peak MO 2 was significantly lower in hypoxic fish (253 mg O 2 kg − 1 h − 1 ) compared to normoxic fish (322 mg O 2 kg − 1 h − 1 ), and the total SDA was also significantly lower in hypoxia. These results show that despite C. striata being an air-breather, the limited aquatic respiration in severe hypoxia impairs its general performance during digestion. These results have implications for the aquaculture practices of C. striata , and probably other species within this genus, because increased oxygen availability in the water would be expected to increase their digestion efficiency. Further studies are needed to understand the underlying mechanisms, and to determine optimal aeration in these aquaculture ponds.

We tested the hypothesis that CO2 supersaturation along the aquatic conduit over Sweden can be explained by processes other than aquatic respiration. A first generalized-additive model (GAM) analys ...

Successful overwintering under ice by an air-breathing vertebrate requires either effective aquatic respiration if dissolved O(2) is available or the capacity for prolonged anaerobic metabolism if O(2) supplies are limiting. Frogs can remain aerobic for many weeks when submerged at low temperature, even at water PO(2) as low as 30 mmHg, but are unable to survive even 1 week in anoxic water. Fuel reserves of hibernating frogs limit aerobic submergence, whereas acidosis may limit anoxic submergence. Freshwater turtles can also satisfy all or most of their O(2) needs in well-aerated water at low temperature by aquatic respiration, but certain species, in particular painted and snapping turtles, can also survive for up to 4-5 months without O(2). Key adaptations of the painted turtles, and presumably snapping turtles, include metabolic depression and the exploitation of the shell and other bones to buffer lactic acid. As in frogs, glycogen and glucose are the only fuel sources during anoxia, and stores do not seem to be limiting in the painted turtle. Significant differences in anoxia tolerance exist among chelonian species that can be attributed, at least in part, to the magnitude of metabolic depression, the effectiveness of lactic acid buffering, and the size of glycogen stores.

The ability of freshwater turtles to exchange respiratory gases with their aquatic environment is well known and facilitates prolonged dive durations among several species. Three main sites have been implicated in aquatic respiration (skin, cloaca and buccopharynx) yet the relative contribution of each to total aquatic O2 uptake has been poorly examined among Australian chelids. In this study we investigated the diving physiology of Elseya albagula, a bimodally respiring turtle from Queensland, Australia. Through partitioning experiments we tested the hypothesis that the cloacal bursae are the main site of aquatic O2 uptake in this species. Aquatic oxygen uptake accounted for 70 ± 8% of total oxygen requirements demonstrating the impressive ability of the species to respire underwater, although this was negatively correlated with body mass. Further, the cloacal bursae were found to account for 48% of total aquatic oxygen uptake, providing strong evidence that they are the primary site of aquatic respiration in E albagula.

River impoundments are characterized by low oxygen levels as a result of reduced water velocity and increased water depth. Bimodally respiring turtle species are likely to be highly sensitive to changes in aquatic PO(2) with decreases in oxygen levels impacting upon their diving ability. The acute and long-term effects of aquatic hypoxia on dive duration, oxygen consumption and blood respiratory properties were examined in hatchlings of the endangered Mary River turtle Elusor macrurus. It was hypothesized that acute exposure to aquatic hypoxia would cause a decrease in dive duration as a consequence of a decrease in reliance on aquatic respiration. With long-term exposure to hypoxia, we predicted that Elu. macrurus would have the capacity to compensate for the acute effect of hypoxia and that dive duration would increase due to an increase in aquatic respiration, haemoglobin concentration and oxygen affinity (P(50)). When exposed to hypoxic conditions, aquatic respiration in Elu. macrurus was substantially reduced resulting in a 51% decrease in dive duration. Contrary to our predictions, Elu. macrurus hatchlings did not acclimate, and long-term exposure to hypoxic conditions caused Elu. macrurus to lose significantly more oxygen to the hypoxic water than the normoxic acclimated turtles. The exacerbation of long-term hypoxia on the respiratory physiology and diving ecology of Elu. macrurus raises concerns about the impacts of long-term environmental change as a result of habitat alteration on the survival of freshwater turtle populations.

Certain plastic morphological responses of animals induced across a range of environmental conditions may be adapted for effective locomotor performance. Larvae of the salamander, Hynobius retardatus, occasionally swim upward to the surface to breathe air because aquatic respiration alone is insufficient to meet their increasing respiratory requirements for growth. We hypothesized that H. retardatus larvae living in deep water would show an induced plastic response affecting locomotor structures, namely, a deeper tail, similar to that induced by predatory dragonfly larvae (Aeschna juncea), to improve their swimming performance. In this study, larval salamanders responded similarly to different cues (waterborne chemicals in a predatory environment and distance to the water's surface) by developing deeper tails. The similar modifications in tail shape presumably increase a larva's swimming performance, thereby improving its ability both to escape an attacking predator and to swim to the surface for air. The response in tail shape induced by the predatory environment was rapid, but was more gradual in larvae raised in deep water, suggesting that animals may quickly assess a dangerous environment and immediately respond, whereas assessment of an environment not requiring an immediate response for survival may be slower, accounting for the delayed response.

We apply a cost-benefit model to investigate whether bimodal turtles change their diving behaviour in response to changing energetic costs of aerial vs. aquatic respiration. This question is significant both in the context of the evolution of specialized respiratory structures in bimodal turtles, and the ecological role of respiratory partitioning. Elseya albagula is a bimodally respiring turtle that can extract oxygen from water via specialized cloacal bursae and can vary its reliance on aquatic respiration. We examined the effect of water depth, velocity and temperature on the surfacing frequency of E. albagula through analysis of submergence durations (dive length). We applied a model of resource gain maximization to predict that as the cost of surfacing increases there will be longer dives made possible by the increased reliance on aquatic respiration. Diving behaviour of juvenile turtles was recorded in a large observation tank at varying water depths (50, 100 and 150 cm) and temperatures (20, 25 and 30 °C). Diving behaviour of adult turtles was also monitored in a flume at water velocities of 5, 15 and 30 cm s−1. Dive length significantly increased with water depth, with dives at 150 cm twofold longer than dives at 50 cm. Dive length was also significantly influenced by temperature, with shorter dives at 30 °C than at 20 °C. In contrast, water velocity had no effect on dive length or on the proportion of a trial adult E. albagula spent using a velocity refuge. Juvenile E. albagula possess the flexibility to adjust dive length in response to changes in water depth and temperature in a manner we would expect if energy use were being optimized. We advance the proposition that the driving force for the evolution of specialized aquatic gas exchange structures in E. albagula is the reduced cost of transport to and from the surface.

Australia has a number of bimodally respiring freshwater turtle species that use aquatic respiration to extend their aerobic dive limit. While species variations in reliance on aquatic respiration are reflected in the diving behaviour and ecology of adults, it is unknown whether these relationships also occur in hatchling and juvenile turtles. This study compared the diving behaviour, aquatic respiration and blood respiratory properties of hatchling and juveniles from five species of Australian freshwater turtles: Rheodytes leukops, Elusor macrurus, Elseya albagula, Elseya latisternum and Emydura signata. Both diving behaviour and physiology differed significantly between species as well as age classes. Dive duration in R. leukops was 17 times longer than the other species, with two hatchlings remaining submerged for the entire 72 h recording period. The long dive duration recorded for R. leukops was supported by a high reliance on aquatic respiration (63–73%) and high blood oxygen affinity (P50=17.24 mmHg). A correlation between dive duration, aquatic respiration and blood respiratory properties was not observed in the remaining turtle species where, despite the longer dive duration of Els. albagula and Elu. macrurus compared with Em. signata and Els. latisternum, there was no difference observed in per cent aquatic respiration or blood oxygen affinity between these species. When compared with adult individuals (data from previous studies), dive duration was positively correlated with body size in Em. signata, Els. albagula and R. leukops, but a negative relationship occurred in Els. latisternum and Elu. macrurus.

Locomotion is a common measure of performance used in studies of thermal acclimation because of its correlation with predator escape and prey capture. However, for sedentary animals such as freshwater turtles, we propose that diving behavior may be a more ecologically relevant measure of performance. Increasing dive duration in hatchling turtles reduces predator exposure and therefore functions as an ecological benefit. Diving behavior is thermally dependent, and in some species of freshwater turtles, it is also reliant on aquatic respiration. This study examined the influence of thermal acclimation on diving behavior, aquatic respiration, and locomotor performance in the endangered, bimodally respiring Mary River turtle Elusor macrurus. Diving behavior was found to partially acclimate at 17 degrees C, with turtles acclimated to a cold temperature (17 degrees C) having a significantly longer dive duration than hatchlings acclimated to a warm temperature (28 degrees C). This increase in dive duration at 17 degrees C was not a result of physiological alterations in metabolic rate but was due instead to an increase in aquatic oxygen consumption. Increasing aquatic oxygen consumption permitted cold-acclimated hatchlings to remain submerged for significantly longer periods, with one turtle undertaking a dive of over 2.5 d. When burst-swimming speed was used as the measure of performance, thermal acclimation was not detected. Overall, E. macrurus demonstrated a partial ability to acclimate to changes in environmental temperature.

Cutaneous gas exchange allows some air-breathing diving ectotherms to supplement their pulmonary oxygen uptake, which may allow prolongation of dives and an increased capacity to withstand anthropogenic and natural threatening processes that increase submergence times. However, little is known of the interplay between metabolism, bimodal oxygen uptake and activity levels across thermal environments in diving ectotherms. Here, we show in two species of sea snake (spine-bellied sea snake; Hydrophis curtus and elegant sea snake; H. elegans) that increasing temperature elevates surfacing rates, increases total oxygen consumption, and decreases dive durations. The majority of dives observed in both species remained within estimated maximal aerobic limits. While cutaneous gas exchange accounted for a substantial proportion of total oxygen consumption (up to 23%), unexpectedly it was independent of water temperature and activity levels, suggesting a diffusion-limited mechanism. Our findings demonstrate that rising water temperature and a limited capability to up-regulate cutaneous oxygen uptake may compromise the proficiency with which sea snakes perform prolonged dives. This may hinder their capacity to withstand ongoing anthropogenic activities like trawl fishing, and increase their susceptibility to surface predation as their natural environments continue to warm.

We investigated whether rates of net primary production (NPP) and biomass turnover of floating grasses in a central Amazon floodplain lake (Lake Calado) are consistent with published evidence that CO2 emissions from Amazon rivers and floodplains are largely supplied by carbon from C4 plants. Ground-based measurements of species composition, plant growth rates, plant densities, and areal biomass were combined with low altitude videography to estimate community NPP and compare expected versus observed biomass at monthly intervals during the aquatic growth phase (January–August). Principal species at the site were Oryza perennis (a C3 grass), Echinochloa polystachya, and Paspalum repens (both C4 grasses). Monthly mean daily NPP of the mixed species community varied from 50 to 96 g dry mass m−2 day−1, with a seasonal average (±1SD) of 64±12 g dry mass m−2 day−1. Mean daily NPP (±1SE) for P. repens and E. polystachya was 77±3 and 34±2 g dry mass m−2 day−1, respectively. Monthly loss rates of combined above- and below-water biomass ranged from 31% to 75%, and averaged 49%. Organic carbon losses from aquatic grasses ranged from 30 to 34 g C m−2 day−1 from February to August. A regional extrapolation indicated that respiration of this carbon potentially accounts for about half (46%) of annual CO2 emissions from surface waters in the central Amazon, or about 44% of gaseous carbon emissions, if methane flux is included.

(1) Interactions between temperature and hypoxia in ectothermic tetrapods (reptiles and amphibians) are reviewed. (2) At temperature extremes, mismatches between oxygen demand and oxygen supply can lead to hypoxemia. Thresholds for both physiological and behavioral responses to hypoxia are elevated at high temperature and aerobic scope is reduced at both high and low temperature. (3) Environmental hypoxia is uncommon for most species in air, and for those living at altitude or in burrows, low metabolic rates and relatively low temperature probably prevents hypoxia from being a major problem. (4) For aquatic species, increasing temperature decreases both the aerobic dive limit and the relative importance of aquatic gas exchange to oxygen supply. (5) Tolerance to anoxic submergence is drastically reduced by increased temperature.

Fish respiration rates that are presumed to represent standard metabolic rates (SMR) may sometimes include an unspecified energy expenditure associated with activity and digestion. This situation may introduce a bias in bioenergetics models because standard metabolism, digestion, and activity may not be affected by the same environmental conditions. The aim of this study was to (1) develop a SMR model for juvenile yellow perch, Perca flavescens (Mitchill), that represent the minimum energy expenditure required to maintain life and (2) compare the results of this study with published perch metabolic rates and bioenergetics models. SMR was estimated for yellow perch over a range of body␣mass (4.4–24.7 g) and water temperature (12–20°C). The intercept of the relationship between fish respiration and swimming velocity obtained during forced swimming experiments was used to determine SMR. SMR estimated by the present study were comparable to values presented by two published studies on Eurasian perch, Perca fluviatilis L. However, estimated SMR were 4.1–20.9 times lower than values of a third respirometry study and predictions of bioenergetics models for perch. The present study suggests that published SMR models may sometimes include a significant fraction of energy expenditures (39.2–75.9%) associated with digestion and activity. This may complicate the implementation and the interpretation of fish bioenergetics models. The present study indicates that the intercept of respiration-velocity relationships and long-term respiration rates during starvation experiments may provide similar and reliable SMR values.

Trichoptera, or caddisflies, are an order of aquatic insects occurring around the world in rivers, streams, and lakes. About 15,000 species are known. The aquatic larvae use silk to construct cases in which they reside or to spin silken nets to capture food suspended in the water column. The adults, with the body and wings covered with fine hairs, are crepuscular and resemble small moths. Larvae are important components of aquatic food webs. Most are intolerant of pollution and serve as biological indicators of water quality. This chapter provides an overview of the geographical, morphological, and ecological diversity of caddisflies. Aquatic respiration, osmoregulation, diapause, and other physiological adaptations are reviewed. The literature on general aspects of life history, ecology and behavior, such as adult emergence, mating behavior, egg laying, predation, construction behavior, food and feeding, drift, and production is reviewed. The effect of climate change and other human impacts on the diversity and distribution of caddisflies is discussed. Finally, methods for collecting, preparing, and observing immature stages and adults for scientific study are presented.

Time-depth recorders were used to investigate the diving performance and behaviour of two bimodally respiring turtle species, Rheodytes leukops and Emydura niacquarii, known to have a high and low reliance on aquatic respiration, respectively. Significant differences in diving performance between R. leukops and E. macquarii were observed in the number of dives/day (39.3 +/- 5.38 vs 112.2 +/- 11.73 dives/day; mean +/- SE), mean dive length (33.1 +/- 7.33 min vs 9.6 +/- 2.26 min) and maximum dive length (623 +/- 104.74 min vs 67.1 +/- 8.14 min), respectively. Differences in diving performance between R. leukops and E macquarii are attributed to the species' reliance (or lack thereof) upon aquatic respiration. Rheodytes leukops displayed a weak bimodal pattern of increased surfacing frequency in the early morning (05:00-07:00) and late afternoon (14:00-18:00), while E. macquarii displayed a strong bimodal pattern of elevated surfacing frequency over similar time periods. Daily patterns of increased surfacing frequency for both species failed to correlate with fluctuating aquatic Po-2 levels or water temperature, and may instead be explained by the heightened activity levels of both species during twilight.

Physiological, anatomical and behavioural adaptations enable the Australian desert goby, Chlamydogobius eremius, to live in mound springs and temporary aquatic habitats surrounding the south-eastern rim of the Lake Eyre drainage basin in the harsh inland of Australia. This study describes the desert goby's respiratory and metabolic responses to hypoxic conditions and its use of buccal air bubbles for gas exchange at the water surface. Oxygen consumption for C. eremius is significantly higher in water than in air under normoxic and hypoxic conditions. In water, total oxygen consumption (V(O(2))) increases from normoxic conditions (253 microl g(-1) h(-1)) to 8% ambient O(2) concentration (377 microl g(-1) h(-1)), then decreases with increasing hypoxia of 4% O(2) (226 microl g(-1) h(-1)) and at 2% O(2) (123 microl g(-1) h(-1)). In air (fish were moist but out of water), V(O(2)) progressively decreases from normoxic conditions to hypoxic conditions (21% O(2), V(O(2)) is 169 microl g(-1) h(-1) to 39 microl g(-1) h(-1) at 2% O(2)). These data indicate oxygen-conforming patterns with increasing hypoxia both in air and in water below 8% O(2). In water, opercular movement rates remain unchanged with increasing hypoxia (139 min(-1) at 21% O(2), 154 min(-1) at 8%, 156 min(-1) at 4% and 167 min(-1) at 2%) but in air, opercular movement rates are significantly lower than in water, corresponding with the lower metabolic rate (71 min(-1) at 21% O(2), 53 min(-1) at 8%, 96 min(-1) at 4% and 64 min(-1) at 2%). Chlamydogobius eremius can use a buccal air bubble for aerial O(2) uptake, most probably in response to increased aquatic hypoxia. In air, C. eremius relies more on the buccal bubble as an oxygen source with increasing hypoxia up to an ambient O(2) of 4% (7.1% of V(O(2)) at 21% O(2); 14.5% at 8% O(2); and 27.1% at 4% O(2)), then when the available supply of O(2) is further reduced, it decreases (15% of V(O(2)) at 2% O(2)) and respiration across the skin again makes a higher relative contribution. The Australian desert goby has a higher metabolic rate in higher salinities (336 microl g(-1) h(-1) in 35 ppt, 426 microl g(-1) h(-1) in 70 ppt) than in freshwater (235 microl O(2) g(-1) h(-1)), presumably because of the increased metabolic cost of osmoregulation. There was no significant difference in V(O(2)) for fish in air that had come from varying salinities.

Aquatic byrrhoid beetles are among the most aquatic of beetles. After terrestrial pupation and a brief dispersal flight, the adults enter the water, usually never to leave it again. Aquatic respiration is accomplished using a plastron, or dense network of setae, that retains a bubble. While the plastron functions well for aquatic respiration in flowing water, it does not function well in still water and, for some unknown reason adults that are removed from water often die quickly. Even when shortly returned to water, they commonly die within an hour (unpublished data; White 1978). As currently known, the genus Postelichus is composed of six described and one undescribed species. Its range extends from the southwestern United States of America through Mexico. It is typically a desert inhabitant and can be the dominant macroinvertebrate in desert streams, often with remarkably high numbers. As with many others who study aquatic byrrhoids I have assumed that all species needed permanent water, and likewise that finding them in a stream is an indicator of the stream’s permanence. However, some cases have argued against the need for constant water (Brown 1987). While working in Arizona in July 2007, with Doug Post, another aquatic beetle specialist, I discovered another such case. The location was: Arizona: Yavapai Co.; Bloody Basin; Tangle Creek (34u08.7669 N, 111u47.7759 W). When we first drove to Tangle Creek it was dried up as far as we could see except for one pool in the shade of a tree. Finding aquatic byrrhoids absent in the

This study quantified the air-breathing frequency (ABf in breaths h−1) and gill ventilation frequency (Vf in ventilations min−1) of tarpon Megalops atlanticusas a function of PO2, temperature, pH, and sulphide concentration. Ten tarpon held at normoxia at 22–33°C without access to atmospheric oxygen survived for eight days, and seven survived for 14 days (at which point the experiment was terminated) suggesting that the species is a facultative, rather than an obligate, air breather. At temperatures of 29°C and below ABf was highest and Vf was lowest at low oxygen partial pressures. Tarpon appear to switch from aquatic respiration to air breathing at PO2levels of roughly 40 torr. The gills were the primary organ for oxygen uptake in normoxia, and the air-breathing organ the primary mechanism for oxygen uptake in hypoxia. At 33°C, both ABf and Vf were elevated but highly variable, regardless of PO2. There were no mortalities in tarpon exposed to total H2S concentrations of 0–232 µM (0–150.9 µM H2S); however, high sulfide concentrations resulted in very high ABf and Vf near zero. Vf was reduced when pH was acidic. We conclude that air breathing provides an effective means of coping with the environmental conditions that characterize the eutrophic ponds and sloughs that juvenile tarpon typically inhabit.

Common map turtles (Graptemys geographica) were collected from a natural underwater hibernaculum in Vermont at monthly intervals during the winter of 1997-1998. Blood was sampled by cardiac puncture and analyzed for pH, PCO(2), PO(2), and hematocrit; separated plasma was tested for Na(+), K(+), Cl(-), total [Ca], total [Mg], [lactate], and osmolality (mOsm kg(-1) H(2)O). Control (eupneic; 1 degrees C) values for pH, PO(2), PCO(2), [HCO(3)(-)], and [lactate] were 7.98 +/- 0.03, 47.4 +/- 18.7, 10.1 +/- 0.7 (mm Hg), 36.1 +/- 0.2 (mmol liter(-1)), and 2.1 +/- 0.1 (mmol liter(-1)), respectively. Between November 1997 and March 1998, ice covered the river and the turtles rested on the substratum, fully exposed to the water, and were apneic. Blood PO(2) was maintained at less than 3 mm Hg (range 0.9 +/- 0.2 to 2.1 +/- 0.7 mm Hg), PCO(2) decreased slightly, plasma [lactate] was

We determined aerial and aquatic oxygen uptake rates (M · o2) of Periophthalmodon schlosseri at rest and after exhaustive exercise at 30°C. Resting M · o2 in air (3.16 ± 0.10 (SE) μmol/ g/hr) was significantly higher than that in air saturated water (2.41 ± 0.06 μmol/g/hr). When the fish was placed in air after 2 min exhaustive exercise, M · o2 immediately increased about 2.5 times, thereby repaying oxygen debt of 5.0 μmol/g. In contrast, M · o2 failed to show any significant eleva- tion from the resting level as long as the fish was confined in water after exercise. However, when the fish was subsequently emerged, M · o2 did increase above the resting level, amounting to an excess oxygen uptake of 5.5 μmol/g. These results demonstrated that the gas transport system of P. schlosseri is better adapted to air breathing and the mode of adaptation limited the capability for water breathing. J. Exp. Zool. 284:265-270, 1999. © 1999 Wiley-Liss, Inc. Mudskippers are amphibious euryhaline fishes inhabiting intertidal mudflats of the Indo-west Pacific and tropical west Africa (Murdy, '89). Al- though these fishes differ in microhabitat, behav- ior, and feeding habits, all of them are more or less adapted to life out of water, and this remark- able ability of leading terrestrial life has been the subject of many studies (for review, see Clayton, '93; Graham, '97). Mudskippers have no specific air-breathing organ, relying instead on the skin, the gills and the buccopharyngeal mucosae. Their gills show different degrees of adaptation for aerial respiration. Periophthalmodon schlosseri is one of the larg- est mudskippers in the world, native to the South- east Asian countries. The fish is highly terrestrial, which has been attested both anatomically and physiologically. The gills of P. schlosseri have branched gill filaments, thick gill rods, and fused secondary lamellae, all indicating that the fish is poorly adapted for aquatic respiration (Low et al., '88, '90). Moreover, Kok et al. ('98) recently re- ported that resting oxygen uptake rates of P. schlosseri increased significantly upon terrestrial exposure. It has been considered that an indication of a species' capability for air breathing can be gained from comparison of the resting oxygen uptake rates in air and in water (Graham, '76). However, capabilities for air and water breathing may be better evaluated by comparing maximum M · o2 which a gas transport system of a species can at

Many intertidal fishes, particularly among the Blenniidae and Cottidae, possess amphibious adaptations, including the ability to breathe in air and to avoid desiccation in terrestrial conditions. These traits are absent in subtidal species of blennies and cottids. Hypsoblennius gilberti, the rockpool blenny, is found in shallow rockpools in the mid to high intertidal areas of Southern California, and deeper to 18 m in the subtidal zone. This broad vertical distribution could indicate that this blenny is adapted for tidal air emergence, although H. gilberti has not been observed out of water in its natural habitat. H. gilberti does not emerge voluntarily from hypoxic sea water in the laboratory, but it easily withstands 3 h out of water. The aerial respiratory exchange ratio (CO2 released compared to O2 consumed) is 0.70, similar to that of amphibious intertidal fishes in air, indicating sufficient release of metabolically produced CO2 while emerged. There is no increase in aquatic respiration following emergence. However, unlike other amphibious fishes that maintain aerial oxygen consumption at a level similar to aquatic oxygen consumption, H. gilberti has an aerial oxygen consumption rate one-third that in water. H. gilberti can recover rapidly from terrestrial water loss, and shows no change in evaporative water loss rates at 93% and 77% relative humidities. The amphibious capabilities in H. gilberti, even if rarely used, permit survival in air during tidal emergence. These findings suggest that H. gilberti may demonstrate an intermediate condition between the amphibious species of intertidal fishes that regularly emerge from water, and the subtidal fishes that do not survive air emergence and are completely restricted to an aquatic habitat.

Understanding the response mechanisms of litter respiration to soil moisture in water-limited semi-arid regions is of vital importance to better understanding the interplay between ecological processes and the local carbon cycle. In situ soil respiration was monitored during 2010-2012 under various conditions (normal litter, no litter, and double litter treatments) in a 30-year-old artificial black locust plantation (Robinia pseudoacacia L.) on the Loess Plateau. Litter respiration with normal and double litter treatments exhibited similar seasonal variation, with the maximum value obtained in summer (0.57 and 1.51 μmol m-2 s-1 under normal and double litter conditions, respectively) and the minimum in spring (0.27 and 0.69 μmol m-2 s-1 under normal and double litter conditions, respectively). On average, annual cumulative litter respiration was 115 and 300 g C m-2 y-1 under normal and double litter conditions, respectively. Using a soil temperature of 17°C as the critical point, the relationship between litter respiration and soil moisture was found to follow quadratic functions well, whereas the determination coefficient was much greater at high soil temperature than at low soil temperature (33-35% vs. 22-24%). Litter respiration was significantly higher in 2010 and 2012 than in 2011 under both normal litter (132-165 g C m-2 y-1 vs. 48 g C m-2 y-1) and double litter (389-418 g C m-2 y-1 vs. 93 g C m-2 y-1) conditions. Such significant interannual variations were largely ascribed to the differences in summer rainfall. Our study demonstrates that, apart from soil temperature, moisture also has significant influence on litter respiration in semi-arid regions.

Ucides cordatus is an abundant mangrove crab in Brazil constructing burrows of up to 2 m depth. Sediment around burrows may oxidize during low tides. This increase in sediment-air contact area may enhance carbon degradation processes. We hypothesized that 1) the sediment CO2 efflux rate is greater with burrows than without and 2) the reduction potential in radial profiles in the sediment surrounding the burrows decreases gradually, until approximating non-bioturbated conditions. Sampling was conducted during the North Brazilian wet season at neap tides. CO2 efflux rates of inhabited burrows and plain sediment were measured with a CO2/H2O gas analyzer connected to a respiration chamber. Sediment redox potential, pH and temperature were measured in the sediment surrounding the burrows at horizontal distances of 2, 5, 8 and 15 cm at four sediment depths (1, 10, 30 and 50 cm) and rH values were calculated. Sediment cores (50 cm length) were taken to measure the same parameters for plain sediment. CO2 efflux rates of plain sediment and individual crab burrows with entrance diameters of 7 cm were 0.7–1.3 µmol m−2s−1 and 0.2–0.4 µmol burrows−1s−1, respectively. CO2 released from a Rhizophora mangle dominated forest with an average of 1.7 U. cordatus burrows−1m−2 yielded 1.0–1.7 µmol m−2s−1, depending on the month and burrow entrance diameter. Laboratory experiments revealed that 20–60% of the CO2 released by burrows originated from crab respiration. Temporal changes in the reduction potential in the sediment surrounding the burrows did not influence the CO2 release from burrows. More oxidized conditions of plain sediment over time may explain the increase in CO2 release until the end of the wet season. CO2 released by U. cordatus and their burrows may be a significant pathway of CO2 export from mangrove sediments and should be considered in mangrove carbon budget estimates.

The Alaska blackfish (Dallia pectoralis) is an air-breathing fish native to Alaska and the Bering Sea islands, where it inhabits lakes that are ice-covered in the winter, but enters warm and hypoxic waters in the summer to forage and reproduce. To understand the respiratory physiology of this species under these conditions and the selective pressures that maintain the ability to breathe air, we acclimated fish to 5°C and 15°C and used respirometry to measure: standard oxygen uptake (Ṁ(O₂)) in normoxia (19.8 kPa P(O₂)) and hypoxia (2.5 kPa), with and without access to air; partitioning of standard Ṁ(O₂) in normoxia and hypoxia; maximum Ṁ(O₂) and partitioning after exercise; and critical oxygen tension (P(crit)). Additionally, the effects of temperature acclimation on haematocrit, haemoglobin oxygen affinity and gill morphology were assessed. Standard Ṁ(O₂) was higher, but air breathing was not increased, at 15°C or after exercise at both temperatures. Fish acclimated to 5°C or 15°C increased air breathing to compensate and fully maintain standard Ṁ(O₂) in hypoxia. Fish were able to maintain Ṁ(O₂) through aquatic respiration when air was denied in normoxia, but when air was denied in hypoxia, standard Ṁ(O₂) was reduced by ∼30-50%. P(crit) was relatively high (5 kPa) and there were no differences in P(crit), gill morphology, haematocrit or haemoglobin oxygen affinity at the two temperatures. Therefore, Alaska blackfish depends on air breathing in hypoxia and additional mechanisms must thus be utilised to survive hypoxic submergence during the winter, such as hypoxia-induced enhancement in the capacities for carrying and binding blood oxygen, behavioural avoidance of hypoxia and suppression of metabolic rate.

Soil respiration (R S) represents a large terrestrial source of CO2 to the atmosphere. Global change drivers such as climate warming and nitrogen deposition are expected to alter the terrestrial carbon cycle with likely consequences for R S and its components, autotrophic (R A) and heterotrophic respiration (R H). Here we investigate the impacts of a 3°C soil warming treatment and a 50 kg ha−1 y−1 nitrogen addition treatment on R S, R H and their respective seasonal temperature responses in an experimental tussock grassland. Average respiration in untreated soils was 0.96±0.09 μmol m−2 s−1 over the course of the experiment. Soil warming and nitrogen addition increased R S by 41% and 12% respectively. These treatment effects were additive under combined warming and nitrogen addition. Warming increased R H by 37% while nitrogen addition had no effect. Warming and nitrogen addition affected the seasonal temperature response of R S by increasing the basal rate of respiration (R 10) by 14% and 20% respectively. There was no significant interaction between treatments for R 10. The treatments had no impact on activation energy (E 0). The seasonal temperature response of R H was not affected by either warming or nitrogen addition. These results suggest that the additional CO2 emissions from New Zealand tussock grassland soils as a result of warming-enhanced R S constitute a potential positive feedback to rising atmospheric CO2 concentration.

International audience; Intertidal rocky shores are characterized by vertical zonation that results from the interplay between environmental conditions, organism physiology, and species interactions. Metabolism of intertidal organisms is highly variable between species and it changes with vertical position along the intertidal gradient. The present study aimed to quantify the carbon metabolism of nine intertidal rocky shore gastropods, in order to clarify their respective roles in carbon production during emersion and immersion. The influences of monthly temperature variation and tidal level were tested for each species. Analyses were performed in the laboratory using the infrared gas analyzer method for measuring aerial respiration rates, and the dissolved inorganic carbon and total alkalinity technique for measuring aquatic respiration rate and calcification. Hourly carbon fluxes were calculated for the mean annual temperature of 13 °C measured in both air and underwater in the study area. Respiration rates were similar for emersion (8-25 μmol CO2 g AFDW−1 h−1) and immersion (10-23 μmol DIC g AFDW−1 h−1). For all species, underwater respiration fluxes were more influenced by monthly temperature variation than by air fluxes, probably as an adaptation to the rapid changes occurring during emersion. Calcification was an important factor influencing annual carbon fluxes for all studied species; every species showed different calcification rates according to its size and position on the intertidal zone. Annual carbon emissions were calculated using the mean immersion/emersion time of each species. Intertidal gastropod carbon emission was primarily influenced by body biomass and their vertical position within the intertidal zone.

We describe a model predicting the effects of low environmental oxygen on vital rates (egg production, somatic growth, and mortality) of the coastal planktonic copepod Acartia tonsa. Hypoxic conditions can result in respiration rate being directly limited by oxygen availability. We hypothesized that A. tonsa egg production, somatic growth, and ingestion rates would all respond in a similar manner to low oxygen conditions, as a result of oxygen dependent changes in respiration rate. Rate data for A. tonsa egg production, somatic growth, and ingestion under low environmental oxygen were compiled from the literature and from supplementary experiments. The response of these rates to oxygen was compared by converting all to the analogous units in terms of oxygen utilization, which we termed analogous respiration rate. These analogous respiration rates, along with published measurements of respiration rates, were used to parameterize and evaluate the relationship between A. tonsa respiration rate and environmental oxygen. At 18 °C, our results suggest that A. tonsa experiences sub-lethal effects of hypoxia below an oxygen partial pressure of 8.1 kPa (~3.1 mg L(-1) = 2.3 mL L(-1)). The results of this study can be used to predict the effects of hypoxia on A. tonsa growth and mortality as related to environmental temperature and oxygen partial pressure. Such predictions will be useful as a way to incorporate the effects of coastal hypoxia into population, community, or ecosystem level models that include A. tonsa. This approach can also be used to characterize the effects of hypoxia on other aquatic organisms.

Aerial and aquatic VO2 measurements of Acanthoclinus fuscus and Forsterygion sp. showed that A. fuscus weighing up to 25 g obtained oxygen from air and water at similar rates, whereas the ratio of aerial to aquatic VO2 for F. sp. was mass dependent. The Q10 for aquatic respiration of A. fuscus and F. sp. was found to be 2.3 and 2.5, respectively. Aerial VO2 measurements showed that A. fuscus could continue to increase its aerial VO2 up to at least 25° C. In contrast the aerial VO2 of F. sp. increased only between 5° C and 15° C and decreased between 20 and 25° C. The Pcrits of both A. fuscus and F. sp. were found to be about 35 torr. Emergence in response to hypoxia occurred between 0 and 16 torr which suggested active emergence was an oxykinetic response and not a behaviour.

The eastern pygmy blue, Brephidium pseudofea (Morrison) (Lepidoptera: Lycaenidae: Polyommatinae), inhabits intertidal environments that are periodically flooded. The immature stages are subject to salt or brackish water inundation during this time and therefore must endure many stressors, including respiratory limitation and salt exposure. Our goal was to investigate possible mechanisms used by the larval stages of B. pseudofea to endure periodic tidal inundation by using physiological and morphological analyses in comparison with several species of terrestrial lepidopteran larvae. A review of tidal charts showed that the immature stages of B. pseudofea would be prone to complete inundation two to five times per month during the summer months (May to August) and partial submersion for up to 20 d per month during the rest of the year. Larvae of several terrestrial lepidopteran species studied consumed oxygen under water for a limited period, but B. pseudofea demonstrated substantially higher oxygen consumption. Light microscopy of B. pseudofea larvae revealed small air pockets in and around the spiracles when submerged in tap water; these air pockets disappeared when exposed to detergent solution. The resulting air pockets may function as a diffusion layer for oxygen to be absorbed from the surrounding water or may act in conjunction with trans-cuticular gas exchange to meet the larva's respiratory needs. Morphological examination by scanning electron microscopy showed that B. psudofea larvae have distinctively small, clavate setae that appear insufficient to effectively support a functional plastron.

The presumption that organisms benefit from thermal acclimation has been widely debated in the literature. The ability to thermally acclimate to offset temperature effects on physiological function is prevalent in ectotherms that are unable to thermoregulate year-round to maintain performance. In this study we examined the physiological and behavioural consequences of long-term exposure to different water temperatures in the aquatic snake Acrochordus arafurae. We hypothesised that long dives would benefit this species by reducing the likelihood of avian predation. To achieve longer dives at high temperatures, we predicted that thermal acclimation of A. arafurae would reduce metabolic rate and increase use of aquatic respiration. Acrochordus arafurae were held at 24 or 32°C for 3 months before dive duration and physiological factors were assessed (at both 24 and 32°C). Although filesnakes demonstrated thermal acclimation of metabolic rate, use of aquatic respiration was thermally independent and did not acclimate. Mean dive duration did not differ between the acclimation groups at either temperature; however, warm-acclimated animals increased maximum and modal dive duration, demonstrating a longer dive duration capacity. Our study established that A. arafurae is capable of thermal acclimation and this confers a benefit to the diving abilities of this snake.

Freshwater turtles have an extraordinary physiological ability to endure dive times that can range from days to months using aquatic respiration. In cryptodires (e.g., white-lipped mud turtle Kinosternon leucostomum) aquatic respiration is via buccal or cutaneous routes whereas in pleurodires (e.g., Fitzroy River turtle Rheodytes leukops), it is achieved primarily via specialized cloacal bursae. This study records the voluntary diving performance of the western sawshelled turtle Myuchelys bellii in Bald Rock Creek from the temperate zone of the Murray-Darling Basin of Australia. Myuchelys bellii has a moderately specialized cloacal bursae morphology compared to other pleurodiran turtles and displays impressive dive durations spanning more than 15 days during the winter months. This is attributed to its ability to maintain aerobic dives via its cloacal bursae and low water temperatures in winter. Myuchelys bellii seasonal and diel diving performance, including its crepuscular habit, is comparable to R. leukops and Elseya albagula. This study also recorded the first aquatic hibernation at depth (>3 m) for any freshwater turtle; and only the second pleurodire to demonstrate aquatic hibernation as an overwintering strategy. Observed thermoregulation behavior in M. bellii is believed to provide multiple life history benefits.

Two techniques for determining community respiration in organically fertilized tilapia grow-out ponds were compared: (1) whole pond respiration (WPR) from changes in nocturnal dissolved oxygen concentrations corrected for diffusion, and (2) the sum of water column (WCR), benthic (BR), and fish respiration (FR), components of community respiration. Mean WPR (0.568 g O2 m−2 h−1) was significantly higher (P

Many fishes in the marine intertidal zone have the ability to exchange respiratory gases in air during brief periods out of water. Previous studies on marine amphibious fishes such as mudskippers and rockskippers have shown that they release CO2 in air at a rate consistent with its release in aquatic respiration. Respiratory Exchange Ratios (RER, CO2 released per O2 consumed) are between 0.7 and 1.0, similar to Respiratory Quotients (CO2 produced metabolically per O2 consumed). However, previous studies of temperate intertidal fishes emerged only at low tides have been less consistent, with two species reported similar in ability to the amphibious skipper fishes, and two others reported with much lower RERs in air. This study examines 12 species of fishes, from six families (Batrachoididae, Cottidae, Gobiesocidae, Kyphosidae, Pholididae, and Stichaeidae), present in the intertidal zone of California. All 12 species exchanged O2 and CO2 in air. Like the amphibious skipper fishes of marine tropical waters, many intertidal fishes of the temperate zone release CO2 during low tide emergence in quantities sufficient to match its metabolic production. These results indicate that CO2 release is not hampered by the change in respiratory medium from water to air.

The invasive Neotropical snail Pomacea canaliculata is usually regarded as amphibious, although the relative significance of aerial and aquatic respiration is unknown. To investigate the degree of dependence on aerial respiration and its influences on microdistribution, experiments were performed in the laboratory and under seminatural and natural conditions. Restriction of aerial respiration negatively affected survivorship, activity and feeding, its effects worsening with temperature and water fouling; females were more seriously affected than males although the effect depended on reproductive effort. Snails were unevenly distributed relative to the access to air, both in a stream and in an outdoor tank, being concentrated less than 2-4 m from the nearest emergent substratum. Accessibility to air would be an important trait of waterbodies prone to invasions of P. canaliculata, especially in tropical areas. The effectiveness of some control measures could be increased by focusing on areas where snails are concentrated due to their dependence on air. © Springer Science+Business Media B.V. 2009. Fil: Seuffert, Maria Emilia. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Bahía Blanca; Argentina. Universidad Nacional del Sur. Departamento de Biología, Bioquímica y Farmacia; Argentina Fil: Martín, Pablo Rafael. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Bahía Blanca; Argentina. Universidad Nacional del Sur. Departamento de Biología, Bioquímica y Farmacia; Argentina