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Aquatic biota often face multiple anthropogenic threats such as river fragmentation and climate change that can contribute to high rates of aquatic species imperilment world-wide. Temperature- induced hypoxia is one under-explored mechanism that can threaten aquatic species in fragmented rivers with reduced flows. We applied ecosystem metabolism models to define the effect of water temperature on net ecosystem production (NEP) of oxygen at 12 sites of a fragmented river channel that supports three fish species at risk and experiences hypoxia. We found that water temperature and precipitation events at 75% of our sites were significantly and negatively correlated to NEP estimates and explained 28% of the variation in NEP within sites. Temperature-induced reductions in NEP at these sites likely contributed to hypoxic conditions threatening the three species at risk as NEP explained 41% of the variation in dissolved oxygen near all sites. Our results have applications for understanding drivers of hypoxic stress in fragmented watercourses, integrating water temperature-NEP effects with oxygen demands of sensitive fish species, and modeling future effects of climate change on aquatic species. Les organismes aquatiques font souvent face a de multiples menaces d'origine humaine telles que la fragmentation des rivieres et les changements climatiques qui peuvent contribuer a accelerer les risques pour les especes aquatiques partout sur terre. L'hypoxie induite par la temperature est un mecanisme sous- explore qui peut menacer les especes aquatiques dans les rivieres fragmentees presentant des debits reduits. Nous utilisons des modeles de metabolisme ecosystemique pour determiner l'effet de la temperature de l'eau sur la production ecosystemique nette (PEN) d'oxygene en 12 sites du chenal d'une riviere fragmentee qui soutient trois especes de poissons en peril et dans laquelle des conditions hypoxiques sont observees. Nous constatons que la temperature de l'eau et les episodes de precipitations dans 75 % des sites etudies presentent des correlations negatives significatives avec la PEN estimee et expliquent 28 % des variations de la PEN a l'interieur des sites. Les baisses de PEN induites par la temperature dans ces sites participent probablement aux conditions hypoxiques qui menacent les trois especes en peril, puisque la PEN explique 41 % des variations des teneurs d'oxygene dissous a proximite de tous les sites. Nos resultats sont importants pour la comprehension des moteurs du stress hypoxique dans les cours d'eau fragmentes, l'integration des effets de la temperature de l'eau sur la PEN aux besoins en oxygene d'especes de poissons sensibles et la modelisation des effets futurs des changements climatiques sur les especes aquatiques. [Traduit par la Redaction], Introduction Ecosystem fragmentation and reduced river flow are widespread anthropogenic impacts that threaten aquatic biodiversity globally. Dynesius and Nilsson (1994) estimated that 77% of the total discharge from large rivers [...]

Alphaproteobacteria of the SAR11 clade form one of the most ecologically dominant organism groups on the planet, representing up to half of the total microbial community in the oxygen-rich surface [...], Bacteria of the SAR11 clade constitute up to one half of all microbial cells in the oxygen-rich surface ocean. SAR11 bacteria are also abundant in oxygen minimum zones (OMZs), where oxygen falls below detection and anaerobic microbes have vital roles in converting bioavailable nitrogen to [N.sub.2] gas. Anaerobic metabolism has not yet been observed in SAR11, and it remains unknown how these bacteria contribute to OMZ biogeochemical cycling. Here, genomic analysis of single cells from the world's largest OMZ revealed previously uncharacterized SAR11 lineages with adaptations for life without oxygen, including genes for respiratory nitrate reductases (Nar). SAR11 nar genes were experimentally verified to encode proteins catalysing the nitrite-producing first step of denitrification and constituted ~40% of OMZ nar transcripts, with transcription peaking in the anoxic zone of maximum nitrate reduction activity. These results link SAR11 to pathways of ocean nitrogen loss, redefining the ecological niche of Earth's most abundant organismal group.

ABSTRACT The seasonal variation and spat recruitment pattern of the scallops Flexopecten glaber and Chlamys varia in the protected aquatic ecosystem of the northwestern Amvrakikos Gulf (Natura, 2000) were examined [...]

Hypoxia and acidification frequently co-occur in coastal marine ecosystems, and will likely become more intense and persistent with anthropogenic climate change. Although the separate effects of these stressors have previously been described, their combined effects on marine phytoplankton are currently unknown. In this novel study, multi-stressor incubation experiments using the harmful dinoflagellate, Amphidinium carterae, examined the effects of acidification and hypoxia both individually and in combination. Long-term (7 days) and short-term (6 h) experiments under controlled carbon dioxide (CO.sub.2) and oxygen (O.sub.2) conditions examined the interactive effects of the stressors and the physiological mechanisms driving their interaction. In the long-term experiment, synergistically negative effects were observed for A. carterae growth, photosynthesis, carbon fixation, nitrate uptake, and photosynthetic efficiency (F.sub.v/F.sub.m) under combined high CO.sub.2 (low pH) and low O.sub.2 conditions. In the short-term experiment, delayed recovery of photosystem II (PSII) reaction centers was observed following photoinhibition, suggesting that high CO.sub.2 and low O.sub.2 conditions negatively affect photosynthesis in A. carterae even after relatively short exposures. Although high CO.sub.2, low O.sub.2 conditions should decrease photorespiration and favor carbon fixation by the key photosynthetic enzyme ribulose-1,5-bisphosphate-carboxylase/oxygenase (RuBisCO), these findings demonstrate that the affinity of RuBisCO for CO.sub.2 relative to O.sub.2 alone does not predict phytoplankton responses to CO.sub.2 and O.sub.2 conditions in vivo, complicating predictions of phytoplankton community responses to hypoxia and acidification. Results of these experiments suggest that the combination of low pH and O.sub.2 concentrations may negatively impact the growth of some harmful dinoflagellates in coastal marine ecosystems., Author(s): Alexandra R. Bausch [sup.1] [sup.2] [sup.3] , Andrew R. Juhl [sup.2] [sup.3] , Natalie A. Donaher [sup.4] , Amanda M. Cockshutt [sup.4] Author Affiliations: (Aff1) 0000000419368956, grid.168010.e, Department of [...]

Zooplankton often migrate vertically to deeper dark water during the day to avoid visual predators such as fish, a process which can strengthen benthic-pelagic coupling. In the Gulf of Finland, Baltic Sea, a pronounced hypoxic layer develops when there is an inflow of anoxic bottom water from the Central Baltic Sea, which could be a barrier for vertical migrants. Here, we report an acoustic study of the distributions of crustacean zooplankton (mysid shrimp and the copepod Limnocalanus macrurus), gelatinous zooplankton (Aurelia aurita) and fish. Zooplankton trawl nets were used to ground-truth acoustic data. Vertical profiles of oxygen concentration were taken, and the physiological impact of hypoxia on mysids was investigated using biochemical assays. We hypothesised that the vertical distribution of zooplankton and fish would be significantly affected by vertical heterogeneity of oxygen concentrations because anoxia and hypoxia are known to affect physiology and swimming behaviour. In addition, we hypothesised that mysids present in areas with hypoxia would exhibit a preparatory antioxidant response, protecting them from oxidative damage during migrations. The acoustic data showed peaks of crustacean zooplankton biomass in hypoxic (75 m), whereas fish shoals and A. aurita medusae were found in normoxic (5-6 mL L.sup.-1) upper water layers (, Author(s): Clare N. Webster[sup.1] [sup.2] , Sture Hansson[sup.3] , Tomas Didrikas[sup.4] , Elena Gorokhova[sup.3] , Heikki Peltonen[sup.5] , Andrew S. Brierley[sup.1] , Maiju Lehtiniemi[sup.5] Author Affiliations: (1) Pelagic Ecology Research [...]

Hypoxia episodes have been generally studied over the last decade for their lethal consequences in coastal areas, which are nurseries for several fish species. The possible long-lasting effects of non-lethal hypoxia exposures at larval stage are, however, poorly documented. We investigated the long-lasting phenotypic impact of an experimental exposure to moderate hypoxia (40% air saturation) between 30 and 38 days post-hatching in European sea bass (Dicentrarchus labrax). At the juvenile stage, our data indicate that this early hypoxia exposure impacted on juvenile growth rate but not on hypoxia tolerance. Growth depression was associated with a regulation of metabolism as suggested by a decrease in blood glycaemia, a decreased hepatic expression of the glucose transporter glut2 and of acaca involved in fatty acid synthesis as well as an increased hepatic expression of glycolytic ldh-a, which is a target gene of hypoxia inducible factors (HIFs). Interestingly, while fish were not exposed to hypoxia, the cellular oxygen sensor egln3 gene, which is also a target of HIFs, exhibited higher expression level in the hepatic tissue of juveniles that have experienced hypoxia at larval stage. Even if further studies are needed to evaluate the functional significance of such effects and to decipher the underlying molecular mechanisms, the present data evidence that early life exposure to a hypoxia event has long-lasting impact on sea bass juvenile physiology., Introduction Over the past 50 years, global warming and anthropogenic activities have greatly influenced coastal marine ecosystems with profound and diverse consequences on water temperature, pH and dissolved oxygen. The [...]

For aquatic breathers, hypoxia and warming can act synergistically causing a mismatch between oxygen supply (reduced by hypoxia) and oxygen demand (increased by warming). The vulnerability of these species to such interactive effects may differ during ontogeny due to differing gas exchange systems. This study examines respiratory responses to temperature and hypoxia across four life-stages of the intertidal porcelain crab Petrolisthes laevigatus. Eggs, megalopae, juveniles and adults were exposed to combinations of temperatures from 6 to 18 °C and oxygen tensions from 2 to 21 kPa. Metabolic rates differed strongly across life-stages which could be partly attributed to differences in body mass. However, eggs exhibited significantly lower metabolic rates than predicted for their body mass. For the other three stages, metabolic rates scaled with a mass exponent of 0.89. Mass scaling exponents were similar across all temperatures, but were significantly influenced by oxygen tension (the highest at 9 and 14 kPa, and the lowest at 2 kPa). Respiratory responses across gradients of oxygen tension were used to calculate the response to hypoxia, whereby eggs, megalopae and juveniles responded as oxyconformers and adults as oxyregulators. The thermal sensitivity of the metabolic rates (Q.sub.10) were dependent on the oxygen tension in megalopae, and also on the interaction between oxygen tension and temperature intervals in adults. Our results thus provide evidence on how the oxygen tension can modulate the mass dependence of metabolic rates and demonstrate changes in respiratory control from eggs to adults. In light of our results indicating that adults show a good capacity for maintaining metabolism independent of oxygen tension, our study highlights the importance of assessing responses to multiple stressors across different life-stages to determine how vulnerability to warming and hypoxia changes during development., Author(s): Félix P. Leiva [sup.1] [sup.2] , Cristóbal Garcés [sup.1] , Wilco C. E. P. Verberk [sup.2] , Macarena Care [sup.1] , Kurt Paschke [sup.3] [sup.4] , Paulina Gebauer [sup.1] [...]

Squat lobster populations found in the Humboldt Current System over the continental shelf from ~ 28 to 37°S release pelagic larvae in sub-surface cold (~ 11°C) hypoxic waters. Larvae subsequently spread throughout the water column encountering both normoxic and hypoxic conditions. We analyzed some short- and long-term responses of Pleuroncodes monodon larval metabolism to hypoxia at 11°C. Routine and postprandial aerobic respiration rates were lower in hypoxia than in normoxia for all zoeal stages. Zoea V oxyconformed, while megalopae oxyregulated down to very low oxygen concentrations. Throughout zoea I development, the rate of nitrogen (protein) accumulation in zoea I was lower, and C:N ratios were higher under hypoxic conditions than in normoxia. Citrate synthase (CS) and malate dehydrogenase (MDH) apparent specific activities (as indicators of aerobic and metabolic potentials, respectively) decreased and remained at the same level, respectively, throughout zoea I reared under hypoxic conditions. Anaerobic to aerobic potential (lactate dehydrogenase (LDH)/CS) was higher in organisms reared under hypoxia, and MDH/LDH potential ratios were characteristic of organisms tolerant to hypoxia. In spite of P. monodon zoea endurance and metabolic adaptations to decreasing oxygen tensions, intense hypoxia as such of their release site would affect their overall condition especially toward the end of the molt cycle. Our results indicate the importance of considering the interaction between environmental oxygen variability and recruitment success., Introduction The presence and spatiotemporal variability of mid-water 'oxygen minimum zones' (OMZs) in the world's oceans shape the pelagic and benthic communities under their influence (Madhu et al. 2003; Gallardo [...]

We evaluated vertical distributions of fish and zooplankton, planktivore consumption, and prey production in Lake Erie during 2005 to determine how hypolimnetic hypoxia alters fish (i.e., rainbow smelt (Osmerus mordax) and emerald shiners (Notropis atherinoides)) and invertebrate planktivore (i.e., Bythotrephes longimanus and Leptodora kindtii) relationships with their mesozooplankton prey. Hypoxia concentrated 45%-76% of fish into a narrow ( Nous avons evalue les repartitions verticales des poissons et du zooplancton, de la consommation par les planctonivores et de la production de proies dans le lac Erie durant l'annee 2005 pour determiner comment l'hypoxie hypolimnique modifie les relations entre des poissons (c.-a-d. l'eperlan (Osmerus mordax) et le mene emeraude (Notropis atherinoides)) et planctonivores invertebres (c.-a-d. Bythotrephes longimanus et Leptodora kindtii) et leurs proies mesozooplanctoniques. L'hypoxie restreignait de 45 % a 76 % des poissons a une mince ( [Traduit par la Redaction], Introduction Seasonal bottom hypoxia ( While one might expect that bottom hypoxia would have little effect on fishes that are not obligate benthivores and are capable of using the entire [...]

Many pteropod species in the eastern tropical North Pacific Ocean migrate vertically each day, transporting organic matter and respiratory carbon below the thermocline. These migrations take species into cold (15-10°C) hypoxic water (, Introduction Regions of low oxygen ([O.sub.2] The distribution of animals interacting with OMZs is complex, with high surface abundance and species-specific patterns of association with low [O.sub.2] waters (Wishner et [...]

In Lake Erie, the duration and extent of hypoxia (dissolved oxygen (DO) ≤ 2 mg x [L.sup.-1]) has increased in recent years, yet little is known on the corresponding impact on its fish, particularly the highly valued walleye (Sander vitreus) fishery. Here, we quantified the impact of hypoxia on walleye habitat quality, using a spatially explicit growth rate potential (GRP) modeling approach, which integrates the spatial arrangement of biological (prey availability) and environmental (DO, temperature, irradiance) measures. Data were collected along two types of transects: 60 km north-south transects (each sampled once during day and night) and 5 km east-west transects (sampled every 4 h for 24 h) during August (pre-hypoxia), September (peak-hypoxia), and October (post-hypoxia) 2005. Overall, the average monthly amount of high quality habitat (GRP > 0 g x [g.sup.-1] x [day.sup.-1]) for walleye declined slightly with hypoxia ( Au lac Erie, la duree et l'importance de l'hypoxie (oxygene dissous (DO) ≤ 2 mg x [L.sup.-1]) ont augmente au cours des dernieres annees; on connait cependant peu l'impact correspondant sur les poissons et, en particulier, sur la peche au dore jaune (Sander vitreus) qui y presente un grand interet. Un modele du potentiel du taux de croissance (GRP) spatialement explicite qui integre l'arrangement spatial des mesures biologiques (disponibilite des proies) et environnementales (DO, temperature, irradiation) nous sert a determiner l'impact de l'hypoxie sur la qualite de l'habitat du dore. Les donnees proviennent de deux types de transects, des transects nord-sud de 60 km (echantillonnes chacun une fois de jour et de nuit) et des transects est-ouest de 5 km (echantillonnes a toutes les 4 heures pendant 24 heures) faits en aout (avant l'hypoxie), en septembre (au faite de l'hypoxie) et en octobre (apres l'hypoxie) en 2005. Globalement, la quantite mensuelle moyenne d'habitats de haute qualite (GRP > 0 g x [g.sup.-1] x [jour.sup.-1]) pour le dore diminue legerement au cours de l'hypoxie ( [Traduit par la Redaction], Introduction Historically, hypoxia (dissolved oxygen (DO) ≤ 2 mg x [L.sup.-1]) has been documented in Lake Erie, especially during summer in the central basin (Rosa and Burns 1987; Bertram 1993). [...]

Size analysis of pyrite framboids has been undertaken on epicontinental Permian--Triassic boundary sections throughout the world in order to evaluate the intensity and duration of anoxia. Mid-paleolatitude sections from the margins of the Boreal (Spitsbergen, Greenland) and Neotethyan oceans (Western Australia) reveal intense anoxia throughout the Permian--Triassic boundary interval with euxinic conditions frequently developing, and dysoxia encountered even in relatively shallow-water settings above storm wave base. At equatorial paleolatitudes, weakly oxygenated (dysoxic) conditions are widely developed in a broad range of water depths including those shallow enough to produce oolite deposition, although euxinia was rare. Western and eastern Tethyan locations reveal a complex and unstable redox history: anoxia in the Hindeodus praeparvus Zone was replaced by oxygenated facies in the Permian--Triassic boundary interval (H. changxingensis to H. parvus zones). Oxygen-poor deposition returned during the succeeding Isarcicella isarcica Zone. The more persistent and intense development of oxygen restriction in cooler water, mid-paleolatitude sections argues against warming and dissolved oxygen decline as the key cause of Permian--Triassic boundary anoxia. In higher paleolatitudes the benthic invertebrate extinctions occurred during a prolonged phase of oxygen-poor deposition, while in equatorial Tethyan locations benthic losses occurred at the end of the first anoxic phase (in the late H. praeparvus Zone). doi: 10.1130/B30042.1

Lakes and reservoirs often experience sudden increases in macrophyte biomass. These changes have the potential to alter the abiotic environment in ways that affect other species. The American lotus (Nelumbo lutea) is expanding its distribution across portions of North America. N. lutea forms a dense canopy over the shallow margins of lakes and may influence the abiotic properties of the littoral zone, but this hypothesis has not been tested. Here we investigate the effects of a growing bed of N. lutea on water quality in Pymatuning Reservoir. In summer 2007 we deployed remote logging sensors to measure dissolved oxygen and temperature inside of a N. lutea bed and in adjacent open water. Dissolved oxygen concentrations were consistently lower in the lotus bed than in open water and oxygen concentrations within the N. lutea bed declined over the course of the summer. In Jul. and Aug. the N. lutea beds experienced hypoxia while oxygen concentrations remained high in open water. Low dissolved oxygen levels in N. lutea beds may affect the distribution of fish and invertebrates and alter biochemical processes in the epibenthos., INTRODUCTION Lakes often experience sudden increases in macrophyte biomass due to colonization or rapid expansion of an invasive species (Jeppesen et al., 1997; Scheffer, 1998; Unmuth et al., 9000). Most [...]

During the Mesozoic greenhouse world, the oceans underwent several oceanic anoxic events (OAEs) characterized by intervals during which organic-rich black shales were deposited, indicating strong oxygen depletion in the marine realm. The Cenomanian-Turonian OAE2 (ca. 93 Ma) represents one of the most prominent events of the Cretaceous, with significant perturbations of the global carbon cycle. Although OAE2 likely reached a global scale, the spatial extent of seawater anoxia during this OAE is poorly constrained. Here we demonstrate that variations in the [sup.238]U/[sup.235]U isotope ratio ([[delta].sup.238]U), a newly developed paleoredox proxy, can be used to quantify the extent of marine anoxia. For black shales from the mid-Cretaceous OAE2 we find a systematic shift toward lighter [[delta].sup.238]U and lower U concentrations as compared to modern equivalent organic-rich sediments from the Black Sea. This shift translates to a global increase of oceanic anoxia during OAE2 by at least a factor of three as compared to the present day or to periods before and after OAE2. The constant offset in U concentrations and isotope compositions of black shales throughout OAE2 compared to modern Black Sea sediments indicates an enhancement of oceanic anoxic conditions already prior to the onset of OAE2. doi: 10.1130/G30652.1

We measured the concentration and the stable isotope ratios of dissolved oxygen in the water column in the Estuary and Gulf of St. Lawrence to determine the relative importance of pelagic and benthic dissolved oxygen respiration to the development of hypoxic deep waters. The progressive landward decrease of dissolved oxygen in the bottom waters along the axis of the Laurentian Channel (LC) is accompanied by an increase in the [sup.18]O : [sup.16]O ratio, as would be expected from O-isotope fractionation associated with bacterial oxygen respiration. The apparent O-isotope effect, [[epsilon].sub.O-app], of 10.8 [per thousand] reveals that community O-isotope fractionation is significantly smaller than if bacterial respiration occurred solely in the water column. Our observation can best be explained by a contribution of benthic [O.sub.2] consumption occurring with a strongly reduced O-isotope effect at the scale of sediment--water exchange ([[epsilon].sub.O-sed] ~ 7 [per thousand]). The value for [[epsilon].sub.O-sed] was estimated from benthic [O.sub.2] exchange simulations using a one-dimensional diffusion-reaction O-isotope model. Adopting this [[epsilon].sub.O-sed] value, and given the observed community O-isotope fractionation, we calculate that approximately two thirds of the ecosystem respiration occurs within the sediment, in reasonable agreement with direct respiration measurements. Based on the difference between dissolved oxygen concentrations in the deep waters of the Lower St. Lawrence Estuary and in the water that enters the LC at Cabot Strait, we estimate an average respiration rate of 5500 mmol [O.sub.2] [m.sup.-2] [yr.sup.-1] for the 100-m--thick layer of bottom water along the LC, 3540 mmol [O.sub.2] [m.sup.-2] [yr.sup.-1] of which is attributed to bacterial benthic respiration.

The Early Cretaceous Ontong Java Plateau was emplaced at almost the same time as marine biotic changes that culminated in oceanic anoxic event 1 (OAE1a). A causative link between these events has been suggested, but direct evidence has been lacking until now. New Os isotope measurements across the Lower Aptian 'Selli Level' black shale deposited during OAE1a in central Italy reveal two negative excursions in marine [sup.187]Os/[sup.188]Os ratios within a period of 2 Ma starting above the Barremian-Aptian boundary and ending just above the Selli Levei horizon, suggesting an order-of-magnitude increase in the global flux of unradiogenic Os. The results are consistent with early and major phases of eruption of the Ontong Java Plateau. The latter phase is estimated to have been as short as ~1 Ma and may have induced widespread oceanic stratification that triggered OAE1a.

The Aptian Oceanic Anoxic Event 1a (OAE1a, ca.120 Ma ago) is one of the most prominent of a series of geologically brief intervals in the Cretaceous characterized by the deposition of organic carbon-rich sediments. OAEs reflect major perturbations in the global carbon cycle evidenced by sedimentary carbon isotope records. However, the triggering mechanisms for OAEs remain controversial. Here we present a bulk-rock and molecular (marine and terrestrial biomarkers) C isotope record at unprecedented time resolution, from the Cismon section of northern Italy, that shows that OAE1a conditions were reached over a period of several thousands of years through a stepwise perturbation of the carbon cycle. The documented sequence of events is most compatible with a trigger associated with increased C[O.sub.2] emissions, possibly leading to a doubling of pC[O.sub.2], which in turn caused larger C isotope fractionation in marine and terrestrial organisms and a major biotic crisis in the calcareous nannoplankton. Our data also show that a release of isotopically light carbon from partial methane hydrate dissociation probably played a minor role in the OAE1a carbon cycle perturbation.

The ratio of RNA to DNA (RNA:DNA) in white muscle tissue of juvenile summer flounder (Paralichthys dentatus) and weakfish (Cynoscion regalis) was used as a proxy for recent growth rate in an estuarine nursery. Variability in RNA:DNA was examined relative to temporal changes in temperature and dissolved oxygen (DO). Initial laboratory experiments indicated (i) a strong positive relationship between RNA:DNA and growth rate, (ii) a rapid response of RNA:DNA to changes in feeding, and (iii) no effect of hypoxia on the relationship between RNA:DNA and growth rate (tested in weakfish only). Diel cycling DO occurred in the nursery throughout the summers of 2002 and 2003. Canonical correlation analysis of field data indicated a strong positive relationship between RNA:DNA and mean DO conditions prior to capture in both species. Correlations were weak or insignificant between stomach content mass (an index of feeding) and mean DO and between RNA:DNA and stomach content mass and DO variability. These results suggest a strong functional relationship between DO concentration and the growth rate of juvenile fishes in an estuarine nursery. Furthermore, growth rates of wild-caught fishes (estimated from RNA:DNA) appear to be more negatively impacted by diel cycling hypoxia than would be expected from published laboratory data. Le rapport ARN sur ADN (ARN:ADN) dans le tissu du muscle blanc du cardeau d'ete (Paralichthys dentatus) et de l'acoupa royal (Cynoscion regalis) a servi de mesure de remplacement du taux de croissance recent dans une nourricerie estuarienne. Nous avons examine la variabilite d'ARNADN en fonction des changements temporels de temperature et d'oxygene dissous (DO). Des experiences initiales en laboratoire indiquent (i) une forte relation positive entre ARNADN et le taux de croissance, (ii) une reaction rapide de ARNADN aux changements d'alimentation et (iii) une absence d'effets de l'hypoxie sur la relation entre ARNADN et le taux de croissance (testee seulement chez l'acoupa royal). Il y a eu un cycle journalier de DO dans la nourricerie tout au cours des etes 2002 et 2003. Une analyse des correlations canoniques des donnees de terrain montre une forte relation positive entre ARNADN et les conditions moyennes de DO avant la capture chez les deux especes. Les correlations sont faibles ou insignifiantes entre la masse du contenu stomacal (un indice alimentaire) et la valeur moyenne de DO et entre ARMADN et la masse du contenu stomacal et la variabilite de DO. Ces resultats indiquent une forte relation fonctionnelle entre les concentrations de DO et le taux de croissance des jeunes poissons dans une nourricerie estuarienne. De plus, les taux de croissance des poissons captures en nature (estimes d'apres ARMADN) semblent etre affectes plus negativement par l'hypoxie cyclique journaliere que ne le laissent prevoir les donnees de laboratoire de la litterature. [Traduit par la Redaction], Introduction Growth rate during the early life stages of marine and freshwater fishes is thought to influence survival and recruitment. In most cases, faster growth is believed to benefit survival [...]

Starting in 1980s, the inner Danish waters have yearly been exposed to seasonal oxygen deficiency (hypoxia). Through spatial-temporal interpolation of monitoring data (1998-2005), we investigated oxygen deficiency impacts on suitable burying habitats for lesser sandeel (Ammodytes tobianus). Furthermore, the consequences of a predicted 4 [degrees]C temperature increase within this century were investigated. Maps of bottom oxygen deficiency (oxygen saturation [is less than or equal to][S.sub.crit] of sandeel) were overlaid on maps of sediment composition. Throughout the study period (1998-2005), about 8% of the suitable sediments were affected by oxygen deficiency during an average year and 23% in the most severe year. Regional differences underlay the interannual variations. The extent of oxygen deficiency in enclosed regions varied from 20% to 33% of the suitable seabed being affected, whereas in open-water regions oxygen deficiency problems were limited during average years. However, large areas of the open-water seabed experienced oxygen deficiency during severe years. In such years, under a 4.0 [degrees]C temperature increase scenario, the extent of oxygen deficiency on open-water suitable patches was predicted to increase from 25% to about 40%. Depuis les annees 1980, les eaux interieures du Danemark sont exposees chaque annee a une carence saisonniere en oxygene (hypoxie). En faisant des interpolations spatio-temporelles dans les donnees de surveillance (1998-2005), nous examinons les impacts de la carence en oxygene sur les habitats d'enfouissement du lancon equille (Ammodytes tobianus). Nous etudions les consequences d'un accroissement predit de temperature de 4 [degrees]C au cours du siecle actuel. Nous avons superpose des cartes de deficit d'oxygene au fond (saturation d'oxygene [is less than or equal to] [S.sub.crit] du lancon) sur des cartes de composition des sediments. Au cours de la periode d'etude (1998-2005), environ 8% des sediments appropries a l'enfouissement sont affectes par le deficit d'oxygene durant une annee moyenne et 23% durant l'annee la plus extreme. Des differences regionales sous-tendent les variations entre les annees. L'etendue du deficit d'oxygene dans les regions fermees couvre de 20% a 33% du fond de mer approprie a l'enfouissement, alors qu'en eau libre, les problemes de deficit d'oxygene sont limites durant les annees moyennes. Cependant, de grandes surfaces du fond de mer en eau libre connaissent un deficit d'oxygene durant les annees extremes. Durant ces annees-la, avec un scenario d'augmentation de la temperature de 4.0 [degrees]C, nous predisons que l'etendue du deficit d'oxygene sur les parcelles appropriees a l'enfouissement en eau libre augmentera de 25% a environ 40%. [Traduit par la Redaction], Introduction The marine coastal zone constitutes a minor part of the world's ocean but is nonetheless highly productive and plays an important role for many fish species (Beck et al. [...]

ABSTRACT Increases in the frequency and duration of hypoxia and the loss of biogenic reefs are two of the most prominent environmental insults to estuaries. We investigated the interaction between [...]

Areas of low flushing and high nutrient loading in shallow estuaries are susceptible to diel-cycling hypoxia and also represent important nursery habitat for juvenile estuary-dependent fishes. Swimming speed, angular correlation, and expected displacement were measured in juvenile weakfish (Cynoscion regalis) in response to diel-cycling hypoxia (cycling between 7.0 and 0.4 mg [O.sub.2] x [L.sup.-1]). Saturation-acclimated (7.0 mg [O.sub.2] x [L.sup.-1]) weakfish exhibited an active response by increasing swimming speed (to a maximum at 2.8 mg [O.sub.2] x [L.sup.-1]) and angular correlation (to a maximum at 1.4 mg [O.sub.2] x [L.sup.-1]) as dissolved oxygen (DO) decreased, after which weakfish exhibited a passive response and both swimming speed and angular correlation decreased by ~50% and 70%, respectively, at 0.4 mg [O.sub.2] x [L.sup.-1]. Weakfish acclimated to hypoxia (cycling between 2.0 and 11.0 mg [O.sub.2] x [L.sup.-1] for 10 days) did not vary swimming speed during decreasing DO or DO recovery (increasing DO) and had an overall swimming speed 46% lower than saturation-acclimated weakfish at 7.0 mg [O.sub.2] x [L.sup.-1]. At the end of DO recovery, saturation- and hypoxia-acclimated weakfish had recovered 60% and 80% of their initial swimming speeds, respectively. The relationship between previous hypoxia exposure and behavior may be an important determinant of habitat utilization in estuarree nursery areas impacted by diel-cycling hypoxia. Les zones de vidange reduite et d'apports importants de nutriments dans les estuaries peu profonds sont sujettes a une hypoxie a cycle journalier; ils representent aussi des habitats de nourricerie precieux pour les jeunes chez les poissons associes aux estuaries. Nous aeons mesure la vitesse de nage, la correlation angulaire et le deplacement attendu chez des jeunes acoupas royaux (Cynoscion regalis) en reaction a une hypoxie a cycle journalier (variant de 7,0 a 0,4 [O.sub.2] x [L.sup.-1]). Des acoupas acclimates a la saturation (7,0 [O.sub.2] x [L.sup.-1]) reagissent de maniere active en augmentant leur vitesse de nage (jusqu'a un maximum a 2,8 [O.sub.2] x [L.sup.-1]) et leur correlation angulaire (jusqu'a un maximum a 1,4 [O.sub.2] x [L.sup.-1]) a mesure que foxygene dissous (OD) decroit, pour ensuite reagir passivement; la vitesse de nage et la correlation angulaire decroissent alors respectivement de --50 % et de 70 % a 0,4 [O.sub.2] x [L.sup.-1]. Les acoupas acclimates a (hypoxie (variant de 2,0 et 11,0 mg [O.sub.2] x [L.sup.-1] pendant 10 fours) ne changent pas leur vitesse de nage durant la decroissance d'OD et la recuperation d'OD (augmentation d'OD) et ont une vitesse globale de nage de 46% inferieure a celle des acoupas acclimates a la saturation a 7,0 mg [O.sub.2] x [L.sup.-1]. A la fin du retablissement d'OD, les acoupas acclimates a la saturation et a (hypoxie avaient recupere respectivement 60 % et 80 % de leur vitesse initiale de nage. La relation entre f exposition anterieure a f hypoxie et le comportement peut etre un facteur determinant important de (utilisation des zones estuariennes de nourricerie affectees par des cycles journaliers d'hypoxie. [Traduit par la Redaction], Introduction Estuaries provide nursery habitat for many economically and ecologically important fishes (Weinstein 1979; Able 1999; Minello et al. 2003). Many studies have emphasized the importance of tidal headwaters as [...]

Abstract: Eutrophication-induced hypoxia may affect both benthic and pelagic organisms in coastal systems. To evaluate the effect of hypoxia on pelagic striped bass (Morone saxatilis), we quantified the growth rate [...]

Seemingly consistent proportional differences in several palatal structures have been noted between Permian and Triassic anomodont therapsids for nearly a century. These patterns have been cited as evidence in support of a decline in atmospheric oxygen concentrations that may have contributed to end-Permian terrestrial extinctions. However, it is not known whether the observed differences are significant, or whether they stem from continued directional selection. If they are not significant, or if their timing does not match that proposed for the oxygen decline, support for the hypoxia-based extinction scenario would be weakened. We tested whether the internal nares and bony secondary palate, two palatal features proposed to be related to respiratory efficiency, are significantly larger in Triassic anomodonts, and whether the variation can be attributed to a long-term tendency for increase. Results based on raw data indicate that Triassic anomodonts have significantly larger secondary palates than Permian anomodonts. They also have significantly larger internal nares, but only when primitive, morphologicallydivergent specimens are not considered. Although nares and palate size are correlated with stratigraphic occurrence, available data reject the hypothesis that the observed differences were the result of a long-term trend. Most of these findings are consistent with the predictions of the hypoxia scenario. However, removing the effects of body size and phylogeny causes some of the differences to break down, indicating that if selection for increased respiratory efficiency affected these characters, it was most likely not the only factor to do so. Therefore, the characters provide only weak evidence in support of the hypoxia scenario, and we recommend against their use for this purpose. Our results emphasize the need for caution when invoking presumed differences between Permian and Triassic vertebrates as support for hypoxia, or other extinction scenarios, without a rigorous study of the character(s) in question.

Corn cultivation in the United States is expected to increase to meet demand for ethanol. Nitrogen leaching from fertilized corn fields to the Mississippi-Atchafalaya River system is a primary cause of the bottom-water hypoxia that develops on the continental shelf of the northern Gulf of Mexico each summer. In this study, we combine agricultural land use scenarios with physically based models of terrestrial and aquatic nitrogen to examine the effect of present and future expansion of corn-based ethanol production on nitrogen export by the Mississippi and Atchafalaya Rivers to the Gulf of Mexico. The results show that the increase in corn cultivation required to meet the goal of 15-36 billion gallons of renewable fuels by the year 2022 suggested by a recent U.S. Senate energy policy would increase the annual average flux of dissolved inorganic nitrogen (DIN) export by the Mississippi and Atchafalaya Rivers by 10-34%. Generating 15 billion gallons of corn-based ethanol by the year 2022 will increase the odds that annual DIN export exceeds the target set for reducing hypoxia in the Gulf of Mexico to >95%. Examination of extreme mitigation options shows that expanding corn-based ethanol production would make the already difficult challenges of reducing nitrogen export to the Gulf of Mexico and the extent of hypoxia practically impossible without large shifts in food production and agricultural management. Gulf of Mexico | hypoxia | nitrogen cycling | biofuels | agriculture

Abstract: Hypoxia is an ever increasing threat to aquatic systems. While fluctuating levels of dissolved oxygen (DO) can be a natural phenomenon, hypoxia caused by eutrophication and organic pollution is [...]

The substrate-induced respiration inhibition under anaerobic and aerobic conditions in combination with [super 15]N gas analysis is utilized to determine the role of formate and hypoxia for the fungal reduction of [super 15]N-labeled nitrate to [super 15][N.sub.2]O. The results showed that plant root exudates could affect [N.sub.2]O production from fungi via the proposed formate-dependent pathway.

Study is conducted to find whether the body sizes of the fish affect its hypoxia tolerance. It is observed that body size has little or no impact on the ability to take up oxygen during hypoxic conditions.

Overwintering forces the aquatic ranid frogs to adapt to the changed climatic conditions. They must survive prolonged period of low temperature and low levels of dissolved oxygen, because of this they spend a significant portion of the winter buried in anoxic mud.