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This study describes an assessment of an ocean-ecosystem model in simulating marine ecosystem dynamics in the Indian coastal waters. Long-term sustained in-situ observations of temperature, salinity, chlorophyll-a and dissolved oxygen (DO) collected in the coastal waters of India, and ship-based observations are used for this assessment. The model captures observed trend of temperature, salinity and chlorophyll-a with high correlation in both eastern and western shelf waters except for salinity and DO along west and DO along east coast. The model performs very well in simulating the Indian coastal shelf ecosystem dynamics. The seasonal occurrence of prominent phytoplankton bloom in the central-east coast during pre-monsoon, south-west coast during monsoon and north-west coast during post-monsoon is realistically reproduced by the model. The model also reproduces the seasonal presence of significantly low DO content in the upwelled water at a shallow depth leading to coastal hypoxia in the south-west and central-east coast of India during summer monsoon. A fine-tuned model is useful in understanding better Indian coastal shelf ecosystem and predicting future changes in time and space, like the occurrence of coastal hypoxia or anticipating phytoplankton blooms. Such information is useful for predicting potential fishing grounds in coastal waters and fisheries management. [ABSTRACT FROM AUTHOR]

Hypoxia and blue tide are the most significant environmental issues in Tokyo Bay as they have been damaging fisheries for a long time. Although studies on modeling these two associated phenomena have been conducted for decades, the scarcity of relevant observational datasets has greatly hindered the progress, and no study has successfully reproduced the entire processes of blue tide or predicted the time and place of its outbreak. To address the problems from limited data, this study proposed a relatively conventional benthic flux model and developed a novel method that converts the total organic carbon content into the fluxes of sediment oxygen consumption and sulfide release to represent the spatial differences in benthic fluxes. A pelagic sulfur model with only three key chemical reactions of blue tide that includes the disproportionation of elemental sulfur was proposed. The method significantly improved the results of dissolved oxygen in bottom water, as seen by the root mean square error decreasing by 15.9% and 18.9% in two simulations with largely different forcings. The sulfur model also accurately predicted the outbreaks of blue tides in each simulation, which is significant to the stakeholders as it facilitates the forecast of blue tides in Tokyo Bay. [ABSTRACT FROM AUTHOR]

Climate-focused coalitions of states and the U.S. national government will now be working toward a shared goal of high ambition on climate. Due to the immediacy of OA in particular states and the flexibility of subnational governments, state leadership represents a unique opportunity to help address climate and ocean change. State and local leaders have been deeply involved in the global response to ocean acidification (OA), partly in response to concerns of local business owners and citizens, and partly in response to regional science findings about OA and other water quality concerns (Cross et al. [5]; Barton et al. [1]). Reducing global carbon dioxide emissions is the fundamental action required to make progress on climate change and to reduce ocean acidification. [Extracted from the article]

State agency alignment and integration of OAH action into climate change policy While OAH issues have been identified and addressed to some extent by Oregon government agencies, there are regular planning and management processes, routine opportunities to integrate OAH into the day-to-day work of agency programs. Without legislative action on broad climate policy to date, Oregon Governor Brown issued I Executive Order 20-04 Directing State Agencies to Take Action to Reduce and Regulate Greenhouse Gas Emissions i (Office of the Governor of Oregon [32]), which includes direction to combat both climate and ocean change, including OAH. Oregon scientists played a key role in the leadership of the 2016 West Coast OAH Science Panel (Science Panel), a collaborative and regionally representative group of marine science experts who described the status of OAH science on the West Coast, and started to identify OAH policy gaps at a regional level that could benefit from incorporation of scientific information (Chan et al. [11]). [Extracted from the article]

Changing ocean conditions, such as ocean acidification, hypoxia, and ocean warming, are impacting marine ecosystems and posing a variety of immediate and future challenges for natural resource managers and affiliated industries. In order to successfully facilitate adaptation and mitigation responses to changing ocean conditions, research efforts and synthesis products should be developed in collaboration with resource managers and decision makers. Using interviews and surveys, we sought to advance collaborative science approaches by identifying the most pressing concerns, barriers, and research and monitoring needs of natural resource managers in Washington State, USA, where marine waters are particularly vulnerable to changing ocean conditions. Survey participants indicated that they are most concerned by ocean acidification, followed by water temperature and hypoxia. Our findings reveal a desire to prioritize laboratory and in situ studies to identify survival thresholds of ecologically or commercially important organisms, specifically zooplankton, fish, Dungeness crab, and conditions that promote harmful algal blooms. Scientific literature and in-person workshops and meetings were the preferred way for survey participants to learn about new science and affiliated results. Our findings highlight a need for continued and expanded monitoring and research efforts, the development of interpretive science products for resource managers, and enhanced communication between entities before information on changing ocean conditions can be effectively incorporated into resource management and policy decisions. [ABSTRACT FROM AUTHOR]

Coastal hypoxia can negatively impact shellfish, but it is unclear if exposure to intensifying diel-cycling hypoxia alters shellfish susceptibility to severe hypoxic events in late summer. In this study, bay scallops (Argopecten irradians) were acclimatized for 50 days at 5 sites along a eutrophication gradient, where scallops rarely, occasionally and frequently encountered hypoxic conditions. In a laboratory experiment, scallops were then exposed to a 24-h hypoxic event and heartbeat rates were recorded with non-invasive infrared sensors during the initial oxygen decline, during extended hypoxia, and for one hour after re-establishment of normoxia. Irrespective of acclimatization site, scallops sustained increased heartbeat rates during hypoxia, but cardiac responses were less pronounced in scallops that frequently encountered hypoxia during acclimatization. This study suggests that cardiac responses to changes in dissolved oxygen concentrations can be affected by exposure history, which may have important ramifications for scallop ecophysiology and resilience in dynamic coastal environments. [ABSTRACT FROM AUTHOR]

Nutrient pollution in South African estuaries is described using a Driver-Pressure-State-Impact-Response framework. The root cause ('driver') of deteriorating water quality is rapid population growth that leads to increasing inputs from wastewater treatment works (WWTWs), stormwater run-off and agricultural return flow ('pressures'). Nationally, half of the country's estuaries are affected by nutrient pollution ('state'). This has elicited marked primary producer and secondary (hypoxia, fish kills, loss of ecosystem services) responses ('impact'). The Sundays and Swartkops Estuaries are eutrophic with phytoplankton blooms (>20 µg l−1) and bottom-water hypoxia. Similarly, the nationally important Knysna Estuary experiences eutrophic conditions associated with macroalgal blooms, whereas the Wildevoëlvlei and Zeekoe systems have transitioned to alternate stable states characterised by toxic cyanobacteria blooms, as a result of WWTW inputs and increased water residence times. The health of the St Lucia Estuary, a UNESCO World Heritage site, is under threat from agricultural inputs from the uMfolozi system. Nationally, better treatment and recycling of WWTW inputs is required to improve and restore estuary health. Owing to excessive WWTW effluent volumes, treatment to South Africa's uniform effluent standards no longer prevent eutrophication. Other urgent interventions needed are compliance monitoring, engineering solutions to reduce stormwater and wastewater input, and prudent application of agricultural fertilisers. [ABSTRACT FROM AUTHOR]

A third of South Africa's freshwater flow no longer reaches the coast, yet few systems have shifted from being permanently open to temporarily closed. For the first time since 1969, the Gamtoos Estuary mouth closed in June 2018, because of extensive drought conditions and freshwater abstraction. Accordingly, physico-chemical gradients, microalgal biomass and species composition were sampled during low (closed mouth), normal (open mouth) and high (breaching event) flow conditions. The closed phase was characterised by polyhaline and homogenous salinity structures and a rapid shift towards eutrophic conditions, as evidenced by bottom water hypoxia (<2 mg l−1), elevated phytoplankton (>20 μg l−1) and microphytobenthos (>100 mg m−2) biomass, and proliferation of a harmful algal bloom (HAB) species (Prorocentrum cordatum, Dinophyceae). An artificial breaching event in September 2018 restored connectivity with the marine environment and within a month re-established the usual physico-chemical gradients that characterise the open phase. Although the current study demonstrates ecosystem recovery from stochastic events, it also highlights the potential impact (e.g. HABs, hypoxia) of shifting an estuary into a new stable state. This is a concern given that mouth closure events in South African estuaries are likely to increase in the future in response to global change pressures. [ABSTRACT FROM AUTHOR]

Climate change and associated permafrost thaw are creating new shallow waterbodies in vast regions of the circumpolar Arctic. These thaw ponds are characterized by high concentrations of colored dissolved organic matter originating from the degrading watershed, inducing a strong vertical thermal and oxygen (O2) stratification. We investigated the zooplankton community and biomass in eight subarctic thaw ponds and evaluated how zooplankton respond to this stratification. In a subset of three ponds, we further examined how other environmental variables, including essential fatty acids (EFA) concentration and phytoplankton, bacteria, and larval phantom midge Chaoborus biomass stratify and contribute to the vertical distribution of zooplankton in this increasingly common type of arctic freshwater system. The zooplankton community was extremely abundant in all ponds (up to 3,548 ind L-1) and dominated mainly by rotifers (35-93 percent of the biomass). Most zooplankton aggregated at the interface between the shallow well-oxygenated mixed surface layer and the deeper hypoxic but algal-rich stratified layer, and their distribution was affected by a combination of O2, Chaoborus, phytoplankton, and EFA that were supplied from opposite directions. Our findings show how water column stratification deeply affects the ecology of planktonic organisms in circumpolar freshwaters and indicate Arctic zooplankton species composition is expected to deeply change with the ongoing warming and browning. [ABSTRACT FROM AUTHOR]

Perioperative brain ischemia and stroke are leading causes of morbidity and mortality. Brief hypoxic preconditioning is known to have protective effects against hypoxic-ischemic insult in the brain. Current studies on the neuroprotective effects of ischemic preconditioning are based on histologic findings and biomarker changes. However, studies regarding effects on memory are rare. To precondition zebrafish to hypoxia, they were exposed to a dissolved oxygen (DO) concentration of 1.0 ± 0.5 mg/L in water for 30 s. The hypoxic zebrafish were then exposed to 1.0 ± 0.5 mg/L DO until the third stage of hypoxia, for 10 min ± 30 s. Zebrafish were assessed for memory retention after the hypoxic event. Learning and memory were tested using the T-maze, which evaluates memory based on whether or not zebrafish moves to the correct target compartment. In the hypoxic preconditioning group, infarct size was reduced compared with the hypoxic-only treated zebrafish group; memory was maintained to a degree similar to that in the hypoxia-untreated group. The hypoxic-only group showed significant memory impairments. In this study, we used a hypoxic zebrafish model and assessed the effects of ischemic preconditioning not only on histological damages but also on brain function, especially memory. This study demonstrated that a brief hypoxic event has protective effects in hypoxic brain damage and helped maintain memory in zebrafish. In addition, our findings suggest that the zebrafish model is useful in rapidly assessing the effects of ischemic preconditioning on memory. [ABSTRACT FROM AUTHOR]

Oxidative stress and hypoxia responses in Centropomus parallelus exposed to three different concentrations of nitrite (0, 0.5, and 10 mg L−1) were evaluated. To determinate toxicity, we used enzymatic analyses and quantifications of oxygen consumption and opercular beats under conditions of normoxia and hypoxia. There was no significant difference in GST, CAT, or GPx enzymes in the liver or in GPx in the gills. Levels of GST were altered at a concentration of 10 mg L−1 in experiment I. Experiment II displayed alterations for GST and CAT in the liver at the same concentration, indicating that exposure to nitrite does not generate differentiated activation in the body’s defense system by the production of oxidative stress enzymes. When nitrite was associated with hypoxia, there was a significant increase in both enzymatic activity and opercular beating under hypoxia in the group exposed to 10 mg L−1 nitrite compared to the control. [ABSTRACT FROM AUTHOR]

Eutrophication of lakes has increased the risk of fish kills during winter under ice cover. If such a lake is isolated, the fish assemblage consists of only oxygen-tolerant species without predatory species. Here, our main aim was to analyze the fate of 99 marked pike (Esox lucius) stocked to a pikeless lake that is known to have low oxygen concentrations under ice cover. These pike (total lengths 33.5–76.9 cm; weights 260–3050 g) were stocked in May 2008 and were followed 7 years. The first marked pike was caught in August 2008 and the last one in September 2012. Between these dates, 21 pike were caught at least once, five pike were caught twice, and two pike were caught three times. Relative condition was based on the length–weight relationship. Both length and weight affected significantly the recapture probability, whereas relative condition had no effect. The growth of marked pike was estimated based on length or weight increments in two separate models with either starting length or weight together with the number of days between observations. In these models, the number of days had positive, and size, either length or weight, had a negative relationship with growth. According to marginalr2, length and the number of days explained 65.5% of variation in length increments, whereas the marginalr2for weight and the number of days was 49.3% for weight increments. The length increment model was used to compare pike growth in Lake Savijärvi with other Finnish lakes. The comparison showed that during the first four growing seasons after stocking, the pike growth in Lake Savijärvi was faster than in the other lakes studied. [ABSTRACT FROM PUBLISHER]

Riverine influences on nearshore oceanic habitats often have detrimental consequences leading to algal blooms and hypoxia. In oligo- to mesotrophic systems, however, nutrient delivery via rivers may stimulate production and even be a vital source of nutrients, as may nutrient supplements from upwelling. We investigated the nutrient content (C, N, P) and stoichiometry of sediment, and several pelagic, benthopelagic and benthic species in the KwaZulu-Natal (KZN) Bight, a narrow shelf area on the south-east coast of South Africa, bordering the Agulhas Current. Three suggested nutrient sources to the bight are the Thukela River in the central region of the bight, upwelling in the northern part and a semi-permanent eddy (Durban Eddy) in the southern part. Elemental content of the various groups studied showed significantly higher values for most groups at the site near the Thukela River. C:P and N:P were highest in the southern part of the bight, and lowest near the Thukela Mouth or at Richards Bay in the north, indicating the latter were the P-richer sites. Sediment organic matter showed lowest elemental content, as expected, and zooplankton stoichiometry was highest compared to all other biotic groups. Environmental heterogeneity played a greater role in organismal C, N and P content and stoichiometry compared to phylogeny, with the exception of the differences in C:P and N:P of zooplankton. From this bight-wide study, the higher elemental content and lower ratios at the Thukela Mouth site supported previous findings of the importance of coastal nutrient sources to the bight ecosystem. Reductions in river flow for water use in the catchment areas may therefore have negative consequences for the productivity of the entire ecosystem. [ABSTRACT FROM AUTHOR]

Courtship is an important part of the reproductive process, ensuring reproductive compatibility and conveying individual quality. One factor in aquatic environments that has the potential to influence courtship behaviours and mating propensity is the level of dissolved oxygen. Furthermore, hypoxic areas are currently spreading due to anthropogenic disturbance, such as eutrophication. In marine environments, hypoxia often occurs in shallow coastal regions that are particularly important areas for reproduction. Here, we investigated how types of reproductive behaviour were affected by mild hypoxia using the well-studied broad-nosed pipefish, Syngnathus typhle. More precisely, we investigated the impact of acute hypoxia on the reproductive behaviour preceding mating, and on the probability of mating, as well as on the latency until these occurred. We found that the latency period to courting and copulation occurring was prolonged in the low-oxygen environment. However, the total time spent courting as well as the probability of mating was unaffected by hypoxia. Other types of reproductive behaviour found in this species, such as dancing, and the unique male pouch-flap behaviour, were also unaffected by the low-oxygen treatment. We conclude that although latency to courting and copulating was prolonged in the hypoxic environment, most reproductive behaviour investigated was unaffected by hypoxia. Thus, hypoxia commonly occurring in shallow coastal regions has the potential to delay certain components of reproduction, but overall the broad-nosed pipefish shows robustness to hypoxic conditions. [ABSTRACT FROM AUTHOR]

Altered flow regimes in lakes can change macrophyte habitats from dynamic, species-rich communities to dense, monotypic communities that can change the physicochemical environment available to fish. We tested whether fish community composition, fish density, fish species richness, and fish species diversity changed across a range of dissolved oxygen concentrations (DO; mg/L) in dense stands of several macrophyte species that are commonly the target of macrophyte control efforts in Florida lakes. We sampled fish communities within growths of 5 emergent macrophyte species including cattail (Typhaspp.), pickerelweed (Pontedaria cordata), smartweed (Polygonumspp.), torpedograss (Panicum repens), and water primrose (Ludwigiaspp.) at lakes Kissimmee and Istokpoga, Florida. Fish communities were sampled using 3 different enclosure gears treated with rotenone, and DO was measured in mid-water column at each site. Macrophyte biomass and DO concentrations were inversely related. Poeciliids accounted for 90% of the catch composition, and density was inversely related to DO. Centrarchid, cyprinodontid, and sport fish densities were highest at DO >4 mg/L. Restoration efforts should reduce dense emergent macrophyte biomass to reestablish habitats with greater habitat heterogeneity, which will increase DO concentrations. These efforts should increase fish species diversity, fish species richness, and improve recreational fisheries in lakes with stabilized water levels. [ABSTRACT FROM AUTHOR]

The effect of lipoic acid supplementation and moderate hypoxia (3 mg/L), followed by re-oxygenation, was analyzed in terms of antioxidant and oxidative damage responses in juvenile shrimpLitopenaeus vannamei. Lipoic acid (LA)-enriched rations (D1: 76.4 ± 6.4; D2: 196.4 ± 70.2; and D3: 397.2 ± 79.97 mg LA/kg) were offered to shrimps. A control group without LA adding was also run. After 45 days, LA-enriched ration increased the activity of the detoxifying enzyme glutathione-S-transferase in gills. Total antioxidant capacity against peroxy radicals was augmented in gills and hepatopancreas at doses D2 and D3. Doses D1 and D2 of LA reduced the levels of oxidative damage (lipid peroxidation) in gills and hepatopancreas. The results showed that certain LA doses (particularly D2) improved not only antioxidant responses but also weight gain. It can be concluded that LA triggered antioxidant and detoxification protection inL. vannamei, allowing the shrimp to cope with environmental stressful factors. [ABSTRACT FROM AUTHOR]

Local oxygen lack in arterial walls (hypoxia) plays a very important role in the initiation, progression and development of intimal hyperplasia (IH) and thrombosis. Aiming to find out whether a helical-type artery bypass graft (ABG) is hypoxia beneficial, a numerical study was carried out to compare oxygen transport between a helical-type ABG and a conventional-type ABG. The dimensionless mass transfer coefficient (Sherwood number) was introduced to evaluate the oxygen mass transfer distribution and detailed oxygen wall flux was computed. The results show that the intrinsic geometry of a helical-type ABG resulted in improved hypoxia and the oxygen-depleted fluid located proximally to the occluded section as compared with that of a conventional-type ABG. However, benefits aside, distinct double low regions (low wall shear stress (WSS) and hypoxia) which might be most prone to IH and more localised and thicker boundary layer of oxygen-depleted fluid were observed at the helical-type ABG. This may explain why the helical flow plays a detrimental role at some locations in the human body. In addition, it was observed that although low WSS region was always accompanied with low oxygen supply, the oxygen transport rate did not adjust simultaneously with flow. The change in oxygen distribution usually lagged behind the flow change. A physiological WSS region may be associated with hypoxia condition. This study captured the qualitative trend of oxygen distribution in ABGs and the effect of helical geometry on reducing hypoxia, which is useful in the structural design of swirling flow vascular devices. [ABSTRACT FROM AUTHOR]

Objective. The aim of this study was to correlate the expression of vascular endothelial growth factor (VEGF) and hypoxia-inducible factor-1α (HIF-1α) with pathological renal artery changes in patients with renal cell carcinoma (RCC). A further aim was to correlate intratumoral microvessel density (MVD) with VEGF and HIF-1α expression and prognostic factors for RCC, including tumour necrosis. Material and methods. Formalin-fixed and paraffin-embedded tissue blocks from 150 patients with RCC and 50 patients with non-tumorous kidney diseases were analysed. The control group consisted of specimens from both renal arteries obtained from 25 decedents at routine autopsy (50 cases in total). Immunohistochemistry was performed using primary antibodies to VEGF, HIF-1α and CD31. Results.Pathological renal artery changes were more common in patients with RCC and non-tumorous kidney diseases than in the control group. MVD was higher in the RCCs of patients with pathological renal artery changes. Tumours with higher HIF-1α expression had higher MVD; however, VEGF expression was not associated with MVD. A significant association was also found between MVD and the extent of tumour necrosis, in that less necrotic tumours had higher MVD. No association between renal artery changes and VEGF and HIF-1α expression was established. Conclusion. Considering the results of this study, the evaluation of renal artery changes in forthcoming research on RCC would be helpful for several reasons: to estimate their incidence in a larger number of patients, to clarify their connection with RCC and to reveal their relationship with MVD in RCC. [ABSTRACT FROM AUTHOR]

To investigate the influence of exposure to high-altitude (HA) hypoxia on the expressions of endothelin-1 (ET-1), endothelin type A (ETA) and endothelin type B (ETB) receptors in broiler chickens, immunohistochemistry studies were performed in the lungs. Six hundred 1-day-old male broiler chickens were randomly divided into two groups: group A, birds maintained under rich oxygen conditions (oxygen content 21%); and group B, birds exposed to HA hypoxia (oxygen content 13%). Our data showed that exposure to altitude elevated ET-1 and ETA gene expressions at 21 and 28 days of age when compared with the rich oxygen group. Meanwhile, a marked decline in ETB expression was observed at 28 days of age in the course of HA, although there were no significant changes (P>0.05) at 7, 14 and 21 days of age. The increased response was accompanied by adverse effects on weekly body weight gain and ascites mortality. These observations suggested that ET-1, ETA and ETB genes are normally expressed in the lungs of birds. Increased levels of ET-1 and ETA and decreased ETB gene expression in the lungs are probably involved in the lung dysfunction of broiler chickens with developmental ascites. [ABSTRACT FROM PUBLISHER]

Multiple environmental mechanisms have been proposed to control bottom water hypoxia (<2 mg O2 L−1) in the northern Gulf of Mexico Louisiana shelf. Near-bottom hypoxia has been attributed to a direct consumption of oxygen through benthic microbial respiration and a secondary chemical reaction between oxygen and reduced metabolites (i.e. ferrous iron and total sulfide) from these populations. No studies to date have examined the metabolically active microbial community structure in conjunction with the geochemical profile in these sediments. Temporal and spatial differences in dissolved and solid phase geochemistry were investigated in the upper 20 cm of the sediment column. Pyrosequencing of reverse transcribed small subunit (SSU) ribosomal ribonucleic acid (rRNA) was used to determine population distribution. Results indicated that populations shallower than 10 cm below surface were temporally variable yet uniform between sites, while below this depth, populations were more site-specific. This suggests a potential interaction between the water column and the benthic microbial population limited to a shallow depth. The presence of dissolved reduced iron in the upper sediment column was indicative of low oxygen concentration, yet sulfide was at or below detection limits. Putative sulfate and iron reducing and oxidizing populations were metabolically active at similar depths suggesting potential recycling of products. Results from this study indicate low carbon concentrations in the shallow sediments limit general metabolic activity, reducing the potential for microbial respiration. Supplemental materials are available for this article. Go to the publisher's online edition of Geomicrobiology Journal to view the supplemental file. [ABSTRACT FROM PUBLISHER]

The first thorough examination of oxygen concentrations in Canadian waters of the Pacific Ocean reveals several patterns in space and time. Sub-surface concentrations of oxygen tend to be lower in shelf waters than in deep-sea waters on the same isopycnal and lower in southern waters of the continental shelf than farther north. The lowest near-bottom concentration was 0.7 ml L−1(31 μmol kg−1) in mid-shelf waters in summer off southwest Vancouver Island in the Juan de Fuca Eddy region. Oxygen concentration there declined at a rate of 0.019 ml L−1 y−1(0.83 μmol kg−1 y−1) from 1979 to 2011. This decline is attributed mainly to changes in oxygen concentrations on the same density surfaces, rather than to changes in the depth of constant-density surfaces. A numerical simulation of ocean currents and nutrient concentrations in and surrounding the Juan de Fuca Eddy in summer reveals persistent upwelling into the centre of this eddy and slow bottom currents within the eddy. Upwelled water at bottom of the Juan de Fuca Eddy has water properties associated with the California Undercurrent on the 26.6 sigma-t surface at 200 m depth, where oxygen concentration is typically 2.0 ml L−1(87 μmol kg−1) and declined at a rate of 0.025 ml L−1 y−1(1.1 μmol kg−1 y−1) from 1981 to 2011, mainly as a result of changes on constant-density surfaces rather than to uplifting isopycnals. We propose that upwelling advects deep, oxygen-poor water onto the continental shelf bottom, and the slow bottom currents allow time for oxidation of organic material in bottom waters to further reduce the oxygen concentration. RÉSUMÉ [Traduit par la rédaction] Le premier examen approfondi des concentrations d'oxygène dans les eaux canadiennes de l'océan Pacifique révèle plusieurs configurations dans le temps et dans l'espace. Les concentrations d'oxygène sous la surface ont tendance à être plus faibles dans les eaux de la plate-forme continentale que dans les eaux de l'océan profond sur la même isopycne et plus faibles dans les eaux du sud de la plate-forme que plus loin au nord. La concentration la plus faible près du fond était de 0.7 ml L−1(31 μmol kg−1) dans les eaux du milieu de la plate-forme en été au large du sud-ouest de l’île de Vancouver dans la région du remous de Juan de Fuca. Les concentrations en oxygène à cet endroit ont diminué au rythme de 0.019 ml L−1 a−1(0.83 μmol kg−1 a−1) entre 1979 et 2011. Cette diminution est principalement attribuée aux changements dans les concentrations d'oxygène sur les surfaces d’égale densité plutôt qu'aux changements dans la profondeur des surfaces de densité constante. Une simulation numérique des courants océaniques et des concentrations de nutrients dans le remous de Juan de Fuca et dans les régions avoisinantes en été révèle des remontées d'eau froide persistantes vers le centre de ce remous et des courants de fond lents à l'intérieur du remous. L'eau qui a remonté au fond du remous de Juan de Fuca a des propriétés liées au sous-courant de Californie sur la surface sigma–t 26.6 à une profondeur de 200 m, où la concentration en oxygène est normalement de 2.0 ml L−1(87 μmol kg−1), et a diminué au taux de 0.025 ml L−1 a−1(1.1 μmol kg−1 a−1) de 1981 à 2011, principalement à cause des changements sur les surfaces de densité constante plutôt que du soulèvement des isopycnes. Nous pausons l'hypothèse que les remontées d'eau advectent des eaux profondes pauvres en oxygène au bas de la plate-forme continentale et que les lents courants de fond donnent le temps à l'oxydation de la matière organique dans les eaux de fond, ce qui réduit davantage la concentration de l'oxygène. [ABSTRACT FROM AUTHOR]

The greater siren (Siren lacertina) can acquire oxygen from both air and water (bimodal breathing). Currently, only physiological measurements have been made on bimodal breathing, with little work being done on the unique surfacing behaviors associated with this process. Flow-through respirometry was used to measure O2 uptake in increasingly hypoxic water. In addition, video recordings were made to capture and quantify the surfacing behavior of greater sirens in response to progressive hypoxia. Greater sirens showed an increase in aerial O2 uptake, a decrease in aquatic O2 uptake, and no change in total O2 uptake as the aquatic O2 tension decreased. Also, greater sirens shifted only the number of surfacing trips they made as the aquatic O2 tension decreased; all other surfacing behaviors remained unchanged. Greater sirens appear to maintain their metabolic rate despite the aquatic O2 tension solely by modifying the number of trips they take to the surface. [ABSTRACT FROM PUBLISHER]

Although Nile perch Lates niloticus is assumed to be sensitive to low oxygen concentrations, it was found in deep water in Lake Victoria, where oxygen depletion is common during the rainy season. Since factors determining Nile perch distribution are not well understood its spatial distribution in the Mwanza Gulf of Lake Victoria was analysed in relation to depth, temperature and dissolved oxygen (DO) concentrations. Of these factors, DO concentration and the interaction of depth and DO concentration explained the distribution of Nile perch, whilst temperature had no significant effect. In periods of normoxia, Nile perch preferred to stay near the bottom at depths of 12-35 m, where densities of shrimps, their main prey, were high. However, Nile perch were apparently driven away from these areas by hypoxic conditions in the rainy season. They apparently escaped the seasonally hypoxic layers in deep water by horizontal inshore migration and by vertical movement in upward direction. Sudden upwelling of these deep layers is a threat to the Nile perch stock and the Nile perch fishery. [ABSTRACT FROM AUTHOR]

Low dissolved oxygen environments (known as hypoxic or dead zones) occur in a wide range of aquatic systems and vary in frequency, seasonality and persistence. While there have always been naturally occurring hypoxic habitats, anthropogenic activities related primarily to organic and nutrient enrichment related to sewage/industrial discharges and land runoff have led to increases in hypoxia and anoxia in both freshwater and marine systems. As a result, over the last 50 years there has been a rapid rise in the areas affected by hypoxia. The future status of hypoxia and its consequences for the environment, society and economies will depend on a combination of climate change (primarily from warming, and altered patterns for wind, currents and precipitation) and land-use change (primarily from expanded human population, agriculture and nutrient loadings). The overall forecast is for hypoxia to worsen, with increased occurrence, frequency, intensity and duration. The consequences of eutrophication-induced hypoxia can be reversed if long-term, broad-scale and persistent efforts to reduce nutrient loads are developed and implemented. [ABSTRACT FROM AUTHOR]

Fundamentally, in land based mediterranean aquaculture, two techniques are applied to supply water with oxygen: paddling water aeration and application of pure oxygen. The two oxygenation techniques result in quite different PO2 regimens and, consequently, different fish growth performance and gill morphology. Data exist showing a reduction in total respiratory surface (RSA) and increasing gas diffusion distance (GDD) in gills of sea bass (Dicentrarchus labrax, L.) farmed under elevated PO2 regimens. That such a modification might have an effect on the ion regulation has been defined elsewhere as osmorespiratory compromise. In this study, European sea bass previously acclimatized to two PO2 regimens, mild hypoxia and mild hyperoxia (70-80% and 130-140% of the saturation value, respectively), were challenged for 1 hour with hypo-osmotic plus manipulation stress in two separate trials. During the first trial, when only Na+ loss was determined, the ion efflux during the first 5 min resulted in a rate of 163.72±31 and 112.23±87 nmol g-1min-1 from hypoxia and hyperoxia sea bass groups, respectively, and, if sustained, would approach 15.3 and 11.2% per hour of the total body Na+, respectively. During the second trial, in which both Na+ and Cl- loss were determined, after 60 min the Na+ loss was shown to be 76.86±12 and 179.28±32 nmol g-1 min-1 for the fish previously acclimatized to hyperoxia and hypoxia regimens, respectively, whereas for Cl- this loss was 62.02±11 and 157.28±28 nmol g-1min-1, respectively. Our data are compatible with the hypothesis of an osmotic advantage of sea bass exposed to an elevated PO2 regimen, achievable with application of pure oxygen, instead of simple water aeration. [ABSTRACT FROM AUTHOR]

Application of a mechanical circulator was considered to reduce hypoxia and anoxia in an estuarine trench by numerical examination in terms of the required flow rate and direction along with the physical mechanism of its effectiveness. We then developed a prototype of the circulator, generating downward flow by an impeller attached to the main body of the circulator floating on the surface, in which the surface water is being transported to the bottom through a flexible draft tube connected to the floating body. The effectiveness of the proposed mechanical circulator was verified by performing field tests in a dredged trench in Tokyo Port of Tokyo Bay, while monitoring current and water and sediment quality. The field test results showed that the mechanical circulator achieved the desired effects, including reduction in hypoxia and improvement of water and sediment quality in the trench. We also applied a primitive equation model and found that the model can successfully reproduce the field test results. The present study shows the availability of a mechanical circulator and an effective application methodology in the field. [ABSTRACT FROM AUTHOR]

The intensification of grain production in the North Central Region of the United States has affected the quality of both surface and ground water resources in the region and also contributed to hypoxia in the Gulf of Mexico. This study revealed a lack of suitable educational programs to assist extension educators in understanding water quality issues. The purpose of this study was to identify the perceptions of extension educators in the North Central Region regarding water quality issues and subsequently to develop a teaching-learning model for educational programs focused on water quality in the area. [ABSTRACT FROM AUTHOR]

The article discusses the hypoxia tolerance of estuarine mysid shrimp Tenagomysis novae-zealandiae to low dissolved oxygen in New Zealand. Hypoxia is caused by eutrophication, which is arguably the most serious threat to coastal marine and estuarine ecosystems worldwide and linked to mass mortality of fish and Crustacea. Based on the study, Tenagomysis novae-zealandiae mortality was negatively related to decreases in dissolved oxygen concentrations with 11% mortality in the 6.3 and 4.0 mg O2/liter treatments and 4.4% mortality at 1.5 mg O2/liter. It is stated that the ability to tolerate short-term hypoxia has obvious advantages for Tenagomysis novae-zealandiae survival but likelihood homeostasis would be affected by hypoxia-induced inactivity.

A reevaluation of the presence of a suboxic zone above the sulphide onset and the fine structure of the oxic/anoxic interface in the Black Sea is discussed. The results qualify this phenomenon as an analytical artefact and that the methods used for dissolved oxygen (DO) profiling are not applicable in the situation. Former and recent studies have established the stability of the oxic/anoxic interface structure with two principal components: the low DO gradient zone situated at the base of oxycline, and of the C-layer located beneath the sulphide onset boundary, where DO and sulphide coexist. The existence of the C-layer does not permit a suboxic zone void of perceptible DO and sulphide. [ABSTRACT FROM AUTHOR]

This paper reports on the validation of bio-optical models in estuarine and nearshore (case 2) waters o New Jersey—New York to retrieve accurate water leaving radiance spectra and chlorophyll concentration from the NASA Airborne Visible Infrared Imaging Spectrometer (AVIRIS) data complemented with in situ measurements. The study area—Hudson/Raritan Estuary—is a complex esiuarine system where tidal and wind-driven currents are modified by freshwater discharges from the Hudson, Raritan, Hackensack, and Passaic rivers. Over the last century the estuarine water quality has degraded, in part due to eutrophication, which has disrupted the pre-existing natural balance, resulting in phytoplankton blooms of both increased frequency and intensity, increasing oxygen demand and leading to episodes of hypoxia. During 1999–2001 data acquisitions by NASA AVIRIS Held measurements were obtained to establish hydrologieal optical properties of the Hudson/Raritan Estuary: (1) concurrent above- and below-surface spectral irradianee; (2) sampling for laboratory determination of inherent optical properties; and (3) concentrations of optically-important water quality parameters. We used a bio-optical model based on Gordon et al. to predict the sub-surface irradianee retlectance from optically important water constituents. Modelling of retlectance is a prerequisite for processing remote sensing data to desired thematic maps for input into the geographical information system (GIS) for use as a management tool in water quality assessment. A Radiative Transfer Code—MODTRAN-4—was applied to remove the effects of the atmosphere so as to infer the water leaving radiance from the AVIRS data. The results of this procedure were not satisfactory, therefore an alternative approach was tested to directly correct the AVIRIS image using modelled spectra based on measured optical characteristics. The atmospherically corrected AVIRIS ratio image was used to calculate a thematic map of water quality parameters (i.e. chlorophyll-a) concentration, which subsequently were integrated into a GIS for management of water quality purposes. [ABSTRACT FROM AUTHOR]

Hypoxia is a common feature of solid tumors, particularly in glioblastoma (GBM), and known to be a poor prognosis factor in GBM patients. The growth of GBM is also associated with a marked inflammation partially characterized by an accumulation of macrophage (MΦ) of the M2 phenotype. However, the transition between M1 MΦ (antitumoral) and M2 MΦ (protumoral) phenotypes is a dynamic process. We made the assumption that oxygen (O2) availability could be a major regulator of this transition and that the intratumoral O2gradient is of importance. We evaluated,in vivo, the impact of hypoxia on MΦ tropism and polarization in two models of human GBM, well differentiated by their degree of hypoxia. MΦ migration in the tumor was more pronounced in the more hypoxic tumor of the two GBM models. In the more hypoxic of the models, we have shown that MΦ migrated at the tumor site only when hypoxia takes place. We also demonstrated that the acquisition of the M2 phenotype was clearly an evolving phenomenon with hypoxia as the major trigger for this transition. In support of thesein vivofinding, M0 but also M1 MΦ cultured in moderate or severe hypoxia displayed a phenotype close to that of M2 MΦ whose phenotype was further reinforced by severe hypoxia. These results highlight the role of hypoxia in the aggressiveness of GBM, in part, by transforming MΦ such that a protumoral activity is expressed. [ABSTRACT FROM PUBLISHER]

Reports on a Stanford University study showing that oceans are vulnerable to fertilizer runoff from farms, which can trigger sudden explosions of marine algae. Ability of the algae to disrupt the ocean ecosystem and produce "dead zones" in the sea; Use of satellite imagery from the Sea of Cortez, a hotspot for marine biodiversity and an important commercial fishing center for Mexico; Toxins released by harmful blooms of algae, which can deplete oxygen in the water and cause larger animals to die of hypoxia.