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1
Plowman, Caitlin Q., Cynthia D. Trowbridge, John Davenport, Colin Little, Luke Harman e Rob McAllen. "Stressed from above and stressed from below: dissolved oxygen fluctuations in Lough Hyne, a semi-enclosed marine lake". ICES Journal of Marine Science 77, n. 6 (5 agosto 2020): 2106–17. http://dx.doi.org/10.1093/icesjms/fsaa108.
Abstract (sommario):
Abstract Dissolved oxygen (DO) concentrations of the fully marine Lough Hyne, SW Ireland, were sampled in biologically different habitats between 2014 and 2019 to investigate the declining water quality in the marine reserve and the severity of oxidative stress on benthic communities. DO was measured above and below shallow subtidal rocks, in the Rapids connection to the Celtic Sea, in seagrass meadows (Zostera marina), and at various water depths (1–15 m) in the South Basin. DO values above rocks were normoxic to hyperoxic in daytime (7.8–17.3 mg l−1); below rocks were often hypoxic (0.24–2 mg l−1). South Basin sites experienced hypoxia less often than the North Basin, except for the Goleen, presumably due to differential current flow. DO fluctuations occurred in spring (before ephemeral macroalgae proliferate), summer (when algal mats smother the benthos), and autumn (when macroalgae decay). While the Rapids were normoxic, the seagrass meadows below them exhibited periodic DO stress. Labhra Cliff (9–14.5 m) was normoxic to hyperoxic in autumn but experienced suboxic and hypoxic events in summer. Many organisms in Lough Hyne are experiencing periods of hypoxia below their published sublethal limits, the effects of which could be exacerbated by periodic hyperoxia.
2
Vaquer-Sunyer, Raquel, e Carlos M. Duarte. "Thresholds of hypoxia for marine biodiversity". Proceedings of the National Academy of Sciences 105, n. 40 (29 settembre 2008): 15452–57. http://dx.doi.org/10.1073/pnas.0803833105.
Abstract (sommario):
Hypoxia is a mounting problem affecting the world's coastal waters, with severe consequences for marine life, including death and catastrophic changes. Hypoxia is forecast to increase owing to the combined effects of the continued spread of coastal eutrophication and global warming. A broad comparative analysis across a range of contrasting marine benthic organisms showed that hypoxia thresholds vary greatly across marine benthic organisms and that the conventional definition of 2 mg O2/liter to designate waters as hypoxic is below the empirical sublethal and lethal O2 thresholds for half of the species tested. These results imply that the number and area of coastal ecosystems affected by hypoxia and the future extent of hypoxia impacts on marine life have been generally underestimated.
3
Hasler-Sheetal, Harald. "Detrimental impact of sulfide on the seagrass Zostera marina in dark hypoxia". PLOS ONE 18, n. 12 (7 dicembre 2023): e0295450. http://dx.doi.org/10.1371/journal.pone.0295450.
Abstract (sommario):
Sulfide poisoning, hypoxia events, and reduced light availability pose threats to marine ecosystems such as seagrass meadows. These threats are projected to intensify globally, largely due to accelerating eutrophication of estuaries and coastal environments. Despite the urgency, our current comprehension of the metabolic pathways that underlie the deleterious effects of sulfide toxicity and hypoxia on seagrasses remains inadequate. To address this knowledge gap, I conducted metabolomic analyses to investigate the impact of sulfide poisoning under dark-hypoxia in vitro conditions on Zostera marina, a vital habitat-forming marine plant. During the initial 45 minutes of dark-hypoxia exposure, I detected an acclimation phase characterized by the activation of anaerobic metabolic pathways and specific biochemical routes that mitigated hypoxia and sulfide toxicity. These pathways served to offset energy imbalances, cytosolic acidosis, and sulfide toxicity. Notably, one such route facilitated the transformation of toxic sulfide into non-toxic organic sulfur compounds, including cysteine and glutathione. However, this sulfide tolerance mechanism exhibited exhaustion post the initial 45-minute acclimation phase. Consequently, after 60 minutes of continuous sulfide exposure, the sulfide toxicity began to inhibit the hypoxia-mitigating pathways, culminating in leaf senescence and tissue degradation. Utilizing metabolomic approaches, I elucidated the intricate metabolic responses of seagrasses to sulfide toxicity under in vitro dark-hypoxic conditions. My findings suggest that future increases in coastal eutrophication will compromise the resilience of seagrass ecosystems to hypoxia, primarily due to the exacerbating influence of sulfide.
4
Thomas, Peter, e Md Saydur Rahman. "Extensive reproductive disruption, ovarian masculinization and aromatase suppression in Atlantic croaker in the northern Gulf of Mexico hypoxic zone". Proceedings of the Royal Society B: Biological Sciences 279, n. 1726 (25 maggio 2011): 28–38. http://dx.doi.org/10.1098/rspb.2011.0529.
Abstract (sommario):
The long-term impacts on marine ecosystems of the recent dramatic worldwide increase in the incidence of coastal hypoxia are unknown. Here, we show widespread reproductive disruption in Atlantic croakers collected from hypoxic sites approximately 120 km apart in the extensive northern Gulf of Mexico continental shelf hypoxic zone. Gonadal growth and gamete production were impaired in croakers from hypoxic sites compared with fish from reference normoxic sites east of the Mississippi River Delta. Male germ cells were detected in approximately 19 per cent of croaker ovaries collected in the hypoxic region, but were absent in ovaries from normoxic sites. In addition, the sex ratio was skewed towards males at the hypoxic sites. The masculinization and other reproductive disruptions were associated with declines in neuroendocrine function, as well as ovarian and brain expression of aromatase (the enzyme that converts androgens to oestrogens). A similar incidence of ovarian masculinization and decline in ovarian aromatase expression were observed in croaker after chronic laboratory hypoxia exposure, indicating that ovarian masculinization is a specific hypoxia response and is due to decreased aromatase activity. The results suggest severe reproductive impairment can occur over large coastal regions in marine fish populations exposed to seasonal hypoxia, with potential long-term impacts on population abundance.
5
Fennel, Katja, e Jeremy M. Testa. "Biogeochemical Controls on Coastal Hypoxia". Annual Review of Marine Science 11, n. 1 (3 gennaio 2019): 105–30. http://dx.doi.org/10.1146/annurev-marine-010318-095138.
Abstract (sommario):
Aquatic environments experiencing low-oxygen conditions have been described as hypoxic, suboxic, or anoxic zones; oxygen minimum zones; and, in the popular media, the misnomer “dead zones.” This review aims to elucidate important aspects underlying oxygen depletion in diverse coastal systems and provides a synthesis of general relationships between hypoxia and its controlling factors. After presenting a generic overview of the first-order processes, we review system-specific characteristics for selected estuaries where adjacent human settlements contribute to high nutrient loads, river-dominated shelves that receive large inputs of fresh water and anthropogenic nutrients, and upwelling regions where a supply of nutrient-rich, low-oxygen waters generates oxygen minimum zones without direct anthropogenic influence. We propose a nondimensional number that relates the hypoxia timescale and water residence time to guide the cross-system comparison. Our analysis reveals the basic principles underlying hypoxia generation in coastal systems and provides a framework for discussing future changes.
6
Su, Jianzhong, Minhan Dai, Biyan He, Lifang Wang, Jianping Gan, Xianghui Guo, Huade Zhao e Fengling Yu. "Tracing the origin of the oxygen-consuming organic matter in the hypoxic zone in a large eutrophic estuary: the lower reach of the Pearl River Estuary, China". Biogeosciences 14, n. 18 (19 settembre 2017): 4085–99. http://dx.doi.org/10.5194/bg-14-4085-2017.
Abstract (sommario):
Abstract. We assess the relative contributions of different sources of organic matter, marine vs. terrestrial, to oxygen consumption in an emerging hypoxic zone in the lower Pearl River Estuary (PRE), a large eutrophic estuary located in Southern China. Our cruise, conducted in July 2014, consisted of two legs before and after the passing of Typhoon Rammasun, which completely de-stratified the water column. The stratification recovered rapidly, within 1 day after the typhoon. We observed algal blooms in the upper layer of the water column and hypoxia underneath in bottom water during both legs. Repeat sampling at the initial hypoxic station showed severe oxygen depletion down to 30 µmol kg−1 before the typhoon and a clear drawdown of dissolved oxygen after the typhoon. Based on a three endmember mixing model and the mass balance of dissolved inorganic carbon and its isotopic composition, the δ13C of organic carbon remineralized in the hypoxic zone was −23.2 ± 1.1 ‰. We estimated that 65 ± 16 % of the oxygen-consuming organic matter was derived from marine sources, and the rest (35 ± 16 %) was derived from the continent. In contrast to a recently studied hypoxic zone in the East China Sea off the Changjiang Estuary where marine organic matter dominated oxygen consumption, here terrestrial organic matter significantly contributed to the formation and maintenance of hypoxia. How varying amounts of these organic matter sources drive oxygen consumption has important implications for better understanding hypoxia and its mitigation in bottom waters.
7
Joyce, William, Karlina Ozolina, Florian Mauduit, Hélène Ollivier, Guy Claireaux e Holly A. Shiels. "Individual variation in whole-animal hypoxia tolerance is associated with cardiac hypoxia tolerance in a marine teleost". Biology Letters 12, n. 1 (gennaio 2016): 20150708. http://dx.doi.org/10.1098/rsbl.2015.0708.
Abstract (sommario):
Hypoxia is a pervasive problem in coastal environments and is predicted to have enduring impacts on aquatic ecosystems. Intraspecific variation in hypoxia tolerance is well documented in fish; however, the factors underlying this variation remain unknown. Here, we investigate the role of the heart in individual hypoxia tolerance of the European sea bass ( Dicentrarchus labrax ). We found individual whole-animal hypoxia tolerance is a stable trait in sea bass for more than 18 months (duration of study). We next examined in vitro cardiac performance and found myocardial muscle from hypoxia-tolerant individuals generated greater force, with higher rates of contraction and relaxation, than hypoxic-sensitive individuals during hypoxic exposure. Thus, whole-animal hypoxia tolerance is associated with cardiac hypoxia tolerance. As the occurrence of aquatic hypoxia is expected to increase in marine ecosystems, our experimental data suggest that cardiac performance may influence fish survival and distribution.
8
Keister, Julie E., Amanda K. Winans e BethElLee Herrmann. "Zooplankton Community Response to Seasonal Hypoxia: A Test of Three Hypotheses". Diversity 12, n. 1 (1 gennaio 2020): 21. http://dx.doi.org/10.3390/d12010021.
Abstract (sommario):
Several hypotheses of how zooplankton communities respond to coastal hypoxia have been put forward in the literature over the past few decades. We explored three of those that are focused on how zooplankton composition or biomass is affected by seasonal hypoxia using data collected over two summers in Hood Canal, a seasonally-hypoxic sub-basin of Puget Sound, Washington. We conducted hydrographic profiles and zooplankton net tows at four stations, from a region in the south that annually experiences moderate hypoxia to a region in the north where oxygen remains above hypoxic levels. The specific hypotheses tested were that low oxygen leads to: (1) increased dominance of gelatinous relative to crustacean zooplankton, (2) increased dominance of cyclopoid copepods relative to calanoid copepods, and (3) overall decreased zooplankton abundance and biomass at hypoxic sites compared to where oxygen levels are high. Additionally, we examined whether the temporal stability of community structure was decreased by hypoxia. We found evidence of a shift toward more gelatinous zooplankton and lower total zooplankton abundance and biomass at hypoxic sites, but no clear increase in the dominance of cyclopoid relative to calanoid copepods. We also found the lowest variance in community structure at the most hypoxic site, in contrast to our prediction. Hypoxia can fundamentally alter marine ecosystems, but the impacts differ among systems.
9
Kraus, Richard T., Carey T. Knight, Troy M. Farmer, Ann Marie Gorman, Paris D. Collingsworth, Glenn J. Warren, Patrick M. Kocovsky e Joseph D. Conroy. "Dynamic hypoxic zones in Lake Erie compress fish habitat, altering vulnerability to fishing gears". Canadian Journal of Fisheries and Aquatic Sciences 72, n. 6 (giugno 2015): 797–806. http://dx.doi.org/10.1139/cjfas-2014-0517.
Abstract (sommario):
Seasonal degradation of aquatic habitats from hypoxia occurs in numerous freshwater and coastal marine systems and can result in direct mortality or displacement of fish. Yet, fishery landings from these systems are frequently unresponsive to changes in the severity and extent of hypoxia, and population-scale effects have been difficult to measure except in extreme hypoxic conditions with hypoxia-sensitive species. We investigated fine-scale temporal and spatial variability in dissolved oxygen in Lake Erie as it related to fish distribution and catch efficiencies of both active (bottom trawls) and passive (trap nets) fishing gears. Temperature and dissolved oxygen loggers placed near the edge of the hypolimnion exhibited much higher than expected variability. Hypoxic episodes of variable durations were frequently punctuated by periods of normoxia, consistent with high-frequency internal waves. High-resolution interpolations of water quality and hydroacoustic surveys suggest that fish habitat is compressed during hypoxic episodes, resulting in higher fish densities near the edges of hypoxia. At fixed locations with passive commercial fishing gear, catches with the highest values occurred when bottom waters were hypoxic for intermediate proportions of time. Proximity to hypoxia explained significant variation in bottom trawl catches, with higher catch rates near the edge of hypoxia. These results emphasize how hypoxia may elevate catch rates in various types of fishing gears, leading to a lack of association between indices of hypoxia and fishery landings. Increased catch rates of fish at the edges of hypoxia have important implications for stock assessment models that assume catchability is spatially homogeneous.
10
Seitaj, Dorina, Regina Schauer, Fatimah Sulu-Gambari, Silvia Hidalgo-Martinez, Sairah Y. Malkin, Laurine D. W. Burdorf, Caroline P. Slomp e Filip J. R. Meysman. "Cable bacteria generate a firewall against euxinia in seasonally hypoxic basins". Proceedings of the National Academy of Sciences 112, n. 43 (7 ottobre 2015): 13278–83. http://dx.doi.org/10.1073/pnas.1510152112.
Abstract (sommario):
Seasonal oxygen depletion (hypoxia) in coastal bottom waters can lead to the release and persistence of free sulfide (euxinia), which is highly detrimental to marine life. Although coastal hypoxia is relatively common, reports of euxinia are less frequent, which suggests that certain environmental controls can delay the onset of euxinia. However, these controls and their prevalence are poorly understood. Here we present field observations from a seasonally hypoxic marine basin (Grevelingen, The Netherlands), which suggest that the activity of cable bacteria, a recently discovered group of sulfur-oxidizing microorganisms inducing long-distance electron transport, can delay the onset of euxinia in coastal waters. Our results reveal a remarkable seasonal succession of sulfur cycling pathways, which was observed over multiple years. Cable bacteria dominate the sediment geochemistry in winter, whereas, after the summer hypoxia,Beggiatoaceaemats colonize the sediment. The specific electrogenic metabolism of cable bacteria generates a large buffer of sedimentary iron oxides before the onset of summer hypoxia, which captures free sulfide in the surface sediment, thus likely preventing the development of bottom water euxinia. As cable bacteria are present in many seasonally hypoxic systems, this euxinia-preventing firewall mechanism could be widely active, and may explain why euxinia is relatively infrequently observed in the coastal ocean.
11
Ok, Jin Hee, Hae Jin Jeong, Hee Chang Kang, Ji Hyun You, Sang Ah Park, Se Hee Eom, Jin Kyeong Kang e Yeong Du Yoo. "Protists in hypoxic waters of Jinhae Bay and Masan Bay, Korea, based on metabarcoding analyses: emphasizing surviving dinoflagellates". Algae 38, n. 4 (15 dicembre 2023): 265–81. http://dx.doi.org/10.4490/algae.2023.38.12.6.
Abstract (sommario):
Hypoxia can indeed impact the survival of protists, which play a crucial role in marine ecosystems. To better understand the protistan community structure and species that can thrive in hypoxic waters, we collected samples from both the surface and bottom waters during the hypoxic period in Jinhae and Masan Bays and the non-hypoxic period in Jinhae Bay. Subsequently, we utilized metabarcoding techniques to identify the protistan species. During hypoxia, with dissolved oxygen concentrations of 0.8 mg L<sup>-1</sup> in Jinhae Bay and 1.8 mg L<sup>-1</sup> in Masan Bay within the bottom waters, the phylum Dinoflagellata exhibited the highest amplicon sequence variants richness among the identified protist phyla. Following the Dinoflagellata, Ochrophyta and Ciliophora also displayed notable presence. In hypoxic waters of Jinhae and Masan Bays, we identified a total of 36 dinoflagellate species that exhibited various trophic modes. These included one autotrophic species, 14 mixotrophic species, 9 phototrophic species with undetermined trophic modes (either autotrophic or mixotrophic), 2 kleptoplastidic species, and 10 heterotrophic species. Furthermore, the hypoxic bottom water exhibited a greater number of heterotrophic dinoflagellate species compared to the non-hypoxic surface water within the same water column or the non-hypoxic bottom water. Therefore, feeding by mixotrophic and heterotrophic dinoflagellates may be partially responsible for their dominance in terms of the number of species surviving in hypoxic waters. This study not only introduces the initial documentation of 26 dinoflagellate species surviving in hypoxic conditions but also establishes a foundation for a more comprehensive understanding of the ecophysiology of dinoflagellates in hypoxic marine environments.
12
Kawachi, Takashi, Shun Tanaka, Akinori Fukuda, Yuji Sumii, Andi Setiawan, Naoyuki Kotoku, Motomasa Kobayashi e Masayoshi Arai. "Target Identification of the Marine Natural Products Dictyoceratin-A and -C as Selective Growth Inhibitors in Cancer Cells Adapted to Hypoxic Environments". Marine Drugs 17, n. 3 (8 marzo 2019): 163. http://dx.doi.org/10.3390/md17030163.
Abstract (sommario):
Hypoxia-adapted cancer cells in tumors contribute to the pathological progression of cancer. The marine spongean sesquiterpene phenols dictyoceratin-A (1) and -C (2) have been shown to induce hypoxia-selective growth inhibition in cultured cancer cells and exhibit in vivo antitumor effects. These compounds inhibit the accumulation of hypoxia-inducible factor-1α (HIF-1α), which is a drug target in hypoxia-adapted cancer cells, under hypoxic conditions. However, the target molecules of compounds 1 and 2, which are responsible for decreasing HIF-1α expression under hypoxic conditions, remain unclear. In this study, we synthesized probe molecules for compounds 1 and 2 to identify their target molecules and found that both compounds bind to RNA polymerase II-associated protein 3 (RPAP3), which is a component of the R2TP/Prefoldin-like (PEDL) complex. In addition, RPAP3-knockdown cells showed a phenotype similar to that of compound-treated cells.
13
Kodama, Keita, Md Saydur Rahman, Toshihiro Horiguchi e Peter Thomas. "Assessment of hypoxia-inducible factor-1α mRNA expression in mantis shrimp as a biomarker of environmental hypoxia exposure". Biology Letters 8, n. 2 (26 ottobre 2011): 278–81. http://dx.doi.org/10.1098/rsbl.2011.0887.
Abstract (sommario):
Efforts to assess the ecological impacts of the marked increase in coastal hypoxia worldwide have been hampered by a lack of biomarkers of hypoxia exposure in marine benthic organisms. Here, we show that hypoxia-inducible factor-1α (HIF-1α) transcript levels in the heart and cerebral ganglion of mantis shrimp ( Oratosquilla oratoria ) collected from hypoxic sites in Tokyo Bay are elevated several-fold over those in shrimp collected from normoxic sites. Upregulation of HIF-1α mRNA levels in the heart after exposure to sub-lethal hypoxia was confirmed in controlled laboratory experiments. HIF-1α transcript levels were increased at approximately threefold after 7 and 14 days of hypoxia exposure and declined to control levels within 24 h of restoration to normoxic conditions. The results provide the first evidence for upregulation of HIF-1α transcript levels in two hypoxia-sensitive organs, heart and cerebral ganglion, in a marine invertebrate exposed to environmental hypoxia. These results suggest that upregulation of HIF-1α transcript levels is an important component in adaptation of mantis shrimp to chronic hypoxia and is a potentially useful biomarker of environmental hypoxia exposure.
14
Zheng, Jingjing, Shan Gao, Guimei Liu, Hui Wang e Xueming Zhu. "Modeling the impact of river discharge and wind on the hypoxia off Yangtze Estuary". Natural Hazards and Earth System Sciences 16, n. 12 (1 dicembre 2016): 2559–76. http://dx.doi.org/10.5194/nhess-16-2559-2016.
Abstract (sommario):
Abstract. The phenomenon of low dissolved oxygen (known as hypoxia) in a coastal ocean system is closely related to a combination of anthropogenic and natural factors. Marine hypoxia occurs in the Yangtze Estuary, China, with high frequency and long persistence. It is related primarily to organic and nutrient enrichment influenced by river discharges and physical factors, such as water mixing. In this paper, a three-dimensional hydrodynamic model was coupled to a biological model to simulate and analyze the ecological system of the East China Sea. By comparing with the observation data, the model results can reasonably capture the physical and biochemical dynamics of the Yangtze Estuary. In addition, the sensitive experiments were also used to examine the role of physical forcing (river discharge, wind speed, wind direction) in controlling hypoxia in waters adjacent to the Yangtze Estuary. The results showed that the wind field and river discharge have significant impact on the hypoxia off the Yangtze Estuary. The seasonal cycle of hypoxia was relatively insensitive to synoptic variability in the river discharge, but integrated hypoxic areas were sensitive to the whole magnitude of river discharge. Increasing the river discharge was shown to increase hypoxic areas, while decreasing the river discharge tended to decrease hypoxic areas. The variations of wind speed and direction had a great impact on the integrated hypoxic areas.
15
Nolan, Sean, Stephen M. Bollens e Gretchen Rollwagen-Bollens. "Diverse taxa of zooplankton inhabit hypoxic waters during both day and night in a temperate eutrophic lake". Journal of Plankton Research 41, n. 4 (luglio 2019): 431–47. http://dx.doi.org/10.1093/plankt/fbz021.
Abstract (sommario):
Abstract As the frequency and intensity of hypoxic events increase in both fresh and marine waters, understanding the ecological effects of hypoxia becomes more important. The extant literature reports varying effects of hypolimnetic hypoxia on the vertical distribution and diel vertical migration (DVM) of zooplankton, with some but not all taxa reported to avoid hypoxic waters. We studied the vertical distribution and DVM of diverse zooplankton taxa throughout three seasons over 2 years (2014 and 2015) in Lacamas Lake, WA, USA. We observed hypoxia (<2 mg L−1 dissolved oxygen) in the hypolimnion of Lacamas Lake during five of six sampling periods, with zooplankton populations often exhibiting ‘h-metric’ values (defined as the proportion of a zooplankton population residing within hypoxic waters) ranged from 0.14 to 1.00, with an overall mean of h = 0.66. Moreover, we observed a lack of DVM in most zooplankton taxa on most occasions. Our findings indicate both community-level and taxon-specific zooplankton tolerances to hypoxia, although the exact mechanisms at play remain to be fully elucidated. Nevertheless, the common residency in hypoxic waters and the lack of DVM by diverse zooplankton taxa that we observed likely have implications for food web dynamics in Lacamas Lake and other water bodies.
16
Kotsyuba, Elena, e Vyacheslav Dyachuk. "Role of the Neuroendocrine System of Marine Bivalves in Their Response to Hypoxia". International Journal of Molecular Sciences 24, n. 2 (7 gennaio 2023): 1202. http://dx.doi.org/10.3390/ijms24021202.
Abstract (sommario):
Mollusks comprise one of the largest phylum of marine invertebrates. With their great diversity of species, various degrees of mobility, and specific behavioral strategies, they haveoccupied marine, freshwater, and terrestrial habitats and play key roles in many ecosystems. This success is explained by their exceptional ability to tolerate a wide range of environmental stresses, such as hypoxia. Most marine bivalvemollusksare exposed to frequent short-term variations in oxygen levels in their marine or estuarine habitats. This stressfactor has caused them to develop a wide variety of adaptive strategies during their evolution, enabling to mobilize rapidly a set of behavioral, physiological, biochemical, and molecular defenses that re-establishing oxygen homeostasis. The neuroendocrine system and its related signaling systems play crucial roles in the regulation of various physiological and behavioral processes in mollusks and, hence, can affect hypoxiatolerance. Little effort has been made to identify the neurotransmitters and genes involved in oxygen homeostasis regulation, and the molecular basis of the differences in the regulatory mechanisms of hypoxia resistance in hypoxia-tolerant and hypoxia-sensitive bivalve species. Here, we summarize current knowledge about the involvement of the neuroendocrine system in the hypoxia stress response, and the possible contributions of various signaling molecules to this process. We thusprovide a basis for understanding the molecular mechanisms underlying hypoxic stress in bivalves, also making comparisons with data from related studies on other species.
17
Li, Guihao, Qinqin Song, Pengfei Zheng, Xiaoli Zhang, Songbao Zou, Yanfang Li, Xuelu Gao, Zhao Zhao e Jun Gong. "Dynamics and Distribution of Marine Synechococcus Abundance and Genotypes during Seasonal Hypoxia in a Coastal Marine Ranch". Journal of Marine Science and Engineering 9, n. 5 (19 maggio 2021): 549. http://dx.doi.org/10.3390/jmse9050549.
Abstract (sommario):
Marine Synechococcus are an ecologically important picocyanobacterial group widely distributed in various oceanic environments. Little is known about the dynamics and distribution of Synechococcus abundance and genotypes during seasonal hypoxia in coastal zones. In this study, an investigation was conducted in a coastal marine ranch along two transects in Muping, Yantai, where hypoxic events (defined here as the dissolved oxygen concentration <3 mg L−1) occurred in the summer of 2015. The hypoxia occurred in the bottom waters from late July and persisted until late August. It was confined at nearshore stations of the two transects, one running across a coastal ranch and the other one outside. During this survey, cell abundance of Synechococcus was determined with flow cytometry, showing great variations ranging from 1 × 104 to 3.0 × 105 cells mL−1, and a bloom of Synechococcus occurred when stratification disappeared and hypoxia faded out outside the ranch. Regression analysis indicated that dissolved oxygen, pH, and inorganic nutrients were the most important abiotic factors in explaining the variation in Synechococcus cell abundance. Diverse genotypes (mostly belonged to the sub-clusters 5.1 and 5.2) were detected using clone library sequencing and terminal restriction fragment length polymorphism analysis of the 16S–23S rRNA internal transcribed spacer region. The richness of genotypes was significantly related to salinity, temperature, silicate, and pH, but not dissolved oxygen. Two environmental factors, temperature and salinity, collectively explained 17% of the variation in Synechococcus genotype assemblage. With the changes in population composition in diverse genotypes, the Synechococcus assemblages survived in the coastal hypoxia event and thrived when hypoxia faded out.
18
Chu, Jackson W. F., Curtis Curkan e Verena Tunnicliffe. "Drivers of temporal beta diversity of a benthic community in a seasonally hypoxic fjord". Royal Society Open Science 5, n. 4 (aprile 2018): 172284. http://dx.doi.org/10.1098/rsos.172284.
Abstract (sommario):
Global expansion of oxygen-deficient (hypoxic) waters will have detrimental effects on marine life in the Northeast Pacific Ocean (NEP) where some of the largest proportional losses in aerobic habitat are predicted to occur. However, few in situ studies have accounted for the high environmental variability in this region while including natural community-assembly dynamics. Here, we present results from a 14-month deployment of a benthic camera platform tethered to the VENUS cabled observatory in the seasonally hypoxic Saanich Inlet. Our time series continuously recorded natural cycles of deoxygenation and reoxygenation that allowed us to test whether a community from the NEP showed hysteresis in its recovery compared to hypoxia-induced decline, and to address the processes driving temporal beta diversity under variable states of hypoxia. Using high-frequency ecological time series, we reveal (i) differences in the response and recovery of the epibenthic community are rate-limited by recovery of the sessile species assemblage; (ii) both environmental and biological processes influence community assembly patterns at multiple timescales; and (iii) interspecific processes can drive temporal beta diversity in seasonal hypoxia. Ultimately, our results illustrate how different timescale-dependent drivers can influence the response and recovery of a marine habitat under increasing stress from environmental change.
19
Hindle, Allyson G. "Diving deep: understanding the genetic components of hypoxia tolerance in marine mammals". Journal of Applied Physiology 128, n. 5 (1 maggio 2020): 1439–46. http://dx.doi.org/10.1152/japplphysiol.00846.2019.
Abstract (sommario):
Marine mammals have highly specialized physiology, exhibited in many species by extreme breath-holding capabilities that allow deep dives and extended submergence. Cardiovascular control and cell-level hypoxia tolerance are key features of this phenotype. Identifying genomic signatures tied to physiology will be valuable in understanding these natural model species, which may generate translational opportunities to human diseases arising from hypoxic stress or tissue injury. Genomic analyses have now been conducted in dolphins, river dolphins, minke whales, bowhead whales, and polar bears, with multispecies studies exploring evolutionary signals across marine mammal lineages, encompassing extinct and extant divers. Single-species genome studies for sirenians do not yet exist. Extant marine mammals arose in three lineages from separate aquatic recolonizations. Their physiological specializations, along with these independent origins create an interesting case to examine convergent evolution. Although molecular mechanisms of hypoxia tolerance are not universally apparent across marine mammal genomic studies, altered evolutionary rates have been identified for genes linked to oxygen binding and transport (e.g., MB, HBA, and HBB), blood pressure control (e.g., endothelin pathway genes), and cell protection in multiple species. Despite convergent phenotypes across clades, instances of identical molecular convergence have been uncommon. Given the inherent logistical and regulatory difficulties associated with functional genetic experiments in marine mammals, several avenues of further investigation are suggested to enable validation of candidate genes for hypoxia tolerance: leveraging phylogeny to better understand convergent phenotypes; ontogenic studies to identify regulation of key genes underlying the elite, adult, hypoxia-tolerant physiology; and cell culture manipulations to understand gene function.
20
Oldham, Tina, Tim Dempster, Philip Crosbie, Mark Adams e Barbara Nowak. "Cyclic Hypoxia Exposure Accelerates the Progression of Amoebic Gill Disease". Pathogens 9, n. 8 (22 luglio 2020): 597. http://dx.doi.org/10.3390/pathogens9080597.
Abstract (sommario):
Amoebic gill disease (AGD), caused by the amoeba Neoparamoeba perurans, has led to considerable economic losses in every major Atlantic salmon producing country, and is increasing in frequency. The most serious infections occur during summer and autumn, when temperatures are high and poor dissolved oxygen (DO) conditions are most common. Here, we tested if exposure to cyclic hypoxia at DO saturations of 40–60% altered the course of infection with N. perurans compared to normoxic controls maintained at ≥90% DO saturation. Although hypoxia exposure did not increase initial susceptibility to N. perurans, it accelerated progression of the disease. By 7 days post-inoculation, amoeba counts estimated from qPCR analysis were 1.7 times higher in the hypoxic treatment than in normoxic controls, and cumulative mortalities were twice as high (16 ± 4% and 8 ± 2%), respectively. At 10 days post-inoculation, however, there were no differences between amoeba counts in the hypoxic and normoxic treatments, nor in the percentage of filaments with AGD lesions (control = 74 ± 2.8%, hypoxic = 69 ± 3.3%), or number of lamellae per lesion (control = 30 ± 0.9%, hypoxic = 27.9 ± 0.9%) as determined by histological examination. Cumulative mortalities at the termination of the experiment were similarly high in both treatments (hypoxic = 60 ± 2%, normoxic = 53 ± 11%). These results reveal that exposure to cyclic hypoxia in a diel pattern, equivalent to what salmon are exposed to in marine aquaculture cages, accelerated the progression of AGD in post-smolts.
21
Herrmann, BethElLee, e Julie E. Keister. "Species Composition and Distribution of Jellyfish in a Seasonally Hypoxic Estuary, Hood Canal, Washington". Diversity 12, n. 2 (29 gennaio 2020): 53. http://dx.doi.org/10.3390/d12020053.
Abstract (sommario):
Seasonal hypoxia (≤2 mg dissolved oxygen L−1) can have detrimental effects on marine food webs. Recent studies indicate that some jellyfish can tolerate low oxygen and may have a competitive advantage over other zooplankton and fishes in those environments. We assessed community structure and distributions of cnidarian and ctenophore jellyfish in seasonally hypoxic Hood Canal, WA, USA, at four stations that differed in oxygen conditions. Jellyfish were collected in June through October 2012 and 2013 using full-water-column and discrete-depth net tows, concurrent with CTD casts to measure dissolved oxygen (DO). Overall, southern, more hypoxic, regions of Hood Canal had higher abundances and higher diversity than the northern regions, particularly during the warmer and more hypoxic year of 2013. Of fifteen species identified, the most abundant—the siphonophore Muggiaea atlantica and hydrozoan Aglantha digitale—reached peak densities > 1800 Ind m−3 and 38 Ind m−3, respectively. M. atlantica were much more abundant at the hypoxic stations, whereas A. digitale were also common in the north. Vertical distributions explored during hypoxia showed that jellyfish were mostly in the upper 10 m regardless of the oxycline depth. Moderate hypoxia seemed to have no detrimental effect on jellyfish in Hood Canal, and may have resulted in high population densities, which could influence essential fisheries and trophic energy flow.
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Garcia, Maria Rita, Paula B. Andrade, Florence Lefranc e Nelson G. M. Gomes. "Marine-Derived Leads as Anticancer Candidates by Disrupting Hypoxic Signaling through Hypoxia-Inducible Factors Inhibition". Marine Drugs 22, n. 4 (23 marzo 2024): 143. http://dx.doi.org/10.3390/md22040143.
Abstract (sommario):
The inadequate vascularization seen in fast-growing solid tumors gives rise to hypoxic areas, fostering specific changes in gene expression that bolster tumor cell survival and metastasis, ultimately leading to unfavorable clinical prognoses across different cancer types. Hypoxia-inducible factors (HIF-1 and HIF-2) emerge as druggable pivotal players orchestrating tumor metastasis and angiogenesis, thus positioning them as prime targets for cancer treatment. A range of HIF inhibitors, notably natural compounds originating from marine organisms, exhibit encouraging anticancer properties, underscoring their significance as promising therapeutic options. Bioprospection of the marine environment is now a well-settled approach to the discovery and development of anticancer agents that might have their medicinal chemistry developed into clinical candidates. However, despite the massive increase in the number of marine natural products classified as ‘anticancer leads,’ most of which correspond to general cytotoxic agents, and only a few have been characterized regarding their molecular targets and mechanisms of action. The current review presents a critical analysis of inhibitors of HIF-1 and HIF-2 and hypoxia-selective compounds that have been sourced from marine organisms and that might act as new chemotherapeutic candidates or serve as templates for the development of structurally similar derivatives with improved anticancer efficacy.
23
Deleja, Mark, José Ricardo Paula, Tiago Repolho, Marco Franzitta, Miguel Baptista, Vanessa Lopes, Silvia Simão, Vanessa F. Fonseca, Bernardo Duarte e Rui Rosa. "Effects of Hypoxia on Coral Photobiology and Oxidative Stress". Biology 11, n. 7 (18 luglio 2022): 1068. http://dx.doi.org/10.3390/biology11071068.
Abstract (sommario):
Global ocean oxygen (O2) content is decreasing as climate change drives declines in oxygen solubility, strengthened stratification of seawater masses, increased biological oxygen consumption and coastal eutrophication. Studies on the biological effects of nocturnal decreased oxygen concentrations (hypoxia) on coral reefs are very scarce. Coral reefs are fundamental for supporting one quarter of all marine species and essential for around 275 million people worldwide. This study investigates acute physiological and photobiological responses of a scleractinian coral (Acropora spp.) to overnight hypoxic conditions (<2 mg/L of O2). Bleaching was not detected, and visual and physical aspects of corals remained unchanged under hypoxic conditions. Most photobiological-related parameters also did not show significant changes between treatments. In addition to this, no significant differences between treatments were observed in the pigment composition. However, hypoxic conditions induced a significant decrease in coral de-epoxidation state of the xanthophyll cycle pigments and increase in DNA damage. Although the present findings suggest that Acropora spp. is resilient to some extent to short-term daily oxygen oscillations, long-term exposure to hypoxia, as predicted to occur with climate change, may still have deleterious effects on corals.
24
Smith, Martin D., Atle Oglend, A. Justin Kirkpatrick, Frank Asche, Lori S. Bennear, J. Kevin Craig e James M. Nance. "Seafood prices reveal impacts of a major ecological disturbance". Proceedings of the National Academy of Sciences 114, n. 7 (30 gennaio 2017): 1512–17. http://dx.doi.org/10.1073/pnas.1617948114.
Abstract (sommario):
Coastal hypoxia (dissolved oxygen ≤ 2 mg/L) is a growing problem worldwide that threatens marine ecosystem services, but little is known about economic effects on fisheries. Here, we provide evidence that hypoxia causes economic impacts on a major fishery. Ecological studies of hypoxia and marine fauna suggest multiple mechanisms through which hypoxia can skew a population’s size distribution toward smaller individuals. These mechanisms produce sharp predictions about changes in seafood markets. Hypoxia is hypothesized to decrease the quantity of large shrimp relative to small shrimp and increase the price of large shrimp relative to small shrimp. We test these hypotheses using time series of size-based prices. Naive quantity-based models using treatment/control comparisons in hypoxic and nonhypoxic areas produce null results, but we find strong evidence of the hypothesized effects in the relative prices: Hypoxia increases the relative price of large shrimp compared with small shrimp. The effects of fuel prices provide supporting evidence. Empirical models of fishing effort and bioeconomic simulations explain why quantifying effects of hypoxia on fisheries using quantity data has been inconclusive. Specifically, spatial-dynamic feedbacks across the natural system (the fish stock) and human system (the mobile fishing fleet) confound “treated” and “control” areas. Consequently, analyses of price data, which rely on a market counterfactual, are able to reveal effects of the ecological disturbance that are obscured in quantity data. Our results are an important step toward quantifying the economic value of reduced upstream nutrient loading in the Mississippi Basin and are broadly applicable to other coupled human-natural systems.
25
Hagens, M., C. P. Slomp, F. J. R. Meysman, D. Seitaj, J. Harlay, A. V. Borges e J. J. Middelburg. "Biogeochemical processes and buffering capacity concurrently affect acidification in a seasonally hypoxic coastal marine basin". Biogeosciences 12, n. 5 (11 marzo 2015): 1561–83. http://dx.doi.org/10.5194/bg-12-1561-2015.
Abstract (sommario):
Abstract. Coastal areas are impacted by multiple natural and anthropogenic processes and experience stronger pH fluctuations than the open ocean. These variations can weaken or intensify the ocean acidification signal induced by increasing atmospheric pCO2. The development of eutrophication-induced hypoxia intensifies coastal acidification, since the CO2 produced during respiration decreases the buffering capacity in any hypoxic bottom water. To assess the combined ecosystem impacts of acidification and hypoxia, we quantified the seasonal variation in pH and oxygen dynamics in the water column of a seasonally stratified coastal basin (Lake Grevelingen, the Netherlands). Monthly water-column chemistry measurements were complemented with estimates of primary production and respiration using O2 light–dark incubations, in addition to sediment–water fluxes of dissolved inorganic carbon (DIC) and total alkalinity (TA). The resulting data set was used to set up a proton budget on a seasonal scale. Temperature-induced seasonal stratification combined with a high community respiration was responsible for the depletion of oxygen in the bottom water in summer. The surface water showed strong seasonal variation in process rates (primary production, CO2 air–sea exchange), but relatively small seasonal pH fluctuations (0.46 units on the total hydrogen ion scale). In contrast, the bottom water showed less seasonality in biogeochemical rates (respiration, sediment–water exchange), but stronger pH fluctuations (0.60 units). This marked difference in pH dynamics could be attributed to a substantial reduction in the acid–base buffering capacity of the hypoxic bottom water in the summer period. Our results highlight the importance of acid–base buffering in the pH dynamics of coastal systems and illustrate the increasing vulnerability of hypoxic, CO2-rich waters to any acidifying process.
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Hagens, M., C. P. Slomp, F. J. R. Meysman, D. Seitaj, J. Harlay, A. V. Borges e J. J. Middelburg. "Biogeochemical processes and buffering capacity concurrently affect acidification in a seasonally hypoxic coastal marine basin". Biogeosciences Discussions 11, n. 11 (18 novembre 2014): 15827–87. http://dx.doi.org/10.5194/bgd-11-15827-2014.
Abstract (sommario):
Abstract. Coastal areas are impacted by multiple natural and anthropogenic processes and experience stronger pH fluctuations than the open ocean. These variations can weaken or intensify the ocean acidification signal induced by increasing atmospheric pCO2. The development of eutrophication-induced hypoxia intensifies coastal acidification, since the CO2 produced during respiration decreases the buffering capacity of the hypoxic bottom water. To assess the combined ecosystem impacts of acidification and hypoxia, we quantified the seasonal variation in pH and oxygen dynamics in the water column of a seasonally stratified coastal basin (Lake Grevelingen, the Netherlands). Monthly water column chemistry measurements were complemented with estimates of primary production and respiration using O2 light-dark incubations, in addition to sediment-water fluxes of dissolved inorganic carbon (DIC) and total alkalinity (TA). The resulting dataset was used to set up a proton budget on a seasonal scale. Temperature-induced seasonal stratification combined with a high community respiration was responsible for the depletion of oxygen in the bottom water in summer. The surface water showed strong seasonal variation in process rates (primary production, CO2 air–sea exchange), but relatively small seasonal pH fluctuations (0.46 units on the total hydrogen ion scale). In contrast, the bottom water showed less seasonality in biogeochemical rates (respiration, sediment–water exchange), but stronger pH fluctuations (0.60 units). This marked difference in pH dynamics could be attributed to a substantial reduction in the acid-base buffering capacity of the hypoxic bottom water in the summer period. Our results highlight the importance of acid-base buffering in the pH dynamics of coastal systems and illustrate the increasing vulnerability of hypoxic, CO2-rich waters to any acidifying process.
27
Luczkovich, Joseph J., Mark W. Sprague e Hans W. Paerl. "Bottom water hypoxia suppresses fish chorusing in estuaries". Journal of the Acoustical Society of America 155, n. 3 (1 marzo 2024): 2014–24. http://dx.doi.org/10.1121/10.0025289.
Abstract (sommario):
Hypoxia in coastal ecosystems is increasing as a result of water quality declines from nutrient pollution. Hypoxia negatively affects fish populations and marine life, limiting their spawning habitats, population size, and growth. In this study, two approaches were used to understand the effect of hypoxia on the chorusing and reproductive behavior of fishes in estuaries. One approach used a water quality meter integrated with a prototype passive acoustic recorder, developed to monitor dissolved oxygen and fish chorusing simultaneously and continuously at sites with normoxic and hypoxic conditions. In a second approach, passive acoustic recorders were deployed near ambient water quality monitoring stations, monitored by the North Carolina agencies in estuaries where hypoxia occurs periodically. In both approaches, when hypoxia (dissolved oxygen < 4.0 mg/L) occurred, fish chorusing was diminished or ceased. A strong correlation was observed between bottom water dissolved oxygen and the power spectral density in a 100–200 Hz frequency band associated with red drum (Sciaenops ocellatus, Sciaenidae) calling. Passive acoustic monitoring stations and integrated passive acoustic and water quality meters should be used in estuarine hypoxia monitoring efforts to examine the expanding areas of hypoxia and its impact on fish critical spawning habitats.
28
Hammarlund, Emma U. "Harnessing hypoxia as an evolutionary driver of complex multicellularity". Interface Focus 10, n. 4 (12 giugno 2020): 20190101. http://dx.doi.org/10.1098/rsfs.2019.0101.
Abstract (sommario):
Animal tissue requires low-oxygen conditions for its maintenance. The need for low-oxygen conditions contrasts with the idea of an evolutionary leap in animal diversity as a result of expanding oxic conditions. To accommodate tissue renewal at oxic conditions, however, vertebrate animals and vascular plants demonstrate abilities to access hypoxia. Here, I argue that multicellular organisms sustain oxic conditions first after internalizing hypoxic conditions. The ‘harnessing’ of hypoxia has allowed multicellular evolution to leave niches that were stable in terms of oxygen concentrations for those where oxygen fluctuates. Since oxygen fluctuates in most settings on Earth's surface, the ancestral niche would have been a deep marine setting. The hypothesis that ‘large life’ depends on harnessing hypoxia is illustrated in the context of conditions that promote the immature cell phenotype (stemness) in animal physiology and tumour biology and offers one explanation for the general rarity of diverse multicellularity over most of Earth's history.
29
SINGH, A. D., S. DAS e K. VERMA. "Impact of climate induced hypoxia on calcifying biota in the Arabian Sea : An evaluation from the micropaleontological records of the Indian margin". MAUSAM 62, n. 4 (16 dicembre 2021): 647–52. http://dx.doi.org/10.54302/mausam.v62i4.388.
Abstract (sommario):
High biological productivity combined with the poor ventilation produces severe oxygen depletion (hypoxia) in upper intermediate waters of the Arabian Sea. The naturally developed Arabian Sea oxygen minimum zone (OMZ) is one of the most pronounced low oxygen ocean environments known today. The OMZ impinges the Indian margin where oxygen concentration reaches values less than 0.05 ml/l leading denitrification. In recent studies, it has been observed that the OMZ strength has varied considerably in the past, in tune with the global climate change. But the effect of changes in natural mid-water hypoxic environment on the marine biota particularly of the eastern Arabian Sea is unknown. Here, we analyzed 30,000 yr record of temporal changes in two major groups of marine calcifying microfauna pteropods secreting aragonitic shells and foraminifera secreting calcitic shells in terms of abundance and diversity variations. This study will provide an insight into our understanding of potential impact of rising atmospheric CO2 on marine ecosystem.
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Peña, M. A., S. Katsev, T. Oguz e D. Gilbert. "Modeling dissolved oxygen dynamics and coastal hypoxia: a review". Biogeosciences Discussions 6, n. 5 (24 settembre 2009): 9195–256. http://dx.doi.org/10.5194/bgd-6-9195-2009.
Abstract (sommario):
Abstract. Hypoxia occurs in marine ecosystems throughout the world, influences biogeochemical cycles of elements and may have severe impacts on marine life. Hypoxia results from complex interactions between physical and biogeochemical processes, which can not be addressed by observations alone. In this paper, we review oxygen dynamical models that have been applied in studies of factors controlling coastal hypoxia and in predictions of future states. We also identify scientific issues that need further development and point out some of the major challenges. Over recent decades, substantial progress has been made in the development of oxygen dynamical models. Considerable progress has been made towards the parameterization of biogeochemical processes in the water column and sediments, such as the dynamic representation of nitrification-denitrification. Recent advances in three-dimensional coupled physical-ecological-biogeochemical models allow better representation of physical-biological interactions. Several types of modelling approaches, from simple to complex, have significantly contributed to improve our understanding of hypoxia. We discuss the applications of these models to the study of the effects of oxygen depletion on biogeochemical cycles, links between nutrient enrichment and hypoxia development, impacts of hypoxia on marine ecosystems and predictions of climate change responses. However, for some processes models are still crude. For example, current representations of organic matter transformations and remineralization are incomplete, as they are mostly based on empirical parameterizations at few locations. For most of these processes, the availability of validation data has been a limiting factor in model development. Another gap is that, in virtually all nutrient load models, efforts have focused on nutrient utilization and organic matter degradation, whereas three-dimensional mixing and advection have been less well represented. Explicit inclusion of physical and biogeochemical processes in models will help us answer several important questions, such as those about the causes of the observed worldwide increase in hypoxic conditions, and future changes in the intensity and spread of coastal hypoxia. At the same time, recent quantitative model intercomparison studies suggest that the predictive ability of our models may be adversely affected by their increasing complexity, unless the models are properly constrained by observations.
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Peña, M. A., S. Katsev, T. Oguz e D. Gilbert. "Modeling dissolved oxygen dynamics and hypoxia". Biogeosciences 7, n. 3 (9 marzo 2010): 933–57. http://dx.doi.org/10.5194/bg-7-933-2010.
Abstract (sommario):
Abstract. Hypoxia conditions are increasing throughout the world, influencing biogeochemical cycles of elements and marine life. Hypoxia results from complex interactions between physical and biogeochemical processes, which can not be understood by observations alone. Models are invaluable tools at studying system dynamics, generalizing discrete observations and predicting future states. They are also useful as management tools for evaluating site-specific responses to management scenarios. Here we review oxygen dynamics models that have significantly contributed to a better understanding of the effects of natural processes and human perturbations on the development of hypoxia, factors controlling the extent and temporal variability of coastal hypoxia, and the effects of oxygen depletion on biogeochemical cycles. Because hypoxia occurs in a variety of environments and can be persistent, periodic or episodic, models differ significantly in their complexity and temporal and spatial resolution. We discuss the progress in developing hypoxia models for benthic and pelagic systems that range from simple box models to three dimensional circulation models. Applications of these models in five major hypoxia regions are presented. In the last decades, substantial progress has been made towards the parameterization of biogeochemical processes in both hypoxic water columns and sediments. In coastal regions, semi-empirical models have been used more frequently than mechanistic models to study nutrient enrichment and hypoxia relationships. Recent advances in three-dimensional coupled physical-ecological-biogeochemical models have allowed a better representation of physical-biological interactions in these systems. We discuss the remaining gaps in process descriptions and suggest directions for improvement. Better process representations in models will help us answer several important questions, such as those about the causes of the observed worldwide increase in hypoxic conditions, and future changes in the intensity and spread of coastal hypoxia. At the same time, quantitative model intercomparison studies suggest that the predictive ability of our models may be adversely affected by their increasing complexity, unless the models are properly constrained by observations.
32
Kordella, Stavroula, Dimitris Christodoulou, Elias Fakiris, Maria Geraga, Sotiris Kokkalas, Giuditta Marinaro, Margarita Iatrou, George Ferentinos e George Papatheodorou. "Gas Seepage-Induced Features in the Hypoxic/Anoxic, Shallow, Marine Environment of Amfilochia Bay, Amvrakikos Gulf (Western Greece)". Geosciences 11, n. 1 (5 gennaio 2021): 27. http://dx.doi.org/10.3390/geosciences11010027.
Abstract (sommario):
Amfilochia Bay (Eastern Amvrakikos Gulf, Western Greece), a complex marine area affected by tectonism, was investigated for seabed seepage manifestations and for possible inter-relationships between shallow gas accumulations and hypoxia. For this purpose, an integrated research methodology that combined geophysical, geochemical, and hydrographic surveys was applied. Marine geophysical and bathymetric surveys led to the discovery of a gas-induced pockmark group in the study area. Oceanographic surveying confirmed that the bay is hypoxic/anoxic below a depth of 15 m (dissolved oxygen from ~4 to 60 μM). Very weak CH4 seepage was detected in correspondence to the pockmark group that seemed to slightly enhance the hypoxic environment locally and close to the seabed, with no effect in shallower waters and the oxycline. Methane isotopic analysis showed variable carbon isotopic composition (from −41‰ to −86‰) which could be either related to differential CH4 oxidation or mixing between microbial and thermogenic gas. However, the pathway of degassing is clearly related to the fault-controlled pockmark group. A protrusion mound, which has erroneously been reported as a submarine “volcano” since 1876, could be the result of mud volcanism based on the geophysical data of this study.
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Mello, Ashley M., Tenzin Ngodup, Yusoo Lee, Katelyn L. Donahue, Jinju Li, Arvind Rao, Eileen S. Carpenter, Howard C. Crawford, Marina Pasca Di Magliano e Kyoung Eun Lee. "Abstract PR03: Hypoxia promotes inflammatory fibroblast formation in pancreatic cancer". Cancer Immunology Research 11, n. 12_Supplement (1 dicembre 2023): PR03. http://dx.doi.org/10.1158/2326-6074.tumimm23-pr03.
Abstract (sommario):
Abstract Pancreatic ductal adenocarcinoma (PDAC) is a deadly malignancy characterized by poor response to all existing therapies. Although immunotherapy has shown great promise against multiple deadly cancers, it has been largely ineffective in PDAC. This lack of response is in part attributed to its extensive, fibroinflammatory stroma and hypoxic microenvironment. Cancer-associated fibroblasts (CAFs) are a predominant and heterogeneous stromal cell type in PDAC, and single-cell transcriptomics of human and mouse PDAC has recently revealed a distinct CAF subpopulation, inflammatory CAFs (iCAFs). These inflammatory fibroblasts produce high levels of cytokines and chemokines in PDAC and have the potential to contribute to its immunosuppressive microenvironment and tumorigenesis. By injecting a hypoxia probe into PDAC mouse models, we recently found that iCAFs predominantly reside in hypoxic tumor regions. We also observed that the hypoxia-related gene signature is positively enriched in iCAFs in human PDAC samples. Importantly, by exposing three-dimensional (3D) co-cultures of pancreatic cancer cells and fibroblasts to either hypoxia or normoxia, we showed that hypoxia induces IL1α from cancer cells and that IL1α is required for hypoxia-mediated iCAF formation. Our data implicate hypoxia as a critical regulator of tumor stroma. Efforts are ongoing to understand the role of hypoxia in the crosstalk between cancer cells, fibroblasts, and immune cells in driving an immunosuppressive tumor microenvironment. Citation Format: Ashley M. Mello, Tenzin Ngodup, Yusoo Lee, Katelyn L. Donahue, Jinju Li, Arvind Rao, Eileen S. Carpenter, Howard C. Crawford, Marina Pasca Di Magliano, Kyoung Eun Lee. Hypoxia promotes inflammatory fibroblast formation in pancreatic cancer [abstract]. In: Proceedings of the AACR Special Conference in Cancer Research: Tumor Immunology and Immunotherapy; 2023 Oct 1-4; Toronto, Ontario, Canada. Philadelphia (PA): AACR; Cancer Immunol Res 2023;11(12 Suppl):Abstract nr PR03.
34
CLAIREAUX, GUY, e JEAN-DENIS DUTIL. "PHYSIOLOGICAL RESPONSE OF THE ATLANTIC COD (GADUS MORHUA) TO HYPOXIA AT VARIOUS ENVIRONMENTAL SALINITIES". Journal of Experimental Biology 163, n. 1 (1 febbraio 1992): 97–118. http://dx.doi.org/10.1242/jeb.163.1.97.
Abstract (sommario):
Atlantic cod (Gadus morhua L.) acclimated to water salinities ranging from 28 ‰ to 7 ‰ were exposed to mild (8.0 kPa) or severe (4.0 kPa) hypoxic conditions for 6h. In each experiment, respiratory, acid-base, ionic, haematological and metabolic disturbances were analyzed. During mild hypoxia, a strong hyperventilatory response was observed, resulting in a respiratory alkalosis that persisted throughout the 6-h trial. Plasma Cl− and pyruvate levels were the only other variables to display significant changes: they both increased. In more severe hypoxic conditions, although the ventilatory response was the same, a weak metabolic acidosis was superimposed. The haematological response (increased haematocrit and decreased mean cellular haemoglobin content) suggested that catecholamines were released into the blood. Both Na+ and Cl− concentrations increased significantly. Metabolic perturbations occurred: plasma lactate, pyruvate and glucose concentrations increased markedly. Though lactate concentrations in liver, heart and white muscle increased, the concentrations of pyruvate, glucose and glycogen did not change significantly. Water salinity affected the amplitude of the ionic responses during hypoxia: the amplitude decreased with decreasing salinity. Irrespective of water salinity, 23 of 29 fish survived the severe hypoxic conditions. This relatively good tolerance of low water oxygenation, as compared with other marine bottom-feeders, suggests that this species may face poorly oxygenated waters in the wild. Together with temperature and salinity, ater oxygen content may thus be an important variable to take into account in the study of the distribution and migration patterns of Atlantic cod.
35
Jang, Min-Chul, Kyoungsoon Shin, Pung-Guk Jang, Woo-Jin Lee e Keun-Hyung Choi. "Mesozooplankton community in a seasonally hypoxic and highly eutrophic bay". Marine and Freshwater Research 66, n. 8 (2015): 719. http://dx.doi.org/10.1071/mf14036.
Abstract (sommario):
A 2-year survey of seawater chemistry and mesozooplankton abundance was carried out in Masan Bay, South Korea, one of the most eutrophic coastal ecosystems known. The study aimed to identify the major factors contributing to the seasonally persistent hypoxia in the bay, to characterise the Bay’s mesozooplankton community and to examine the effects of low oxygen on the distribution of mesozooplankton. Hypoxia (<2mgO2L–1) was present only in summer, with ultrahypoxia (<0.2mg O2 L–1) in the bottom waters of the inner bay in both years. Low summer oxygen can be attributed to high summer phytoplankton stocks, together with reduced oxygen solubility at high temperature and stratification of the water column that limits downward diffusion of oxygen. A seasonally and spatially distinct mesozooplankton community was identified in summer when there was greater influence of freshwater discharge in the inner bay. Marine cladocerans were very abundant, with a population outburst of Penilia avirostris in the inner bay (>4000 individuals m–3) during summer. During hypoxic events, the abundance of Penilia avirostris was positively related to oxygen levels in the bottom water, suggesting that hypoxic conditions may cause mortality or have sublethal negative effects on population growth of this filter-feeding cladoceran.
36
Lucey, Noelle M., Curtis A. Deutsch, Marie-Hélène Carignan, Fanny Vermandele, Mary Collins, Maggie D. Johnson, Rachel Collin e Piero Calosi. "Climate warming erodes tropical reef habitat through frequency and intensity of episodic hypoxia". PLOS Climate 2, n. 3 (1 marzo 2023): e0000095. http://dx.doi.org/10.1371/journal.pclm.0000095.
Abstract (sommario):
Climate warming threatens marine life by increasing metabolic oxygen demand while decreasing oxygen availability. Tropical species living in warm, low oxygen environments may be most at risk, but their tolerances and exposures to these stressors remain poorly documented. We evaluated habitat restrictions for two brittle star species from Caribbean coral reefs by integrating field observations, laboratory experiments and an ecophysiological model. The absence of one species from the warmest reefs results from vital activity restrictions during episodic low oxygen extremes, even though average conditions are well within physiological tolerance limits. Over the past decade, warmer temperatures have been significantly correlated with a greater frequency and intensity of hypoxic events. Continued warming will progressively exclude hypoxia-tolerant species, even if average oxygen remains constant. A warming-driven increase in frequency or intensity of low oxygen extremes could similarly accelerate habitat loss across other marine ecosystems.
37
Díaz Asencio, Lisbet, Yusmila Helguera, Raúl Fernández-Garcés, Miguel Gómez-Batista, Guillermo Rosell, Yurisbey Hernández, Anabell Pulido e Maickel Armenteros. "Two-year temporal response of benthic macrofauna and sediments to hypoxia in a tropical semi-enclosed bay (Cienfuegos, Cuba)". Revista de Biología Tropical 64, n. 1 (28 giugno 2016): 177. http://dx.doi.org/10.15517/rbt.v64i1.18519.
Abstract (sommario):
Hypoxia is the depletion of dissolved oxygen below 2 mg O2/L. Relatively few studies on hypoxia and its effects on benthic macrofauna have been done in tropical marine ecosystems. This study describes the temporal response of the water column, sediments and macrofauna to seasonal hypoxia in a semi-enclosed bay (Cienfuegos, Caribbean Sea). The Calisito site was sampled monthly from June 2010 until February 2012, yielding 21 sampling times. At each sampling event water and sediment samples were collected for measuring the abiotic variables (temperature, salinity, dissolved oxygen, nutrients, redox potential discontinuity, silt/clay and organic matter content) and macrofauna (abundance and species richness). Temperature and surface salinity followed a typical temporal pattern during the summer/rainy and the winter/dry periods. Salinity stratification occurred in the rainy period, lasting three months in 2010 and six months in 2011. The bottom water dissolved oxygen indicated hypoxic and anoxic events during the wet periods of 2010 and 2011 associated with salinity stratification, low hydrodynamics and oxidation of the accumulated organic matter. Over the study period, 817 individuals were collected and identified. Polychaetes were the dominant group in terms of abundance (57 % of total) followed by mollusks (41%). Hypoxia (and occasionally anoxia) caused strong deleterious effects on the abundance and species richness of macrofaunal communities in the study site. The most abundant polychaetes were opportunistic species with high tolerance to hypoxic conditions: Prionospio steenstrupi, Polydora sp.and Paraprionospio pinnata. Most of them colonized relatively fast once hypoxia ended. Persistent species such as Caecum pulchellum and Parvanachis obesa were present during hypoxia with fluctuating densities and apparently recover to higher abundances when normoxic conditions are re-established. Macoma tenta and Tellina consobrina colonized approximately 1-2 months later than the first polychaete peak during normoxia. Probably, the deleterious effects of hypoxia on the macrofauna were intensified by negative interspecific relationships such as competition by suitable space and predation. The recolonization of macrofauna depended possibly on local transport by currents within the bay because the connection with the Caribbean Sea is relatively limited. In summary, seasonal hypoxia in Cienfuegos Bay influences the water and sediment geochemistry and reduces both the abundance and diversity of macrofauna.
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Coffin, Michael R. S., Simon C. Courtenay, Kyle M. Knysh, Christina C. Pater e Michael R. van den Heuvel. "Impacts of hypoxia on estuarine macroinvertebrate assemblages across a regional nutrient gradient". FACETS 3, n. 1 (1 ottobre 2018): 23–44. http://dx.doi.org/10.1139/facets-2017-0044.
Abstract (sommario):
In this study, we examined the effects of dissolved oxygen, via metrics based on hourly measurements, and other environmental variables on invertebrate assemblages in estuaries spanning a gradient of nutrient loading and geography in the southern Gulf of St. Lawrence, Canada. Upper areas (15–25 practical salinity units (PSU)) of 13 estuaries that were dominated by either seagrass ( Zostera marina Linnaeus, 1753) or macroalgae ( Ulva spp. Linnaeus, 1753) were sampled from June to September 2013. Macroinvertebrate assemblages from Z. marina were found to be distinct from Ulva assemblages for both epifauna and infauna. Small snails dominated each vegetation type, specifically cerithids in Z. marina and hydrobids in Ulva. Although Z. marina had higher species richness, approximately 70% of species were common to both habitats. Faunal communities differed among estuaries with large, within-estuary, temporal variance only observed at Ulva sites impacted by hypoxia and particularly at sites with long water residence time. Indeed, abundances varied by several orders of magnitude in Ulva ranging from zero to thousands of macroinvertebrates. There was a strong negative correlation between hypoxic or anoxic water, 48 h prior to sampling, with relative abundances of amphipods, and a positive correlation with the relative abundances of snails. As one of the first studies to use high-frequency oxygen monitoring, this study revealed probable impacts and the transient nature of hypoxia in eutrophication.
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Hrustić, Enis, e Svjetlana Bobanović-Ćolić. "Hypoxia in deep waters of moderately eutrophic marine lakes, Island of Mljet, eastern Adriatic Sea". Scientia Marina 81, n. 4 (15 dicembre 2017): 431. http://dx.doi.org/10.3989/scimar.04523.25a.
Abstract (sommario):
In this study, we explored the impact of eutrophication and stratification on hypoxia in deep waters of moderately warm Croatian marine lakes. Although the Mljet Lakes (MLs) are predominantly oligotrophic, mesotrophic conditions are present at depths below 20 m in the Small Lake (SL) and below 30 m in the Big Lake (BL), along with higher apparent oxygen utilization (AOU). Hypoxia at depths ≥ 25 m in SL and and ≥ 40 m in BL was observed between October 2009 and January 2010, and in SL in summer (July and September 2010). Significant differences (p < 0.05) in several physical, biological and chemical parameters were detected between the lakes, while AOU, derived oxygen utilization rate (OUR) and organic carbon remineralization rate (OCRR) were not significantly different (p >0.05) between the lakes. An intense and persistent pycnocline throughout the year, comparatively high water temperature, extended water renewal time and summer phytoplankton bloom were identified as physical and biological parameters which might have significantly contributed to increased frequency of hypoxic events in a shallow SL. Significantly (p < 0.05) higher ammonium concentration in SL, especially in its deep water, seems to be a long-term chemical feature related to the poor ventilation and higher sediment oxygen demand. At the current level of eutrophication and the present climate change trends, the MLs and similar systems may experience more persistent and intense stratification, which could further prevent mixing between upper and deep waters, likely leading to increasing duration of hypoxia and its negative impacts on the biodiversity of benthic communities.
40
Graham, Helen, Samuel P. S. Rastrick, Helen S. Findlay, Matthew G. Bentley, Stephen Widdicombe, Anthony S. Clare e Gary S. Caldwell. "Sperm motility and fertilisation success in an acidified and hypoxic environment". ICES Journal of Marine Science 73, n. 3 (13 ottobre 2015): 783–90. http://dx.doi.org/10.1093/icesjms/fsv171.
Abstract (sommario):
Abstract The distribution and function of many marine species is largely determined by the effect of abiotic drivers on their reproduction and early development, including those drivers associated with elevated CO2 and global climate change. A number of studies have therefore investigated the effects of elevated pCO2 on a range of reproductive parameters, including sperm motility and fertilisation success. To date, most of these studies have not examined the possible synergistic effects of other abiotic drivers, such as the increased frequency of hypoxic events that are also associated with climate change. The present study is therefore novel in assessing the impact that an hypoxic event could have on reproduction in a future high CO2 ocean. Specifically, this study assesses sperm motility and fertilisation success in the sea urchin Paracentrotus lividus exposed to elevated pCO2 for 6 months. Gametes extracted from these pre-acclimated individuals were subjected to hypoxic conditions simulating an hypoxic event in a future high CO2 ocean. Sperm swimming speed increased under elevated pCO2 and decreased under hypoxic conditions resulting in the elevated pCO2 and hypoxic treatment being approximately equivalent to the control. There was also a combined negative effect of increased pCO2 and hypoxia on the percentage of motile sperm. There was a significant negative effect of elevated pCO2 on fertilisation success, and when combined with a simulated hypoxic event there was an even greater effect. This could affect cohort recruitment and in turn reduce the density of this ecologically and economically important ecosystem engineer therefore potentially effecting biodiversity and ecosystem services.
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McCormick, Lillian R., e Lisa A. Levin. "Physiological and ecological implications of ocean deoxygenation for vision in marine organisms". Philosophical Transactions of the Royal Society A: Mathematical, Physical and Engineering Sciences 375, n. 2102 (7 agosto 2017): 20160322. http://dx.doi.org/10.1098/rsta.2016.0322.
Abstract (sommario):
Climate change has induced ocean deoxygenation and exacerbated eutrophication-driven hypoxia in recent decades, affecting the physiology, behaviour and ecology of marine organisms. The high oxygen demand of visual tissues and the known inhibitory effects of hypoxia on human vision raise the questions if and how ocean deoxygenation alters vision in marine organisms. This is particularly important given the rapid loss of oxygen and strong vertical gradients in oxygen concentration in many areas of the ocean. This review evaluates the potential effects of low oxygen (hypoxia) on visual function in marine animals and their implications for marine biota under current and future ocean deoxygenation based on evidence from terrestrial and a few marine organisms. Evolutionary history shows radiation of eye designs during a period of increasing ocean oxygenation. Physiological effects of hypoxia on photoreceptor function and light sensitivity, in combination with morphological changes that may occur throughout ontogeny, have the potential to alter visual behaviour and, subsequently, the ecology of marine organisms, particularly for fish, cephalopods and arthropods with ‘fast’ vision. Visual responses to hypoxia, including greater light requirements, offer an alternative hypothesis for observed habitat compression and shoaling vertical distributions in visual marine species subject to ocean deoxygenation, which merits further investigation. This article is part of the themed issue ‘Ocean ventilation and deoxygenation in a warming world’.
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Hueter, Alexander, Stefan Huck, Stéphane Bodin, Ulrich Heimhofer, Stefan Weyer, Klaus P. Jochum e Adrian Immenhauser. "Central Tethyan platform-top hypoxia during Oceanic Anoxic Event 1a". Climate of the Past 15, n. 4 (18 luglio 2019): 1327–44. http://dx.doi.org/10.5194/cp-15-1327-2019.
Abstract (sommario):
Abstract. Short-term hypoxia in epeiric water masses is a common phenomenon of modern marine environments and causes mass mortality in coastal marine ecosystems. Here, we test the hypothesis that during the early Aptian, platform-top hypoxia temporarily established in some of the vast epeiric seas of the central Tethys and caused, combined with other stressors, significant changes in reefal ecosystems. Potentially interesting target examples include time intervals characterized by the demise of lower Aptian rudist–coral communities and the establishment of microencruster facies, as previously described from the central and southern Tethys and from the proto-North Atlantic domain. These considerations are relevant as previous work has predominantly focused on early Aptian basinal anoxia in the context of Oceanic Anoxic Event (OAE) 1a, whereas the potential expansion of the oxygen minimum zone (OMZ) in coeval shallow-water environments is underexplored. Well-known patterns in the δ13C record during OAE 1a allow for a sufficiently time-resolved correlation with previously studied locations and assignment to chemostratigraphic segments. This paper presents and critically discusses the outcome of a multi-proxy study (e.g., rare earth elements (REEs), U isotopes, and redox-sensitive trace elements) applied to lower Aptian shallow-water carbonates today exposed in the Kanfanar quarry in Istria, Croatia. These rocks were deposited on an extensive, isolated high in the central Tethys surrounded by hemipelagic basins. Remarkably, during chemostratigraphic segment C2, the depletion of redox-sensitive trace elements As, V, Mo, and U in platform carbonates, deposited in normal marine oxic waters, record the first occurrence of basinal, organic-rich sediment deposition in which these elements are enriched. During the C3 segment, seawater oxygen depletion established on the platform top as indicated by the patterns in Ce/Ce* and U isotopes. Shifts in redox-sensitive proxies coincide with the expansion of microencruster facies. Segment C4 witnesses the return to normal marine reefal faunas on the platform top and is characterized by patterns in redox-sensitive proxies typical of normal marine dissolved oxygen levels. It remains unclear, however, if platform-top hypoxia resulted from the expansion and upwelling of basinal, oxygen-depleted water masses or if spatially isolated, shallow hypoxic water bodies formed on the platform. Data shown here are relevant as they shed light on the driving mechanisms that control poorly understood faunal patterns during OAE 1a in the neritic realm and provide evidence on the intricate relation between basinal and platform-top water masses.
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Wohlgemuth, S. E., A. C. Taylor e M. K. Grieshaber. "Ventilatory and metabolic responses to hypoxia and sulphide in the lugworm Arenicola marina (L.)". Journal of Experimental Biology 203, n. 20 (15 ottobre 2000): 3177–88. http://dx.doi.org/10.1242/jeb.203.20.3177.
Abstract (sommario):
We examined the effects of hypoxia and sulphide levels on the ventilatory activity of Arenicola marina and determined whether ventilation compensates for oxygen deficiency and affects the mode of energy provision. A. marina ventilated intermittently, irrespective of ambient P(O2) and sulphide concentration. The ventilation rate was 28.5+/−16 ml h(−1) g(−1) wet mass during normoxia, but increased to 175+/−60% of this value during moderate hypoxia, during which aerobic energy metabolism was maintained. Below a P(O2) of 6.2 kPa, A. marina reduced the ventilated volume to 54+/−16% of the normoxic value and became anaerobic, as indicated by the accumulation of succinate and strombine. Incubation with 27 micromol l(−1) ambient sulphide had no effect on the normoxic and hypoxic ventilation rates or on the P(O2) below which anaerobiosis started (P(cM)). Increased sulphide concentrations reduced the ventilation rate and shifted the P(cM) towards a higher P(O2) below 10.7 kPa. Sulphide diffused into the body and was at least partially detoxified to thiosulphate when oxygen was present. Under normoxia, sulphide accumulated in the body wall tissue and coelomic fluid when ambient sulphide levels exceeded 117 micromol l(−1) and 216 micromol l(−1), respectively. A decrease in P(O2) in the presence of 27 or 117 micromol l(−1) ambient sulphide had no significant effect on sulphide accumulation.
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Riisgård, Hans Ulrik. "Oxygen Extraction Efficiency and Tolerance to Hypoxia in Sponges". Journal of Marine Science and Engineering 12, n. 1 (10 gennaio 2024): 138. http://dx.doi.org/10.3390/jmse12010138.
Abstract (sommario):
Sponges have always been filter feeders, in contrast to all the other filter-feeding invertebrate groups for which this feeding mode is a secondary adaptation. This study calls attention to this aspect, which explains why sponges are tolerant to hypoxia, but probably not more tolerant than the other filter-feeding invertebrates. The measurement of respiration rates at decreasing oxygen concentrations along with an estimation of the oxygen extraction efficiency in the marine demosponge Halichondria panicea have been used to understand why sponges are tolerant to low oxygen concentrations. It was found that the respiration rate was constant down to about 1.5 mL O2 L−1, which shows that the extraction efficiency increases with a decreasing oxygen concentration. It is argued that the relationship between the filtration rate and oxygen consumption in filter feeders is controlled by the resistance to the diffusion of oxygen across the boundary layer between the feeding current and the tissues of the body. A high tolerance to hypoxia is a consequence of the adaptation to filter feeding, and sponges do not have a special capacity to overcome hypoxic events.
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Kanatous, S. B., R. W. Davis, R. Watson, L. Polasek, T. M. Williams e O. Mathieu-Costello. "Aerobic capacities in the skeletal muscles of Weddell seals: key to longer dive durations?" Journal of Experimental Biology 205, n. 23 (1 dicembre 2002): 3601–8. http://dx.doi.org/10.1242/jeb.205.23.3601.
Abstract (sommario):
SUMMARYIn contrast to terrestrial animals that function under hypoxic conditions but display the typical exercise response of increasing ventilation and cardiac output, marine mammals exercise under a different form of hypoxic stress. They function for the duration of a dive under progressive asphyxia,which is the combination of increasing hypoxia, hypercapnia and acidosis. Our previous studies on short-duration, shallow divers found marked adaptations in their skeletal muscles, which culminated in enhanced aerobic capacities that are similar to those of atheltic terrestrial mammals. The purpose of the present study was to assess the aerobic capacity of skeletal muscles from long-duration divers. Swimming and non-swimming muscles were collected from adult Weddell seals, Leptonychotes weddelli, and processed for morphometric analysis, enzymology, myoglobin concentrations and fiber-type distribution. The results showed that the skeletal muscles of Weddell seals do not have enhanced aerobic capacities compared with those of terrestrial mammals but are adapted to maintain low levels of an aerobic lipid-based metabolism, especially under the hypoxic conditions associated with diving. The lower aerobic capacity of Weddell seal muscle as compared with that of shorter-duration divers appears to reflect their energy-conserving modes of locomotion, which enable longer and deeper dives.
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Zillén, L., e D. J. Conley. "Hypoxia and cyanobacterial blooms are not natural features of the Baltic Sea". Biogeosciences Discussions 7, n. 2 (15 marzo 2010): 1783–812. http://dx.doi.org/10.5194/bgd-7-1783-2010.
Abstract (sommario):
Abstract. During the last century (1900s) industrialized forms of agriculture and human activities have caused extensive eutrophication of Baltic Sea waters. As a consequence, the Baltic Sea developed a hypoxic zone that has caused serve ecosystem disturbance. Climate forcing has also been proposed to be responsible for the reported trends in hypoxia (<2 mg/l O2) both during the last c. 100 years and during the Medieval Period. By contrast, investigations on the degree of anthropogenic forcing on the ecosystem on long time-scales (millennial) have not been thoroughly addressed. This paper critically examines evidence for anthropogenic disturbance of the marine environment beyond the last century through the analysis of the population growth, technological development and land-use changes in the drainage area. Natural environmental changes, i.e. changes in the morphology and depths of the Baltic basin and the sills, were probably the main driver for large-scale hypoxia during the early Holocene (8000–4000 cal. yr BP). We show that hypoxia during the last two millennia has followed the general expansion and contraction trends in Europe and that human perturbations have been an important driver for hypoxia during that time. Hypoxia occurring during the Medieval Period coincides with a doubling of the population (from c. 4.6 to 9.5 million), a massive reclamation of land in both established and marginal cultivated areas and significant increases in soil nutrient release. The role of climate forcing on hypoxia in the Baltic Sea has yet to be convincingly demonstrated, although it could have contributed to sustain hypoxia through enhanced salt water inflows or through changes in hydrological inputs. In addition, cyanobacteria blooms are not natural features of the Baltic Sea as previously hypothesized, but are a consequence of enhanced phosphorus release that occurs together with hypoxia.
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Gomaa, Fatma, Daniel R. Utter, Christopher Powers, David J. Beaudoin, Virginia P. Edgcomb, Helena L. Filipsson, Colleen M. Hansel, Scott D. Wankel, Ying Zhang e Joan M. Bernhard. "Multiple integrated metabolic strategies allow foraminiferan protists to thrive in anoxic marine sediments". Science Advances 7, n. 22 (maggio 2021): eabf1586. http://dx.doi.org/10.1126/sciadv.abf1586.
Abstract (sommario):
Oceanic deoxygenation is increasingly affecting marine ecosystems; many taxa will be severely challenged, yet certain nominally aerobic foraminifera (rhizarian protists) thrive in oxygen-depleted to anoxic, sometimes sulfidic, sediments uninhabitable to most eukaryotes. Gene expression analyses of foraminifera common to severely hypoxic or anoxic sediments identified metabolic strategies used by this abundant taxon. In field-collected and laboratory-incubated samples, foraminifera expressed denitrification genes regardless of oxygen regime with a putative nitric oxide dismutase, a characteristic enzyme of oxygenic denitrification. A pyruvate:ferredoxin oxidoreductase was highly expressed, indicating the capability for anaerobic energy generation during exposure to hypoxia and anoxia. Near-complete expression of a diatom’s plastid genome in one foraminiferal species suggests kleptoplasty or sequestration of functional plastids, conferring a metabolic advantage despite the host living far below the euphotic zone. Through a unique integration of functions largely unrecognized among “typical” eukaryotes, benthic foraminifera represent winning microeukaryotes in the face of ongoing oceanic deoxygenation.
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Casini, Michele, Filip Käll, Martin Hansson, Maris Plikshs, Tatjana Baranova, Olle Karlsson, Karl Lundström, Stefan Neuenfeldt, Anna Gårdmark e Joakim Hjelm. "Hypoxic areas, density-dependence and food limitation drive the body condition of a heavily exploited marine fish predator". Royal Society Open Science 3, n. 10 (ottobre 2016): 160416. http://dx.doi.org/10.1098/rsos.160416.
Abstract (sommario):
Investigating the factors regulating fish condition is crucial in ecology and the management of exploited fish populations. The body condition of cod ( Gadus morhua ) in the Baltic Sea has dramatically decreased during the past two decades, with large implications for the fishery relying on this resource. Here, we statistically investigated the potential drivers of the Baltic cod condition during the past 40 years using newly compiled fishery-independent biological data and hydrological observations. We evidenced a combination of different factors operating before and after the ecological regime shift that occurred in the Baltic Sea in the early 1990s. The changes in cod condition related to feeding opportunities, driven either by density-dependence or food limitation, along the whole period investigated and to the fivefold increase in the extent of hypoxic areas in the most recent 20 years. Hypoxic areas can act on cod condition through different mechanisms related directly to species physiology, or indirectly to behaviour and trophic interactions. Our analyses found statistical evidence for an effect of the hypoxia-induced habitat compression on cod condition possibly operating via crowding and density-dependent processes. These results furnish novel insights into the population dynamics of Baltic Sea cod that can aid the management of this currently threatened population.
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Rabalais, N. N., R. J. Díaz, L. A. Levin, R. E. Turner, D. Gilbert e J. Zhang. "Dynamics and distribution of natural and human-caused coastal hypoxia". Biogeosciences Discussions 6, n. 5 (1 ottobre 2009): 9359–453. http://dx.doi.org/10.5194/bgd-6-9359-2009.
Abstract (sommario):
Abstract. Water masses can become undersaturated with oxygen when natural processes alone or in combination with anthropogenic processes create enough carbon that is aerobically decomposed faster than the rate of oxygen re-aeration. The dominant natural processes usually involved are photosynthetic carbon production and microbial respiration. The re-aeration rate is indirectly related to its isolation from the surface layer. Hypoxic water masses (<2 mg L−1, or approximately 30% saturation) can form, therefore, under "natural" conditions, and is more likely to occur in marine systems when the water residence time is extended, water exchange and ventilation is minimal, stratification occurs, and where carbon production and export to the bottom layer are relatively high. Hypoxia has occurred throughout geological time and naturally occurs in oxygen minimum zones, deep basins, eastern boundary upwelling systems and fjords. Hypoxia development and continuation in many areas of the world's coastal ocean is accelerated by human activities, especially where nutrient loading increased in the Anthropocene. This higher loading set in motion a cascading set of events related to eutrophication. Nutrient loading is likely to increase further as population growth and resource intensification rises, especially in developing countries dependent on crops using fertilizers, and it is likely that the occurrence and persistence of hypoxia will be even more widespread and have more impacts than presently observed. Climate change will further complicate the causative factors.
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Broman, Elias, Varvara Sachpazidou, Mark Dopson e Samuel Hylander. "Diatoms dominate the eukaryotic metatranscriptome during spring in coastal ‘dead zone’ sediments". Proceedings of the Royal Society B: Biological Sciences 284, n. 1864 (4 ottobre 2017): 20171617. http://dx.doi.org/10.1098/rspb.2017.1617.
Abstract (sommario):
An important characteristic of marine sediments is the oxygen concentration that affects many central metabolic processes. There has been a widespread increase in hypoxia in coastal systems (referred to as ‘dead zones’) mainly caused by eutrophication. Hence, it is central to understand the metabolism and ecology of eukaryotic life in sediments during changing oxygen conditions. Therefore, we sampled coastal ‘dead zone’ Baltic Sea sediment during autumn and spring, and analysed the eukaryotic metatranscriptome from field samples and after incubation in the dark under oxic or anoxic conditions. Bacillariophyta (diatoms) dominated the eukaryotic metatranscriptome in spring and were also abundant during autumn. A large fraction of the diatom RNA reads was associated with the photosystems suggesting a constitutive expression in darkness. Microscope observation showed intact diatom cells and these would, if hatched, represent a significant part of the pelagic phytoplankton biomass. Oxygenation did not significantly change the relative proportion of diatoms nor resulted in any major shifts in metabolic ‘signatures’. By contrast, diatoms rapidly responded when exposed to light suggesting that light is limiting diatom development in hypoxic sediments. Hence, it is suggested that diatoms in hypoxic sediments are on ‘standby’ to exploit the environment if they reach suitable habitats.