scholarly journals Low oxygen levels caused by Noctiluca scintillans bloom kills corals in Gulf of Mannar, India

2020 ◽  
Vol 10 (1) ◽  
Author(s):  
K. Diraviya Raj ◽  
G. Mathews ◽  
David O. Obura ◽  
R. L. Laju ◽  
M. Selva Bharath ◽  
...  
Keyword(s):  
Coral Reefs ◽  
Algal Blooms ◽  
Global Climate ◽  
Disease Outbreaks ◽  
Gulf Of Mannar ◽  
Coral Mortality ◽  
Low Oxygen ◽  
Noctiluca Scintillans ◽  
Oxygen Levels ◽  
Hypoxic Conditions

AbstractCoral reefs around the world are undergoing severe decline in the past few decades. Mass coral mortalities have predominantly been reported to be caused by coral bleaching or disease outbreaks. Temporary hypoxic conditions caused by algal blooms can trigger mass coral mortalities though are reported rarely. In this study in Gulf of Mannar (GoM), southeast India, we report a significant coral mortality caused by a bloom of the ciguatoxic dinoflagellate Noctiluca scintillans during September–October 2019. Dissolved oxygen levels declined below 2 mg l−1 during the bloom causing temporary hypoxia and mortality (up to 71.23%) in the fast growing coral genera Acropora, Montipora and Pocillopora. Due to global climate change, more frequent and larger algal blooms are likely in the future. Hence, it is likely that shallow water coral reefs will be affected more frequently by episodic hypoxic conditions driven by algal blooms. More studies are, however, required to understand the mechanism of coral mortality due to algal blooms, impacts on community composition and the potential for subsequent recovery.

scholarly journals The effects of acute oxygen changes on heart rate in the freshwater crab Poppiana dentata (Randall, 1840)

2020 ◽  
Vol 48 (3) ◽  
pp. 480-487
Author(s):  
Delezia Shivani Singh ◽  
Mary Alkins-Koo ◽  
Luke Victor Rostant ◽  
Azad Mohammed
Keyword(s):  
Heart Rate ◽  
Invasive Technique ◽  
Cardiac Physiology ◽  
Low Oxygen ◽  
Heart Rates ◽  
Oxygen Levels ◽  
Non Invasive ◽  
Hypoxic Conditions ◽  
Cardiac Responses ◽  
Insight Into

Heart rate is a key physiological feature that can be used to assess the response of organisms to changing environmental conditions in aquatic habitats, such as acute fluctuations in oxygen levels and hypoxic conditions. This experiment, therefore, investigated cardiac responses in a freshwater brachyuran species, Poppiana dentata, exposed to low oxygen levels. Heart rate was derived from beats per minute (bpm) signals (n = 576) using an infrared, non-invasive technique over a 96 h period, under different dissolved oxygen (DO) conditions. These involved three regimes: normoxic (6.8 ± 0.1 mg L-1), decreasing DO to hypoxic levels (6.2 to 1.7 mg L-1), and recovery with normoxic levels (6.3 ± 0.1 mg L-1). Changes in heart rates among the three regimes were significant (P < 0.05); reflecting the shift in heart rate during different conditions of oxygen availability, normoxic (59 to 61 bpm), declining DO (54 to 62 bpm) and recovery DO (53 to 64 bpm). Additionally, the normal rhythmicity of heart rates under the normoxic condition was not maintained throughout most of the declining DO and recovery periods. P. dentata has demonstrated cardiac compensations in heart rate during low oxygen levels, providing insight into the species cardiac physiology.

Exceptional Algal Blooms in Dutch North Sea Waters

1991 ◽  
Vol 24 (10) ◽  
pp. 251-260 ◽  
Author(s):  
W. Zevenboom ◽  
M. Rademaker ◽  
F. Colijn
Keyword(s):  
Coastal Zone ◽  
North Sea ◽  
Algal Blooms ◽  
Large Scale ◽  
Late Summer ◽  
Weather Conditions ◽  
Low Oxygen ◽  
Noctiluca Scintillans ◽  
Toxic Species ◽  
Calm Weather

During airborne and sea-going surveys, phytoplankton composition, and dynamics as well as relevant factors involved, were studied in Dutch North Sea waters. The aim of the study is to increase our understanding of phytoplankton dynamics, the impacts of eutrophication and the measures that are taken to reduce the risk of adverse eutrophication effects. In the coastal zone during spring (April), the relative abundance of diatoms is small when compared with the dominant scum-forming species Phaeocystis pouchetii (71-96% of total). Some potentially toxic species, like Dinophysis acuminata. were present predominantly in late summer and autumn during calm weather conditions, in the coastal zone and northern offshore waters (Oyster grounds, Dogger Bank), but in lower concentrations in 1988 and 1989 when compared with 1976, 1979 and 1981. During these three years Dinophysisacuminata blooms gave rise to mussel infection (DSP) in the Dutch Wadden Sea. The potentially toxic species Gyrodinium aureolum showed higher abundance in somewhat deeper waterlayers than at the surface. The presence of the potentially toxic species Gonyaulax(Alexandrium)tamarensis was for the first time recorded in June 1989 in concentrations of ca. 2000 cells per litre. The results further indicate an increase in occurrence of the non-toxic species Noctiluca scintillans in Dutch North Sea waters. Airborne surveys from 1979 onwards demonstrated an annual occurrence of large-scale surface algal blooms with a total annual area coverage ranging from 30 km2 (in 1982) to 1860 km2 (in 1989). Surface algal blooms are predominantly occurring during May through August, and are likely to be promoted by calm sunny weather conditions, with windforce &lt; 5 Bft over several days. Distinct “stratified” algal layers of some dominant species within an algal patch were observed, with Noctiluca in the top layer, and rather low oxygen concentrations below the large surface algal blooms. Since nutrient availability in Dutch coastal waters has remained rather constant and high over the last 10-15 years, the risks of occurrence of nuisance algal blooms and their adverse effects have remained unchanged.

Adaptation of Human CD4+ T Cells to Pathophysiological Hypoxia: A Transcriptome Analysis

2009 ◽  
Vol 36 (12) ◽  
pp. 2655-2669 ◽  
Author(s):  
TIMO GABER ◽  
THOMAS HÄUPL ◽  
GRIT SANDIG ◽  
KAROLINA TYKWINSKA ◽  
MONIQUE FANGRADT ◽  
...  
Keyword(s):  
T Cells ◽  
Synovial Tissue ◽  
Cd4 T Cells ◽  
Protein Modification ◽  
Quantitative Polymerase Chain Reaction ◽  
Low Oxygen ◽  
Rheumatoid Synovium ◽  
Tissue Samples ◽  
Oxygen Levels ◽  
Hypoxic Conditions

Objective.Inflamed tissues are usually characterized by low oxygen levels. We investigated whether pathophysiological hypoxia (pO2 < 1%) as found in the rheumatoid synovium modulates the transcriptome of human CD4+ T cells.Methods.We analyzed the extent to which hypoxia influences the transcriptome in the rheumatoid synovium according to a gene cluster reflecting adaptation to low oxygen levels. Hypoxia-inducible factor-1α (HIF-1α) was detected in the rheumatoid synovium using immunohistochemistry. Isolated human CD4+ T cells were exposed to hypoxia and analyzed using microarray analysis, quantitative polymerase chain reaction, and immunoblot detection.Results.In rheumatoid arthritis (RA) synovial tissue samples, hypoxia modulates the transcription profile. This profile is similar, but not identical, to that found in isolated CD4+ T cells incubated under hypoxic conditions. We show that HIF-1α is expressed in synovial tissue samples and in hypoxic CD4+ cells; and that hypoxia directly affects differential gene expression in human T cells with up to 4.8% modulation of the transcriptome. Functional genome analysis revealed substantial effects of hypoxia on immune response, transcriptional regulation, protein modification, cell growth and proliferation, and cell metabolism.Conclusion.Severe hypoxia, a feature of joint inflammation, considerably modulates the transcriptome of cells found in the rheumatoid synovium. Human CD4+ T cells adapt to hypoxic conditions mainly by HIF-1-driven effects on the transcriptome reflecting a profound influence on immune functions. Thus, hypoxia must be taken into account when therapeutically targeting inflammation.

scholarly journals A mathematical dissection of the adaptation of cell populations to fluctuating oxygen levels

2019 ◽  
Author(s):  
Aleksandra Ardaševa ◽  
Robert A Gatenby ◽  
Alexander R A Anderson ◽  
Helen M Byrne ◽  
Philip K Maini ◽  
...  
Keyword(s):  
Competitive Advantage ◽  
Phenotypic Variation ◽  
Evolutionary Dynamics ◽  
Chronic Hypoxia ◽  
Evolutionary Strategies ◽  
Metabolic Phenotype ◽  
Cell Populations ◽  
Low Oxygen ◽  
Oxygen Levels ◽  
Hypoxic Conditions

AbstractThe disordered network of blood vessels that arises from tumour angiogenesis results in variations in the delivery of oxygen into the tumour tissue. This brings about regions of chronic hypoxia (i.e. sustained low oxygen levels) and regions with alternating phases of low and relatively higher oxygen levels within vascularised tumours, and makes it necessary for cancer cells to adapt to fluctuating environmental conditions. We use a phenotype-structured model to dissect the evolutionary dynamics of cell populations exposed to fluctuating oxygen levels. In this model, the phenotypic state of every cell is described by a continuous variable that provides a simple representation of its metabolic phenotype, ranging from fully oxidative to fully glycolytic, and cells are grouped into two competing populations that undergo heritable, spontaneous phenotypic variations at different rates. Model simulations indicate that, depending on the rate at which oxygen is consumed by the cells, nonlinear dynamic interactions between cells and oxygen can stimulate chronic hypoxia and cycling hypoxia. Moreover, the model supports the idea that under chronic-hypoxic conditions lower rates of phenotypic variation lead to a competitive advantage, whereas higher rates of phenotypic variation can confer a competitive advantage under cycling-hypoxic conditions. In the latter case, the numerical results obtained show that bet-hedging evolutionary strategies, whereby cells switch between oxidative and glycolytic phenotypes, can spontaneously emerge. We explain how these results can shed light on the evolutionary process that may underpin the emergence of phenotypic heterogeneity in vascularised tumours.

scholarly journals Nitrogen enrichment in macroalgae following mass coral mortality

Coral Reefs ◽  
2021 ◽  
Author(s):  
Eleanor J. Vaughan ◽  
Shaun K. Wilson ◽  
Samantha J. Howlett ◽  
Valeriano Parravicini ◽  
Gareth J. Williams ◽  
...  
Keyword(s):  
Coral Reefs ◽  
Coral Cover ◽  
Strong Association ◽  
French Polynesia ◽  
Mass Mortality ◽  
Transplant Experiment ◽  
Bleaching Event ◽  
Coral Mortality ◽  
Absolute Increase ◽  
Inorganic Matter

AbstractScleractinian corals are engineers on coral reefs that provide both structural complexity as habitat and sustenance for other reef-associated organisms via the release of organic and inorganic matter. However, coral reefs are facing multiple pressures from climate change and other stressors, which can result in mass coral bleaching and mortality events. Mass mortality of corals results in enhanced release of organic matter, which can cause significant alterations to reef biochemical and recycling processes. There is little known about how long these nutrients are retained within the system, for instance, within the tissues of other benthic organisms. We investigated changes in nitrogen isotopic signatures (δ15N) of macroalgal tissues (a) ~ 1 year after a bleaching event in the Seychelles and (b) ~ 3 months after the peak of a bleaching event in Mo’orea, French Polynesia. In the Seychelles, there was a strong association between absolute loss in both total coral cover and branching coral cover and absolute increase in macroalgal δ15N between 2014 and 2017 (adjusted r2 = 0.79, p = 0.004 and adjusted r2 = 0.86, p = 0.002, respectively). In Mo’orea, a short-term transplant experiment found a significant increase in δ15N in Sargassum mangarevense after specimens were deployed on a reef with high coral mortality for ~ 3 weeks (p < 0.05). We suggest that coral-derived nutrients can be retained within reef nutrient cycles, and that this can affect other reef-associated organisms over both short- and long-term periods, especially opportunistic species such as macroalgae. These species could therefore proliferate on reefs that have experienced mass mortality events, because they have been provided with both space and nutrient subsidies by the death and decay of corals.

scholarly journals Effects of the Marine Biotoxins Okadaic Acid and Dinophysistoxins on Fish

2021 ◽  
Vol 9 (3) ◽  
pp. 293
Author(s):  
Mauro Corriere ◽  
Lucía Soliño ◽  
Pedro Reis Costa
Keyword(s):  
Okadaic Acid ◽  
Harmful Algal Blooms ◽  
Algal Blooms ◽  
Current Knowledge ◽  
Global Climate ◽  
Scientific Evidence ◽  
Shellfish Poisoning ◽  
Morphological Alterations ◽  
The Impact ◽  
Dsp Toxins

Natural high proliferations of toxin-producing microorganisms in marine and freshwater environments result in dreadful consequences at the socioeconomically and environmental level due to water and seafood contamination. Monitoring programs and scientific evidence point to harmful algal blooms (HABs) increasing in frequency and intensity as a result of global climate alterations. Among marine toxins, the okadaic acid (OA) and the related dinophysistoxins (DTX) are the most frequently reported in EU waters, mainly in shellfish species. These toxins are responsible for human syndrome diarrhetic shellfish poisoning (DSP). Fish, like other marine species, are also exposed to HABs and their toxins. However, reduced attention has been given to exposure, accumulation, and effects on fish of DSP toxins, such as OA. The present review intends to summarize the current knowledge of the impact of DSP toxins and to identify the main issues needing further research. From data reviewed in this work, it is clear that exposure of fish to DSP toxins causes a range of negative effects, from behavioral and morphological alterations to death. However, there is still much to be investigated about the ecological and food safety risks related to contamination of fish with DSP toxins.

scholarly journals Connectivity Map Analysis Indicates PI3K/Akt/mTOR Inhibitors as Potential Anti-Hypoxia Drugs in Neuroblastoma

Cancers ◽  
2021 ◽  
Vol 13 (11) ◽  
pp. 2809
Author(s):  
Paolo Uva ◽  
Maria Carla Bosco ◽  
Alessandra Eva ◽  
Massimo Conte ◽  
Alberto Garaventa ◽  
...  
Keyword(s):  
Expression Profiles ◽  
Gene Expression Profiles ◽  
Drug Repurposing ◽  
Enrichment Analysis ◽  
Mtor Inhibitors ◽  
Gene Set Enrichment Analysis ◽  
Low Oxygen ◽  
Connectivity Map ◽  
Hypoxic Conditions ◽  
Connectivity Score

Neuroblastoma (NB) is one of the deadliest pediatric cancers, accounting for 15% of deaths in childhood. Hypoxia is a condition of low oxygen tension occurring in solid tumors and has an unfavorable prognostic factor for NB. In the present study, we aimed to identify novel promising drugs for NB treatment. Connectivity Map (CMap), an online resource for drug repurposing, was used to identify connections between hypoxia-modulated genes in NB tumors and compounds. Two sets of 34 and 21 genes up- and down-regulated between hypoxic and normoxic primary NB tumors, respectively, were analyzed with CMap. The analysis reported a significant negative connectivity score across nine cell lines for 19 compounds mainly belonging to the class of PI3K/Akt/mTOR inhibitors. The gene expression profiles of NB cells cultured under hypoxic conditions and treated with the mTORC complex inhibitor PP242, referred to as the Mohlin dataset, was used to validate the CMap findings. A heat map representation of hypoxia-modulated genes in the Mohlin dataset and the gene set enrichment analysis (GSEA) showed an opposite regulation of these genes in the set of NB cells treated with the mTORC inhibitor PP242. In conclusion, our analysis identified inhibitors of the PI3K/Akt/mTOR signaling pathway as novel candidate compounds to treat NB patients with hypoxic tumors and a poor prognosis.

Seasonal variations of the dinoflagellate algae Noctiluca scintillans abundance in the western Arabian Sea and the northern Black Sea

2021 ◽  
Author(s):  
Sergey Piontkovski ◽  
Khalid Al Hashmi ◽  
Yuliya Zagorodnaya ◽  
Irina Serikova ◽  
Vladislav Evstigneev ◽  
...  
Keyword(s):  
Black Sea ◽  
Mixed Layer ◽  
Algal Blooms ◽  
Arabian Sea ◽  
Temporal Dynamics ◽  
The Black Sea ◽  
Northeast Monsoon ◽  
Major Peak ◽  
Noctiluca Scintillans ◽  
Upper Mixed Layer

&lt;p&gt;Seasonal variability is a powerful component of the spatio-temporal dynamics of plankton communities, especially in the regions with oxygen-depleted waters. The Arabian Sea and the Black Sea are typical representatives of these regions. In both, the dinoflagellate Noctiluca scintillans (Macartney) Kofoid &amp; Swezy, 1921, is one of the abundant plankton species which forms algal blooms. Sampling on coastal stations in the upper mixed layer by the plankton nets with the 120-140 &amp;#181;m mesh size was carried out in 2004-2010. Monthly data were averaged over years. A comparison of seasonal patterns of Noctiluca abundance pointed to the persistence of a bimodal seasonal cycle in both regions. The major peak was observed during spring in the Black Sea and during the winter (Northeast) monsoon in the Arabian Sea. The timing of the second (minor) peak was different over regions as well. This peak was modulated by advection of seasonally fluctuating velocity of coastal currents which transport waters enriched by nutrients by coastal upwelling. The abundance of Noctiluca of the major peak (with the concentration around 1.5*10&lt;sup&gt;6&lt;/sup&gt; cells m&lt;sup&gt;-3&lt;/sup&gt;) was from one to two orders as much high in the western Arabian Sea compared to the northern Black Sea. The remotely sensed chlorophyll-a concentration during the time of the major seasonal peak exhibited a fivefold difference over these regions. In terms of nutrient&lt;sub&gt;&lt;/sub&gt;concentration in the upper mixed layer (in particular, nitrates and silicates), a difference of about one order of magnitude was observed.&lt;/p&gt;

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