Distribution of sub-littoral meiobenthos off Goa coast,India

Vertical and horizontal distribution of meiofauna was studied off Goa coast. Bottom deposit included mainly fine sand and silt. Total number of animals ranged from 250 to 2925/10 cm². Highest faunal density was in the top 6 cm layer. The fauna consisted of two main groups, nematodes and foraminiferans which together formed 60 to 80% of the total meiofauna. Fine sand supported a rich fauna. Interstitial water and organic content of the sediment was found to be the limiting factor in the distribution of meiobenthos.     

Production and organ distribution of succinate in rice seedlings during anoxia

Anaerobic production of succinate, a common feature in animals able to sustain anoxia, has seldom been reported in plants. By the use of ¹H-nuclear magnetic resonance spectroscopy we show here that succinate is produced by rice seedlings (Oryza sativa L. cv. Arborio) subjected to anoxic conditions. Starting from levels below I μmol (g fresh weight)⁻¹ in air, after 48 h of anoxia the levels of alanine, succinate and lactate had increased to 23.8, 5.2 and 1.0 μmol (g fresh weight) ⁻¹, respectively, in shoot tissues. Succinate was accumulated in shoots, notably in the coleoptiles, but not in roots of the rice seedlings, suggesting its involvement in rice coleoptile elongation under anoxia. Other possible functions of succinate production in rice seedling, an organism highly tolerant to anoxia, are discussed.     

Anaerobic denitrification in fungi from the coastal marine sediments off Goa, India

Denitrification is a microbial process during which nitrate or nitrite is reduced under anaerobic condition to gaseous nitrogen. The Arabian Sea contains one of the major pelagic denitrification zones and in addition to this, denitrification also takes places along the continental shelf. Prokaryotic microorganisms were considered to be the only players in this process. However recent studies have shown that higher microeukaryotes such as fungi can also adapt to anaerobic mode of respiration and reduce nitrate to harmful green house gases such as NO and N₂O. In this study we examined the distribution and biomass of fungi in the sediments of the seasonal anoxic region off Goa from two stations. The sampling was carried out in five different periods from October 2005, when dissolved oxygen levels were near zero in bottom waters to March 2006. We isolated mycelial fungi, thraustochytrids and yeasts. Species of Aspergillus and thraustochytrids were dominant. Fungi were isolated under aerobic, as well as anaerobic conditions from different seasons. Four isolates were examined for their denitrification activity. Two cultures obtained from the anoxic sediments showed better growth under anaerobic condition than the other two cultures that were isolated from oxic sediments. Our preliminary results suggest that several species of fungi can grow under oxygen deficient conditions and participate in denitrification processes.     

Mechanism of the cerebrocortical vasodilatation during anoxia.

The possible role of cerebrocortical ion homeostasis, NAD/NADH redox state and of cortical oxygen tension was investigated in the initiation of hypoxic cortical vasodilatation. In addition, changes in cerebrocortical extracellular concentrations of Na+, K+, and Cl- during anoxia were studied. The results were as follows. a) The cerebrocortical reflectance decrease, e.g. cerebral vasodilatation, lagged behind the cortical pO2 decrease by 1-2 sec, but preceded the decrease of arterial blood pressure and ECoG as well as the extracellular Na+, K+, Cl- increases by 20-30 sec. Since the cortical pO2 decreased first and the ion changes lagged behind the onset of vasodilatation by 20-30 sec, it is suggested that the CBF increase in hypoxia is mediated via the cortical pO2 decrease. b) A significant NAD reduction was already present after 20 sec. of nitrogen breathing. Since the ECoG and MABP decreased, and K+ activity increased much later than this, it is presumed that the NAD reduction during the first 30-40 sec of anoxia indicates an increased rate of glycolysis, but not mitochondrial hypoxia. c) In the predepolarization phase a 17% K+, 4% Na+, 5% Cl- increase is probably the result of a reduction of the extracellular spaces caused by water movement and by the migration of Na+ and Cl- from the extracellular to the intracellular space. The large K+, Na+, Cl- changes during terminal depolarization can be interpreted as a result of the failure of the membrane bound Na+ -K+ pump and of the altered ion permeability of the cell membranes.     

Longer duration of seasonal stratification contributes to widespread increases in lake hypoxia and anoxia

The concentration of dissolved oxygen (DO) is an important attribute of aquatic ecosystems, influencing habitat, drinking water quality, biodiversity, nutrient biogeochemistry, and greenhouse gas emissions. While average summer DO concentrations are declining in lakes across the temperate zone, much remains unknown about seasonal factors contributing to deepwater DO losses. It is unclear whether declines are related to increasing rates of seasonal DO depletion or changes in seasonal stratification that limit re-oxygenation of deep waters. Furthermore, despite the presence of important biological and ecological DO thresholds, there has been no large-scale assessment of changes in the amount of habitat crossing these thresholds, limiting the ability to understand the consequences of observed DO losses. We used a dataset from >400 widely distributed lakes to identify the drivers of DO losses and quantify the frequency and volume of lake water crossing biologically and ecologically important threshold concentrations ranging from 5 to 0.5 mg/L. Our results show that while there were no consistent changes over time in seasonal DO depletion rates, over three-quarters of lakes exhibited an increase in the duration of stratification, providing more time for seasonal deepwater DO depletion to occur. As a result, most lakes have experienced summertime increases in the amount of water below all examined thresholds in deepwater DO concentration, with increases in the proportion of the water column below thresholds ranging between 0.9% and 1.7% per decade. In the 30-day period preceding the end of stratification, increases were greater at >2.2% per decade and >70% of analyzed lakes experienced increases in the amount of oxygen-depleted water. These results indicate ongoing climate-induced increases in the duration of stratification have already contributed to reduction of habitat for many species, likely increased internal nutrient loading, and otherwise altered lake chemistry. Future warming is likely to exacerbate these trends.     

Neural dynamics during anoxia and the "wave of death"

Recent experiments in rats have shown the occurrence of a high amplitude slow brain wave in the EEG approximately 1 minute after decapitation, with a duration of 5-15 s (van Rijn et al, PLoS One 6, e16514, 2011) that was presumed to signify the death of brain neurons. We present a computational model of a single neuron and its intra- and extracellular ion concentrations, which shows the physiological mechanism for this observation. The wave is caused by membrane potential oscillations, that occur after the cessation of activity of the sodium-potassium pumps has lead to an excess of extracellular potassium. These oscillations can be described by the Hodgkin-Huxley equations for the sodium and potassium channels, and result in a sudden change in mean membrane voltage. In combination with a high-pass filter, this sudden depolarization leads to a wave in the EEG. We discuss that this process is not necessarily irreversible.     

Structuro-functional changes in bushy interoceptors during protracted anoxia

The bushy receptors of the frog urinary bladder respond to the effect of 60-minute-long anoxia with a complex combination of morphological. tinctorial and electrophysiological reactions. A biphase change in dynamics of bioelectrical activity takes place (an initial increase of frequency with its successive decrease), prolongation of the vital staining periods with methylene blue, change in the character of staining and decoloration of the receptory plates: increase in homogeneity and in intensity of staining, discontinuance of granuloformation and weakening of processes of the plates mobility. The ultrastructural changes are mainly concerned with mitochondria, where either crists reduce and osmiophility decreases, or increases. A part of mitochondria does not change. Certain heterogeneity in reactive changes of the receptors is noted. This is considered as manifestation of functional heterogeneity of the receptory units and their structural elements.     

Protein stability in Artemia embryos during prolonged anoxia

Encysted embryos (cysts) of the brine shrimp, Artemia franciscana, are arguably the most stress-resistant of all animal life-history stages. One of their many adaptations is the ability to tolerate anoxia for periods of years, while fully hydrated and at physiological temperatures. Previous work indicated that the overall metabolism of anoxic embryos is brought to a reversible standstill, including the transduction of free energy and the turnover of macromolecules. But the issue of protein stability at the level of tertiary and quaternary structure was not examined. Here I provide evidence that the great majority of proteins do not irreversibly lose their native conformation during years of anoxia, despite the absence of detectable protein turnover. Although a modest degree of protein denaturation and aggregation occurs, that is quickly reversed by a brief post-anoxic aerobic incubation. I consider how such extraordinary stability is achieved and suggest that at least part of the answer involves massive amounts of a small heat shock protein (p26) that acts as a molecular chaperone, the function of which does not appear to require ribonucleoside di- or tri-phosphates.     

Stress response in Drosophila subobscura. II. Puff activity during anoxia and recovery from anoxia

When individuals of Drosophila subobscura at 0 hr prepupa are submitted to anoxia (4 hr and 24 hr, respectively), their puffing pattern is very similar to that shown by individuals at the moment of development in which treatment began. The same expression of genes (the same puffing pattern and the same protein pattern) is induced in this species by recovery from anoxia as well as by heat shock treatment at 31 degrees C.     

A concept to protect fisheries recruits by seasonal closure during spawning periods for commercial fishes off Taiwan and the East China Sea

The 72 most important commercial fish species as well as nine unidentified fish groups representing hundreds of fish species as the major and minor target species caught in waters off Taiwan and the East China Sea were selected from the ‘Fisheries Yearbook Taiwan Area.’ All available published and grey literature as well as the Fish Database of Taiwan and Fishbase websites were thoroughly reviewed for a total of 108 fish species, including 51 out of 72 major and 57 minor target fish species, on their reproductive periods in waters off Taiwan and the East China Sea. The spawning periods from these commercial fish species were then summarized. An imperative adjustment was recommended for the established fishing season closure, i.e. for an earlier start, from April to June, in the southern East China Sea. This suggested correction corresponded with the spawning period of most fishes so as to maximize the protection of spawning cohorts for at least 68 major and minor target fish species, which would account for over 53% of the total fish yield in Taiwanese offshore fisheries.     

Organic carbon dynamics in shelf edge sediments off the hebrides: A seasonal perspective

A benthic transect across the Hebridean Shelf Edge was sampled 9 times during 1995–96. Sediment samples from within the surface mixed layer were analysed for organic and inorganic carbon content, porosity, grain size and stable carbon isotope ratio. The organic carbon content is always <1% dry weight. Inorganic carbon content is 17–65% CaCO₃. There is no significant seasonal variation in organic or inorganic carbon contents despite changing productivity in the water column. However, there is an inverse relationship between organic carbon content and median grain size. The isotopic composition shows strong seasonal variation which reflects the increase in phytoplankton detritus at the sediment-water interface during spring/summer. The results suggest a small but rapid burial flux. However, the study area is not a significant depocentre for organic carbon.