Reproduction and winter biology of polar cod Boreogadus saida from Svalbard waters

Polar cod (Boreogadus saida) is considered to be a key species in the Arctic marine ecosystems. Yet detailed or even basic knowledge regarding its biology and adaptations, especially during the polar night, are in many cases poor. No field data is presently available on the gonad development of polar cod, its reproductive biology and associated bioenergetics. Accordingly, polar cod was sampled at different locations in Svalbard waters in August, September, November and January. Gonadosomatic index (GSI) and hepatosomatic (HSI) indices were calculated as indicators of the physiological state of the fish. Maturity stages were determined by microscopic histological techniques. Energy reserves (total lipids, proteins and carbohydrates) were quantified in liver and gonads as well as cellular respiration through Electron Transport System (ETS) activity. Results indicated that polar cod prepared for spawning and started developing their gonads in August and September. The fish with GSI≥4% were considered mature as they had spawned at least once or were preparing for their first spawning. A general increase in GSI was observed together with a general increase in the total energy content in polar cod gonads from August to January. Males showed fully developed gonads in November, i.e. two months earlier than females. HSI and total energy content in liver tended to be constant over time, except for males where HSI was lower in January compared to the other months. Furthermore, only mature males showed a negative correlation between GSI and HSI that indicated a drain of energy from liver to gonads in males. It was hypothesized that female and male polar cod had different reproductive strategies. Based on histological analysis of the gonads, female polar cod were confirmed to be iteroparous and to be able to spawn more than once in their lifetime. Indeed, the presence of post-ovulatory follicles in the ovaries of mature females in August indicated that the fish had spawned the previous winter, while the progressive oocytes at the stages of cortical alveoli and lipid inclusion formation showed that there would be a new reproductive cycle in the coming spawning season. The histology did not allow concluding a similar unequivocal characterisation of the male reproductive strategy and samples from post-spawning period would be needed. However, results tended to show a higher energy investment and a higher metabolic activity in males than females and a decrease in their abundance compared to females with age. It is therefore hypothesized that males may be semelparous. In the harsh Arctic conditions this gender-specific strategy can be a successful opportunity to maximise the reproduction process and maintain high abundance of the polar cod population. Males should always be ready to spawn, because the timing of female gonad development can be different and dependent on environment

Experimental study of chemiluminescence in UV and VIS range at hydrogen-oxygen mixtures ignition

The nonequilibrium radiation in the spectral range of 210-415 nm at ignition of a 10% stoichiometric hydrogen-oxygen mixture with additives of combustion inhibitors diluted with argon behind shock waves was registered. The detected chemiluminescence is presumably attributed to electronically excited H2O* and H2O2 *. Instead of the expected quenching of excited radicals and molecules in the ignition zone, with the addition of halogenated hydrocarbons inhibitors, the increase of radiation, particularly in the range of 330-415 nm, was observed. The possible reasons of this phenomenon are discussed

Gender specific reproductive strategies of an arctic key species (Boreogadus saida) and implications of climate change

The Arctic climate is changing at an unprecedented rate. What consequences this may have on the Arctic marine ecosystem depends to a large degree on how its species will respond both directly to elevated temperatures and more indirectly through ecological interactions. But despite an alarming recent warming of the Arctic with accompanying sea ice loss, reports evaluating ecological impacts of climate change in the Arctic remain sparse. Here, based upon a large-scale field study, we present basic new knowledge regarding the life history traits for one of the most important species in the entire Arctic, the polar cod (Boreogadus saida). Furthermore, by comparing regions of contrasting climatic influence (domains), we present evidence as to how its growth and reproductive success is impaired in the warmer of the two domains. As the future Arctic is predicted to resemble today's Atlantic domains, we forecast changes in growth and life history characteristics of polar cod that will lead to alteration of its role as an Arctic keystone species. This will in turn affect community dynamics and energy transfer in the entire Arctic food chain

Diversity of Metabolically Active Bacteria in Water-Flooded High-Temperature Heavy Oil Reservoir

The goal of this work was to study the overall genomic diversity of microorganisms of the Dagang high-temperature oilfield (PRC) and to characterize the metabolically active fraction of these populations. At this water-flooded oilfield, the microbial community of formation water from the near-bottom zone of an injection well where the most active microbial processes of oil degradation occur was investigated using molecular, cultural, radiotracer, and physicochemical techniques. The samples of microbial DNA and RNA from back-flushed water were used to obtain the clone libraries for the 16S rRNA gene and cDNA of 16S rRNA, respectively. The DNA-derived clone libraries were found to contain bacterial and archaeal 16S rRNA genes and the alkB genes encoding alkane monooxygenases similar to those encoded by alkB-geo1 and alkB-geo6 of geobacilli. The 16S rRNA genes of methanogens (Methanomethylovorans, Methanoculleus, Methanolinea, Methanothrix, and Methanocalculus) were predominant in the DNA-derived library of Archaea cloned sequences; among the bacterial sequences, the 16S rRNA genes of members of the genus Geobacillus were the most numerous. The RNA-derived library contained only bacterial cDNA of the 16S rRNA sequences belonging to metabolically active aerobic organotrophic bacteria (Tepidimonas, Pseudomonas, Acinetobacter), as well as of denitrifying (Azoarcus, Tepidiphilus, Calditerrivibrio), fermenting (Bellilinea), iron-reducing (Geobacter), and sulfate- and sulfur-reducing bacteria (Desulfomicrobium, Desulfuromonas). The presence of the microorganisms of the main functional groups revealed by molecular techniques was confirmed by the results of cultural, radioisotope, and geochemical research. Functioning of the mesophilic and thermophilic branches was shown for the microbial food chain of the near-bottom zone of the injection well, which included the microorganisms of the carbon, sulfur, iron, and nitrogen cycles

Description of the maturing fraction of polar cod.

<p>Percentage maturing individuals (GSI>10%), their gonado-somatic index (mean ±SD) and the estimated number of eggs per female per size class (total length, cm) from the Arctic (n = 207) and Atlantic (n = 107) domains, combined for January 2011, 2012, and 2013. Different letters (a, b, c) represent significant differences (Welch-ANOVA and Dunnett's T3) in GSI between size classes for each sex and domain.</p

Total length (cm) of polar cod in relation to otolith based age (years) and maturity status.

<p>Mature (grey boxes) and immature (white boxes) individuals sampled in January 2011, 2012 and 2013 within the Arctic (n = 66) and Atlantic (n = 104) domains. For both domains, both genders were merged due to otherwise small sample size and because gender was not found to explain variability in length in the linear model operating on the larger dataset. Plots represent the median (line), 25%–75% percentiles (box), non-outlier range (wisker) and outliers (circle). Numbers above each box are n. Asterisks show significant (t-test without corrections for multiple comparisons, p<0.05) differences between mature and immature fish within domain and age-group.</p

Frequency of occurrence (%) of preys in polar cod stomachs.

<p>Stomach contents of polar cod sampled in September 2013, from the Arctic (Rijpfjorden) and Atlantic (Kongsfjorden) domains. Only stomachs with content were included in the calculations.</p

Seasonal temperature plots in an “Atlantic” and “Arctic” type fjord.

<p>Temperature plots from moored observatories between 4^th of October 2012 and 1^st of September 2013 in Rijpfjorden (upper) and Kongsfjorden (lower).</p

Population fecundity estimates.

<p>Estimation of the total amount of maturing females and eggs produced in the catch of five trawl hauls (January 2013, 2013) in the Arctic domain (Rijpfjorden) and Atlantic domain (Adventfjorden, Isfjorden and Kongsfjorden). The numbers were estimated based on data from <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0098452#pone-0098452-g003" target="_blank">Figure 3</a>, <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0098452#pone-0098452-t002" target="_blank">Table 2</a> and the total polar cod population of each trawl haul (<a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0098452#pone.0098452.s003" target="_blank">Fig S3</a>).</p