Spatial distribution of copepods in fast ice of eastern Antarctica

The distribution and abundance of sympagic copepods in fast ice of the Australian Antarctic Territory (AAT) were investigated between October and December 1995. Copepods were collected from six sites between the northern Vestfold Hills (Murphy Rocks) and Mawson Station, a distance of approximately 650km. Nine species of copepods were identified from the ice cores, however, of these only three were recorded regularly : Paralabidocera antarctica, Drescheriella glacialis and Stephos longipes. The density of copepods was highest in the bottom few cm of ice, with abundances reaching up to 147l^. The highest concentrations of chlorophyll α were also found in the bottom portion of ice, suggesting that the copepods congregated in regions of high food availability. All developmental stages of Drescheriella glacialis were observed during this study, often from within a single core. In contrast, Paralabidocera antarctica occurred mainly as early copepodite stages, and Stephos longipes mainly as nauplii. These observations were consistent with the documented life cycles for each species. Drescheriella glacialis appears to reproduce and breed within the ice, Paralabidocera antarctica overwinters in the ice but enters a pelagic phase as late-stage copepodids, while nauplii of Stephos longipes are the predominant stages which associate closely with sea ice

Real-time event detection using Twitter

Twitter has become the social network of news and journalism. Monitoring what is said on Twitter is a frequent task for anyone who requires timely access to information: journalists, traders, and the emergency services have all invested heavily in monitoring Twitter in recent years. Given this, there is a need to develop systems that can automatically monitor Twitter to detect real-world events as they happen, and alert users to novel events. However, this is not an easy task due to the noise and volume of data that is produced from social media streams such as Twitter. Although a range of approaches have been developed, many are unevaluated, cannot scale past low volume streams, or can only detect specific types of event. In this thesis, we develop novel approaches to event detection, and enable the evaluation and comparison of event detection approaches by creating a large-scale test collection called Events 2012, containing 120 million tweets and with relevance judgements for over 500 events. We use existing event detection approaches and Wikipedia to generate candidate events, then use crowdsourcing to gather annotations. We propose a novel entity-based, real-time, event detection approach that we evaluate using the Events 2012 collection, and show that it outperforms existing state-of-the-art approaches to event detection whilst also being scalable. We examine and compare automated and crowdsourced evaluation methodologies for the evaluation of event detection. Finally, we propose a Newsworthiness score that is learned in real-time from heuristically labelled data. The score is able to accurately classify individual tweets as newsworthy or noise in real-time. We adapt the score for use as a feature for event detection, and find that it can easily be used to filter out noisy clusters and improve existing event detection techniques. We conclude with a summary of our research findings and answers to our research questions. We discuss some of the difficulties that remain to be solved in event detection on Twitter and propose some possible future directions for research into real-time event detection on Twitter

The Response of Antarctic Sea Ice Algae to Changes in pH and CO2

Ocean acidification substantially alters ocean carbon chemistry and hence pH but the effects on sea ice formation and the CO2 concentration in the enclosed brine channels are unknown. Microbial communities inhabiting sea ice ecosystems currently contribute 10–50% of the annual primary production of polar seas, supporting overwintering zooplankton species, especially Antarctic krill, and seeding spring phytoplankton blooms. Ocean acidification is occurring in all surface waters but the strongest effects will be experienced in polar ecosystems with significant effects on all trophic levels. Brine algae collected from McMurdo Sound (Antarctica) sea ice was incubated in situ under various carbonate chemistry conditions. The carbon chemistry was manipulated with acid, bicarbonate and bases to produce a pCO2 and pH range from 238 to 6066 matm and 7.19 to 8.66, respectively. Elevated pCO2 positively affected the growth rate of the brine algal community, dominated by the unique ice dinoflagellate, Polarella glacialis. Growth rates were significantly reduced when pH dropped below 7.6. However, when the pH was held constant and the pCO2 increased, growth rates of the brine algae increased by more than 20% and showed no decline at pCO2 values more than five times current ambient levels. We suggest that projected increases in seawater pCO2, associated with OA, will not adversely impact brine algal communities

How to process sea ice for chlorophyll-based photosynthesis measurement of the ice algae?

The Tenth Symposium on Polar Science/Ordinary sessions: [OB] Polar Biology, Wed. 4 Dec. / 3F Multipurpose conference room, National Institute of Polar Researc

Quantitative relationships between benthic diatom assemblages and water chemistry in Macquarie Island lakes and their potential for reconstructing past environmental changes

This study is the first published survey of diatom-environment relationships Oil sub-Antarctic Macquarie Island. Fifty-eight sites in 50 coastal and inland lakes were sampled for benthic diatoms and water chemistry. 208 diatom species from 34 genera were identified. Multivariate analyses indicated that the lakes were distributed along nutrient and conductivity gradients. Conductivity, pH, phosphate (SRP), silicate and temperature all explained independent portions of the variance in the diatom data. Transfer functions provide a quantitative basis for palaeolimnological studies of past climate change and human impacts, and can be used to establish baseline conditions for assessing the impacts of recent climate change and the introduction of non-native plants and animals. Statistically robust diatom transfer functions for conductivity, phosphate and silicate were developed, while pH and temperature transfer functions performed less well. The lower predictive abilities of the pH and temperature transfer functions probably reflect the broad pH tolerance range of diatoms on Macquarie Island and uneven distribution of lakes along the temperature gradient. This study contributes to understanding the current ecological distribution of Macquarie Island diatoms and provides transfer functions that will be applied in studies of diatoms in lake sediment cores to quantitatively reconstruct past environmental changes

Ocean acidification alters the benthic biofilm communities in intertidal soft sediments

Microphytobenthos (MPB) and bacterial biofilms play crucial roles in primary and secondary production, nutrient cycling and invertebrate settlement in coastal ecosystems, yet little is known of the effects of ocean acidification (OA) on these communities in intertidal soft sediments. To fill in this gap, a 28-day CO2 enhancement experiment was conducted for the benthic biofilms in soft intertidal sediments (muds and sands) from Qingdao, China. This experiment included three CO2 treatments: 400 ppm CO2 (control), 700 ppm CO2 and 1000 ppm CO2 (IPCC predicted value in 2100), which were established in a three-level CO2 incubator that can adjust the CO2 concentration in the overlying air. The effects of OA on benthic biofilms were assessed in the following three aspects: MPB biomass, biofilm community structure and microbial biogeochemical cycling (e.g., C-cycle, N-cycle and S-cycle). This study found that the 700 ppm CO2 treatment did not significantly affect the benthic biofilms in intertidal soft sediments, but the 1000 ppm CO2 treatment significantly altered the biofilm community composition and potentially their role in microbial biogeochemical cyc\ling in sediments (especially in sandy sediments). For the bacterial community in biofilms, the 1000 ppm CO2 enhancement increased the relative abundance of Alteromonadales and Bacillales but decreased the relative abundance of Rhodobacterales and Flavobacteriales. For microbial biogeochemical cycling, the 1000 ppm CO2 treatment enhanced the potential of chemoheterotrophic activity, nitrate reduction and sulfur respiration in sediments, likely resulting in a more stressful environment (hypoxic and enriched H2S) for most benthic organisms. Even though incubations in this study were only 28 days long and thus couldn’t fully accommodate the range of longer-term adaptions, it still suggests that benthic biofilms in intertidal sandy sediments are likely to change significantly near the end of the century if anthropogenic CO2 emissions unmitigated, with profound implications on local ecosystems and biogeochemical cycling

Recent environmental change and trace metal pollution in World Heritage Bathurst Harbour, southwest Tasmania, Australia

Bathurst Harbour in World Heritage southwest Tasmania, Australia, is one of the world's most pristine estuarine systems. At present there is a lack of data on pollution impacts or long-term natural variability in the harbor. A ca. 350-year-old 210Pb-dated sediment core was analysed for trace metals to track pollution impacts from local and long-range sources. Lead and antimony increased from AD 1870 onwards, which likely reflects remote (i.e. mainland Australian and global) atmospheric pollution sources. Variability in the concentrations of copper and zinc closely followed the history of mining activities in western Tasmania, which began in the AD 1880s. Tin was generally low throughout the core, except for a large peak in AD 1989±0.5years, which may be a consequence of input from a local small-scale alluvial tin mine. Changes in diatom assemblages were also investigated. The diatom flora was composed mostly of planktonic freshwater and benthic brackish-marine species, consistent with stratified estuarine conditions. Since mining began, however, an overall decrease in the proportion of planktonic to benthic taxa occurred, with the exception of two distinct peaks in the twentieth century that coincided with periods of high rainfall. Despite the region's remoteness, trace metal analyses revealed evidence of atmospheric pollution from Tasmanian and possibly longer-range mining activities. This, together with recent low rainfall, appears to have contributed to altering the diatom assemblages in one of the most pristine temperate estuaries in the worl

Editorial : Thematic issue on polar and alpine microbiology

No abstract availablehttps://academic.oup.com/femsecpm2021Genetic

A predator-prey interaction between a marine Pseudoalteromonas sp. and Gram-positive bacteria

Predator-prey interactions play important roles in the cycling of marine organic matter. Here we show that a Gram-negative bacterium isolated from marine sediments (Pseudoalteromonas sp. strain CF6-2) can kill Gram-positive bacteria of diverse peptidoglycan (PG) chemotypes by secreting the metalloprotease pseudoalterin. Secretion of the enzyme requires a Type II secretion system. Pseudoalterin binds to the glycan strands of Gram positive bacterial PG and degrades the PG peptide chains, leading to cell death. The released nutrients, including PG-derived D-amino acids, can then be utilized by strain CF6-2 for growth. Pseudoalterin synthesis is induced by PG degradation products such as glycine and glycine-rich oligopeptides. Genes encoding putative pseudoalterin-like proteins are found in many other marine bacteria. This study reveals a new microbial interaction in the ocean