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Hawes I.,University of Canterbury | Safi K.,NIWA Ltd | Webster-Brown J.,University of Canterbury | Sorrell B.,University of Aarhus | Arscott D.,Stroud Water Research Center
Antarctic Science | Year: 2011

Abstract We observed ice formation and water column attributes in four shallow Antarctic ponds between January and 7 April 2008. During that time ponds went from ice-free to > 80 cm thick ice, near-freshwater to hypersaline, well-lit to near darkness and temperatures fell to below zero. Here we examine shifts in biological activity that accompanied these changes. During February, freeze-concentration and ongoing photosynthesis increased dissolved oxygen concentration to up to 100 mg l-1, with a near-equivalent decrease in dissolved inorganic carbon and a pH rise. Benthic photosynthesis was responsible for 99% of estimated biological oxygen production. Net oxygen accumulation ceased in late February, pH began to fall and inorganic carbon to increase, but the pool of dissolved oxygen was depleted only slowly. Anoxia had been attained in only one pond by April and there was little accumulation of indicators of anaerobic activity. The nitrogen and phosphorus balances of the ponds were dominated by organic forms, which, like DOC and CDOM, behaved conservatively. Conversely, inorganic nitrogen and phosphorus uptake was evident throughout the study period, at a molar ratio of 16N:1P in two of three ponds, consistent with uptake into biological material. We found no coupling between N and P uptake and photosynthesis. © Antarctic Science Ltd 2011.


Safi K.,NIWA Ltd | Hawes I.,University of Canterbury | Sorrell B.,University of Aarhus
Antarctic Science | Year: 2012

The planktonic microbial communities of three meltwater ponds, located on the McMurdo Ice Shelf, were investigated from the end of January 2008 to early April, during which almost the entire pond volumes froze. The ponds were comprised of an upper mixed layer overlying a salt-stabilized density gradient in which planktonic communities were primarily embedded. Plankton comprised all components of the "microbial loop", though carnivorous protists were rare. As the ponds froze and light became increasingly limited, it was expected conditions would induce physiological changes altering the functional role of autotrophic and heterotrophic microplankton within the ponds. The results showed that microbial groups responded to the onset of winter by declining in abundance, though an exception was the appearance of filamentous cyanobacteria in the water column in March. As freezing progressed, autotrophs declined more rapidly than heterotrophs and grazing rates and abundances of mixotrophic and heterotrophic organisms increased. Grazing pressure on bacteria and picophytoplankton also increased, in part explaining their decline over time. The results indicate that stressors imposed during freezing select for increasing heterotrophy within the remaining microbial communities, although all components of the food web eventually decline as the final freeze approaches. © Copyright Antarctic Science Ltd 2012.


Hawes I.,University of Canterbury | Safi K.,NIWA Ltd | Sorrell B.,University of Aarhus | Webster-Brown J.,University of Canterbury | Arscott D.,Stroud Water Research Center
Antarctic Science | Year: 2011

Abstract Meltwater ponds are one of the most widespread aquatic habitats in ice-free areas of continental Antarctica. While most studies of such systems occur during the Antarctic summer, here we report on ice formation and water column attributes in four meltwater ponds on the McMurdo Ice Shelf during autumn, when they went from ice-free to > 80 cm thickness of ice. Ice thickness grew at an average rate of 1.5 cm d-1 in all ponds and as ice formed, salts and gases were excluded. This resulted in conductivity rising from 3-5 to > 60 mS cm-1 and contributed to the ebullition of gases. Incorporation of gas bubbles in the ice resulted in a high albedo and under-ice irradiance declined faster than incident, the former falling below 1 W m-2 (daily average) by early April. After two months of ice formation, only 0-15% of the volume of each pond was still liquid, although this represented 5-35% of the pond sediment area, where much of the biological activity was concentrated. We suggest that the stresses that the freezing process imposes may be as important to structuring the biotic communities as those during the more benign summer growth period. © Antarctic Science Ltd 2011.


Pinkerton M.H.,NIWA - National Institute of Water and Atmospheric Research | Bradford-Grieve J.M.,NIWA - National Institute of Water and Atmospheric Research | Hanchet S.M.,NIWA Ltd
CCAMLR Science | Year: 2010

A quantitative food web of the Ross Sea is presented here as a step towards investigating ecosystem effects of the fishery for Antarctic toothfish (Dissostichus mawsoni). The model consolidates quantitative information on trophic links across all the major biota of the Ross Sea and tests for data consistency. The model has 38 trophic groups and is balanced in terms of annual fows of organic carbon in an average recent year (1990-2000). The focus of the model is on the role of Antarctic toothfish in the food web which means that the model has greater taxonomic resolution towards the top of the food web than the base. A survey of the available literature and both published and unpublished data provided an initial set of parameters describing the annual average abundance, imports, exports, energetics (growth, reproduction, consumption) and trophic linkages (diets, key predators) for each model group. The relative level of uncertainty on these parameters was also estimated. This set of parameters was not self consistent, and a method is described to adjust the initial parameter set to give a balanced model, taking into account the estimates of parameter uncertainty and the large range of magnitude (>6 orders of magnitude) in trophic fows between groups. Parameters for biomass, production rate, growth efficiency, diet fractions and other transfers of biomass between groups were adjusted simultaneously. It was found that changes to the initial set of parameters needed to obtain balance were reasonably small for most groups and most parameters. The mean absolute change for all key parameters (biomass, production rate, growth efficiency) and all groups together was 1.7%, and for diet fractions was 0.6%. Large but not implausible changes in biomass, production/biomass and production/consumption parameters were needed to balance the microzooplankton (34-47%), ice bacteria (61-72%), and ice protozoa (24-54%), components of the model. Trophic levels are in close agreement with those derived from isotope and other ecosystems. In the balanced model, there is only enough large (>100 cm) toothfish production to satisfy 6.5% of the diet of Weddell seals, 5.6% of the diet of orca and 2.6% of the diet of sperm whales. The model does not support the hypothesis that depletion of Antarctic toothfish by fishing would change the diet of predators of toothfish (Weddell seals, orca, sperm whales) by large amounts throughout the Ross Sea, though the importance of toothfish as prey items to these predators is not tested and requires further investigation. The model shows that large toothfish consume 61% of the annual production of medium-sized demersal fishes and 14% of the annual production of small demersal fishes, implying a potential for the fishery to affect these prey through trophic cascades. There is a need to establish monitoring of medium and small demersal fishes in the Ross Sea, and to model potential changes to these groups due to the fishery.


Sutton C.P.,NIWA - National Institute of Water and Atmospheric Research | Horn P.L.,NIWA Ltd
CCAMLR Science | Year: 2011

Antarctic silverfish (Pleuragramma antarcticum) were sampled during a trawl survey in the Ross Sea, Antarctica. Biological data, including fish length, weight, sex, gonad maturity, liver weight and diet analysis were collected from 311 specimens. Standard length and weight were well correlated (r 2 = 0.99). Counts of growth zones in 304 thin-sectioned otoliths were used to estimate ages and von Bertalanffy growth parameters. The species is relatively slow-growing with a moderate longevity; the maximum estimated age was 14.3 years. Von Bertalanffy parameters derived for both sexes combined are: L ∞ 22.1 cm SL; K 0.167 y -1; t 0 -0.4 years. Parameter estimates were also derived for the sexes separately. Female Antarctic silverfish appear to reach a larger size than males, but none of the estimated von Bertalanffy parameters were statistically significantly different between sexes. All parameter estimates are preliminary as the ageing method is unvalidated and about two-thirds of the sampled fish could not be sexed. Precision estimates and age bias plots indicated that there was good within-reader and between-reader agreement, so the otolith sections appear able to be consistently interpreted. The standard lengths of the sampled Antarctic silverfish ranged from 4.6 to 22.9 cm. Pronounced modes in the length-frequency distribution occurred at 7.1-7.5, 10.6-11.0 and 15.1-15.5 cm. Mean lengths of 4.9 and 7.3 cm (at ages 1.3 and 2.3 years respectively) are consistent with those presented in the literature. The age-frequency distribution exhibited a mode from age 6 to 9 years.


Parkerk S.J.,NIWA - National Institute of Water and Atmospheric Research | Bowden D.A.,NIWA Ltd
CCAMLR Science | Year: 2010

Implementing measures to avoid significant adverse impacts to vulnerable marine ecosystems (VMEs) requires a specific list of the taxa that are considered vulnerable in the fishery being assessed. New Zealand identified an interim list of taxa to monitor in fishery by-catch in the Ross Sea as part of its benthic fisheries impact assessment. The rationale for including or excluding each taxonomic group is described relative to the group's fragility, longevity, organism size and spatial distribution. Additional considerations such as organism mobility, community diversity, endemism, taxonomic resolution and presence in fishery by-catch are also important. Thirteen coarse-resolution taxonomic groups are identified as vulnerable to bottom longline fishing activities in the Ross Sea region, including two indicator-only taxa.


Hanchetk S.M.,NIWA - National Institute of Water and Atmospheric Research | Mormede S.,NIWA Ltd | Dunn A.,NIWA Ltd
CCAMLR Science | Year: 2010

This paper summarises knowledge of the distribution and relative abundance of Antarctic toothfish (Dissostichus mawsoni) on the Ross Sea shelf (defined here as the continental shelf out to the edge of the shelf break at about 600-800 m depth). The focus is on D. mawsoni catches from the shelf, as this area is likely to have the greatest overlap between D. mawsoni and potential predators, and thus where any ecosystem effects would be most likely to occur. The shelf catch has been taken mainly in depths greater than 800 m from three localised fishing grounds of deep water off Terra Nova Bay, Ross Island, and in the south of small-scale research unit (SSRU) 881L (adjacent to the Ross Ice Shelf). The catch rates from the exploratory longline fishery typically show high temporal and spatial variability, even between consecutive sets within the main fishing grounds. Most toothfish caught in the southern Ross Sea were sub-adult and maturing fish, typically ranging from 60-130 cm in length, with some evidence for an ontogenetic migration from east to west as they grow. From the fisheries data available, there is no evidence for a northward contraction in the range of D. mawsoni over the course of the fishery. Nevertheless, it would seem prudent to have a monitoring system in place so that changes in relative abundance of these sub-adult fish could be detected. It is recommended that CCAMLR consider developing a sub-adult longline survey to monitor this part of the population.


Parkerk S.J.,NIWA - National Institute of Water and Atmospheric Research | Grimes P.J.,NIWA Ltd
CCAMLR Science | Year: 2010

This study uses histological assessments to determine age- and length-at-spawning for female and male Antarctic toothfish (Dissostichus mawsoni) from fish sampled in the Ross Sea spanning the 2000-2009 fishing seasons. A characterisation of the oocyte developmental cycle of D. mawsoni shows that once development begins, oocytes grow and accumulate at the cortical alveoli stage for at least one year. Individual oocytes are then recruited into the vitellogenic phase over at least a 6-12 month period, resulting in a developed group of oocytes accumulating at the final maturation stage by approximately May each year. The age at 50% spawning for females on the Ross Sea slope region is 16.6 years (95% CI 16.0-17.3) or 133.2 cm (95% CI 130.9-135.7) by length. On average, males spawn at a younger age with an A50% of 12.8 years (95% CI 11.9-14.0) or 120.4 cm (95% CI 114.8-126.7) by length. Evidence of skip-spawning was observed for females only and results in a fatter, right-shifted ogive, increasing the functional difference between male and female ogives. The degree to which the overall population ogive is biased right (older) by applying the slope-derived ogive to the northern Ross Sea region depends on the proportion of the total population occurring in the northern Ross Sea region, which is currently unknown.


Lassey K.R.,NIWA Ltd | Pinares-Patino C.S.,Agresearch Ltd. | Martin R.J.,NIWA Ltd | Molano G.,Agresearch Ltd. | McMillan A.M.S.,NIWA Ltd
Animal Feed Science and Technology | Year: 2011

The sulphur hexafluoride (SF6) tracer technique has been widely applied to determine CH4 emission rates by ruminants since its development in the mid-1990s. It remains the only viable method for determining emission rates from individual grazing animals. Essential parts of the method for each participating animal are pre-insertion into the rumen of a source of SF6 with known release rate and breath sample collections near the nose and mouth for CH4 and SF6 analysis. Breath samples are accumulated over an 'averaging period' of usually 24h to yield estimates of CH4 emissions. As a tracer, SF6 is biologically inert and has a very low detection limit (i.e., 10-12), enabling release rates of a few tens of μl/h to be sustained for many months by an initial SF6 charge of ∼1g. Any departure from a uniform SF6 collection rate, such as through SF6 interactions in the digestive tract, could introduce variability into the inferred CH4 emission rate, which has the potential to explain reports of higher variability in CH4 emission rates estimated with this technique compared with whole animal chamber techniques. Our study examined SF6 and CH4 excretion rates for their variability using a novel automated gas chromatography system that isolated and analysed 20min breath samples collected successively for 6d from each of 9 housed sheep. We found that that SF6 was not excreted into the breath stream at a uniform rate, but its daily pattern of excretion was strongly correlated with that of CH4, suggesting that some SF6 is retained within the digestive tract and later ventilated with eructated gases following feeding. Methane emission rates can be estimated for different averaging periods through different combinations of the 20min data. Methane emission rate estimates for each sheep are independent of averaging period between 3h and 6d, although inter-period variability is highest for averaging periods less than 1d. Improved understanding of the SF6 tracer technique supports it as a reliable unbiased estimator of enteric CH4 emission rate in ruminants.This paper is part of the special issue entitled: Greenhouse Gases in Animal Agriculture - Finding a Balance between Food and Emissions, Guest Edited by T.A. McAllister, Section Guest Editors; K.A. Beauchemin, X. Hao, S. McGinn and Editor for Animal Feed Science and Technology, P.H. Robinson. © 2011 Elsevier B.V.


Kingham S.,University of Canterbury | Longley I.,NIWA Ltd | Salmond J.,University of Auckland | Pattinson W.,University of Auckland | Shrestha K.,University of Auckland
Environmental Pollution | Year: 2013

This research assessed the comparative risk associated with exposure to traffic pollution when travelling via different transport modes in Christchurch, New Zealand. Concentrations of PM1, UFPs and CO were monitored on pre-defined routes during the morning and evening commute on people travelling concurrently by car, bus and bicycle. It was found that car drivers were consistently exposed to the highest levels of CO; on-road cyclists were exposed to higher levels of all pollutants than off-road cyclists; car and bus occupants were exposed to higher average levels of UFP than cyclists, and travellers were occasionally exposed to very high levels of pollution for short periods of time. PM10 and PM2.5 were found to be poor indicators of exposure to traffic pollution. Studying Christchurch adds to our understanding as it was a lower density city with limited traffic congestion compared most other cities previously studied. © 2013 Elsevier Ltd. All rights reserved.

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