Subantarctic Macquarie Island Research Articles

The influence of vegetation and soil properties on springtail communities in a diesel-contaminated soil

Soil health is important for the functioning of all terrestrial ecosystems, but may be impacted by contamination. Soil contamination may in turn necessitate rehabilitation and remediation works, but many of the techniques currently used cause physical disturbance to the soil structure, which may in itself affect soil assemblages. An understanding of the relative influence of these two types of disturbance on soil biota is needed to inform in situ remediation activities. Subantarctic Macquarie Island provides an ideal location to study these interactions because soil biodiversity is naturally low and a number of diesel spills have undergone active in situ remediation in recent years. In this study, soil cores were collected in triplicate from 21 locations. Springtails were extracted and identified to genus/species level. Total petroleum hydrocarbon (TPH) concentrations were measured at the surface and at 0.5m depth at each site, as was vegetation coverage and a range of soil properties. The relationships between these data were examined using distance-based linear models.Together, all environmental variables (vegetation and soil properties) explained a total of 76% of the variation in springtail assemblages. Soil properties alone accounted for 52% of the variation in springtail assemblages, of which bulk density was most important followed by soil conductivity and pH. Vegetation cover by the four plant taxa accounted for 34% of variation observed, with Leptinella plumosa and Poa foliosa having the greatest influence. Surface and underlying TPH concentration did not have a significant effect on springtail assemblages. Overall, factors that can be linked to physical soil disturbance had greater influence over springtail assemblages than did soil contamination. This finding may influence the selection of the most appropriate contaminant management approach for environmentally sensitive sites.

Wind Distortion in Alpine and Subantarctic Plants is Constant among Life Forms but does not Necessarily Reflect Prevailing Wind Direction

ABSTRACTWoody plants in windy environments have been used as indicators of prevailing wind direction, because wind can influence plant growth form. We investigated whether non-woody plants also display consistent prevailing wind deformation by observing the direction of asymmetry in growth form of cushion plants, graminoids, and prostrate shrubs growing in highly wind-exposed treeless environments in alpine Tasmania and subantarctic Macquarie Island. Wind distortion of individual plants was inferred from vertical photographs of feldmark and alpine heath vegetation. High correspondence in growth direction between plants of different types suggests a uniform wind influence on plants at the local scale (within <2 m). Dominant wind direction inferred from plant distortion was not consistent with the strongest and most frequent winds. On a relatively dry mountain with shallow soils the plants responded to strong northwest winds in an apparent desiccation response. Elsewhere, they responded to strong southwest winds in an apparent ice abrasion response. We conclude that, in maritime alpine and subantarctic environments, the direction of wind distortion can be measured using any of shrubs, graminoids, or cushion plants, but that this direction is not necessarily a response to the prevailing strongest winds, but rather winds that most damage foliage, the cause of damage varying with environmental context.

Range expansion of two invasive springtails on sub-Antarctic Macquarie Island

Collembola are an important group of indigenous terrestrial invertebrates in the sub-Antarctic region and, compared to the most continental regions, their limited diversity is well known. Several invasive species, introduced by humans, have also established in the region, with some of these widespread while others are more restricted to disturbed areas. In this study, we report the spread of two non-indigenous Collembola species on Macquarie Island. Protaphorura fimata (Gisin, 1952) (Collembola:Poduromorpha: Onychiuridae) and Proisotoma minuta (Tullberg, 1871) (Entomobryomorpha:Isotomidae) are both cosmopolitan species that have been present on the island for several decades, but restricted to the area around the research station. Here, we report their spread up to 3 and 11 km, respectively, from the research station. We discuss the implications of this finding for biosecurity across the Antarctic region. We also document the presence of a new non-indigenous species, Parisotoma notabilis (Schaffer, 1896) (Entomobryomorpha:Isotomidae).

Permeable bio-reactive barriers to address petroleum hydrocarbon contamination at subantarctic Macquarie Island

A reliance on diesel generated power and a history of imperfect fuel management have created a legacy of petroleum hydrocarbon contamination at subantarctic Macquarie Island. Increasing environmental awareness and advances in contaminant characterisation and remediation technology have fostered an impetus to reduce the environmental risk associated with legacy sites. A funnel and gate permeable bio-reactive barrier (PRB) was installed in 2014 to address the migration of Special Antarctic Blend diesel from a spill that occurred in 2002, as well as older spills and residual contaminants in the soil at the Main Power House. The PRB gate comprised of granular activated carbon and natural clinoptilolite zeolite. Petroleum hydrocarbons migrating in the soil water were successfully captured on the reactive materials, with concentrations at the outflow of the barrier recorded as being below reporting limits. The nutrient and iron concentrations delivered to the barrier demonstrated high temporal variability with significant iron precipitation observed across the bed. The surface of the granular activated carbon was largely free from cell attachment while natural zeolite demonstrated patchy biofilm formation after 15 months following PRB installation. This study illustrates the importance of informed material selection at field scale to ensure that adsorption and biodegradation processes are utilised to manage the environmental risk associated with petroleum hydrocarbon spills. This study reports the first installation of a permeable bio-reactive barrier in the subantarctic.

Land-based observations of cetaceans and a review of recent strandings at subantarctic Macquarie Island

The occurrence of cetaceans around subantarctic Macquarie Island is poorly known. The current study provides the first quantitative assessment of the occurrence of various cetacean species in inshore waters during 391 systematic, one-hour observation periods over 59 weeks, in 2002 and 2003. Nine species of cetacean were identified during these surveys. Killer whales, long-finned pilot whales and sperm whales were all detected with some frequency. All other species were detected on single occasions. Eight previously unpublished stranding records are also summarised. These results support the notion that most cetacean species are relatively uncommon in the inshore waters of Macquarie Island. Routine archiving of cetacean sightings obtained during shipping activities in surrounding waters is encouraged as this will further contribute to our understanding of the region’s marine megafauna.

Managing invasive plants on sub-Antarctic Macquarie Island

The Antarctic region is one of the most inhospitable frontiers on earth for weed invasion. On Australia’s world heritage sub-Antarctic Macquarie Island only three species of invasive weeds are well established (Poa annua L., Stellaria media (L.) Vill. and Cerastium fontanum Baumg.), although isolated occurrences of other species have been found and removed. These weed species are believed to have initially been introduced through human activity, a threat which is likely to increase, although strict biosecurity is in place. All three weeds are palatable and may have been suppressed to some extent by pest herbivore (rabbit) grazing. Given the high conservation value of Macquarie Island and threats to ecosystem structure and function from weed proliferation following rabbit eradication, well targeted invasive plant control management strategies are vital. We propose that a successful restoration program for Australia’s most southerly rangeland ecosystem should integrate both control of non-native plants as well as non-native herbivores. Of the non-native plants, S. media may most easily be managed, if not eradicated, because of its more limited distribution. Little, however, is known about the soil seed bank or population dynamics after rabbit eradication, nor the effect of herbicides and non-chemical control methods in cold conditions. A current research project on this non-grass species is helping to fill these knowledge gaps, complementing and building on data collected in an earlier project on the ecology and control of the more widespread invasive grass, P. annua. With an interest in off-target herbicide impacts, our work also includes a study of the movement and fate of herbicides in the cold climate Macquarie Island soils. Research in such a remote, cold, wet and windy place presents a range of logistical challenges. Nevertheless, outcomes are informing the development of effective, low-impact control or eradication options for sub-Antarctic weeds.

Rabbit haemorrhagic disease: Macquarie Island rabbit eradication adds to knowledge on both pest control and epidemiology

Rabbit haemorrhagic disease virus (RHDV), introduced into in Australia and New Zealand as a biological-control agent for wild rabbits, is least efficacious in cool humid areas where a non-pathogenic calicivirus (RCV-A1) also circulates. Heavy rabbit mortality following release of RHDV on cold sub-Antarctic Macquarie Island, where RCV-A1 was apparently absent, not only complemented the planned rabbit eradication operations, especially by reducing secondary poisoning of sea-birds from aerial baiting, but also ruled out cool or humid climate as a major limiting factor of disease spread. In turn, this has advanced the idea that RCV-A1 antibodies inhibit RHDV spread as well as reducing disease severity and mortality.

Hydrothermal contributions to global biogeochemical cycles: Insights from the Macquarie Island ophiolite

Hydrothermal circulation is a fundamental process in the formation and aging of the ocean crust, with the resultant chemical exchange between the crust and oceans comprising a key component of global biogeochemical cycles. Sections of hydrothermally altered ocean crust provide time-integrated records of this chemical exchange. Unfortunately, our knowledge of the nature and extent of hydrothermal exchange is limited by the absence of complete oceanic crustal sections from either submarine exposures or drill core. Sub-Antarctic Macquarie Island comprises ~10Ma ocean crust formed at a slow spreading ridge, and is the only sub-aerial exposure of a complete section of ocean crust in the ocean basin in which it formed. Hydrothermally altered rocks from Macquarie Island therefore provide a unique opportunity to evaluate the chemical changes due to fluid–rock exchange through a complete section of ocean crust. Here we exploit the immobile behavior of some elements during hydrothermal alteration to determine the precursor compositions to altered Macquarie whole rock samples, and evaluate the changes in bulk rock chemistry due to fluid–rock interaction throughout the Macquarie crust. The extent to which elements are enriched or depleted in each sample depends upon the secondary mineral assemblage developed, and hence the modal abundances of the primary minerals in the rocks and the alteration conditions, such as temperature, fluid composition, and water:rock ratios. Consequently the chemical changes vary with depth, most notably within the lava–dike transition zone where enrichments in K, S, Rb, Ba, and Zn are observed. Our results indicate that hydrothermal alteration of the Macquarie crust resulted in a net flux of Si, Ti, Al, and Ca to the oceans, whereas the crust was a net sink for H2O, Mg, Na, K, and S. Our results also demonstrate the importance of including the contribution of elemental uptake by veins for some elements (e.g., Si, Fe, Mg, S). Extrapolation of our results, assuming a crustal production rate of 3km2/yr, yields estimates of the hydrothermal contribution to global geochemical cycles. For example, the Mg flux to the crust is estimated to be 3.3±1.1×1012mol/year, sufficient to balance the riverine Mg input to the oceans given the uncertainties involved. However, the relationship between spreading rate and hydrothermal chemical exchange fluxes remains poorly understood, and the approach described here should be applied to crust produced at a range of spreading rates to refine the global hydrothermal flux estimates.

Seawater temperature effect on metal accumulation and toxicity in the subantarctic Macquarie Island isopod, Exosphaeroma gigas

Very little is currently known of subantarctic nearshore invertebrates’ sensitivity to environmental metals and the role of temperature in this relationship. This study investigated Cu and Zn toxicity in the common subantarctic intertidal isopod, Exosphaeroma gigas, and the influence of temperature on Cu toxicity and bioaccumulation kinetics. Adult E. gigas are insensitive to Cu and Zn at concentrations of 3200 and 7400μg/L respectively in non-renewal tests at 5.5°C (ambient subtidal temperature) over 14days. Under renewed exposures over the same temperature and time period the LC50 for copper was 2204μg/L. A 10-fold increase in Cu body burden occurred relative to zinc, indicating E. gigas has different strategies for regulating the two metals. Copper toxicity and time to mortality both increased with elevated temperature. However, temperature did not significantly affect Cu uptake rate and efflux rate constants derived from biodynamic modelling at lower Cu concentrations. These results may be attributable to E. gigas being an intertidal species with physiological mechanisms adapted to fluctuating environmental conditions. Cu concentrations required to elicit a toxicity response indicates that E. gigas would not be directly threatened by current levels of Cu or Zn present in Macquarie Island intertidal habitats, with the associated elevated temperature fluctuations. This study provides evidence that the sensitivity of this subantarctic intertidal species to metal contaminants is not as high as expected, and which has significance for the derivation of relevant guidelines specific to this distinct subpolar region of the world.

Moss δ13C: Implications for subantarctic palaeohydrological reconstructions

Southern Ocean Islands, despite their equitable oceanic climates, have recently experienced a number of pronounced climate variations. Shifts in water availability in this region are of concern; however, methods of measuring water availability are currently inadequate. Recent advances using stable carbon isotopes (δ13C) in Antarctic mosses to record long-term variations in water availability suggest that this technique might be applicable in other locations where conditions are cold enough to produce meaningful moss growth for reconstructions. Verification of this technique at each new location is essential, however, due to disparity between species and climates. Here, variations in δ13CBULK with growth water availability were measured in three moss species on subantarctic Macquarie Island. We found these subantarctic mosses showed no difference in δ13CBULK signatures between growth water environments and displayed more negative δ13CBULK ranges than those from East Antarctica, suggesting that climatic differences override the microclimate signal. Despite significant differences in leaf cell morphology there was no variation in δ13CBULK between these subantarctic species. It may be that these species are unsuitable as biological proxies due to their growth form being less dense than the turf forming Antarctic species. This underlines the need to carryout preliminary research into moss carbon isotope fractionation for each new region, and for each species, where palaeohydrological reconstructions are planned – a step that is often not given appropriate consideration in palaeo-research.

Change in the distribution of the indigenous grass Poa litorosa on sub-Antarctic Macquarie Island following the eradication of rabbits.

The recent eradication of rabbits, rats and mice from Macquarie Island has resulted in unprecedented changes to the vegetation. One unforeseen outcome is the expansion in the known distribution of the indigenous grass, Poa litorosa (L.) which was known from only four restricted populations on Macquarie Island prior to 2014. An increase in abundance of P. litorosa was observed in 2014 and so we undertook surveys to document changes in the known distribution of the species and established fixed transects in the new and previously recorded populations to monitor future changes. Monitoring of an exclosure and control plot over a 24-year period gave insights into past effects of rabbit grazing on the species. Our surveys documented a dramatic increase in the known distribution of the species. Existing populations have expanded and new populations have been recorded. Monitoring of the exclosure and control plot revealed suppression of P. litorosa plants in control plots in comparison to fenced plots during peak rabbit numbers, and so we attribute the population expansion to the recent eradication of rabbits and subsequent release of grazing pressure. This research contributes to the increasing bank of knowledge of changes occurring on Macquarie Island post-eradication and highlights the importance of monitoring to detect unforeseen changes.

Assessing the invasive risk of two non-native Agrostis species on sub-Antarctic Macquarie Island

Two small swards of two grass species (Agrostis stolonifera and Agrostis capillaris) previously unrecorded on Macquarie Island (54°30′S, 158°56′E) were found during the 2013–2014 austral summer. Their discovery leads to an assessment of their introduction status and invasive risk. Several evaluations were conducted on the plants regarding their extent, taxonomy, reproductive status and invasive potential. It is possible that the two species were accidentally introduced by human activities due to their proximity to human-frequented sites. No further occurrences were found, indicating that although the species were established, they were, respectively, restricted to two small swards of less than 1 m2 each. Observations of floral development in the field at the end of summer suggested that no sexually reproductive material was produced. Indoor cultivation of sampled specimens at the island station showed a faster development with mature flowers at the end of the summer but still no seeds. The bioclimatic niches of the two species were modeled with MaxEnt software. Biomodeling results indicate that reasonably favorable habitat is available on Macquarie Island for the successful colonization of both species. Agrostis stolonifera showed a higher invasion risk than A. capillaris. Our observations indicate that the two species are strong candidates for invading the island despite having phenological constraints. As a result, the two swards were removed by the island’s management authority. Further introductions and establishment of non-native plant species are expected to occur on sub-Antarctic islands under current global change scenarios.

Change in the distribution of the indigenous grass Poa litorosa on sub-Antarctic Macquarie Island following the eradication of rabbits

The recent eradication of rabbits, rats and mice from Macquarie Island has resulted in unprecedented changes to the vegetation. One unforeseen outcome is the expansion in the known distribution of the indigenous grass, Poa litorosa (L.) which was known from only four restricted populations on Macquarie Island prior to 2014. An increase in abundance of P. litorosa was observed in 2014 and so we undertook surveys to document changes in the known distribution of the species and established fixed transects in the new and previously-recorded populations to monitor future changes. Monitoring of an exclosure and control plot over a 24-year period gave insights into past effects of rabbit grazing on the species. Our surveys documented a dramatic increase in the known distribution of the species. Existing populations have expanded and new populations have been recorded. Monitoring of the exclosure and control plot revealed suppression of P. litorosa plants in control plots in comparison to fenced plots during peak rabbit numbers, and so we attribute the population expansion to the recent eradication of rabbits and subsequent release of grazing pressure. This research contributes to the increasing bank of knowledge of changes occurring on Macquarie Island post-eradication and highlights the importance of monitoring to detect unforeseen changes.

New Additions to the Liverwort Flora of Subantarctic Macquarie Island

Abstract Sixteen species of liverworts, two of which are represented by non-type varieties only, are reported for the first time from subantarctic Macquarie Island. These are Acrobolbus cinerascens (Lehm.) Schiffn., A. ochrophyllus (Hook.f. et Taylor) R.M.Schust., Andrewsianthus marionensis (S.W.Arnell) Grolle, Cephaloziella varians (Gottsche) Steph., Cryptolophocolea mitteniana (Colenso) L.Soderstr. var. obtusa (J.J.Engel) L.Soderstr., Herbertus oldfieldianus (Steph.) Rodway, Herzogobryum atrocapillum (Hook.f. et Taylor) Grolle, Isotachis montana Colenso, Lepidozia obtusiloba Steph., Lophocolea novaezeelandiae (Lehm.) Nees var. grandistipula (Schiffn.) Vaňa, comb. nov., L. semiteres (Lehm.) Mitt., Metzgeria flavovirens Colenso, Radula aneurismalis (Hook.f. et Taylor) Gottsche, Lindenb. et Nees, Schistochila altissima E.A.Hodgs., Syzygiella teres (Carrington et Pearson) Vaňa and Temnoma quadripartitum (Hook.) Mitt. Considering these records, the liverwort flora of Macquarie Island now totals 62 species an...

Soil invertebrate community change over fuel-contaminated sites on a subantarctic island: An ecological field-based line of evidence for site risk assessment.

A number of fuel spills, of both recent and historic origins, have occurred on World Heritage-listed subantarctic Macquarie Island. Sites contaminated by mainly diesel fuels are undergoing remediation by the Australian Antarctic Division. The risks posed by these sites are being managed using a "weight of evidence" approach, for which this study provides a preliminary line of evidence for the ecological assessment component of this site management decision framework. This knowledge is pertinent, given the absence of environmental guidelines for fuel contaminants in subantarctic ecosystems. We provide a field-based, site-specific ecological risk assessment for soil invertebrate communities across the fuel spill sites, before the commencement of in situ remediation activities. Springtails (Collembola) were the most abundant taxa. Springtail community patterns showed only limited correlations with the level of fuel contamination at the soil surface, even when elevated levels occurred in the substratum layers. Of the environmental variables measured, community patterns were most strongly correlated with vegetation cover. We identify a suite of 6 species that contribute most to the community dynamics across these sites. A subset of these we propose as useful candidates for future development of single-species toxicity tests: Folsomotoma punctata, Cryptopygus caecus, Cryptopygus antarcticus and Parisotoma insularis. Findings from this study advance our understanding of soil invertebrate community dynamics within these contaminated sites, directly contributing to the improved management and restoration of the sites. Not only does this study provide an important line of evidence for the island's ecological risk assessment for fuel contaminants, it also enhances our understanding of the potential impact of fuels at other subantarctic islands.

New insights into the cardiorespiratory physiology of weaned southern elephant seals (Mirounga leonina).

Southern elephant seal (Mirounga leonina) pups must strike a balance between conserving energy during their post-weaning fast and simultaneously developing diving abilities to attain nutritional independence. Little is known about environmental influences on cardiorespiratory patterns, hence energy use, throughout the 6 week fast. Continuous heart rates were recorded for free-ranging, newly weaned southern elephant seals using heart rate time-depth recorders for 5-9 days at Sub-Antarctic Macquarie Island, during October 1994 (n = 1), 1995 (n = 4) and 1996 (n = 1). Daytime observations of respiration and behaviour were made throughout. We present the first instance of synchronous heart rate traces recorded simultaneously for individual weaners. Generalized additive models revealed that a sinusoidal pattern of diurnal heart rate elevation and nocturnal depression was evident in all seals and, on at least one occasion, a conspicuous break in this pattern coincided with an extreme cold weather event. Seals in this study were capable of considerable cardiorespiratory control and regularly demonstrated bradycardia during periods of resting apnoea. Apnoeic duration ranged from 33 to 291 s (mean 134 s). Apnoeic heart rates (mean 67 ± 15 beats min(-1), range 40-114 beats min(-1)) were on average 19.7% lower than those exhibited during periods of eupnoea (mean 83 ± 15 beats min(-1), range 44-124 beats min(-1)). The early development of the cardiorespiratory response is characterized by arrhythmic heart and respiration rates. The strong temporal patterns observed are being driven by the opposing requirements of maximizing time spent fasting in order to develop diving capabilities and of maximizing departure mass. This pilot study has highlighted a potentially large effect of ambient weather conditions on newly weaned southern elephant seal cardiorespiratory activity. Given the increasing westerlies and more erratic and increasing storminess associated with the Southern Annular Mode predicted in the Southern Ocean, the patterns observed here warrant further investigation.

Historical ecology: a critique of François Péron’s account of Southern Elephant Seals, Mirounga leonina (Linn.),

Francois Peron’s quite detailed observations of Southern Elephant Seals, Mirounga leonina (Linn.), at King Island, Tasmania, in December 1802, are considered in the light of current knowledge of this species. Acute observations of the elephant seal and its behaviour, as well as remarks about its life history, which appears to have differed slightly from that observed recently at sub-Antarctic Macquarie Island, the nearest current breeding site, were recorded. There is a suggestion that the breeding season at King Island may have been earlier than where Southern Elephant Seals now occur in the sub-Antarctic, possibly due to King Island being closer to the equator. Peron noted that Aborigines at Port Jackson called them Mirourong, from which their current generic name was derived, and they still frequent this coast. He does not mention seeing small immature elephant seals at King Island in December when this age class hauls out to moult on Macquarie Island. The presence then of (probably exaggeratedly) large males again suggests that the annual cycle at King Island may have been in advance of that observed at Macquarie Island today. Peron’s growth rates were far in excess of those now known for the species anywhere: how he arrived at them he does not record; possibly this and other information was related to him by the sealers.

Phytoremediation of hydrocarbon contaminants in subantarctic soils: An effective management option

Accidental fuel spills on world heritage subantarctic Macquarie Island have caused considerable contamination. Due to the island's high latitude position, its climate, and its fragile ecosystem, traditional methods of remediation are unsuitable for on-site clean up. We investigated the tolerance of a subantarctic native tussock grass, Poa foliosa (Hook. f.), to Special Antarctic Blend (SAB) diesel fuel and its potential to reduce SAB fuel contamination via phytoremediation. Toxicity of SAB fuel to P. foliosa was assessed in an 8 month laboratory growth trial under growth conditions which simulated the island's environment. Single seedlings were planted into 1 L pots of soil spiked with SAB fuel at concentrations of 1000, 5 000, 10 000, 2000 and 40 000 mg/kg (plus control). Plants were harvested at 0, 2, 4 and 8 months and a range of plant productivity endpoints were measured (biomass production, plant morphology and photosynthetic efficiency). Poa foliosa was highly tolerant across all SAB fuel concentrations tested with respect to biomass, although higher concentrations of 20 000 and 40 000 mg SAB/kg soil caused slight reductions in leaf length, width and area. To assess the phytoremediation potential of P. foliosa (to 10 000 mg/kg), soil from the planted pots was compared with that from paired unplanted pots at each SAB fuel concentration. The effect of the plant on SAB fuel concentrations and the associated microbial communities found within the soil (total heterotrophs and hydrocarbon degraders) were compared between planted and unplanted treatments at the 0, 2, 4 and 8 month harvest periods. The presence of plants resulted in significantly less SAB fuel in soils at 2 months and a return to background concentration by 8 months. Microbes did not appear to be the sole driving force behind the observed hydrocarbon loss. This study provides evidence that phytoremediation using P. foliosa is a valuable remediation option for use at Macquarie Island, and may be applicable to the management of fuel spills in other cold climate regions.

Using long-term population trends of an invasive herbivore to quantify the impact of management actions in the sub-Antarctic

Accurate, long-term population estimates of invasive vertebrate pests are a key element of ecosystem management. Not only can they clarify the role of invasive species in changing ecosystem dynamics, they are also necessary to evaluate and assess management actions. Rabbits were first introduced to sub-Antarctic Macquarie Island in the 1870s, and since the 1960s have been targeted and influenced by a range of management programs. Here, for the first time, we model population trends of rabbits on Macquarie Island from the beginning of these management actions to the end of a recent, successful eradication attempt. We show that over a 38-year time frame, the population has undergone substantial fluctuations, peaking at over 350,000 individuals (27 indiv ha−1) in the late 1970s, before declining to less than 30,000 individuals (2–3 indiv ha−1) through the 1980s and early 1990s. From the late 1990s to 2005, the population increased relatively rapidly, this time peaking at approximately 221,000 individuals. After the commencement of eradication operations in 2010, the population dropped sharply, decreasing from 135,707 ± 25,995 to effectively zero in just over 12 months. This research contributes to our understanding of the complex population dynamics of sub-Antarctic invasive species and highlights the importance of monitoring in planning, understanding and assessing management actions. The development of models described here allowed population trends to be identified on Macquarie Island, despite ‘noise’ in the data from seasonality or sporadic observations. In consequence, the impacts of both long- and short-term management actions could be quantified. These techniques are applicable to other locations and species where long-term census data exist.

Spatial and temporal variation in damage and dieback in a threatened subantarctic cushion species

A decline was observed in the subantarctic Macquarie Island endemic cushion, Azorella macquariensis, during the summer of 2008–2009, resulting in the listing of the species as critically endangered in 2010. Photographs of A. macquariensis in the period 2009–2013 were used to (1) identify types of damage, (2) determine the likely causes of three distinct types of damage, (3) establish whether dieback was spreading from affected to unaffected sites and (4) find out whether dieback was associated with the expansion of Agrostis magellanica. Grey damage occurred on the most wind-exposed parts of cushions and on the most wind-exposed sites. Speck damage occurred in the opposite situations and was consistent in its location, attributes and timing with rabbit grazing. Yellow dieback was sporadic in its occurrence. Its symptoms were consistent with those of a pathogen. Yellow damage expanded between spring 2009 and autumn 2010, with neither grey nor speck damage increasing. Yellow damage was associated with a marked decline in live cushion cover in plots between 2010 and 2013. The cushion was not eliminated from any plots, despite increased cover of A. magellanica in plots with dead cushions. Only one site not affected by yellow damage in 2010 had become affected by 2013. Given these results, and given that yellow damage has been observed in the past, 2008–2010 may have been an infrequent extreme outbreak of a pathogen and/or a response of a pathogen to ongoing climatic change.