Ecophysiology and ecological impacts of an Antarctic invader: the chironomid, Eretmoptera murphyi.

Antarctica has entered a period of rapid, and potentially drastic, change. The combined pressures of anthropogenic climate change, which disproportionately affects the polar regions, and an increase in human activity and connectivity in and around the Antarctic, is opening the least invaded continent on the planet to new species. As ice retreats, terrestrial habitats ripe for colonisation by both humans and non native species are increasing, and so must our knowledge of the biology, ecology and impact of invading species. This thesis explores these issues through the model invasive species, the chironomid, Eretmoptera murphyi Schaeffer (Diptera: Chironomidae), which has successfully colonised Signy Island in the maritime Antarctic, following introduction by humans in the 1960s. Through whole organism experiments and field observations, we confirm parthenogenesis and adult emergence throughout summer on Signy. Physiological studies are employed to assess the midge’s potential to establish further south, and/or cope with climate change. Differing responses to temperature are identified in different life stages, which at various points in the life cycle must endure microclimate temperatures from +30 ºC to -20 ºC, on Signy Island. The impact of microhabitat temperature and moisture conditions on development and overwintering survival is examined, with oviposition sites found to be an important factor in determining reproductive success, especially considering a warming climate. The extent of E. murphyi’s distribution on Signy is updated, doubling previous estimates of its range, and finding that it is on the brink of moving into new valley systems. Where it occurs, the midge is capable of increasing soil nitrates by as much as five times the background levels, bringing nitrogen levels up to that seen in association with seal colonies. As the only true insect on the island, and a significant detritivore, E. murphyi has the potential to affect change to local vegetation and is arguably a new keystone species in this nutrient-poor ecosystem. Existing biosecurity measures in place seem unlikely to limit its spread which appears to be tracking footpaths used by researchers on the island. Larval stages are also able to survive several weeks in sea water, suggesting there is little impediment to its eventual colonisation of other islands and the Antarctic Peninsula, where it would likely flourish. This body of work encompasses a range of disciplines from whole organism biology through to ecosystem function, and highlights the impact that a single, and seemingly innocuous invasive species can have on an Antarctic terrestrial ecosystem

Surviving the Antarctic winter - Life stage cold tolerance and ice entrapment survival in the invasive chironomid midge Eretmoptera murphyi.

An insect’s ability to tolerate winter conditions is a critical determinant of its success. This is true for both native and invasive species, and especially so in harsh polar environments. The midge Eretmoptera murphyi (Diptera, Chironomidae) is invasive to maritime Antarctic Signy Island, and the ability of fourth instar larvae to tolerate freezing is hypothesized to allow the species to extend its range further south. However, no detailed assessment of stress tolerance in any other life stage has yet been conducted. Here, we report that, although larvae, pupae and adults all have supercooling points (SCPs) of around −5 °C, only the larvae are freeze-tolerant, and that cold-hardiness increases with larval maturity. Eggs are freeze-avoiding and have an SCP of around −17 °C. At −3.34 °C, the CTmin activity thresholds of adults are close to their SCP of −5 °C, and they are likely chill-susceptible. Larvae could not withstand the anoxic conditions of ice entrapment or submergence in water beyond 28 d. The data obtained here indicate that the cold-tolerance characteristics of this invasive midge would permit it to colonize areas further south, including much of the western coast of the Antarctic Peninsula

Moving out of town? The status of alien plants in high‐Arctic Svalbard, and a method for monitoring of alien flora in high‐risk, polar environments

Abstract Rising human activity in the Arctic, combined with a warming climate, increases the probability of introduction and establishment of alien plant species. While settlements are known hotspots for persistent populations, little is known about colonization of particularly susceptible natural habitats. Systematic monitoring is lacking and available survey methods vary greatly. Here, we present the most comprehensive survey of alien vascular plant species in the high‐Arctic archipelago of Svalbard to date, aimed at (i) providing a status within settlements; (ii) surveying high‐risk habitats such as those with high visitor numbers and nutrient enrichment from sea bird colonies; (iii) presenting a systematic monitoring method that can be implemented in future work on alien plant species in Arctic environments; and (iv) discuss possibilities for mapping alien plant habitats using unmanned aerial vehicles. The systematic grid survey, covering 1.7 km2 over three settlements and six bird cliffs, detected 36 alien plant species. Alien plant species were exclusively found in areas of human activity, particularly areas associated with current or historic animal husbandry. The survey identified the successful eradication of Anthriscus sylvestris in Barentsburg, as well as the rapid expansion of Taraxacum sect. Ruderalia over the last few decades. As there is currently no consistent method for monitoring alien plant species tailored to polar environments, we propose a systematic methodology that could be implemented within a structured monitoring regime as part of an adaptive monitoring strategy towards alien species in the Arctic

Ecological consequences of a single introduced species to the Antarctic: Terrestrial impacts of the invasive midge Eretmoptera murphyi on Signy Island

The nutrient-poor soils of Antarctica are sensitive to change. Recent increases in the number of anthropogenic introductions mean that understanding the impact of non-native species on Antarctic soils is pertinent, and essential for developing future risk assessments and management strategies. Through comparative baseline assessments of vegetation, microbes, soil chemistry, substrate composition and micro-arthropod abundance, this study explored if there are detectable terrestrial ecosystem impacts resulting from the introduction of the chironomid midge Eretmoptera murphyi to Signy Island in maritime Antarctica. The key finding was that E. murphyi is the likely driver of an increase in inorganic nitrogen availability within the nutrient-poor soils in which it occurs. When compared with the levels of inorganic nitrogen present in soils influenced by native vertebrate wildlife aggregations, the increase in local nitrate availability associated with E. murphyi was similar to that caused by deposits from seals and giant petrel colonies. Overall, available nitrate has increased by three-to five-fold in soils colonised by the midge, relative to undisturbed soils. This may ultimately impact rates of decomposition as well as the native plant and micro-arthropod communities of Signy Island

Ocean currents as a potential dispersal pathway for Antarctica’s most persistent non-native terrestrial insect

The non-native midge Eretmoptera murphyi is Antarctica’s most persistent non-native insect and is known to impact the terrestrial ecosystems. It inhabits by considerably increasing litter turnover and availability of soil nutrients. The midge was introduced to Signy Island, South Orkney Islands, from its native South Georgia, and routes of dispersal to date have been aided by human activities, with little known about non-human-assisted methods of dispersal. This study is the first to determine the potential for dispersal of a terrestrial invertebrate species in Antarctica by combining physiological sea water tolerance data with quantitative assessments of ocean current journey times. Fourth instar larvae tolerated sea water submergence for up to 21 days, but submerged egg sacs had significantly reduced hatching success. Using near-surface drifter data, we conclude that ocean current dispersal from Signy Island would not present a risk of species transfer beyond the South Orkney Islands on the tested timescales. However, if E. murphyi were to be introduced to the South Shetlands Islands or Adelaide Island, which are located offshore of the Antarctic Peninsula, there would be a risk of successful oceanic dispersal to neighbouring islands and the Antarctic Peninsula mainland. This study emphasises the need for effective biosecurity measures and demonstrates the role that currently undocumented pathways may have in dispersing non-native species

The effectiveness of Virkon® S disinfectant against the invasive chironomid Eretmoptera murphyi and implications for Antarctic biosecurity practices

The flightless midge Eretmoptera murphyi is thought to be continuing its invasion of Signy Island via the treads of personnel boots. Current boot-wash biosecurity protocols in the Antarctic region rely on microbial biocides, primarily Virkon® S. As pesticides have limited approval for use in the Antarctic Treaty area, we investigated the efficacy of Virkon® S in controlling the spread of E. murphyi using boot-wash simulations and maximum threshold exposures. We found that E. murphyi tolerates over 8 h of submergence in 1% Virkon® S. Higher concentrations increased effectiveness, but larvae still exhibited > 50% survival after 5 h in 10% Virkon® S. Salt and hot water treatments (without Virkon® S) were explored as possible alternatives. Salt water proved ineffective, with mortality only in first-instar larvae across multi-day exposures. Larvae experienced 100% mortality when exposed for 10 s to 50°C water, but they showed complete survival at 45°C. Given that current boot-wash protocols alone are an ineffective control of this invasive insect, we advocate hot water (> 50°C) to remove soil, followed by Virkon® S as a microbial biocide on ‘clean’ boots. Implications for the spread of invasive invertebrates as a result of increased human activity in the Antarctic region are discussed

Combining correlative and mechanistic niche models with human activity data to elucidate the invasive potential of a sub-Antarctic insect

[Aim]: Correlative species distribution models (SDMs) are subject to substantial spatio-temporal limitations when historical occurrence records of data-poor species provide incomplete and outdated information for niche modelling. Complementary mechanistic modelling techniques can, therefore, offer a valuable contribution to underpin more physiologically informed predictions of biological invasions, the risk of which is often exacerbated by climate change. In this study we integrate physiological and human pressure data to address the uncertainties and limitations of correlative SDMs and to better understand, predict and manage biological invasions.[Location]: Western archipelagos of the Southern Ocean and martime Antarctica.[Taxon]: Eretmoptera murphyi (Chironomidae), invertebrates.[Methods]: Mahalanobis Distances were used for correlative SDM construction for a species with few records. A mechanistic SDM was built around different fitness components (larval survival and life stage progression) as a function of temperature. SDM predictions were combined with human activity levels in Antarctica to generate a site vulnerability index to the assess colonization risk of E. murphyi. Future scenarios of ecophysiological suitability were built around the warming trends in the region.[Results]: Both SDMs converge to predict high environmental suitability in the species' native and introduced ranges. However, the mechanistic model indicates a slightly larger invasive potential based on larval performance at different temperatures. Human activity levels across the Antarctic Peninsula play a key role in discerning site vulnerabilities. Niche suitability in Antarctica grows considerably under long-term climate scenarios, leading to a substantially higher invasive threat to the Antarctic ecosystems. In turn changing conditions result in growing physiological mismatches with the environment in the native range in South Georgia.[Main conclusions]: Long-term studies of invasion potential under climate benefit from integrating correlative predictions with physiological experiments, as the invasion potential varies depending on the area and the timescale examined. This study also highlights a conservation paradox whereby the accidental introduction of an insect represents a threat to the Antarctic ecoystems that contrasts with its endangered status at the native range.LRP was supported by a contract associated to the project NICHEAPPS (CGL2014-56416-P) granted to PA. JB is funded by the Natural Environment Research Council (NERC) through the Central England NERC Training Alliance (CENTA) Doctoral Training Partnership (DTP) (RRBN19276), and her PhD studentship is supported by the University of Birmingham and the British Antarctic Survey (BAS). PA was supported by an extended Spanish ‘Ramón y Cajal’ contract (RYC-2011-07670). Antarctic Science Ltd. is also thanked for awarding a 2017 bursary to support LRP's research. PC and KH are supported by NERC core funding to the BAS ‘Biodiversity, Evolution and Adaptation' Team and Environment Office, respectively. GCV and MAOT were supported by the project ANTECO from the Spanish Ministry of Science, Innovation and Universities (CGL2017-89820-P). GAD was supported by an Australian Research Council Discovery Early Career Researcher Award (DE190100003) funded by the Australian Government