Non-native and invasive species can threaten Antarctic species. This threat is likely to increase with climate change, and with increasing speed and volume of travel to Antarctica by tourists and national programs. Recent risk assessments have identified 14 invasive species at highest risk of establishing in the most rapidly changing and highest-traffic areas on the Antarctic Peninsula, comprising 9 marine invertebrates, 2 terrestrial invertebrates, a kelp and 2 terrestrial flowering plants (Hughes et al. 2020). In 2011, the Committee for Environmental Protection adopted the Non-native species manual, which provides guidelines to help parties prevent or minimise the introduction of non-native species to Antarctica. The manual makes recommendations about the transfer of species into the Antarctic terrestrial and marine environments, as well as between sites in Antarctica (CEP 2011). Terrestrial species The Antarctic and subantarctic environments are fragile and vulnerable. Australia has obligations under the Antarctic Treaty System, and national and state legislation to protect the environment. This includes robust biosecurity measures to reduce the risk of introducing non-native species to the environment. The introduction of non-native, sometimes invasive, species has significantly altered the landscape, the composition of ecosystems and species interactions on many subantarctic islands (Frenot et al. 2005). Various factors increase the potential for non-native species to establish in the terrestrial environment. These include glacier retreat, an increase in ambient temperatures, and precipitation falling as rain rather than snow. These changes are furthering the establishment of non-native plants and microbes. Human activities can also introduce seeds and microbes, particularly at or near research stations and during field activities. At Macquarie Island, 5 non-native vascular plants have become established since the island’s discovery. Two of these species were successfully eradicated, but the remaining 3 are still thriving. The 2 main non-native invasive plant species are the annual meadow grass Poa annua, a small grass that can outcompete some native species, and the perennial chickweed Cerastium fontanum (March-Salas & Pertierra 2020). Disturbed sites, such as walking tracks, are particularly suited to colonisation by annual meadow grass. Research is currently underway to evaluate its distribution and impact to find ways to eradicate this invasive species in the near future (Williams et al. 2013). Throughout the subantarctic, many Eurasian weeds have established. Many of those originate from alpine or boreal environments and are thus already cold adapted. The effects of climate change, including increases in temperatures, and changes in precipitation and wind conditions, may allow more non-native plant species to survive and reproduce, while native species may not be able to adapt to the new conditions (March-Salas & Pertierra 2020). On Macquarie Island, there are also 28 introduced invertebrate species. The presence of some introduced invertebrates may have a negative impact on the richness and density of native invertebrate species (Terauds et al. 2011). Non-native invertebrates include 2 terrestrial crustaceans (an isopod – Styloniscus otakensis, and an amphipod – Puhuruhuru patersoni) (Greenslade et al. 2008), 2 species of predatory flat worms (Kontikia andersoni and Arthurdendyus vegrandis) (Greenslade et al. 2007) and two species of springtails (Protaphorura fimata and Proisotoma minuta) (Phillips et al. 2017). When and how these organisms were introduced to the island are difficult to establish. Should their distribution spread across the island, it might be difficult to eliminate them. Non-native predatory species may have particularly damaging impacts on native populations. There is also a risk of invertebrates being transported unintentionally to Antarctica. Beetles (Coleoptera), flies (Diptera) and butterflies (Lepidoptera) often enter large cargo containers. Many insects are still alive when they reach Antarctica (Houghton et al. 2016). For example, at Casey Station, a small fly (Lycoriella ingenua) was first recorded in the wastewater treatment plant and subfloor spaces in 1998, and proved very difficult to eradicate. Recent eradication efforts appear to have been successful, but monitoring is continuing (COMNAP 2019). Introduced vertebrates can also have a devastating impact on native species. On various subantarctic islands, house mice (Mus musculus) caused widespread decreases in the breeding success of several seabird species by taking eggs and attacking live chicks (Dilley et al. 2017). There is evidence that mice attack adult seabirds, such as northern giant petrels (Macronectes halli) and albatrosses (Jones et al. 2019). Since a successful eradication program at Macquarie Island in 2010–11, the island has remained free of mice (Springer 2018). Marine species Non-native marine species can find their way into Antarctic waters via different pathways. Microorganisms, plants and animals may be transported on the hull of ships (fouling) or in ballast water (Lewis et al. 2003). Although many ship hulls are painted with antifouling paint, the constant abrasion of the hull of Antarctic vessels travelling through sea ice diminishes the paint’s effectiveness. Ships with long layover periods outside the Antarctic shipping season are particularly at risk of carrying non-native species into subantarctic or Antarctic waters (Lewis et al. 2003). Although ballast water tends to be taken up rather than discharged in Antarctic waters (e.g. after vessels have resupplied a station), the Antarctic Treaty nations agreed to a set of guidelines for the exchange of ballast water in the treaty area (Secretariat of the Antarctic Treaty 2006). These include recommendations for ships to have a Ballast Water Management Plan and a record of ballast water operations. For many years, exchange of ballast water appeared to be the main transport mechanism for marine non-native species. However, rafts of non-Antarctic kelp carry a vast array of organisms and can drift across very long distances into Antarctic waters (Fraser et al. 2018). In the past, these organisms may not have survived in the frigid waters of the Southern Ocean, but, as sea temperatures increase, so does the likelihood that potentially invasive species may reach Antarctica and establish there (Avila et al. 2020). The first settlement of a mussel (Mytilus cf. platensis) was reported from the South Shetland Islands, West Antarctica, in 2019 (Cárdenas et al. 2020). Assessment Pressures on the Antarctic environment 2021 Adequate confidence The impacts of climate change and pollution on the Antarctic environment are high and increasing. Legend How was this assessment made Share on Twitter Share on Facebook Share on Linkedin Share this link Assessment Climate change 2021 Adequate confidence 2016 2011 Climate change is ongoing and increasingly affects Antarctic ecosystems. Assessment Marine pollution 2021 Adequate confidence 2016 2011 Marine pollution is a global challenge; although Antarctica is still less affected than other regions, micro- and nano-plastics have been detected in the food web. Assessment Commercial fisheries 2021 Adequate confidence 2016 2011 All commercial fisheries in the Southern Ocean are managed by the Commission on the Conservation of Antarctic Marine Living Resources, which applies an ecosystem-based management approach. Exploratory fisheries for toothfish operate in East Antarctica. Assessment Tourism 2021 Adequate confidence 2016 2011 Impacts of tourism vary with the site visited. Some sites receive many more visitors than others. Assessment Non-native species – animals 2021 Adequate confidence 2016 2011 Eradication of non-native introductions (e.g. rabbits and rodents on Macquarie Island) has been successful. Assessment Non-native species – plants 2021 Very limited confidence 2016 2011 Invasive plants may be spreading.