Invasive non-native species have caused substantial negative impacts on biodiversity and ecosystem structure and function in many areas of the Earth including the sub-Antarctic region (considered as an associated and dependent ecosystem by the Treaty) where over 200 non-native species have been introduced (1). Substantial biodiversity and ecosystem structural changes on some sub-Antarctic islands show what may happen in Antarctica as climate changes and levels of human activity continue to increase (1,2). Antarctica currently has few known terrestrial non-native species, with those reported mostly limited to flowering plants and invertebrates (Figure 1 and 2; 1,3,4). Nevertheless, recent monitoring activities have increased our understanding of species number and distribution (5,6).
Most non-native species have been introduced unintentionally through importation of cargo, fresh foods, clothing and personal effects (1,3,7,8). Some non-native species have been found on Antarctic stations and in hydroponic facilities (1). For example, insects persist in some station sewage systems, despite eradication attempts, and may disperse to establish in the local environment (4,9).
Little is known about levels of non-native species introductions to Antarctic marine environments but species could be imported in ballast water or on ship hulls (1,10). The introduction of non-native microorganisms is also little understood but may affect wildlife health (11) and allow the introduction of novel genetic material into native microbial communities, with unforeseen consequences for microbial community structure and function (12).
Most known Antarctic non-native species have been found within the Antarctic Peninsula region but some have been found in other Antarctic regions (Figure 1; 1,4). This distribution correlates strongly with areas predicted to be at greatest risk of non-native species introductions due to high levels of national operator and tourist visitation and favourable climatic conditions (8). For example, Deception Island (South Shetland Islands) is one of the most frequently visited locations in Antarctica, but is also the most invaded, with nine non-native invertebrate species (4,8,9,13).
Climate change and an expanding human footprint put the whole of Antarctica at increased risk of invasion (8). Climate change may make environmental conditions more favourable for new introductions and increase the likelihood that established non-native populations will increase their distribution and capacity to compete with native species (3,5). Human travel between Antarctic regions may transfer existing non-native species to other Antarctica areas (5). For example, research has shown that a flightless midge (Eretmoptera murphyi), accidentally introduced to the South Orkney Islands, could survive and complete its life cycle under climatic conditions found c. 750 km further south on the Antarctic Peninsula (14). Human activities may potentially also transfer native Antarctic species to areas within Antarctica where they are not found naturally, which could disrupt established ecosystems (15).
Not all non-native species are of equal threat to Antarctic ecosystems. Poa annua (annual bluegrass) is invasive on most sub-Antarctic islands and has recently been described as invasive in Antarctica (1,5,16). The variety of reproductive strategies available to this species may explain, in part, its colonisation success. The Antarctic distribution of the grass has increased recently,having been reported from six locations on the Peninsula and South Shetland Islands, with the successful removal of small populations at four sites (5,16). Genetic studies of Poa annua from King George Island revealed that it was introduced on multiple occasions, from both European and South American sources (17). Poa annua can have negative effects on native plant species and at one Antarctic location it has spread from its initial introduction site into the local ecosystem (5,18).
Invasive species can greatly affect ecosystem structure and function. For example, the predatory beetle Merizodus soledadinus, accidently introduced to the sub-Antarctic Kerguelen Islands, has attacked and consumed native invertebrate populations and thereby reduced nutrient cycling in the invaded ecosystem (2). In Antarctica, larvae of the midge Eretmoptera murphi may be able to cycle soil nutrients up to nine times faster than native invertebrate populations and, if dispersed, could alter terrestrial habitats across the Peninsula (14).
In Antarctica, non-native species have been found mainly in the vicinity of research stations and visitor landing sites, suggesting that their presence, establishment and increase in abundance are facilitated by human activities (8,16). For example, soil disturbance can increase the abundance and germination of non-native Poa annua, but not native plants (16). The biology of some invasive species enables them to survive under a wide range of environmental conditions, a characteristic which may facilitate a rapid increase in their Antarctic distribution (1,8,14). Hypogastrura viatica is the most widely dispersed non-native springtail (Collembola) in Antarctica having been found at five Peninsula locations, including popular visitor sites (4,13). With a preference for disturbed ground, the species has already been shown to out-compete native species in the sub-Antarctic. First reported on Deception Island in 1949, it is now found there in densities of over 5,500 individuals per litre of soil. As yet, Hypogastrura viatica is not found on neighbouring King George Island, but high levels of human activity within the region may put this large area of ice-free ground at substantial risk of invasion (4,8,13).
Differentiating between new introductions transported through human activities (non-native species) and those introduced by wind, ocean current or wildlife (natural colonists) can be difficult (9). For example, available evidence was insufficient to ascertain categorically if the South American aster Nassauvia magellanica on Deception Island or the seeds of the rush Juncus bufonius, found within Antarctic Specially Protected Area 128 Western Shore of Admiralty Bay, were introduced by human or natural processes (9,19). Correct differentiation is important for subsequent management as non-native species should be eradicated, according to the Protocol (9). Within the Antarctic Treaty area, several non-native plants present as single individuals or in low numbers have been removed (4,5,9) and larger scale eradications have been initiated. Attempts have also been made to eradicate vertebrates, invertebrates and plants on the sub-Antarctic islands, for example, reindeer and rats on South Georgia, cats and the invertebrate Porcellio scaber on Marion Island and the grasses Anthoxanthum odoratum and Rumex crispus from Macquarie Island (1,9).
Further scientific research could usefully investigate:
- the biology and functional characteristics of existing non-native species to determine methods for their eradication or control
- the rate, extent and impacts of microbial and marine introductions
- the level and impacts of transfer of native organisms between different eco-regions of Antarctica (15)
Risk assessment protocols showing which non-native species are most likely to become invasive should they be introduced have been produced for some biological groups for the sub-Antarctic, and could also be usefully developed for Antarctica (13,20).