The pressures on the Antarctic terrestrial environment operating on a global scale include anthropogenic climate change, such as atmospheric warming and changes to water regimes. Local pressures include the introduction of non-native species and impact from human activities, particularly on stations and their immediate surroundings.
Pressures on the terrestrial environment
Pressures on the terrestrial environment
Climate change impacts in Antarctica and the subantarctic include changes in trends in climate parameters (e.g. air temperature, precipitation, wind speed), and increased frequency and impact of extreme or pulse events (Nielsen et al. 2011). The impacts of both trends and extremes can be regionally and species specific. Changes to local environments can start follow-on degradation, such as erosion driven by alteration of surface properties (Levy et al. 2013). Flooding from an extreme summer warming event in 2002 altered species abundances in nematode communities in the McMurdo Dry Valleys (4800 km2 of ice-free valleys west of McMurdo Sound) (Nielsen et al. 2011). The lichen Usnea antarctica is likely to be vulnerable to regional environmental change. Climate simulation experiments showed that this slow-growing lichen suffers a negative carbon balance because of an increase in respiration rates in winter and a decrease in photosynthetic activity in summer. However, mosses and microarthropods showed no signs of negative impact under the experimental conditions (Bokhorst et al. 2015).
Introduction of non-native species
The introduction of non-native species has significantly altered the landscape, composition of ecosystems and species interactions on many subantarctic islands that are not under Australian jurisdiction (Frenot et al. 2005). Studies of the flora at the French subantarctic Kerguelen Islands date back to 1874 when 3 introduced plants were collected (Frenot et al. 2005). Large-scale surveys, mainly in the 1970s and 1980s, discovered a total of 168 introduced plant species on Possession, Kerguelen and Amsterdam islands. During a survey in 2000, 118 of these were still present. On some islands, the introduced species are well established and outnumber the native species. For example, at the Kerguelen Islands, 68 introduced plant species were present in 2000 compared with only 14 native species (Frenot et al. 2005). In addition, there are 30 known introduced invertebrate species.
The northern part of the Antarctic Peninsula is the only Antarctic region with naturally occurring flowering (vascular) plants: Antarctic hairgrass (Deschampsia antarctica) and Antarctic pearlwort (Colobanthus quitensis). However, in recent years, several species of non-native vascular plants have been found there, and they appear to be spreading. Furthermore, non-native plants have recently been rediscovered in areas from where they had been removed. The warming of the peninsula has allowed such biological invasions and establishment of non-natives. They displace the native plants and are deemed to be a serious threat to the integrity of the ecosystem (Molina-Montenegro et al. 2015).
At Macquarie Island, 5 non-native vascular plants have become established since the island’s discovery. Two plant species were successfully eradicated, but the remaining 3 are still thriving. Disturbed sites, such as walking tracks, are particularly suited to colonisation by annual meadow grass (Poa annua), a small grass that can outcompete some native species. Research is currently under way to evaluate the distribution and impact of P. annua to find ways to eradicate this invasive species in the near future (Williams et al. 2013). On Macquarie Island, there are also 28 introduced invertebrate species. Research has suggested that the presence of some introduced invertebrates has a negative impact on the richness and density of native invertebrate species (Terauds et al. 2011).
Macquarie Island’s flora suffered severe degradation through overgrazing by rabbits (Oryctolagus cuniculus), resulting in erosion and landslides (PWS 2014). For seabirds, introduced cats (Felis catus), rats (Rattus spp.) and rabbits posed the most significant conservation problems at Macquarie Island. The mammals directly affected seabirds through predation of eggs, chicks and adults; and rabbits damaged the vegetation, leading to erosion, increased exposure to natural predators and loss of breeding habitat (Baker et al. 2002). Following successful eradication of cats on the island in 2000, a comprehensive eradication program for rabbits, rats and mice (Mus spp.) started in 2010 and was completed successfully in 2014. The elimination of cats, rabbits and rodents has had a positive effect on plant and seabird communities (see Box ANT1).
The McDonald Islands in the southern Indian Ocean may be the only islands in the subantarctic that are free from introduced species. Nearby Heard Island has 2 known introduced plants: annual meadow grass and a perennial herb (Leptinella plumosa). It also has 3 introduced invertebrate species: the earthworm Dendrodrilus rubidus, the mite Tyrophagus putrescentiae and Californian wingless thrips (Apterothrips apteris) (AAD & Director of National Parks 2005). No introduced vertebrates exist on Heard Island.
The pressures of climate change and introduced species may combine (Convey 2005, 2010). New species that become established in a warming environment tend to be more competitive than native species because of better dispersal mechanisms or a lack of predators, or because they occupy niches that previously did not exist (Chown et al. 2012). Under such circumstances, food webs and ecosystem functioning could be altered dramatically (Convey & Lebouvier 2009).
Tourism is particularly concentrated on the Antarctic Peninsula, which was visited by about 42,800 travellers and support staff in the 2015–16 season. Although there is limited evidence-based assessment of human disturbance of wildlife, a recent meta-analysis of available data found statistically significant negative effects on physiological and population responses at a variety of visit sites in the Antarctic and subantarctic (Coetzee & Chown 2016).
Pollution of the Antarctic environment occurs mainly at the centres of human activity, such as stations. For example, alkaline particles can become airborne and drift downwind during building operations that require concrete. Damage to lichens caused by this airborne pollution lead to bleaching about 90 metres from the site (Adamson & Seppelt 1990). Airborne pollutants, such as POPs, have been found in the atmosphere above Antarctica, albeit at lower levels than in the Arctic (Vecchiato et al. 2015).
Station personnel (including researchers) tend to disturb wildlife more near stations than in remote areas.