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
Antarctic environment (2016)
Pressures on the terrestrial environment
Climate change
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).
Box ANT1 Successful eradication of alien mammals and environmental recovery on Macquarie Island
Feral cats (Felis catus) had been present on Macquarie Island since the 19th century. They preyed on small, unattended chicks of many seabird species, as well as rabbits and rodents (Rounsevell & Brothers 1984). From 1975 to 1984, a program was in place to keep the cat population under control, but the numbers of burrowing seabirds continued to decrease. Hence, from 1998 to 2000, an intensive cat eradication program was conducted and, in June 2000, the last cat on the island was destroyed (PWS 2015).
From 2000 to 2006, rabbit numbers increased dramatically on Macquarie Island (Terauds et al. 2014) after the cats had been eradicated (Bergstrom et al. 2009, Robinson & Copson 2014). In 1978, the Tasmanian Parks and Wildlife Service estimated that some 150,000 rabbits inhabited Macquarie Island, and introduced myxomatosis to reduce the rabbit population.
However, from 1999 to 2003, the number of rabbits increased, and it became clear that myxomatosis was no longer as effective as it had been when it was introduced. The increasing rabbit population caused widespread vegetation damage and destruction through overgrazing. The vegetation cover was so overgrazed that the substratum became eroded. Many coastal slopes were transformed from lush, waist-high vegetation to grazed lawns or bare ground; these were increasingly prone to landslips from high-rainfall events and seismic activity, which killed flying seabirds and penguins. Seabird colonies also lost the protection provided by vegetation and lost habitat at their breeding grounds. Some vegetation types, such as the prickly shield fern (Polystichum vestitum), were also threatened (Bergstrom et al. 2009), and remaining patches were fenced to maintain existing populations.
In 2006, an eradication program for rabbits, rats and mice on Macquarie Island was developed (PWS 2007). It cost approximately $20 million over 7 years, and was jointly funded by the Tasmanian and Australian governments.
The field phase of the eradication of rabbits and rodents started in June 2010 when helicopters dropped bait pellets containing brodifacoum (an anticoagulant poison), targeting rabbits, rats and mice across the island. However, because of inclement weather, only 8 per cent of the island’s area could be baited, and it was decided to continue the project in the 2011 winter (Springer 2016).
Some nontarget species, most likely scavenging species such as skuas and giant petrels, were expected to possibly be affected by the eradication efforts. By 9 February 2011, 947 dead birds had been found, including 298 northern giant petrels (Macronectes halli; approximately 8 per cent of the breeding population on the island), 16 southern giant petrels (M. giganteus; 0.3 per cent), and 226 subantarctic skuas (Catharacta antarctica; 11 per cent). The actual number of bird mortalities is likely to have been higher, because not all areas of Macquarie Island could be intensively searched, and an unknown number of individuals may have died at sea.
Additionally, 4 southern giant petrels (1 bird banded at Macquarie Island) were found dead in the New Zealand subantarctic area and tested positive for brodifacoum. Further, although only 10 northern giant petrel carcases were examined, 9 were males, probably because of their more coastal-oriented foraging (females tend to be more pelagic), exacerbating the impact on the breeding population. The primary cause of bird deaths was brodifacoum poisoning resulting from the secondary ingestion of poisoned carcases of bird and target species, the accessibility of these carcases, and the scavenging behaviour of the bird species. Because brodifacoum has a particularly long half-life in a carcase, it remains active months after an animal dies. Deaths of kelp gulls and black gulls may have been caused by both primary and secondary poisoning.
The 2010 operations were reviewed (PWS 2014). To reduce the impact of the eradication program on nontarget species, several changes were made, including increasing the efforts to systematically search for, and remove, poisoned target and bird carcases.
Some 10 weeks before the second aerial baiting phase started, rabbit haemorrhagic disease virus was released on the island, which reduced the rabbit population by about 80–90 per cent (Springer & Carmichael 2012). From May to July 2011, 2 island-wide bait drops were completed. Intense hunting pressure was exerted on the remaining rabbits immediately after the baiting phase to prevent the population from increasing again. In July, the rabbit-hunting teams arrived on the island with 12 specially trained dogs to follow up on the ground and eliminate rabbits that had survived the baiting.
For 4 years, field teams used a range of techniques, including shooting, fumigating burrows and trapping, to ensure that all rabbits were removed. In April 2013, additional teams were landed, including 3 rodent-detecting dogs (Springer 2016). Teams carried GPS equipment to ensure complete coverage of the island. Collectively, the teams tracked 92,000 kilometres from August 2011 to March 2014.
In 2014, the operation was declared a success, and the island is now recognised as being free from introduced vertebrate pests (Springer 2016). Vegetation recovery has been rapid in most areas in the absence of rabbits (Shaw et al. 2011), and small burrowing birds are already increasing in numbers because of widespread vegetation recovery and the absence of rats.
Quarantine and monitoring of Macquarie Island continue, and should ensure that the island remains free from non-native mammals. Several long-term collaborative projects are under way to monitor and report on the post-eradication recovery of island ecosystems.
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).
Human activities
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.
Klekociuk A, Wienecke B (2016). Antarctic environment: Pressures on the terrestrial environment. In: Australia state of the environment 2016, Australian Government Department of the Environment and Energy, Canberra, https://soe.environment.gov.au/theme/antarctic-environment/topic/2016/pressures-terrestrial-environment, DOI 10.4226/94/58b65b2b307c0
Dr Andrew Klekociuk
Dr Barbara Wienecke
