Invasive aliens in Antarctica
Even the remote Antarctic continent and its sub-Antarctic islands and seas are troubled by invasive alien species. By Anne M Treasure
The introduction of invasive alien species has been recognised as a major threat to biodiversity and ecosystems and the resulting effects have been recorded around the world. In fact the Global Invasive Species Programme (http://www.gisp.org) has identified that the spread of invasive alien species is one of the most significant ecological and economic threats to the planet. Humans have served as both accidental and deliberate dispersal agents of invasive alien species and the frequency and extent of introductions worldwide is alarming.
What are invasive alien species and why are they a problem?
Alien species (also called introduced, exotic, non-native, or non-indigenous species) are those plants, animals or any other types of organism, that are found in areas where they did not occur naturally in the past. These species were introduced through the accidental or deliberate actions of humans. An alien species that manages to maintain a large reproducing population with the potential to spread over large areas is known as an invasive species. Invasive species can cause a number of problems costing millions of rands of damage every year by, for example, being agricultural pests or vectors of disease. Invasive species that spread can outcompete and exclude indigenous species that occur in the area naturally. In this way, natural species interactions are disrupted, changing ecosystems and the services they deliver. Invasive species can also lead to the extinction of indigenous species.
Invasive species are found in every taxonomic group, from viruses, fungi and plants to invertebrates, birds and mammals. These species have had substantial impacts in virtually every region and habitat on earth. Despite its remoteness, Antarctica is no exception.
Endemic species: A species that is only found in a particular geographic location and nowhere else in the world.
Indigenous/native species: A species that occurs naturally in an area, without human intervention. Not all indigenous species are endemic species, as an indigenous species can naturally occur in more than one area.
Alien species: A species of plant, animal or any other type of organism found in an area where it did not naturally occur in the past. Its presence in this area is due to deliberate or unintentional human involvement.
Naturalised or established species: An alien species that has maintained a reproductive population for at least 10 years without direct intervention by people.
Invasive species: An alien species that manages to maintain a large reproducing population with the potential to spread over large areas.
Invasions in the Antarctic
The Antarctic region includes the Antarctic Continent and Peninsula, sub-Antarctic islands and the Southern Ocean.
Alien microbes, fungi, plants and animals occur on most sub-Antarctic islands and some parts of the Antarctic continent and ocean. The consequences of invasive species in Antarctica are widely reported and impacts on indigenous species and communities have been recorded. There has therefore been much interest in the region, particularly as it is of considerable conservation importance due to the large number of indigenous and endemic species found there. In the past, rats and mice were inadvertently introduced from visiting ships to many sub-Antarctic islands.
Islands have also seen the intentional introduction of species such as rabbits (on Kerguelen and Macquarie) and reindeer (on South Georgia and Kerguelen) for food, or cats on Marion and Macquarie islands. Once feral, these animals started causing widespread environmental damage. For example, introduced cats on Marion and Macquarie islands substantially reduced seabird populations before they were finally eradicated by the early 1990s on Marion and by 2000 on Macquarie. Rabbits and reindeer cause severe damage to native vegetation. Invasive mice have been introduced to numerous islands such as Marion, Macquarie, South Georgia, Crozet and Kerguelen where they are having severe impacts on indigenous invertebrates and plants. Mice and rats also pose a serious threat to seabirds on which they are known to prey. The Kerguelen archipelago is the island group with the highest number of invasive mammals and is suffering large consequences due to seven invasive species now present on the islands: mice, rats, rabbits, sheep, reindeer, mouflon and cats.
Invasive plants and invertebrates (mostly introduced unintentionally through, for example, animal fodder, cargo (including food supplies) or attached to clothing, are widespread on most islands and have also been found on the Antarctic Peninsula. These introductions have had considerable impacts, which include direct reductions in population sizes of indigenous species, as well as changes in food webs and the functioning of ecosystems. The introduction of fungi, microorganisms and diseases have also been linked to human activities.
These threats are set to continue as the Antarctic is facing an increase in the rate of introduction of invasive species. This is mostly because the routes for colonisation have increased substantially due to increased human traffic to Antarctica. Tourist numbers have increased three-fold from 1998/1999 (10 013) to 2010/2011 (33 824) (available on http://iaato.org). Furthermore, government operators now employ around 5 000 scientists and support staff, who visit the region for short or long time periods, and there are over 65 year-round and summer-only research stations in Antarctica. Each of these stations has to be resupplied at least once a year with personnel, food, cargo and building materials. The number of ships as well as aircraft entering the region has increased, meaning that there are many more opportunities for alien species to be introduced. In addition, many tourist and research vessels go from place to place covering a number of different Antarctic and sub-Antarctic locations. Therefore, species that are already pre-adapted to cold conditions in their native region may be transported to other regions within Antarctica where they do not occur naturally.
Although many countries now have stricter controls to prevent introductions than were in place in the past, terrestrial alien species are still brought into Antarctica in cargo and attached to clothing, and marine species are introduced by hull fouling, the intake and subsequent discharge of ballast water, scientific equipment or they can be transported on floating man-made debris. Marine introductions are of a particular concern as most visitors and cargo are transported to the Antarctic in ships. However, much less is known about marine invasions than about terrestrial invasions. This is in part due to poor knowledge of the diversity of many near-shore environments in Antarctica, which makes it difficult to identify whether invasive species have been introduced.
The first alien marine species to be recorded in Antarctic seas was the North Atlantic spider crab (Hyas araneus). Both a male and a female of this shelf species, native to the North Atlantic and Arctic Oceans, was found on the Antarctic Peninsula in 2004. It is suspected that this species entered Antarctic waters either on ships’ sea-chests or through ballast water. The invasive green alga Enteromorpha intestinalis is also thought to have been introduced via the hulls of visiting ships and now grows in dense mats on intertidal rocks on the South Shetland Islands. These pathways for marine invasions are a significant threat. A study on the highly invasive Mediterranean mussel (Mytilus galloprovincialis) showed this species to predominate in the sea chests of the South African polar vessel the S.A. Agulhas and that at least some of these individuals survived multiple voyages to the Antarctic region.
The survival of this species in Antarctic conditions demonstrated that the mussels are capable of surviving polar conditions, at least in the short-term. This study also highlighted the limited effectiveness of antifouling technology employed by such vessels. Another potential source of marine introductions is transport used on re-supply expeditions for ship to shore transfers. The presence of large numbers of organisms found on the bottom of a barge taken from Hobart, Australia, to Macquarie Island for this purpose (including algae, barnacles, numerous crustaceans, starfish, mussels, and crabs) highlighted this risk.
Attempts to introduce salmonid fish have been made at a number of islands, including the Falklands, Kerguelen, Possession, Crozet, South Georgia and Marion. These fish only flourished on Kerguelen, which has relatively large rivers. Once introduced to a few rivers, the fish were able to expand their territory to neighbouring rivers by short sea migrations.
Invasive eradication: Dr Jennifer Lee
What is your current job and what does it entail?
I work as the Environment Officer for the Government of South Georgia and the South Sandwich Islands. I am responsible for all matters related to managing the terrestrial environment, including biosecurity and habitat restoration. Lots of my work is about policy and ensuring that the government meets its obligations to international agreements such as the Agreement on the Conservation of Albatross and Petrels. About half of my time is spent in the office planning and writing policy documents and the other half is spent in the field overseeing various environmental management projects.
What invasive problems do you face on the islands and what impacts are these invasions having?
Although there are now strict measures in place to prevent the introduction of alien species, early whaling and sealing expeditions introduced a number of non-indigenous species to South Georgia. Some species such as rats and dandelions were introduced accidentally, whereas others such as reindeer were deliberately introduced as a source of food. At the time, nobody knew what impact these species would have, but in the absence of natural predators or disease populations have grown rapidly and there are severe impacts on the island’s native flora and fauna. In particular rats and reindeer both have severe impacts on the islands burrowing bird species. Rats eat chicks and eggs and reindeer graze vegetation above the burrows causing the ground to dry out and the burrows collapse. Reindeer also facilitate the spread of non-native plant species like the annual blue grass, which thrives in the disturbed ground.
How are you controlling these?
Currently there are programmes in place to eradicate both rats and reindeer from the island. Rats will be eradicated by dropping poison bait from helicopters. This is the largest rat eradication programme that has ever been attempted. Reindeer will be controlled by herding them from outlying areas to a central point where they will be killed under veterinary supervision. Controlling invasive species is very costly. The rat and reindeer eradication projects will cost millions of pounds. There are also environmental impacts of eradication attempts. When poison bait is dropped to kill the rats, they will probably also be eaten by some of the native birds such as pintails and sheathbills. When these birds and the rats die, larger birds will eat the carcasses causing the poison to build up in the food chain. However, even though it is expected that some birds will die, it is likely that populations will recover rapidly once the rats have been removed.
What is your background and what previous work have you done on invasions?
I did my PhD and post-doctoral research at the Centre for Invasion Biology at Stellenbosch University. I worked closely with the South African National Antarctic Programme to look at how invasive species moved into and around the Antarctic region. I was lucky enough to be able to work on both marine and terrestrial systems and looking at what sort of alien species were being transported inside ships going to the Antarctic and what was being carried underneath them on their hulls.
What skills and aptitudes do you need to do a job like this?
To work as an environment officer you need to be able to think on your feet and face up to a challenge. The daily workload is incredibly varied and can involve anything from issuing permits so scientists can collect samples for their research to planning how to herd reindeer across a rugged mountain pass. One of the big attractions of the job is being able to spend time on South Georgia. However, when in the field the hours are long and the accommodation is basic (usually a tent!). It is important to be able to work independently, be physically fit and able to look after yourself and those around you in a remote environment.
Implications of climate change
The low temperatures in Antarctica represent a significant challenge to survival for alien species. However, the Antarctic is facing rapid climate change, which is predicted to facilitate the introduction of invasive species. Interactions between climate change and invasive species are poorly understood, but evidence for such interaction is accumulating. For example, warming conditions can facilitate colonisation success and give invasive species a physiological advantage over indigenous species. Warming conditions can also facilitate easier dispersal of invasive species. This is already well documented on sub-Antarctic islands for invasive plants and invertebrates. Warming waters would also favour increased transport, establishment and spread of marine alien species. Increasing temperatures can also enable species to expand their ranges into new areas faster than would occur naturally, which can have serious consequences for native species that have not evolved defences against such intrusions. For example, warming of the Western Antarctic Peninsula shelf waters appears to be facilitating the movement of the cold-intolerant king crab (Neolithodes yaldwyni) into this area. This crushing predator is having devastating ecological effects on the shelf, where they voraciously prey on echinoderms (the group of animals that includes the starfish and sea urchins). Antarctic marine invertebrates are inherently weakly calcified, making them particularly susceptible to the crabs. The crabs are also modifying the physical environment and altering other animals’ habitat by disturbing sediment on the seafloor when they dig for worms and other creatures. Intrusion of sub-Antarctic waters into Antarctica has also resulted in alien species, most probably of South American origin being found off King George Island.
Control and the future
Eradicating an alien marine or terrestrial species once it has become invasive is difficult and costly, and most times impossible. In fact, there are no reports of successful removal of a marine invasive species from the sea once they have invaded. Therefore, the best way to combat the problem is to prevent alien species from reaching Antarctica in the first place. Awareness of the risks that visitors may pose to ecosystems in Antarctica and the sub-Antarctic through the introduction of alien species has increased in recent years. Because of this, some national and tourism operators have implemented quarantine procedures such as boot washing and educational programmes. Various types of inspection, washing and extraction procedures can be done to minimise terrestrial introductions. Cargo should be cleaned properly and fumigated if necessary. Prevention should focus on pre-departure measures first, but biosecurity officers with biological backgrounds should also accompany all voyages to the region to undertake supervision of clothing and equipment cleaning en route. Good examples of further policies are ones that South Africa has in place for Marion and Prince Edward Islands such as banning the importation of fresh produce (which could contain invasive insect pests or fungi) and chicken on the bone (which could introduce bird diseases), and irradiating fresh chicken eggs (also to prevent bird diseases).
Modern shipping can quickly move species thousands of kilometres against natural barriers to migration such as currents. Measures can be taken to prevent marine invasions such as painting the hulls of ships with anti-fouling paints to prevent marine organisms from attaching to the boats. Guidelines are also in place for the management of ballast water in Antarctica (see http://www.ats.aq/documents/recatt/Att345_e.pdf). Awareness of the potential risks are crucial and simple changes to operating procedures may reduce the chance of introductions in the future. For example, changing the length of time that ships stay in port before visiting Antarctica thereby reducing the opportunity for invasive species to establish on hulls.
If limiting or reducing the number of visitors to the region is not possible, then education to increase awareness for all involved in activities in the region is key, including managers of national programmes, visitors (tourists and scientists), crew of boats (tourist, scientific and fishing), tour operators and cargo facility staff. Various resources are available for this, including documentation (see for example pamphlets on: http://iaato.org/dont-pack-a-pest, http://iaato.org/decontamination-guidelines, http://www.asoc.org/storage/documents/tourism/ASOC_Know_Before_You_Go_tourist_pamphlet_2009_editionv2.pdf) and videos (for example Instructional video on cleaning (Aliens in Antarctica Project, 2010: http://academic.sun.ac.za/cib/video/Aliens_cleaning_video%202010.wmv).
If prevention has not been possible, then early detection and quick response is vital. Having good baseline data on indigenous species is important and regular monitoring of sites (particularly high risk sites such as around research stations or tourist visitation sites) is essential. If an invasive species is detected, an eradication programme should be implemented as soon as possible to prevent the species from spreading and to make the eradication more cost effective. The quicker the response, the more effective the eradication will be. Follow up surveys should be conducted to ensure that the eradication was successful. If eradication is not possible, regulation and control of the invasive populations should be explored.
Much research is being conducted on invasive species in Antarctica and the impacts they have on indigenous species and ecosystems (see for example www.sun.ac.za/cib). Findings from this research inform policy and international collaborative programmes to combat the problems. An inter-disciplinary committee called the Scientific Committee for Antarctic Research (SCAR: www.scar.org) is charged with initiating, developing and coordinating high quality international scientific research in the region. SCAR also provides scientific advice to Antarctic Treaty Consultative Meetings and makes recommendations that influence policy and international agreements, which provide protection for the ecology and environment of the Antarctic. Working in this field is very rewarding as one can make a real difference to the conservation of this unique and beautiful part of the world.
Dr Anne Treasure is a postdoctoral research fellow in the Oceanography Department at the University of Cape Town. Her research focuses on ecosystem responses to climate
change-driven shifts of the sub-Antarctic front in the vicinity of the Prince Edward Islands. She completed her PhD on the impacts of invasive species and climate
change on Marion and Prince Edward Islands.