Subantarctic hitchhikers: expeditioners as vectors for the introduction of alien organisms.
Subantarctic islands have depauperate floras and faunas. When combined with recent changes in climate, these factors increase the likelihood of alien species establishing in the subantarctic. Cargo, food and expeditioners in transit to the subantarctic as part of the Australian Antarctic Program (AAP) were inspected to determine their potential as vectors for alien species. All cargo items were found to have the potential to act as vectors for alien species introductions. Cargo containers were found to harbour plant material, seeds and spider webs. A major potential source of contamination is transport used on resupply expeditions for ship to shore transfers. The presence of large numbers of littoral organisms on the bottom of a barge highlighted the real risk of a potential pathway for the introduction of marine taxa. Insect infestation, scale, fungal infection and the presence of soil were all problems associated with the provision of fresh food to subantarctic stations. Equipment identified as high risk vectors included equipment cases, day packs and the cuffs and Velcro® closures of outer clothing. Many expeditioners had travelled overseas in the six months prior to embarkation and had recently visited alpine or high latitude environments. A total of 981 propagules and five moss shoots were collected from clothing and equipment of 64 expeditioners. Ninety species from 15 families were identified, most of which were grass caryopses. Asteraceae and Poaceae contained the greatest diversity of propagules. In germination trials a total of 163 plants (24 species) were identified. A risk assessment was prepared to determine issues posing a threat to subantarctic quarantine and assess possible logistic and management changes to minimize these threats. Many changes suggested have since been implemented resulting in a reduction in the number of alien species recorded in subsequent inspections.