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Signatories to the Antarctic Treaty System’s Environmental Protocol are committed to preventing incursions of non-native species into Antarctica, but systematic surveillance is rare. Environmental DNA (eDNA) methods provide new opportunities for enhancing detection of non-native species and biosecurity monitoring. To be effective for Antarctic biosecurity, eDNA tests must have appropriate sensitivity and specificity to distinguish non-native from native Antarctic species, and be fit-for-purpose. This requires knowledge of the priority risk species or taxonomic groups for which eDNA surveillance will be informative, validated eDNA assays for those species or groups, and reference DNA sequences for both target non-native and related native Antarctic species. Here, we used an expert elicitation process and decision-by-consensus approach to identify and assess priority biosecurity risks for the Australian Antarctic Program (AAP) in East Antarctica, including identifying high priority non-native species and their potential transport pathways. We determined that the priority targets for biosecurity monitoring were not individual species, but rather broader taxonomic groups such as mussels (Mytilus species), tunicates (Ascidiacea), springtails (Collembola), and grasses (Poaceae). These groups each include multiple species with high risks of introduction to and/or establishment in Antarctica. The most appropriate eDNA methods for the AAP must be capable of detecting a range of species within these high-risk groups (e.g., eDNA metabarcoding). We conclude that the most beneficial Antarctic eDNA biosecurity applications include surveillance of marine species in nearshore environments, terrestrial invertebrates, and biofouling species on vessels visiting Antarctica. An urgent need exists to identify suitable genetic markers for detecting priority species groups, establish baseline terrestrial and marine biodiversity for Antarctic stations, and develop eDNA sampling methods for detecting biofouling organisms. This work was supported as a Science Innovation Project by the Department of Agriculture, Water and the Environment’s Science Innovation Program funding 2021–22 (project team: A.J.M., L.J.C., D.M.B., C.K.K., J.S.S. and L.S.). Support was also provided (to J.D.S, E.L.J., S.A.R., J.S.S., M.I.S., J.M.S., N.G.W.) from Australian Research Council SRIEAS grant SR200100005. P.C. and K.A.H. are supported by NERC core funding to the BAS Biodiversity, Evolution and Adaptation Team and Environment Office, respectively. L.R.P. and M.G. are supported by Biodiversa ASICS funding.

Southern Ocean islands have long been sites of scientific interest, due to their isolation, climate, geology and biology. This study investigated reproductive ecology of vascular plants on subantarctic Macquarie I. The persistence of plant species in a community relies on life history strategies which ensure population growth and sustainability. This can be via either vegetative or sexual reproduction. Many studies have shown that for alpine and high latitude plants sexual reproduction is not an important life history trait. The study identified that 26 species flowered, 22 dispersed seed and 12 produced seedlings over the study period on Macquarie I. This represents 72%, 61 % and 33% of the angiosperm flora of the island, respectively. There was a strong seasonality with almost all species flowering and fruiting in spring and summer. Overall sexual reproduction coincided with an increase in day length in summer. Seed rain of several plant communities was measured across eight sites of differing environments. At most sites seed rain was representative of standing vegetation, with the most widespread and abundant species1 on the island being the most widespread and abundant species present in the seed rain. The study has shown that several species (particularly Pleurophyllum hookeri and Stilbocarpa polaris) produced large numbers of seeds (over 13, 300 seeds `m^-2`) which are greater seed rain densities than previously recorded in arctic and alpine studies. Both species of large leaved megaherb (P. hookeri and S. polaris) are abundant on the island. S. polaris and P. hookeri allocated resources similarly as both species were found to allocate over 50 % of their total biomass to leaf tissue and a substantial proportion of biomass (20+%) to sexual reproduction. The study identified that seed germination occurred for megaherbs across a range of altitudes. Seedling densities recorded for both species were extremely high (up to 10, 000 `m^2`). Despite high seedling mortality during the study many seedling were observed to survive to become juvenile plants. P. hookeri population demography was investigated across four different populations. All were found to be dominated by large old plants. Despite some demographic variation between populations, seedlings were recruited into the population at most sites. Alien species were found to have deleterious impacts on megaherb species through seed predation, seedling herbivory, and site disturbance. This study has shown that plants on subantarctic Macquarie I. allocated considerable resources to sexual reproduction which is an important plant life history strategy for plants growing in this environment.