Establishment and eradication of an alien plant species in Antarctica: Poa annua at Signy Island

Invasive alien species are among the most significant conservation threats for Antarctica, and the South Orkney Islands are highly exposed to this threat because of their location and intensity of human activity. The alien flowering plant species Poa annua is known to occur at several locations in the Antarctic Peninsula and the South Shetland Islands. Here we report the first occurrence record of P. annua observed in the natural environment on Signy Island, South Orkney Islands. This archipelago is distant from previous records of the species in Antarctica (> 1500 km), and at local scale also distant (c. 2 km) from the main concentration of human activity close to the research station on the island. During the austral summer 2017/2018 we recorded one clump of P. annua on the island, and eradicated all individuals as well as removing the associated soil. No reproductive structures were apparent on the plants, and the soil did not contain a seed bank. Molecular analyses using available sequence data in GenBank confirmed the taxonomic species identification and, at a global scale identified six different haplotypes, confirming that the Signy Island material belongs to a distinct lineage within the species. Given Signy’s northern and relatively mild location in the maritime Antarctic, likely closer to the natural climatic and environmental niche of P. annua, the island may be at high risk of invasion, meaning that monitoring and biosecurity efforts need to be enhanced and extended well beyond the immediate vicinity of the research station area.