Continent-wide risk assessment for the establishment of nonindigenous species in Antarctica

Abstract

Invasive alien species are among the primary causes of biodiversity change globally, with the risks thereof broadly understood for most regions of the world. They are similarly thought to be among the most significant conservation threats to Antarctica, especially as climate change proceeds in the region. However, no comprehensive, continent-wide evaluation of the risks to Antarctica posed by such species has been undertaken. Here we do so by sampling, identifying, and mapping the vascular plant propagules carried by all categories of visitors to Antarctica during the International Polar Year's first season (2007-2008) and assessing propagule establishment likelihood based on their identity and origins and on spatial variation in Antarctica's climate. For an evaluation of the situation in 2100, we use modeled climates based on the Intergovernmental Panel on Climate Change's Special Report on Emissions Scenarios Scenario A1B [Nakićenović N, Swart R, eds (2000) Special Report on Emissions Scenarios: A Special Report of Working Group III of the Intergovernmental Panel on Climate Change (Cambridge University Press, Cambridge, UK)]. Visitors carrying seeds average 9.5 seeds per person, although as vectors, scientists carry greater propagule loads than tourists. Annual tourist numbers (∼33,054) are higher than those of scientists (∼7,085), thus tempering these differences in propagule load. Alien species establishment is currently most likely for the Western Antarctic Peninsula. Recent founder populations of several alien species in this area corroborate these findings. With climate change, risks will grow in the Antarctic Peninsula, Ross Sea, and East Antarctic coastal regions. Our evidence-based assessment demonstrates which parts of Antarctica are at growing risk from alien species that may become invasive and provides the means to mitigate this threat now and into the future as the continent's climate changes.

Fig. 1.

Proportion of visitors carrying seeds, number of seeds per visitor carrying seeds, and number of seeds per visitor across all visitors. (A) Proportion of visitors (mean and 95% bootstrapped CI) carrying seeds within each of the visitor categories. (B) Mean (and 95% bootstrapped CI) number of seeds per visitor by category for those visitors carrying seeds. (C) Mean (and 95% bootstrapped CI) number of seeds per visitor by category for all visitors (i.e., those with and without seed loads). Sample sizes are given above all bars.

Fig. 2.

Distribution of cumulative annual degree days for 2007–2008 in the Antarctic. These were calculated by using a −5 °C threshold and mean daily near-surface temperature data from the Modern Era Retrospective-analysis for Research and Applications Reanalysis office (provided by the NASA Global Modeling and Assimilation) (50) on a 0.67° longitude × 0.5° latitude grid, interpolated to a 50-km square grid. Inset shows degree day detail on the Antarctic Peninsula. Ice-free ground is shown in gray. Ice-free landing data for tourists (A) and scientists (B) are shown.

Fig. 3.

Relative risk of alien vascular plants establishing in Antarctica. Visitor-free, ice-free areas are allocated a small value to represent the minor chance of establishment in the absence of visitor landings. Insets show risk index detail for the Antarctic Peninsula and the western Ross Sea. Ice-free areas are shown in dark gray, continental areas in light gray, and ice shelf/ice-tongue areas in light blue.

Fig. 4.

Increase in annual cumulative degree days under SRES Scenario A1B (24) indicating increasing risk of alien species establishment. Increase in annual cumulative degree days, on ice-free areas of Antarctica, using 2090–2100 temperature means to estimate future degree days and annual cumulative degree days from 2007 to 2008 based on a lower temperature threshold of −5 °C for plant establishment. Ice-free areas are shown in dark gray, continental areas in light gray, and ice shelf areas in light blue.