Alien species and propagules in the Antarctic: movements through space and time

Although the impacts of biological invasions are widely appreciated, a bias exists in research effort to post‐dispersal processes because of the difficulties of measuring propagule pressure and the detecting of newly established species. Here the Antarctic is used as a model system in which to quantify the initial dispersal of alien species and investigate the factors that contribute to the establishment and range dynamics of alien species once they have arrived in the region.Human movements are known to transport alien species into the Antarctic, some of which have successfully established and had wide ranging consequences in recipient ecosystems. Considering terrestrial flora, this research found that over 700 seeds from 99 taxa, including some species known to be invasive, are transported into the Antarctic each year in association with South African National Antarctic Programme (SANAP) passenger luggage and cargo. The first ever assessment of propagule drop‐off indicated that 30‐50% of these propagules will enter the recipient environment. Further results suggested that the construction of the British Antarctic Survey Halley VI station will facilitate the transport of over 5000 seeds from 34 taxa into the region, making this a significant pathway for introductions.Propagule pressure due to SANAP logistics is also considerable for marine species. Fouling assemblages on the external hull surfaces of the SANAP resupply vessel, the SA Agulhas, form only once the vessel’s anti‐fouling paint has been damaged by travel through sea ice and are characterised by low diversity. Ice scour prevents fouling assemblages from being transported to the Antarctic continent, but assemblages remain largely intact when travelling to sub‐Antarctic Islands. In the sea‐chests of the vessel populations of a known invasive, Mytilus galloprovincialis, were found with some individuals having survived transportation to the Antarctic region on multiple occasions.Once species have overcome initial dispersal barriers, they face further ecological and physiological challenges in order to establish in the recipient region. The parasitoid wasp Aphidius matricariae was first recorded on Marion Island in 2001. Surveys around the island show that adult abundance and the frequency of aphid parasitism are highest adjacent to a common anchor point of the SA Agulhas and decline away from this region. Genetic diversity was low, suggesting that the population was established from a single introduction. This highlights that high propagule pressure is not necessary for successful establishment of introduced invertebrates.Another species that has overcome the dispersal barrier is the terrestrial slug Deroceras panormitanum, which was introduced to Marion Island in the 1970’s and has since spread throughout much of the coastal habitat of the island. For this species range limits are set by intolerance of low temperature and salinity, and abundance structure is characterized by patches and gaps which are associated with this species inability to tolerate dry conditions.To prevent further alien introductions in the region, targeted management of high risk pathways is required. In addition, increased vigilance is needed to detect and manage newly established aliens before their ranges expand.

尽管生物入侵的影响已被广泛认可，但鉴于测量繁殖压力和检测新建立物种的困难，研究工作在散布后过程中的努力存在偏差。本研究以南极洲为模型系统，量化外来物种的初始散布，并探讨一旦它们到达该地区，何种因素有助于外来物种的建立和分布动态。众所周知，人类活动会将外来物种带入南极，其中一些物种已成功建立并对其接收生态系统产生了广泛的影响。针对陆地植物，研究发现每年与南非国家南极计划（SANAP）的乘客行李和货物相关联，有超过700种来自99个分类群（包括一些已知为入侵物种）的种子被带入南极。首次对繁殖压力的评估表明，其中30%-50%的繁殖体将进入接收环境。进一步的结果表明，英国南极调查哈雷VI站的建设将促进超过5000种来自34个分类群的种子进入该地区，使其成为引入的重要途径。由于SANAP物流的繁殖压力，对海洋物种来说也相当可观。在SANAP补给船SA Agulhas的外壳表面，由于穿越海冰时防污漆被破坏而形成的附着生物群落，仅当船只的防污漆受损后才会形成，其特征是多样性低。冰蚀阻止附着生物群落被运送到南极大陆，但在前往亚南极岛屿时，群落大体保持完整。在船只的船舱中发现了已知入侵物种，如牡蛎属（Mytilus galloprovincialis）的一些个体，它们多次成功运输到南极地区。一旦物种克服了初始散布障碍，它们在接收区域建立的过程中还将面临进一步的生态和生理挑战。寄生蜂Aphidius matricariae首次于2001年在马里恩岛上记录。围绕岛屿的调查显示，成年蜂的丰富度和蚜虫寄生的频率在SA Agulhas的常见锚点附近最高，并随着远离该区域而下降。遗传多样性低，表明该种群是由单一引入而建立的。这表明，高繁殖压力并非引入无脊椎动物成功建立所必需的。另一个克服了散布障碍的物种是陆地蜗牛Deroceras panormitanum，它在1970年代被引入马里恩岛，并自此在该岛的大部分沿海栖息地中扩散。对于这个物种，其分布范围受到对低温和盐度不耐受性的限制，其丰度结构以斑块和缺口为特征，这与该物种无法耐受干燥条件的能力相关。为了防止该地区进一步的外来物种引入，需要针对高风险途径进行有针对性的管理。此外，需要提高警惕，以检测和管理新建立的物种，防止其分布范围扩大。