species; this suggests that invasive plants too will benefit more from a milder climate
than native plants (Mathakutha et al. 2019).
More generally, climate matching approaches conducted across the sub-Antarctic
islands suggest that these islands, including the PEIs, will become more vulnerable
to invasions under climate change (Steyn 2017; Duffy et al. 2017).
8.6.2 Marine Invasions
The threat of marine invasions at the PEIs, and how these are changing, has received
relatively little attention. Nevertheless, increasing vessel traffic in the Southern
Ocean has been highlighted as a substantial factor promoting marine introductions
(Barnes et al. 2006; Lee and Chown 2007; Hughes and Ashton 2017). Prolonged
survival of hull-fouling marine taxa, including the highly invasive bivalve Mytilus
galloprovincialis (Mediterranean Mussel), has been demonstrated on research vessels travelling to the Prince Edward Islands (Lee and Chown 2007). There is some
consolation in the notion that the predominant direction of transport of any alien
species via ship’s ballast water is likely to be from the Southern Ocean northwards
due to intake of ballast at destinations within the Southern Ocean. Conversely
however, transport of hull-fouling communities is predominantly expected to be
southwards following winter docking in mainland ports (Lewis et al. 2003).
There is an increasing likelihood that regions of the Southern Ocean will receive
introductions of new marine species stemming from weakening or disrupted climatic
and oceanographic barriers, and long-distance transport via kelp and plastic debris
(Aronson et al. 2007; Fraser et al. 2018; Waters et al. 2018). This is particularly true
with respect to the location of the PEIs relative to southward variations in the
position of the sub-Antarctic Front and associated oceanographic eddies which, for
example, are known to facilitate cross-frontal transport of zooplankton within the
PEI region (Pakhomov and Chown 2003; Bernard et al. 2007). Technically, new
introductions associated with kelp rafting would be considered natural range expansions, as they are not assisted by humans (Blackburn et al. 2011); however, new
introductions associated with floating waste are considered to be invasion events
(Gregory 2009). Indeed, the rise in anthropogenic debris (mostly plastic) globally
means there is much more material on which marine species can raft (Barnes 2002;
Eriksen et al. 2014). Despite the lowest colonisation rates for anthropogenic debris
occurring at high latitudes (>50
) globally, it is estimated that such material has
tripled the transmission of fauna in these latitudes (Barnes 2002).
Targeted systematic long-term sampling of marine habitats, and meaningful
oversight of ballast water and hull-fouling are essential to ongoing information
gathering and prevention of marine invasions to the PEI. Although detection is
difficult given the very large and inaccessible environment, including oceanic and
deep benthos across the 500,000 km
2 exclusive economic zone, focused sampling
efforts will provide some chance of early detection. Efforts should include welldefined sentinel areas such as intertidal shores and leeward anchorages, and opportunistic observations of benthic fauna brought up as bycatch from long-line fishing
activities.
8 Biological Invasions in South Africa’s Offshore Sub-Antarctic Territories
219
than native plants (Mathakutha et al. 2019).
More generally, climate matching approaches conducted across the sub-Antarctic
islands suggest that these islands, including the PEIs, will become more vulnerable
to invasions under climate change (Steyn 2017; Duffy et al. 2017).
8.6.2 Marine Invasions
The threat of marine invasions at the PEIs, and how these are changing, has received
relatively little attention. Nevertheless, increasing vessel traffic in the Southern
Ocean has been highlighted as a substantial factor promoting marine introductions
(Barnes et al. 2006; Lee and Chown 2007; Hughes and Ashton 2017). Prolonged
survival of hull-fouling marine taxa, including the highly invasive bivalve Mytilus
galloprovincialis (Mediterranean Mussel), has been demonstrated on research vessels travelling to the Prince Edward Islands (Lee and Chown 2007). There is some
consolation in the notion that the predominant direction of transport of any alien
species via ship’s ballast water is likely to be from the Southern Ocean northwards
due to intake of ballast at destinations within the Southern Ocean. Conversely
however, transport of hull-fouling communities is predominantly expected to be
southwards following winter docking in mainland ports (Lewis et al. 2003).
There is an increasing likelihood that regions of the Southern Ocean will receive
introductions of new marine species stemming from weakening or disrupted climatic
and oceanographic barriers, and long-distance transport via kelp and plastic debris
(Aronson et al. 2007; Fraser et al. 2018; Waters et al. 2018). This is particularly true
with respect to the location of the PEIs relative to southward variations in the
position of the sub-Antarctic Front and associated oceanographic eddies which, for
example, are known to facilitate cross-frontal transport of zooplankton within the
PEI region (Pakhomov and Chown 2003; Bernard et al. 2007). Technically, new
introductions associated with kelp rafting would be considered natural range expansions, as they are not assisted by humans (Blackburn et al. 2011); however, new
introductions associated with floating waste are considered to be invasion events
(Gregory 2009). Indeed, the rise in anthropogenic debris (mostly plastic) globally
means there is much more material on which marine species can raft (Barnes 2002;
Eriksen et al. 2014). Despite the lowest colonisation rates for anthropogenic debris
occurring at high latitudes (>50
) globally, it is estimated that such material has
tripled the transmission of fauna in these latitudes (Barnes 2002).
Targeted systematic long-term sampling of marine habitats, and meaningful
oversight of ballast water and hull-fouling are essential to ongoing information
gathering and prevention of marine invasions to the PEI. Although detection is
difficult given the very large and inaccessible environment, including oceanic and
deep benthos across the 500,000 km
2 exclusive economic zone, focused sampling
efforts will provide some chance of early detection. Efforts should include welldefined sentinel areas such as intertidal shores and leeward anchorages, and opportunistic observations of benthic fauna brought up as bycatch from long-line fishing
activities.
8 Biological Invasions in South Africa’s Offshore Sub-Antarctic Territories
219