impoverished diet, consisting mainly of terrestrial invertebrates; it is thus unlikely
that the species had a major impact on the river system (Cooper et al. 1992).
Some algal surveys have been conducted on the PEIs (van de Vijver et al. 2008;
van Staden 2011) but no alien species have been detected (Greve et al. 2017).
8.5 Marine Invaders
For the Southern Ocean, invasion of marine habitats by alien species is a widely-held
concern (Barnes 2005; Frenot et al. 2005; Aronson et al. 2007). However, there are
currently no known cases of alien marine species establishing anywhere in the
region, including the Prince Edward Islands and surrounds (Barnes 2005). Nevertheless, the concern is well-founded as there have been several documented occurrences of alien marine species from the Southern Ocean (Ralph et al. 1976; Thatje
and Fuentes 2003; Tavares and De Melo 2004).
At Marion Island, intertidal and subtidal shelf habitats have been periodically
sampled over the past five decades, allowing a reasonable degree of confidence of
the absence of marine alien species. The earliest descriptions of the subtidal macrobenthos and fishes come from the Challenger (1873) and Discovery II (1935) expeditions, while the intertidal habitats of Marion Island were first surveyed by Fuller
(1967), with more detailed work following in the 1970s and 1980s (de Villiers 1976;
Blankley and Grindley 1985). The shores were re-surveyed in 2017, and no alien
species were recorded (M. Pfaff pers. comm.). Likewise, subtidal habitats on the northeastern coast of Marion Island were surveyed by SCUBA divers to a depth of 15 m in
1988 (Beckley and Branch 1992). Extensive dredge and photographic surveys of the
deeper benthos of the island plateau and shelf edge (35–750 m) were completed over
the same period (Branch et al. 1993). This resulted in the production of detailed
taxonomic keys and the description of several new species (e.g. Arnaud and Branch
1991; Branch et al. 1991; Branch 1994, 1998; Branch and Hayward 2007). These
stations are now the subject of long-term monitoring by the South African Environmental Observation Network, with photographic resampling undertaken in 2013, 2015
and 2017. Although this work has identified shifts in the relative composition of
benthic assemblages, no alien species have yet been recorded (von der Meden et al.
2017). A major caveat here, of course, is that the deep-sea (>800 m) benthic
ecosystems surrounding the PEIs remain almost entirely unsampled, leaving the status
of biological invasions in these environments unknown.
8.6 Changes to the Likelihood of Introductions and Spread
of Invasive Alien Species
8.6.1 Terrestrial Invasions
As the role of the PEIs has changed from being mainly of commercial/exploitation
interest (pre-annexation), to being a politically strategic outpost (post-annexation), to
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M. Greve et al.
that the species had a major impact on the river system (Cooper et al. 1992).
Some algal surveys have been conducted on the PEIs (van de Vijver et al. 2008;
van Staden 2011) but no alien species have been detected (Greve et al. 2017).
8.5 Marine Invaders
For the Southern Ocean, invasion of marine habitats by alien species is a widely-held
concern (Barnes 2005; Frenot et al. 2005; Aronson et al. 2007). However, there are
currently no known cases of alien marine species establishing anywhere in the
region, including the Prince Edward Islands and surrounds (Barnes 2005). Nevertheless, the concern is well-founded as there have been several documented occurrences of alien marine species from the Southern Ocean (Ralph et al. 1976; Thatje
and Fuentes 2003; Tavares and De Melo 2004).
At Marion Island, intertidal and subtidal shelf habitats have been periodically
sampled over the past five decades, allowing a reasonable degree of confidence of
the absence of marine alien species. The earliest descriptions of the subtidal macrobenthos and fishes come from the Challenger (1873) and Discovery II (1935) expeditions, while the intertidal habitats of Marion Island were first surveyed by Fuller
(1967), with more detailed work following in the 1970s and 1980s (de Villiers 1976;
Blankley and Grindley 1985). The shores were re-surveyed in 2017, and no alien
species were recorded (M. Pfaff pers. comm.). Likewise, subtidal habitats on the northeastern coast of Marion Island were surveyed by SCUBA divers to a depth of 15 m in
1988 (Beckley and Branch 1992). Extensive dredge and photographic surveys of the
deeper benthos of the island plateau and shelf edge (35–750 m) were completed over
the same period (Branch et al. 1993). This resulted in the production of detailed
taxonomic keys and the description of several new species (e.g. Arnaud and Branch
1991; Branch et al. 1991; Branch 1994, 1998; Branch and Hayward 2007). These
stations are now the subject of long-term monitoring by the South African Environmental Observation Network, with photographic resampling undertaken in 2013, 2015
and 2017. Although this work has identified shifts in the relative composition of
benthic assemblages, no alien species have yet been recorded (von der Meden et al.
2017). A major caveat here, of course, is that the deep-sea (>800 m) benthic
ecosystems surrounding the PEIs remain almost entirely unsampled, leaving the status
of biological invasions in these environments unknown.
8.6 Changes to the Likelihood of Introductions and Spread
of Invasive Alien Species
8.6.1 Terrestrial Invasions
As the role of the PEIs has changed from being mainly of commercial/exploitation
interest (pre-annexation), to being a politically strategic outpost (post-annexation), to
216
M. Greve et al.