during the 1970s. This mussel likely invaded the South African coastline after being
released as larvae from ballast water (Grant and Cherry 1985), which cannot vector
endolithic bacteria. These parasites are therefore thought to be cosmopolitan in their
distribution and native to South Africa (Marquet et al. 2013). Interestingly, endolithic parasitism appears to have a greater impact on South African
M. galloprovincialis populations than on native populations in Portugal (Marquet
et al. 2013), possibly due to the low genetic variability of the mussel in South Africa
(Zardi et al. 2009; Marquet et al. 2013). However, despite the negative effects of
shell parasites on M. galloprovincialis, this mussel persists as the most successful
marine invasive species along the South African coastline (Robinson et al. 2005,
2020, Chap. 9). Characteristics such as high fecundity and recruitment rates (van
Erkom Schurink and Griffiths 1991; Harris et al. 1998), fast growth (Griffiths et al.
1992), and high desiccation tolerance (Hockey and van Erkom Schurink 1992),
enable it to overcome the negative impacts imposed by parasites like endolithic
bacteria. Mytilus galloprovincialis invasions also had some positive impacts on
native species in South Africa. This invasive mussel now makes up a large part of
the diet of the endemic African black oystercatcher (Haematopus moquini), southern
Africa’s second-rarest coastal bird (Coleman and Hockey 2008).
In contrast to the post-introduction accumulation of parasites in
M. galloprovincialis, the intentional introduction of molluscs for aquaculture often
leads to the co-introduction of their parasites (Naylor et al. 2001). For example, ten
shell-boring polychaete worm species are known to infect shells of cultured molluscs, mainly oysters and abalone, along the South African coastline (Simon and
Sato-Okoshi 2015). Two of these parasites are invasive in South Africa, namely
Polydora hoplura and Boccardia proboscidia (Simon et al. 2006, 2009; David and
Simon 2014). The former was detected in the 1950s, while B. proboscidia was first
recorded in 2004 (Simon et al. 2006, 2009). The ability of females of these two
polychaetes to produce multiple larval types (poecilogonous), and to survive and
reproduce across a wide range of temperatures and substrates, all contribute to their
invasion success in South Africa (David and Simon 2014). The excavation of
burrows on shell surfaces of molluscs by polydorid annelids such as P. hoplura
and B. proboscidia, not only leads to shell damage, but also causes reduced growth
and condition, and ultimately increased mortality rates (Simon et al. 2006). While
such parasitism is initially limited to cultured molluscs, these organisms can escape
from aquaculture facilities and infect wild molluscs. The parasites thus represent
economic and ecological threats. Both species are now found along most of the
South African coastline (David and Simon 2014), and although transport of cultured
animals among aquaculture facilities is being more strictly regulated, the threats
posed to both farmed and wild molluscs remain.
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J. J. Le Roux et al.
released as larvae from ballast water (Grant and Cherry 1985), which cannot vector
endolithic bacteria. These parasites are therefore thought to be cosmopolitan in their
distribution and native to South Africa (Marquet et al. 2013). Interestingly, endolithic parasitism appears to have a greater impact on South African
M. galloprovincialis populations than on native populations in Portugal (Marquet
et al. 2013), possibly due to the low genetic variability of the mussel in South Africa
(Zardi et al. 2009; Marquet et al. 2013). However, despite the negative effects of
shell parasites on M. galloprovincialis, this mussel persists as the most successful
marine invasive species along the South African coastline (Robinson et al. 2005,
2020, Chap. 9). Characteristics such as high fecundity and recruitment rates (van
Erkom Schurink and Griffiths 1991; Harris et al. 1998), fast growth (Griffiths et al.
1992), and high desiccation tolerance (Hockey and van Erkom Schurink 1992),
enable it to overcome the negative impacts imposed by parasites like endolithic
bacteria. Mytilus galloprovincialis invasions also had some positive impacts on
native species in South Africa. This invasive mussel now makes up a large part of
the diet of the endemic African black oystercatcher (Haematopus moquini), southern
Africa’s second-rarest coastal bird (Coleman and Hockey 2008).
In contrast to the post-introduction accumulation of parasites in
M. galloprovincialis, the intentional introduction of molluscs for aquaculture often
leads to the co-introduction of their parasites (Naylor et al. 2001). For example, ten
shell-boring polychaete worm species are known to infect shells of cultured molluscs, mainly oysters and abalone, along the South African coastline (Simon and
Sato-Okoshi 2015). Two of these parasites are invasive in South Africa, namely
Polydora hoplura and Boccardia proboscidia (Simon et al. 2006, 2009; David and
Simon 2014). The former was detected in the 1950s, while B. proboscidia was first
recorded in 2004 (Simon et al. 2006, 2009). The ability of females of these two
polychaetes to produce multiple larval types (poecilogonous), and to survive and
reproduce across a wide range of temperatures and substrates, all contribute to their
invasion success in South Africa (David and Simon 2014). The excavation of
burrows on shell surfaces of molluscs by polydorid annelids such as P. hoplura
and B. proboscidia, not only leads to shell damage, but also causes reduced growth
and condition, and ultimately increased mortality rates (Simon et al. 2006). While
such parasitism is initially limited to cultured molluscs, these organisms can escape
from aquaculture facilities and infect wild molluscs. The parasites thus represent
economic and ecological threats. Both species are now found along most of the
South African coastline (David and Simon 2014), and although transport of cultured
animals among aquaculture facilities is being more strictly regulated, the threats
posed to both farmed and wild molluscs remain.
400
J. J. Le Roux et al.