alien taxa. This key skill is presently underrepresented within the marine research
community in South Africa (Griffiths et al. 2010) and the shortage of specialist
taxonomists has been highlighted as an impediment to the development of a comprehensive list of alien marine species for the region (Griffiths et al. 2009). Despite
this obstacle, marine invasion biology in South Africa is a growing field of study.
This is reflected most clearly in the publication of 36 peer-reviewed papers in the
decade ending 2008, followed by an almost doubling to 70 publications in the
decade ending 2018. Pre-2000 most studies considered the establishment and spread
of alien taxa in easily accessed habitats such as rocky shores and reported the results
of field surveys (Alexander et al. 2016). Since that time there has been an increased
focus on experimental studies (both laboratory and field-based) and an emphasis on
understanding biological interactions (e.g. Steffani and Branch 2003; Zardi et al.
2006; Branch et al. 2008, 2010; Bownes and McQuaid 2010) and intra-regional
spread (Peters et al. 2017).
9.2 Status of Marine Alien Species
In total 95 alien species are known from South Africa, with an additional 39 species
being reported as cryptogenic (Table 9.1). These species represent a variety of
taxonomic groups, including micro-organisms such as protists (Mirofolliculina
limnoriae) and dinoflagellates (e.g. Alexandrium minutum), polychaete worms
(e.g. Polydora hoplura), starfish (Heliaster helianthus) and even algae
(e.g. Codium fragile). The majority of species are crustaceans (including barnacles,
copepods, amphipods, isopods and crabs), which account for 32% of recognised
alien species (Fig. 9.1). Cnidarians (including anemones and hydrozoans) and
molluscs (including gastropods and bivalves) account for 14% and 13%, respectively, while 12 different taxonomic groups account for the remaining species.
Of the 95 alien species, 56 are considered to be invasive. It is notable that 80%
of these invasive species have been recorded in natural habitats although only three,
the Mediterranean Mussel Mytilus galloprovincialis, the Chilean Mussel Semimytilus
algosus and the Pacific Barnacle Balanus glandula have become abundant and
widespread along the open coast. Table 9.1 lists all of these species, including the
ecoregions that they have invaded in South Africa (see Sink et al. 2012). Six of the
remaining 39 alien species are considered naturalised (i.e. they support self-sustaining
populations) but have not yet spread from their points of introduction.
Tracking changes in numbers of alien species can be difficult, especially in
marine habitats, where they can remain unobserved for many years after their
introduction. In addition, temporal patterns of introductions can be masked by
changing research effort through time. Nonetheless, some clear patterns emerge
when considering the number of marine alien species known from the
South African coast through time. The earliest record dates back to 1852, when
the bryozoan Virididentula dentata (previously known as Bugula dentata) was first
noted (Mead et al. 2011b). In total, only four alien species were recorded in the
1800s. This is in contrast with the 1900s, when 65 species were noted, giving a
9 Coastal Invasions: The South African Context
231
community in South Africa (Griffiths et al. 2010) and the shortage of specialist
taxonomists has been highlighted as an impediment to the development of a comprehensive list of alien marine species for the region (Griffiths et al. 2009). Despite
this obstacle, marine invasion biology in South Africa is a growing field of study.
This is reflected most clearly in the publication of 36 peer-reviewed papers in the
decade ending 2008, followed by an almost doubling to 70 publications in the
decade ending 2018. Pre-2000 most studies considered the establishment and spread
of alien taxa in easily accessed habitats such as rocky shores and reported the results
of field surveys (Alexander et al. 2016). Since that time there has been an increased
focus on experimental studies (both laboratory and field-based) and an emphasis on
understanding biological interactions (e.g. Steffani and Branch 2003; Zardi et al.
2006; Branch et al. 2008, 2010; Bownes and McQuaid 2010) and intra-regional
spread (Peters et al. 2017).
9.2 Status of Marine Alien Species
In total 95 alien species are known from South Africa, with an additional 39 species
being reported as cryptogenic (Table 9.1). These species represent a variety of
taxonomic groups, including micro-organisms such as protists (Mirofolliculina
limnoriae) and dinoflagellates (e.g. Alexandrium minutum), polychaete worms
(e.g. Polydora hoplura), starfish (Heliaster helianthus) and even algae
(e.g. Codium fragile). The majority of species are crustaceans (including barnacles,
copepods, amphipods, isopods and crabs), which account for 32% of recognised
alien species (Fig. 9.1). Cnidarians (including anemones and hydrozoans) and
molluscs (including gastropods and bivalves) account for 14% and 13%, respectively, while 12 different taxonomic groups account for the remaining species.
Of the 95 alien species, 56 are considered to be invasive. It is notable that 80%
of these invasive species have been recorded in natural habitats although only three,
the Mediterranean Mussel Mytilus galloprovincialis, the Chilean Mussel Semimytilus
algosus and the Pacific Barnacle Balanus glandula have become abundant and
widespread along the open coast. Table 9.1 lists all of these species, including the
ecoregions that they have invaded in South Africa (see Sink et al. 2012). Six of the
remaining 39 alien species are considered naturalised (i.e. they support self-sustaining
populations) but have not yet spread from their points of introduction.
Tracking changes in numbers of alien species can be difficult, especially in
marine habitats, where they can remain unobserved for many years after their
introduction. In addition, temporal patterns of introductions can be masked by
changing research effort through time. Nonetheless, some clear patterns emerge
when considering the number of marine alien species known from the
South African coast through time. The earliest record dates back to 1852, when
the bryozoan Virididentula dentata (previously known as Bugula dentata) was first
noted (Mead et al. 2011b). In total, only four alien species were recorded in the
1800s. This is in contrast with the 1900s, when 65 species were noted, giving a
9 Coastal Invasions: The South African Context
231