associated with their dry ballasts (Griffiths et al. 2009). Dry ballast consisted of rocks
and sand placed in the hull to maintain stability and trim and was offloaded when
vessels filled their hulls with cargo, depositing associated species in new regions.
With the development of steel ships, the suite of species being transported changed.
While wood-boring species were no longer transported, hull fouling remained as an
important vector for the transfer of alien species, particularly fouling in the niche
areas (such as the rudder, propeller, propeller shafts and sea chests). The transition to
steel ships also saw a change in the type of ballast used, with ballast water replacing
solid ballast. This resulted in an important shift in the types of species that were
associated with shipping. Notably, species associated with dry ballast were no longer
inadvertently moved, but planktonic species, and those with planktonic life stages,
were taken up along with ballast water and released into novel ranges (Griffiths et al.
2009). Additionally, benthic species associated with sediment taken up along with
ballast water could be translocated (Hewitt et al. 2009). Furthermore, the change
from using sails to using steam and then oil increased the speed at which vessels
could travel. The speed, size and number of vessels has increased dramatically since
the 1970s (UNCTAD 2007), and with this it is expected that the number of
successful invasions has increased as well (Hulme 2009). Moreover, the increased
speed resulted in shorter transit times which in turn resulted in increased likelihood
of survival and likelihood of introduction of associated species.
The recognition of the dominant role that shipping plays in marine introductions
resulted in international efforts to regulate ballast water through the International
Convention for the Control and Management of Ships’ Ballast Water and Sediments
(BWM Convention). The aim of this convention is to prevent, minimise and
eliminate the risks associated with transferring harmful organisms in ballast water
(IMO 2004) and in 2017 the Convention entered into force (IMO 2017). Since the
initial development of this Convention, the role of ballast water in transporting
marine species is likely to have been reduced and although hull fouling was always
present, this has emerged as the dominant vector for marine species transfer (Hewitt
et al. 2009; Williams et al. 2013). Shipping is responsible for approximately 91% of
marine introductions to South Africa, but it is extremely difficult to associate
particular introductions with ballast water or hull fouling, as many species can be
introduced via either vector. Nonetheless, this separation has been possible for some
introductions to South Africa, with 23% of introductions being due to fouling only
and 5% associated with ballast water only (Fig. 9.4). Two other vectors have been
responsible for introductions to this coast, these being mariculture (Haupt et al.
2012) and oil and gas infrastructure (Sink et al. 2010). To date, mariculture has been
linked to the introduction of only five species to the region. Whilst this number may
appear low, three of the five species (the polychaete Boccardia proboscidea, the
oyster Crassostrea gigas and the brachiopod Discinisca tenuis) have become invasive. Oil and gas infrastructure is an emerging vector in the region and while it has
potentially been responsible for only one introduction to date (the European shore
crab Carcinus maenas), efforts by the South African government to establish
South African ports as a premier destination for oil rig maintenance suggest that
this vector may become more important in the future. Although it has not yet
introduced any marine alien species to South Africa, the aquarium and pet trade is
236
T. B. Robinson et al.
and sand placed in the hull to maintain stability and trim and was offloaded when
vessels filled their hulls with cargo, depositing associated species in new regions.
With the development of steel ships, the suite of species being transported changed.
While wood-boring species were no longer transported, hull fouling remained as an
important vector for the transfer of alien species, particularly fouling in the niche
areas (such as the rudder, propeller, propeller shafts and sea chests). The transition to
steel ships also saw a change in the type of ballast used, with ballast water replacing
solid ballast. This resulted in an important shift in the types of species that were
associated with shipping. Notably, species associated with dry ballast were no longer
inadvertently moved, but planktonic species, and those with planktonic life stages,
were taken up along with ballast water and released into novel ranges (Griffiths et al.
2009). Additionally, benthic species associated with sediment taken up along with
ballast water could be translocated (Hewitt et al. 2009). Furthermore, the change
from using sails to using steam and then oil increased the speed at which vessels
could travel. The speed, size and number of vessels has increased dramatically since
the 1970s (UNCTAD 2007), and with this it is expected that the number of
successful invasions has increased as well (Hulme 2009). Moreover, the increased
speed resulted in shorter transit times which in turn resulted in increased likelihood
of survival and likelihood of introduction of associated species.
The recognition of the dominant role that shipping plays in marine introductions
resulted in international efforts to regulate ballast water through the International
Convention for the Control and Management of Ships’ Ballast Water and Sediments
(BWM Convention). The aim of this convention is to prevent, minimise and
eliminate the risks associated with transferring harmful organisms in ballast water
(IMO 2004) and in 2017 the Convention entered into force (IMO 2017). Since the
initial development of this Convention, the role of ballast water in transporting
marine species is likely to have been reduced and although hull fouling was always
present, this has emerged as the dominant vector for marine species transfer (Hewitt
et al. 2009; Williams et al. 2013). Shipping is responsible for approximately 91% of
marine introductions to South Africa, but it is extremely difficult to associate
particular introductions with ballast water or hull fouling, as many species can be
introduced via either vector. Nonetheless, this separation has been possible for some
introductions to South Africa, with 23% of introductions being due to fouling only
and 5% associated with ballast water only (Fig. 9.4). Two other vectors have been
responsible for introductions to this coast, these being mariculture (Haupt et al.
2012) and oil and gas infrastructure (Sink et al. 2010). To date, mariculture has been
linked to the introduction of only five species to the region. Whilst this number may
appear low, three of the five species (the polychaete Boccardia proboscidea, the
oyster Crassostrea gigas and the brachiopod Discinisca tenuis) have become invasive. Oil and gas infrastructure is an emerging vector in the region and while it has
potentially been responsible for only one introduction to date (the European shore
crab Carcinus maenas), efforts by the South African government to establish
South African ports as a premier destination for oil rig maintenance suggest that
this vector may become more important in the future. Although it has not yet
introduced any marine alien species to South Africa, the aquarium and pet trade is
236
T. B. Robinson et al.