new areas, including South Africa (Brunel 2009; Maki and Galatowitsch 2004).
Alien submerged plants are traded either under their correct names, their synonyms,
or common names (Hussner et al. 2014). Unfortunately, the general public and plant
dealers are often unaware of the ecological repercussions of the species they trade.
These species are released intentionally or unintentionally into water bodies and
subsequently spread via plant fragments, with water flow and water sport equipment
having been identified as the major vectors (Coetzee et al. 2009; Heidbüchel et al.
2016). This lack of knowledge regarding invasive aquatic species results in less care
being given to the overflow of ponds or the disposal of plants, which are often
discarded into ponds, ditches, streams and rivers (Duggan 2010). Invasive submerged plants in particular, most likely originating from aquarium releases, pose a
significant negative environmental and economic threat to South Africa. They have
been allowed to escape and spread with few or no control measures, as most
attention has been paid to controlling the more obvious floating aquatic plant
invasions. Awareness and publicity programmes on potential new threats could go
a long way towards preventing their introduction and trade, as well as improved
phytosanitary efforts and border control (Hill and Coetzee 2017).
4.4 Drivers of Invasion
The biology of freshwater macrophytes contributes to their invasiveness as they are
capable of rapid asexual reproduction, and the most damaging species (e.g. Water
Hyacinth and Water Lettuce) produce long-lived seeds. Once established, four
factors contribute significantly to the invasiveness of these macrophytes: the lack
of competition due to the paucity of native floating macrophytes (Cook 2004); the
lack of co-evolved natural enemies in their adventive range (McFadyen 1998);
disturbance, which includes eutrophication (Coetzee and Hill 2012); and the alteration of hydrological flows through the impoundment of streams and rivers, creating
permanent waterbodies that are no longer prone to flooding or drought (Hill and
Olckers 2001). Thus, aquatic plant invasions in South Africa are examples of ‘backseat drivers’ (sensu Bauer 2012) in that they rely on the broad ecosystem disturbance
(MacDougall and Turkington 2005) of slow-flowing permanent waters caused by
impoundments, and eutrophication, which facilitates their establishment. This,
linked with a lack of natural enemies, allows them to proliferate, thereby gaining a
competitive advantage over native aquatic plants (Coetzee and Hill 2012).
4.5 Impacts
The negative socio-economic and environmental impacts of invasive aquatic plants
have been well documented globally (e.g. Cilliers et al. 2003; Coetzee et al. 2018).
Invasive floating plants and dense populations of submerged invasive plants form
102
M. P. Hill et al.
Alien submerged plants are traded either under their correct names, their synonyms,
or common names (Hussner et al. 2014). Unfortunately, the general public and plant
dealers are often unaware of the ecological repercussions of the species they trade.
These species are released intentionally or unintentionally into water bodies and
subsequently spread via plant fragments, with water flow and water sport equipment
having been identified as the major vectors (Coetzee et al. 2009; Heidbüchel et al.
2016). This lack of knowledge regarding invasive aquatic species results in less care
being given to the overflow of ponds or the disposal of plants, which are often
discarded into ponds, ditches, streams and rivers (Duggan 2010). Invasive submerged plants in particular, most likely originating from aquarium releases, pose a
significant negative environmental and economic threat to South Africa. They have
been allowed to escape and spread with few or no control measures, as most
attention has been paid to controlling the more obvious floating aquatic plant
invasions. Awareness and publicity programmes on potential new threats could go
a long way towards preventing their introduction and trade, as well as improved
phytosanitary efforts and border control (Hill and Coetzee 2017).
4.4 Drivers of Invasion
The biology of freshwater macrophytes contributes to their invasiveness as they are
capable of rapid asexual reproduction, and the most damaging species (e.g. Water
Hyacinth and Water Lettuce) produce long-lived seeds. Once established, four
factors contribute significantly to the invasiveness of these macrophytes: the lack
of competition due to the paucity of native floating macrophytes (Cook 2004); the
lack of co-evolved natural enemies in their adventive range (McFadyen 1998);
disturbance, which includes eutrophication (Coetzee and Hill 2012); and the alteration of hydrological flows through the impoundment of streams and rivers, creating
permanent waterbodies that are no longer prone to flooding or drought (Hill and
Olckers 2001). Thus, aquatic plant invasions in South Africa are examples of ‘backseat drivers’ (sensu Bauer 2012) in that they rely on the broad ecosystem disturbance
(MacDougall and Turkington 2005) of slow-flowing permanent waters caused by
impoundments, and eutrophication, which facilitates their establishment. This,
linked with a lack of natural enemies, allows them to proliferate, thereby gaining a
competitive advantage over native aquatic plants (Coetzee and Hill 2012).
4.5 Impacts
The negative socio-economic and environmental impacts of invasive aquatic plants
have been well documented globally (e.g. Cilliers et al. 2003; Coetzee et al. 2018).
Invasive floating plants and dense populations of submerged invasive plants form
102
M. P. Hill et al.