1 nematode, 1 oligochaete, 6 crustacean, 16 insect, 7 mollusc and 21 fish species.
Their origins include all continents except Antarctica and the main pathways for
their introduction into the wild are intentional releases (42% of taxa), as parasitic
contaminants (35%) or stowaways (14%). Escape from captivity has been relatively
unimportant (one fish and one crayfish) and direct introductions for fisheries (49% of
taxa), biological control (19%) and stowaways or contaminants (22%) are the most
common vectors. The chapter provides an overview of the alien freshwater taxa that
are naturalised in South Africa and offers insights into which areas of research are
data deficient. Generally, the introduction pathways and vectors for intentionally
introduced taxa, such as insects imported for biological control or fishes introduced
for fisheries, are well understood and documented. Data on other taxa, and particularly on invertebrates, are scant and only certain groups, such as the parasites of
fishes, and snails, for which there is directed research interest, are documented. As a
result, increased survey effort is urgently required.
6.1 Introduction
6.1.1 Background
While alien species introductions are, after habitat modification and pollution,
considered the third most important threat to freshwater biodiversity in southern
Africa (Darwall et al. 2009), some are useful and important as biocontrol agents
(Hill and Coetzee 2017) or provide nutritional, economic or recreational values
to society (Ellender et al. 2014). Management through monitoring and control
are therefore national priorities in South Africa. This requires knowledge on
which taxa are present in the country and on their current distributions. Here we
provide information on 77 freshwater alien taxa which include parasitic ciliates,
mongeneans and nematodes; jellyfish, earthworms, molluscs, crustaceans and
fishes (Table 6.1). Amphibians and reptiles are discussed in Chap. 5 (Measey et al.
2020).
Although there are many extralimital invasions of native species, this chapter
focusses on biota introduced across the geopolitical boundary of South Africa. It is
based on a comprehensive literature review of the introduction status, known
distribution and impact of alien freshwater taxa that are documented to have
naturalised in South Africa. We focus primarily on taxa that have naturalised, but
discuss failed introductions where appropriate.
6.1.2 Pathways and Vectors
The origins of aquatic biota include all continents except Antarctica (Fig. 6.1a) and
the main introduction pathways into the wild are intentional releases (42% of taxa),
154
O. L. F. Weyl et al.
Their origins include all continents except Antarctica and the main pathways for
their introduction into the wild are intentional releases (42% of taxa), as parasitic
contaminants (35%) or stowaways (14%). Escape from captivity has been relatively
unimportant (one fish and one crayfish) and direct introductions for fisheries (49% of
taxa), biological control (19%) and stowaways or contaminants (22%) are the most
common vectors. The chapter provides an overview of the alien freshwater taxa that
are naturalised in South Africa and offers insights into which areas of research are
data deficient. Generally, the introduction pathways and vectors for intentionally
introduced taxa, such as insects imported for biological control or fishes introduced
for fisheries, are well understood and documented. Data on other taxa, and particularly on invertebrates, are scant and only certain groups, such as the parasites of
fishes, and snails, for which there is directed research interest, are documented. As a
result, increased survey effort is urgently required.
6.1 Introduction
6.1.1 Background
While alien species introductions are, after habitat modification and pollution,
considered the third most important threat to freshwater biodiversity in southern
Africa (Darwall et al. 2009), some are useful and important as biocontrol agents
(Hill and Coetzee 2017) or provide nutritional, economic or recreational values
to society (Ellender et al. 2014). Management through monitoring and control
are therefore national priorities in South Africa. This requires knowledge on
which taxa are present in the country and on their current distributions. Here we
provide information on 77 freshwater alien taxa which include parasitic ciliates,
mongeneans and nematodes; jellyfish, earthworms, molluscs, crustaceans and
fishes (Table 6.1). Amphibians and reptiles are discussed in Chap. 5 (Measey et al.
2020).
Although there are many extralimital invasions of native species, this chapter
focusses on biota introduced across the geopolitical boundary of South Africa. It is
based on a comprehensive literature review of the introduction status, known
distribution and impact of alien freshwater taxa that are documented to have
naturalised in South Africa. We focus primarily on taxa that have naturalised, but
discuss failed introductions where appropriate.
6.1.2 Pathways and Vectors
The origins of aquatic biota include all continents except Antarctica (Fig. 6.1a) and
the main introduction pathways into the wild are intentional releases (42% of taxa),
154
O. L. F. Weyl et al.