THE THEMATIC ASSESSMENT REPORT ON INVASIVE ALIEN SPECIES AND THEIR CONTROL
29SUMMARY FOR POLICYMAKERS
of biological invasion occur where land-use change interacts 
with one or more additional drivers (established but 
incomplete) {3.5.1, 3.5.2, 3.5.3}. For example, interactions 
among land-use change, climate change and nutrient 
pollution have driven the introduction, establishment and 
spread of Pontederia crassipes (water hyacinth) across 
Africa (well established) {Box 3.12}. Extraction of natural 
resources is closely linked with major economic and 
demographic drivers and can lead to a range of wider 
ecosystem impacts, including habitat degradation and loss, 
which facilitates invasive alien species (well established)
{3.3.2, 3.4.2}. Climate change is predicted to lead to major 
changes in land- and sea-use and, in some regions, in 
human migration patterns (established but incomplete)
{3.3.4}, but also to more extreme events among natural 
drivers, such as droughts, floods, wildfires, tropical storms 
and oceanic storm waves (established but incomplete)
{3.3.4.3}. Additionally, invasive alien plants, especially trees 
and grasses, can sometimes be highly flammable and 
therefore promote more intense and frequent fire regimes, 
causing increased risks to nature and people and increased 
carbon release into the atmosphere (well established) {Box 
1.4}. Climate change is also predicted to enhance the 
competitive ability of some invasive alien species and to 
extend areas suitable for them thus offering new 
opportunities for introductions and establishment 
(established but incomplete) {3.3.4}. Invasive alien species 
can facilitate the establishment and spread of other invasive 
alien species, resulting in positive feedback that increases 
impacts through a process known as "invasional meltdown" 
(well established) {3.3.5.1}. Biodiversity loss can reduce the 
resilience of ecosystems to invasive alien species, with 
Box SPM 2 The International Convention for the Control and Management of Ships' 
Ballast Water and Sediments: an example of international collaboration to 
prevent biological invasions.
Many invasive alien species have been introduced to coastal 
and inland water ecosystems globally through ballast water 
discharges {3.2.3.1}. For example, following its introduction its 
introduction via ballast water discharge, Dreissena polymorpha
(zebra mussel) has become widespread in the Great Lakes 
of North America {Box 2.9}. Dreissena polymorpha has been 
implicated in the transfer of botulinum toxin to higher trophic 
levels, which has been further 
facilitated by climate change, 
specifically by increased water 
temperatures, leading to mortality 
of waterfowl in the Great Lakes 
{Box 4.5}. Furthermore, the shells 
of Dreissena polymorpha can 
cause skin injuries to recreational 
swimmers and commercial fishers 
{Box 4.15}. The International 
Maritime Organization has 
developed an international 
instrument to address the transfer 
of harmful aquatic organisms 
and pathogens in ballast water 
of maritime vessels {5.5.1}. The 
International Convention for the 
Control and Management of Ships' 
Ballast Water and Sediments 
was adopted by the International 
Maritime Organization in 2004 and 
came into force in 2017 {5.5.1}. 
It is the first international legally binding legislation requiring 
ships to manage their ballast water so that aquatic organisms 
and pathogens are eliminated before the ballast water is 
released in a new location {3.2.3.1, 5.5.1, 6.1.3, 6.31}. While 
the global efficacy of ballast water management cannot be 
assessed yet, there is evidence that it has reduced invasive 
alien species introductions in the Great Lakes of North America 
{5.5.1}: between 1959 and 2006, one new alien species was 
discovered every seven months, but there was an abrupt 
shift (85 per cent decline) in the number of newly established 
alien species following the implementation of the ballast water 
regulations by Canada and the United States of America in 
2006 and 2008 respectively {Box 2.9}.
Dreissena polymorpha (zebra mussel) was introduced through 
ballast water discharge in the Great Lakes of North America, 
causing a negative impact on nature, nature's contributions to 
people, and good quality of life.
Photo credit:Thirdwavephoto, WM Commons - CC BY 4.0
29SUMMARY FOR POLICYMAKERS
19SUMMARY FOR POLICYMAKERS
BACKGROUND
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