THE THEMATIC ASSESSMENT REPORT ON INVASIVE ALIEN SPECIES AND THEIR CONTROL
21SUMMARY FOR POLICYMAKERS
example, the ctenophore Mnemiopsis leidyi (sea walnut) has 
depleted zooplankton, the main food source of the anchovy, 
and consequently contributed to the collapse of anchovy 
populations in the Black Sea, but this has not occurred in 
the Mediterranean Sea, the Baltic Sea or the North Sea (well 
established) {4.3.2.3}.
A3 On islands, invasive alien species are a major 
cause of biodiversity loss (well established) {Box 
2.5, 4.3.1.1, Box 4.4}. Islands, and particularly remote 
islands with high endemism, are more susceptible to 
impacts from invasive alien species than mainlands (well 
established) {1.6.8, 4.3.1.1}. Indeed, in addition to the 
NATURE
NATURE'S
CONTRIBUTIONS
TO PEOPLE 
GOOD 
QUALITY OF 
LIFE 
Water hyacinth
Red fox
Red imported
fire ant 
Southern house
mosquito 
Sea walnut
Sea vase
Nile perch
Giant African
land snail 
Zebra mussel
IMPACTS
Chytrid 
fungus 
Lantana
Mesquite
Figure SPM 2 Examples of invasive alien species with a negative impact on nature (green), 
and, in some cases, nature's contributions to people (yellow) and/or good 
quality of life (teal). 
Many invasive alien species have documented negative cross-cutting impacts, indicated by multiple colours in the examples: 
16 per cent of invasive alien species have a negative impact on both nature and nature's contributions to people; 7 per cent on both 
nature and good quality of life; and 5 per cent on nature, nature's contributions to people and good quality of life {4.2}. The scientific 
names of the example species are Lantana camara (lantana); Lates niloticus (Nile perch); Dreissena polymorpha (zebra mussel); Ciona 
intestinalis (sea vase); Lissachatina fulica (giant African land snail); Culex quinquefasciatus (southern house mosquito); Mnemiopsis 
leidyi (sea walnut); Pontederia crassipes (water hyacinth); Prosopis juliflora (mesquite); Solenopsis invicta (red imported fire ant); Vulpes 
vulpes (red fox); and Batrachochytrium dendrobatidis (chytrid fungus).
21SUMMARY FOR POLICYMAKERS
19SUMMARY FOR POLICYMAKERS
BACKGROUND
A. Invasive alien species are a major threat to nature, 
nature's contributions to people, and good quality of li