Zebra mussel

Research theme: Invasive species

Ecology is a branch of biology that deals with organisms, their interaction with each other and the physical environment around them. Usually each individual species occupies a very particular position or niche within the environment and this allows them to co-exist in balance. Natural ecosystems, while usually robust and resilient enough to recover from various impacts, can collapse under extreme circumstances, leading to a loss of biodiversity, species extinctions and permanent transformation of the ecosystem.

An invasive alien species is a species that has been introduced to a location outside of its natural range and threatens the local environment by damaging habitat and competing with native organisms. They include animals, plants and micro-organisms.

Giant hogweed

Invasive alien species pose an ecological threat because they enter a new system with little natural coping mechanisms to control their spread. Normal controls might include the likes of natural predators, competitors or endemic parasites and diseases. Without these controls, invasive species can spread rampantly in a relatively short period of time. This is why biosecurity and disinfection measures are so important. 

Lagarosiphon major

The majority of introduced species will have no significant impact on their new location and may naturalise to become part of the flora and fauna. An introduced species, however, will be considered invasive if it proliferates, upsets the natural balance or causes damage. It is, therefore, necessary to be vigilant and prevent new species introductions before they become potentially uncontrollable and impossible to manage.

Invasive species are usually introduced to new locations by intentional and unintentional human activities. Examples include boating (hull fouling and ballast water), gardening (garden and pond escapees) and angling (live-baiting and transferring fish between waterbodies). Once introduced to a new location, an invasive species can spread rapidly, for example, along river corridors and across open expanses of water.


Information leaflets and factsheets published by the CAISIE Project are available for invasive and potentially invasive species in Ireland:

Invasive species alert - Asian clam (Corbicula fluminea)
(851.75 KB)
Invasive species id sheet - Bohemian knotweed (Fallopia x bohemica)
(4.83 MB)
Invasive species id sheet - Curly waterweed (Lagarosiphon major)
(4.77 MB)
Invasive species alert - Freshwater jellyfish (Craspedacusta sowerbyi)
(2.73 MB)
Invasive species id sheet - Giant hogweed (Heracleum mantegazzianum)
(6.56 MB)
Invasive species id sheet - Giant knotweed (Fallopia sachalinensis / Reynoutria sachalinensis)
(5.82 MB)
Invasive species id sheet - Himalayan balsam (Impatiens glandulifera)
(4.38 MB)
Invasive species id sheet - Himalayan knotweed (Persicaria wallichii)
(5.68 MB)
Invasive species id sheet - Japanese knotweed (Fallopia japonica / Reynoutria japonica)
(5.99 MB)
Invasive species alert - Killer shrimp (Dikerogammarus villosus)
(997.6 KB)
Invasive species id sheet - New Zealand pygmyweed (Crassula helmsii)
(4.67 MB)
Invasive species id sheet - Nuttall’s pondweed (Elodea nuttallii)
(4.16 MB)
Invasive species id sheet - Water primrose (Ludwigia grandiflora)
(4.77 MB)