​What are invasive alien species?

Alien species are animals, plants, fungi, and other organisms, which are introduced into a natural environment where they are not normally found (outside of their natural range). In the event where such introduced species survive, become established and proliferate, they are deemed as ‘invasive’. Invasive alien species (IAS) may cause harm to the local biodiversity, human health or the economy. Examples of harmful environmental effects include predation on local species, competition with native species for resources, spread of diseases, hybridisation with native species, alteration of landscapes and habitats, and the reduction of ecosystem services.

Century plant
Century plant

Means of transport

Globalisation and improved means of transport by air, land and sea have greatly aided in the introduction and spread of invasive alien species. Whilst considering the various methods of introduction for alien species, it should be noted that such introductions can be either accidental or deliberate. An example through which accidental introduction can occur is shipping. All conventional cargo ships use ballast water to increase their stability, and hence prevent heavy rolling or capsizing. As a ship fills up its ballast tanks with water, it inevitably takes in crustaceans, fish larvae, algae, invertebrates, and even bacteria and viruses. When a ship reaches its next port of call, whilst loading its cargo, it will discharge the contents of its ballast tanks, introducing these silent travellers into a new environment.

Gum tree
Gum tree

Whilst the former introduction would classify as unintentional, the deliberate release of alien species into the wild to serve specific purpose, such as pest control, dune stabilisation, flora or fauna improvement, game animals, etc., would construe as an intentional one. The horticulture industry is a typical example through which deliberate introductions occur, where species such as  the century plant (MT: l-agave; SN: Agave spp.) and the crimson fountaingrass (MT: il-pjuma; SN: Pennisetum setaceum) have been planted in various public open spaces, from where they spread.

Therefore, shipping, horticulture and pet trade are considered as prime examples of sources for the introduction of invasive alien species around the world.

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