Biodiversity, the variety of organisms in an ecosystem or in a given area, is the effect that natural selection operates on populations of plants and animals in an environment or a geographical area, in response to certain biological and physical factors: availability food, predation and competition phenomena, climatic and morphological changes. It is visually expressed in the number and type of organisms and has its foundation in all the genetic code of each living organism in a given territory.

A heritage, so complex and sophisticated, time-tested by interactions between members of the community living, is now increasing its level of contamination by human activities. In particular, contamination by species – both plants and animals – introduced without any control in territories in which they were not originally living. These are non-native species, entirely foreign to local communities composed by native species.

The relocation of alien species, only in some cases the result of spontaneous migration, it is usually due to human interaction and in particular to the intensive technological development in recent years. In fact, the so-called biogeographical barriers unsually obstacle the spread of organisms in similar or compatible environments placed in different areas.

The presence of these “uninvited guests” can lead to interference with native species in a given environment and to undesirable consequences such as the reduction and disappearance of entire indigenous peoples. In fact, newcomers, in absence of limiting factors such as predators, parasites or food shortages, may be more competitive with local species.

The Lagoon of Venice differs considerably from other Mediterranean coastal lagoon environments for a variety of geographical, climatic, environmental and biological characteristics. These environmental and biological characteristics may represent, at least in part, the reason for which the Lagoon of Venice is the first station of arrival for many exotic species in the Mediterranean area. For this reason, the Natural History Museum of Venice Giancarlo Ligabue monitors continuously the presence and distribution of exotic species in the Lagoon, with particular attention to marine organisms.