Invasive species occur outside their natural range. They are nonnative plants and animals that harm or endanger native plants and animals or other aspects of biodiversity. Alien invasive species occur in all groups of plants and animals. They include competitors, predators, pathogens and parasites. They have invaded almost every type of native ecosystem and caused hundreds of extinctions.
The rapid means of transportation of human in sea has lead to an increase in the transfer of such species from one place to another and human actions are the primary means of invasive species introductions. For e.g. The aquarium-bred "killer algae" that have run rampant in the Mediterranean represent just one of hundreds of introduced species that have inflicted havoc around the world, disturbing economies, destructing habitats, and forcing native plants and animals into extinction. Thousands of species of marine organisms were and are moved around the world on ship bottoms, and hundreds more have been moved globally by the wholesale transfer of edible oysters for replanting. It is estimated that more than 10,000 marine species each day may hitch rides around the globe in the ballast water of cargo ships.
In the early 1980s, the guardian of the tropical saltwater aquarium at the Wilhelmina Zoo in Stuttgart noticed the exceptional properties of a bright green, beautiful green alga, Caulerpa taxifolia, used as tank decoration in the presentation of multicolored tropical fish. It escaped from human control in 1980s and has spread like a cancer in Mediterranean. Since then the alga has colonized huge areas and is still progressing unchecked into new habitats in unstoppable manner. The algae grow everywhere, from the surface to the lower limits of underwater vegetation to capes swept by storms and currents, on the soft bottoms of sheltered bays. With its highly toxic defense cocktail, it......
