Today invasive alien species (IAS) are recognised as the second leading cause of threat to biodiversity on a global scale including Croatia. Each alien species in the ecosystem represents a potential threat since it may cause permanent and adverse changes in that ecosystem which can in turn have irreversible consequences for the environment as a whole as well as for the socioeconomic situation of a certain area and can also have an adverse impact on human life and health.
The impact of invasive species on ecosystems, autochthonous habitats and species has increased significantly with the global increase in mobility, trade, tourism and other human activities. In Europe this adverse impact is a result of using some invasive species for economic purposes, especially in agriculture, fisheries, aquaculture, horticulture and forestry. One of the biggest problems in preventing the expansion of invasive alien species is the late detection of adverse impacts after their introduction, when it may be too late for efficient action. Examples from Croatia include spreading of plant species of the common ragweed (Ambrosia artemisiifolia) and false indigo (Amorpha fruticosa), green algae of the genus Caulerpa in the Adriatic Sea, fish Gambusia affinis in stagnant waters, problems caused by alien wild game introduced on the islands and many other. Additional information can be found on the new web site on IAS in the Republic of Croatia.
The Nature Protection Act adopted the most important determinants from international treaties related to alien invasive species. They involve the prevention of spreading, control and, when possible, extermination of alien species that pose a threat to ecosystems, habitats and species. The issue of alien species is under competence of several sectors that could have impact on the overall biodiversity, and that issue is governed by different regulations in the field of hunting, agriculture, animal welfare, marine and freshwater fisheries, environmental protection, etc.
Under the Nature Protection Act, it is prohibited to introduce alien species into nature on the territory of the Republic of Croatia and into ecological systems which they do not populate naturally, except when the Ministry explicitly authorises so in cases where introduction is scientifically and technically founded and acceptable from the standpoint of nature protection and sustainable management. The acceptability of introduction of an alien species is evaluated based on a risk assessment study. The method of preparing and implementing risk assessment studies is prescribed by the Ordinance on the method of preparing and implementing risk assessment studies with respect to introduction, reintroduction and breeding of wild taxa (OG 35/08).