“Non-indigenous species introduced by human activities are at levels that do not adversely alter the ecosystems”
The Convention on Biological Diversity (CBD) defines non-indigenous species as species whose introduction or spread threaten biodiversity. Non-indigenous species are species introduced outside their natural past or present range, which might survive and subsequently reproduce. These species are introduced in situations where exchange of people or goods takes place between countries and continents, by shipping for example.
Non-indigenous species in the marine environment
Oyster bank © Annemieke Kouwenberg, 2010
Dreissena polymorpha © Lars Peters
D vexillum © Woods Hole Science Centre
In many cases non-indigenous species do not harm the regional ecology and economics. However, in certain cases, non-indigenous species can become “invasive” species and have enormous and long-lasting impacts on the region. The Marine Directive states therefore that non-indigenous species should be at levels that do not adversely alter the ecosystem.
Non-indigenous species can harm a local ecosystem. They can expand rapidly if they can outcompete indigenous species and when natural enemies are absent. By competition for space, food or other factors, non-indigenous species can sometimes replace indigenous species in the area. Non-indigenous species can also prey upon indigenous species or introduce diseases to a local system, to which indigenous species are not resistant. Non-indigenous species are referred to as ‘invasive species’ if they expand dramatically. Highly invasive species are very often species, which reproduce fast, quickly adapt to a broad range of situations (water quality, food availability), have a diverse gene pool and/or are associated to human activities.
Why does it matter if non-indigenous species replace local species? First of all, such invasive species can dominate a whole area, reducing natural biodiversity and making ecosystems less resilient to changes. In addition, if these non-indigenous species are not preyed upon by local species or if they outcompete and replace a local species that serves as a major food resource, they can have a significant impact on the local food web. Another important impact of the invasion of alien species is the economic damage it causes if the introduced species expels commercially valuable species. In addition, management measures taken to control invasive species are costly: controlling invasive species and repairing the damage they do is estimated to cost European economies at least €12 billion each year.
The number of introductions of non-indigenous species has increased globally and at the European level over the past century, as illustrated by this graph from the European Environment Agency, due to the increase use of maritime transport for food and goods over the world.
Several human activities form pathways for the introduction of non-indigenous species:
Species can also be introduced intentionally, for instance in aquaculture, foreign species are introduced on a large scale for economic reasons. For new enterprises, it is attractive to invest in the exploitation of well-known species like the Pacific oyster (Crassostrea gigas) because a lot of knowledge is available on the best practices for their breeding. Moreover, a consumer market already exists. However, these introduced species may be invasive in the local environment.
Recognizing the stranger!
Early detection of an invasive species is important to be able to stop it from expanding. Detection of species occurs for example during standard monitoring programmes for local species, by people who are commercially involved in aquaculture or by recreational amateurs such as divers. These people recognise species that do not belong in the region from their experience in the marine environment. Non-experienced people can be trained for detection of known invaders to enhance early detection of non-indigenous species.
Policy and legislative measures
In 2004, the International Convention on the Control and Management of Ships’ Ballast Water and Sediments (BWM Convention) was adopted. It aims to prevent the potentially devastating effects of the spread of invasive species carried by ships' ballast water from one region to another. This is be done through the strict control and management of ships' ballast water and sediments. The entry into force of the BWM Convention is a crucial step towards the reduction of the spread of non-indigenous species regionally and worldwide.
Addressing the issue of invasive species is one of the six key objectives of the EU Biodiversity Strategy. The European Commission is currently working on a dedicated legislative instrument on Invasive Alien Species, which is due to be adopted in 2012. In its Communication "Towards an EU Strategy on Invasive Species", the Commission proposes a number of possible options to tackle the issue of invasive species, including the immediate setting up of a Europe-wide early warning and information system to report new and emerging species and voluntary codes of conduct to encourage responsible behaviour by retailers and consumers.In addition, in 2007, the EU adopted a regulation on the use of non-indigenous and locally absent species in aquaculture aiming to create a framework governing aquacultural practices in order to ensure adequate protection of the aquatic environment from the risks associated with the use of non-native species.
What can YOU do?