Photo: iStochphoto

Alien marine species

The introduction of alien species is one of the greatest threats to the global marine environment. Maritime transport and aquaculture are responsible for large-scale transfers of marine organisms between the world’s oceans.

Many species that are introduced to new areas can displace native species and change ecosystems. Species that pose a threat to native biodiversity and ecosystems are known as invasive alien species.

Globally, the introduction of alien organisms is considered to be the second most important cause of the loss of biodiversity.

Ballast water – an important pathway of introduction

The majority of species that are transferred from one area to another are carried in ships’ ballast tanks. Ships use seawater as ballast to maintain stability when they are not carrying cargo. They take water on board in one port and discharge it in another. The seawater contains large numbers of marine organisms that are native to the area where the water was taken on board. If the ballast water is discharged in a different part of the world, a completely different set of species may be introduced – for example, to Norwegian waters.

Most marine organisms have a planktonic stage in their life cycle, generally larvae that drift or swim in the water column. This is why even relatively large species such as fish and crabs can be transferred to new areas via ballast tanks. Although most organisms do not survive for long in ballast tanks, some are still alive when discharged.

Maritime transport accounts for more than 80 % of all goods transport in the world. A single supertanker carries enough ballast water to fill 2 000 Olympic-size swimming pools. It is estimated that roughly four billion tonnes of ballast water is transferred to different areas every year, and that at any given time, more than 4 500 species are being carried in ballast tanks.

Introduced algae from ballast water have caused several large-scale algal blooms in Norway. The fish farming industry has suffered serious commercial losses as a result.

Ballast Water Convention

Towards the end of the 1980s, the International Maritime Organization (IMO) began to discuss the introduction of alien marine species with ballast water and what could be done to solve the problem. Several sets of guidelines were drawn up with the aim of preventing the introduction of invasive alien species. In February 2004, the Ballast Water Convention was adopted by IMO’s member states.

The Convention applies to all ships in international traffic, and its aim is to reduce and in the long term eliminate the risk of spreading harmful aquatic organisms with ballast water. As an intermediate solution, ships are being required to exchange ballast water in mid-ocean to reduce the risk of spreading invasive alien species.

There are standards for ballast water exchange, and ships are required to be at least 200 nautical miles from the nearest land and in an area where the water is at least 200 metres deep during ballast water exchange. If this is not possible, ships must be as far from land as possible, and always at least 50 nautical miles from the nearest land and in water at least 200 metres in depth. If it is impossible to meet these requirements, coastal states are allowed to designate areas closer to the coast for ballast water exchange.

Norway ratified the convention in March 2007, and was one of the first states to do so. The convention has not yet entered into force. When it does so, its requirements for ballast water management and treatment are to be phased in gradually. However, Norway has already implemented some of its requirements in its Ballast Water Regulations, which entered into force on 1 July 2010

Impacts of alien species

Other pathways of introduction for alien species are via hull fouling and fishing gear, and through the import of new aquaculture species. Aquaculture organisms can spread further after deliberate introduction, and may be accompanied by “hitchhikers” including parasites and pathogens.

Two reports focusing specifically on alien marine species in Norwegian waters were published in 2001.One was published by the Environment Agency and discusses the actual and potential effects of such organisms in all Norway’s waters, including Svalbard. The other was commissioned by the Ministry of the Climate and Environment, and deals with alien marine species in the North Sea area. It gives examples of introduced species that are known to have caused economic losses and ecological damage in the region .

The Environment Agency also commissioned a report on mapping and monitoring of alien marine species in Norway, including recommendations for future activities. The report  was drawn up by the Institute of Marine Research and the research company UNIFOB, and was published in 2008.