Alien species in the Belgian part of the North Sea and adjacent estuaries

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Alien species in the Belgian part of the North Sea and adjacent estuaries

One of the results of the project ‘Alien species from the Belgian North Sea and adjacent estuaries’ is an updated list and information of the non-‘local’ marine and coastal species, which is provided on the following pages.

In this list you can click through to factsheets with extensive information about the life cycle and ecology of the species, method of introduction and distribution, the potential impacts or measurable impact of the species on the environment and possible policy measures. Taxonomic information, pictures and relevant links can also be found on these pages.

The preparation and updating of this list is made possible thanks to the cooperation and expertise of Flemish / Belgian scientists.

Alien species?

Worldwide, many plant and animal species have successfully colonized new habitats. Alien species also occur in the marine environment, coming from all over the world. And once an alien or non-indigenous species has settled here, there is usually no way back.

The problem non-indigenous species is not new. Early in history we find reports of such introductions. But for some species it is rather difficult to say whether they are indigenous or not. Our knowledge of some groups of marine organisms does not go far back in time. The reason is that, for the study of certain, often small organisms, our knowledge and research techniques are insufficient...

But what impact do these alien species have on their environment? Do they have an anthropogenic or economic impact? And how can we limit the damage made by non-indigenous species?


Study area

An overview of all known alien species for the Belgian coast, the Belgian part of the North Sea, the Spuikom in Ostend, and the Scheldt estuary is given.

Sudiegebied project niet inheemse soorten.jpg

List of alien species

While we strive to present a thorough list of alien species (NL), this is not an easy task. Alien species are often discovered by coincidence and some groups are less known, such as plankton that consists of microscopic plants and animals. In addition, non-indigenous species can be difficult to distinguish from local species, which can lead to the erroneous designation of an alien species.

To the list (NL)

What is on this list:

  • all currently known non-indigenous species occurring in brackish and marine environments in the Belgian coastal area, the Belgian part of the North Sea, the Spuikom in Ostend and the Scheldt estuary
  • if there is a presumption that a cryptogenic species was introduced, this species was also added to the list
  • species that were - intentionally or not - introduced by man.

What is NOT on this list:

  • alien species reported along our coast, without permanently established populations
  • species that occur only in freshwater
  • species that arrived in the Belgian coastal waters by natural distribution.


The Flanders Marine Institute (VLIZ) aims to make fact sheets of all known alien species along the Belgian coast, comprising the following information:

  • initial distribution of the species
  • when the species was first observed on the Belgian coast
  • occurrence and spread of the species in our neighboring countries
  • how the species was introduced
  • what factors influence the spread of the species
  • the possible impact on humans and the local ecosystem

How does Belgium deal with introduced species?

(Inter)national policy

Under article 11 of the Marine Environmental Law (‘MMM Wet’) it is forbidden to introduce non-indigenous species into the marine areas under Belgian jurisdiction. Internationally, the introduction of alien species is considered as a common problem (OSPAR Quality Status Report 2000).

ICES set up two working groups to study biological invasions and non-indigenous species: the Working Group on Introductions and Transfers of Marine Organisms (WGITMO) and the Working Group on Ballast and other Ship Vectors (WGBOSV)

In 2004, the ICES ‘Code of Practice’ from 1995 was updated. Here, a number of procedures and activities reducing the risk on imports of non-native species are defined

The IMO Guidelines for the control and treatment of ballast water to reduce the transfer of harmful organisms (Resolution A.868 (20)) of 1997 provides voluntary recommendations for reducing and preventing the uptake and / or flushing of contaminated ballast water and for the safety feature in re-ballasting services at sea. Ships should be informed about areas where harmful pathogenic organisms are present, or where wastewater is discharged into the sea to reduce the inclusion of ballast water in these areas to a minimum. Vessels should avoid taking on ballast water in shallow water or in areas where the screws touch the bottom sediments. Unnecessary ballast should be avoided. There are three procedures to deal with the problem, being re-ballasting services at sea, discharge of the ballast water to reception facilities at the port or treatment of the ballast water.

The IMO Ballast Water Convention of 2004 (BWM - 13.02.2004) commits vessels to the formulation of a ‘Ballast Water Management Plan’ and the establishment of a ‘Ballast Water Record Book’ on board, in which all ballast operations are registered. A third option is ballast water exchange at sea, preferably beyond 200 nautical miles from the mainland. If this is not possible, ballast water should be exchanged at least beyond 50 nautical miles from the coast and in water of at least 200 meters deep.

Monitoring and policy in the Belgian part of the North Sea

Observations of non-indigenous species in the Belgian part of the North Sea (BNZ) and coastal areas are reported to the ICES Working Group (WGITMO) by MUMM.

But the BNZ is not systematically checked for non-indigenous species. To assess the effects of alien species and set measures to protect the ecosystem, a systematic monitoring and targeted research is needed. Policies and specific measures should strongly align to such monitoring. The Flemish Environment Agency (VMM) reports and updates already existing knowledge and initiatives in the background document ‘Kust en Zee’.

Flanders Marine Institute will continue to monitor the study on alien species in Belgium and the occasional sightings of new species, so the list can be supplemented or further improved.

Do you have comments or additions to this list?
Then let us know

VLIZ Alien Species Consortium

This project was realised by Flanders Marine Insitute (VLIZ) in consortium in consortium with or institutes.