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Key Message

Twelve new non-indigenous species (NIS) or cryptogenic species (CS) have appeared for the first time in the Baltic Sea during the assessment period 2011-2016.

The Baltic Sea assessment units in which these new NIS/CS have been detected are the Kattegat, Great Belt, Kiel Bay, Bay of Mecklenburg, Arkona Basin, Bornholm Basin and Gulf of Riga. The new NIS have been detected both through regular environmental monitoring activities, and in many cases based on incidental sightings. The data have been verified by national experts. Monitoring is not considered to sufficiently cover all areas of the Baltic Sea and hot spot areas for new introductions (e.g. ports) to allow for the conclusion that in areas where no new NIS have been observed there have not been any new introductions.


NIS key message figure 1.png

Key message figure 1. Status assessment results based evaluation of the indicator 'Trends in arrival of new non-indigenous species'. The assessment is carried out using Scale 1 HELCOM assessment units (defined in the HELCOM Monitoring and Assessment Strategy Annex 4). Click here to access interactive maps at the HELCOM Map and Data Service: Trends in arrival of new non-indigenous species


The trend in arrival of new NIS has been increasing since the beginning of the 1900s, indicating a degraded status in the entire Baltic Sea during the period leading up to 2016. However, there has been a slight decrease in the number of new NIS detected in recent years (HELCOM, 2014a). The heavy maritime activity in the Baltic Sea is linked to the number of NIS detected in the region.

Monitoring data does not cover all habitats, taxonomical groups or port areas in most of the countries surrounding the Baltic Sea. The confidence in the assessment for areas where detections of new NIS have been made is high. In assessment units where no detections have been made, the confidence may be low if no regular monitoring is conducted. This however varies between assessment units.

The indicator is applicable in the waters of all countries bordering the Baltic Sea and operational only in the assessed areas due to availability of monitoring data.


Relevance of the core indicator

NIS are one of the major external stressors and can drive changes in marine ecosystems, the impacts of which are often unpredictable. Over 170 NIS and CS have been observed in the Baltic Sea (AquaNIS 2018). The pathways responsible for the currently established species (59% of all introduced species) are shipping and natural spread from neighbouring areas. Substantial uncertainty in the information on introduction pathways (except for deliberate releases) hampers detailed analyses and makes it very difficult to assess new human-mediated introductions both into and within the Baltic Sea. Thus the indicator assesses only the new introductions for the whole Baltic Sea, but reports these new sightings at a sub-basin scale.

NIS and CS comprise not only the established organisms but all new species even if they will not establish as species that do not establish self-sustaining populations are also regarded as failed management. Thus, the number of NIS and CS evaluates the successfulness of preventive management as well as the status of the ecosystem by indicating the areas where the level of unpredictable risk is high.


Policy relevance of the core indicator

  BSAP Segment and ObjectivesMSFD Descriptors and Criteria
Primary link
  • No introductions of alien species from ships

D2 Non-indigenous species

D2C1 The number of non-indigenous species which are newly introduced via human activity into the wild, per assessment period (6 years), measured from the reference year as reported for the initial assessment under Article 8(1) of Directive 2008/56/EC, is minimised and where possible reduced to zero.

Secondary link 
Other relevant legislation: IMO Ballast Water Management Convention, 2004.


Cite this indicator

HELCOM (2018). Trends in arrival of new non-indigenous species. HELCOM core indicator report. Online. [Date Viewed], [Web link].

ISSN 2343-2543


Download full indicator report

Trends in arrival of new non-indigenous species HELCOM core indicator 2018 (pdf)