Assessment Protocol

The majority of the relevant data is in point format. The processing required for making an evaluation against the baseline species list for an assessment unit only requires summing the number of new species introduced to the Baltic Sea per assessment unit. The 17 sub-basin assessment units (HELCOM Scale 2) are used for the assessment but due to differing monitoring efforts the indicator evaluation (against the threshold) is done on the whole Baltic scale (scale 1).

The borders of the sub-basins reflect the large scale environmental gradients typical of the Baltic Sea, with salinity often being the most relevant gradient in relation to the introduction and potential large-scale spreading of NIS. The relevance of evaluating the number of new introductions on the scale of sub-basins is also due to the relatively low current detection rate of new arrivals. Monitoring programmes do not currently cover coastal areas adequately, however some monitoring activities are carried out in the coastal areas. Also, future wider implementation of port surveys and other monitoring programmes may warrant evaluations based on the coastal assessment units. Thus, existing programmes should be used for the indicator and be adapted, if possible. A further opportunity is the implementation of a cost-efficient rapid-assessment program on NIS, which already exists in some countries.


Indicator calculation

The main parameters used to evaluate whether the threshold value is achieved in this core indicator are the new species introduced by human actions to the Baltic Sea per assessment unit after the year used to determine the baseline. However, in order to increase regional coherence and comparability between the HELCOM and OSPAR environmental assessments, the same indicator parameter processing is proposed. Therefore, the parameters 'inventory' and 'dispersal' are also considered in this core indicator. These two parameters are to be considered as supporting parameters that provide important information and their use in providing information of the spread of NIS might become more strongly incorporated in the indicator concept at a later stage of development.

Indicators evaluating the negative effects of NIS are not currently being developed in HELCOM. Advantages with the approach of the current indicator is considered to be that the indicator:

  • is based on quantitative and qualitative data, not on expert judgement,
  • works on a short time scale (in contrast to assessing environmental impact),
  • can reflect the effectiveness of measures,
  • evaluation is not dependent on earlier evaluations
  • can be applied to a range of monitoring types and efforts,
  • pragmatic, simple and considered to be effective,
  • takes into account the current levels of uncertainty in relation to requirements for monitoring for NIS in the marine environment, and
  • incorporates the same parameters as the comparable OSPAR indicator promoting regional coherence.


1. Species-Parameter

This main parameter describes how many new NIS/CS have been recorded in the Baltic Sea per assessment unit due to human actions during the assessment period. Only this parameter is used in the trend evaluation at this point in time.

SP (assessment period) = number of new introduced non-indigenous and cryptogenic species in the Baltic Sea per assessment unit

Regular monitoring of species has to be conducted to identify new human-mediated arrivals. The parameter depends on the 2010 baseline list of NIS, and only documents new species detected after 2010 per assessment unit. This parameter can be used to measure the effectiveness of measures aimed at stopping or reducing the human-mediated introductions of NIS.

The parameter can also be used to evaluate the provisional threshold value, i.e. the rate of introduction. This could provide the most accurate indication of the effectiveness of implemented management measures. For example the species parameter could be used to show the trend in the annual numbers of introductions after the implementation of ballast water management measures to enable conclusions on the ballast water management effectiveness as a management option.

2. Inventory-Parameter

The calculation of the Inventory-Parameter is not applied to the trend assessment, but contains additional information for the state of the NIS community:

IP (assessment period) = number of NIS and CS in the assessment unit - number of NIS in the same assessment unit from the previous assessment period.

The parameter focuses on changes in the number of NIS detected in a specific assessment unit irrespective of regional species-baseline lists. The 'inventory' parameter quantifies whether the NIS species composition changes over time and focuses on changes in the total number of NIS individuals independent of the species list.

This supporting parameter enables an evaluation of whether recently introduced species persist over a longer period of time or vanishes after, for example, the following winter. The inventory parameter concentrates on the community of NIS and changes therein.

The inventory is negative if the number of disappearing NIS is higher than the number of newly introduced NIS, i.e. reflecting a good status. Should there be measures to eradicate unwanted species or NIS in general (e.g. cleaning pontoons in marinas); the Inventory Parameter can monitor the effectiveness of these measures and can provide additional information on management effectiveness at the regional and/or local level.

3. Dispersal-Parameter

The supporting parameter 'dispersal' enables an evaluation of the spreading of the NIS. New species will first appear at a certain or possibly a few locations within an assessment unit after which, depending on the degree of invasiveness, these NIS will spread to other nearby locations. The dispersal parameter is calculated for each NIS separately:

NIS equation.png

A positive dispersal parameter value indicates that the species or its range is reducing within the assessment unit, while a negative dispersal parameter value indicates that the species is present at more locations than previously recorded and is therefore spreading. The dispersal parameter is therefore able to indicate the speed at which the NIS is spreading and the effectiveness of counter-measures. It is widely accepted, that large scale eradication measures are unlikely to succeed in the marine environment. However, there are exceptions where eradication may be feasible, especially in the first phase of a new introduction. Also, there are methods aimed at reducing the local spread of NIS (i.e. the cleaning of ship and boat hulls).


Assessment units

The indicator is assessed for the scale 2 assessment units, making up 17 sub-basins in the HELCOM area. The assessment units are defined in the HELCOM Monitoring and Assessment Strategy Annex 4.

The large uncertainty related to new introductions, especially concerning their vectors/pathways, prevents the use any more detailed scale in the assessment with this current indicator. At present the indicator only considers new introduction to the Baltic Sea but the indicator results show these introductions per assessment units. This approach however underestimates the NIS introductions in many areas as we cannot obtain reliable data for intra-Baltic spread (for vectors/pathways) and thus we cannot assess the status of new arrivals per assessment unit, which would give a better view of the status.