Data and updating

This pre-core indicator and its threshold values are yet to be commonly agreed in HELCOM.
The indictor is included as a test indicator for the purposes of the 'State of the Baltic Sea' report 2018, and the results are to be considered as intermediate.

Access and use

The data and resulting data products (tables, figures and maps) available on the indicator web page can be used freely given that the source is cited. The indicator should be cited as following: 

HELCOM (2018) Cyanobacteria bloom index. HELCOM pre-core indicator report. Online. [Date Viewed], [Web link].

ISSN 2343-2543



Result: Cyanobacterial bloom index


Data source: 

The remote sensing data source was the daily surface algae products of the Finnish Environment Institute (SYKE) from the years 2003-2014 (operative version of the product can be found on, which are in turn based on the respective chlorophyll a and turbidity products. The remote sensing data used in this study were produced with same methods as the operative version but reprocessed in order to provide as harmonized data set as possible.

Chlorophyll a concentrations were derived for the MERIS observations using BEAM plug-in processor MERIS Case-2 Water Properties Processor (FUB) according to Schroeder et al. (2007) and Schroeder et al. (2007a; 2007b). The MERIS turbidity estimations applied the BEAM plug-in processor Case 2 Regional (C2R; version 1.6.2) according to Doerffer and Schiller (2007).  The use of this processor for MERIS data is supported also by other studies conducted in the Baltic Sea by Kratzer et al. (2008), Beltrán-Abaunza et al. (2014) and Harvey et al. (2015). The MODIS chlorophyll a and turbidity were derived according to Maritorena et al. (2002; 2010) and O'Reilly et al. (1998; 2000). In the case of MODIS data, the algorithms for chlorophyll a and turbidity were adjusted to the best performance when compared to in situ data (available monitoring programme observations).

The cyanobacteria biomass was collected and analysed by the HELCOM PEG group.

Geographical coverage: 

  • Spatial coverage of remote sensing observations, namely the average cloud-free area in satellite images varied between 18-31%. It must be noted that totally cloudy images were included in these calculations. The indicator can be applied for the open sea and outer coastal assessment areas of the Baltic Sea.
  • Cyanobacteria biomass was observed at HELCOM COMBINE stations situated in the Kiel Bay, Bay of Mecklenburg, Arkona Basin, Bornholm Basin, Eastern Gotland Basin, Northern Baltic Proper, Gulf of Riga, Gulf of Finland and Bothnian Sea.

    Temporal coverage: 
  • Remote sensing is observed to give at least one valid observation in an assessment area on an average of 49% of days between June 20th – August 31th
  • cyanobacteria biomass observations were monthly.

Data aggregation: The 2011-2015 values for each sub-basin were estimated as an inter-annual summer (20th of June – 31st of August) averages.