HELCOM Baltic Sea Environment Fact Sheet 2019; Published 10 January 2020
Information from the Phytoplankton Expert Group (PEG)
Authors: Janina Kownacka1, Susanne Busch2, Jeanette Göbel3, Sławomira Gromisz1, Heidi Hällfors4, Helena Höglander5, Siv Huseby6, Andres Jaanus7, Hans Henrik Jakobsen8, Marie Johansen9, Marléne Johansson6, Iveta Jurgensone10, Wojciech Kraśniewski11, Sirpa Lehtinen4, Irina Olenina12, Mario v. Weber13, Norbert Wasmund2
- The different areas of the Baltic Sea are characterized by different magnitudes of biomass of the nitrogen-fixing (diazotrophic) cyanobacteria genera Aphanizomenon, Nodularia and Dolichospermum. The highest biomass (for the studied months June-August, during the study period from year 1990 to 2018) occurs in the Gulf of Finland, whereas no or low biomass of nitrogen-fixing cyanobacteria appears in the Bothnian Bay and the Kiel Bay/Kattegat area.
- Biomass of nitrogen-fixing cyanobacteria may show opposing trends between different sea areas. For example, biomass was extremely low in the Arkona Basin and Bornholm Basin in 2004, 2005, 2017 and 2018 but relatively high in the neighbouring Eastern Gotland Basin. In 2017, cyanobacteria biomass was high in the gulfs, but low in the southern Baltic Proper. This confirms that the sea areas have to be evaluated separately.
- The year-to-year variability in the biomass of bloom-forming cyanobacteria is high. A tendency of decreasing cyanobacteria biomass in the Arkona Basin (1990-2014) was interrupted by high biomass values in 2015 and 2016, but continued by extremely low biomass in 2017 and 2018. Decreasing tendency was observed as well in the Gulf of Riga, Eastern Gotland and Bornholm Basins but in the Eastern Gotland Basin the decreasing tendency was interrupted in 2018. Cyanobacteria biomass is increasing in the Bothnian Sea since the mid of the 1990s and to a small extent at the Landsort Deep.
- The genus Nodularia is more common in the central and southern part of the Baltic Sea compared to the northern part, namely the Gulfs of Bothnia, Finland and Riga, where the genus Aphanizomenon dominates.
Results and Assessments
Relevance of the indicator for describing developments in the environment
Nitrogen-fixing (diazotrophic) cyanobacteria are an important component of the ecosystem. By their ability to fix molecular nitrogen, the bloom-forming cyanobacteria of the genera Aphanizomenon, Nodularia and Dolichospermum prevent severe nitrogen shortage and resulting starvation in all trophic levels of the ecosystem in the summer. However, human activity has imported a surplus of nutrients into the Baltic Sea for decades which turned the originally indispensable cyanobacteria into a nuisance because their nitrogen fixation counteracts the measures to reduce eutrophication, as specified in the following section.
According to Wasmund (1997), nitrogen-fixing cyanobacteria may be considered as a “bloom concentration” when biomass is about 200 µg/L in the mixed upper water layer from 0 m to the depth of 10 m. If this biomass is floating and enriched at the water surface it becomes visible and is also clearly perceived from satellites (Kahru & Elmgren 2014).
Policy relevance and policy references
The blooms of nitrogen-fixing cyanobacteria seem to have increased at least since the 1960s (Finni et al. 2001, Funkey et al. 2014). If cyanobacteria occur in large blooms, they indicate and contribute to eutrophication, oxygen depletion in deep waters and toxic effects. The displeasing view of the coloured surface scum alone may impair the touristic use of the coasts in summer. The changes in cyanobacteria biomass and composition represent changes in the ecosystem with far-reaching consequences. Their trends are of high relevance and interest. This Baltic Sea Environment Fact Sheet (BSEFS) “Cyanobacteria Biomass” serves the long-term documentation of the nitrogen-fixing cyanobacteria biomass development.
An Indicator Fact Sheet on a “Cyanobacteria bloom index” covering semi-quantitative rank data from year 1999 to 2007 was presented by Kaitala and Hällfors (2008). Information about the spatial extension of the bloom during summer based on satellite data is available (BSEFS “Cyanobacterial blooms in the Baltic Sea”, Öberg 2018). In contrast to semi-quantitative rank data and satellite image data, our BSEFS presents quantitative biomass data and gives additional information about the species composition in the water column. The species composition is relevant also because Nodularia and Dolichospermum have the potential to be hepatotoxic whereas similar hepatotoxicity of Aphanizomenon has not been confirmed in the Baltic Sea, even though Cox et al. (2005) have reported potential for production of a neurotoxic amino acid β-N-methylamino-L-alanine (BMAA) within the strains of Baltic Sea Aphanizomenon.
Owing to the high ecological importance of cyanobacterial blooms, they may serve as indicators in the sense of the EU-Marine Strategy Framework Directive (European Union 2008). A new HELCOM pre-core eutrophication indicator Cyanobacterial bloom index is implemented (HELCOM 2018a) and used in the Second HELCOM holistic assessment (HELCOM 2018b). It tries to combine satellite observation data with the biomass monitoring data delivered by the HELCOM Phytoplankton Expert Group (PEG). The biomass data are identical with the data used for this Baltic Sea Environment Fact Sheet, but this BSEFS gives also deeper additional information on the differences in the biomasses of genera Nodularia, Aphanizomenon and Dolichospermum in different Baltic Sea areas.
The first Baltic Sea Environment Fact Sheet on the cyanobacteria biomass was published in 2011. Just like the earlier Indicator Fact Sheet on a “Cyanobacteria bloom index”, it concentrates on the open sea. However, owing to the COMBINE strategy, also coastal stations are considered. The situation near the coast may be different from that in the open sea. Therefore, clusters of coastal stations have been kept apart from open sea stations if they were separated by a long distance (> 70 km). Such separated stations from the Latvian, Lithuanian and Polish coast did not meet the quality criteria of one sampling per month at least (cf. section “technical information”, point 5) and are therefore neglected in this report. However, if coastal and open sea stations were close to each other (e.g. Gulf of Riga, Gdańsk Basin), differentiation between them is difficult. We combined the data from the coastal and open sea areas if the coastal stations were near to the central open sea stations (< 70 km).
Stations were pooled by sea area (Fig. 1) in order to get representative data. This pooling also included stations which are rarely sampled (in the Bornholm Basin and the southern parts of the Eastern Gotland Basin), but which are not specified in Fig.1. The data were treated as explained in the technical information below. The seasonal means of the total biomass of the nitrogen-fixing filamentous cyanobacteria in the summer period (June-August) are presented in Fig.1. In the Bothnian Sea, cyanobacteria blooms may extend up to October; therefore the season is defined in this area from June to October. Recently, blooms have extended to September and even later also in some other areas. In order to keep consistency with earlier reports, we still considered only the period from June to August. As shown in earlier fact sheets of the PEG, phytoplankton trends may be even opposite in the different sea areas (e.g. Jaanus et al. 2007). Therefore, separate diagrams for the most relevant sea areas were produced.
In this BSEFS on Cyanobacteria biomass, only nitrogen-fixing species of the genera Aphanizomenon, Nodularia and Dolichospermum are considered, since these are the main genera that form blooms in the Baltic Sea. Specific information on these three cyanobacteria genera is shown in Fig. 2 and 3.
In the Bothnian Bay, the cyanobacteria biomass, dominated mainly by Aphanizomenon, is usually low (monthly average < 50 µg/L) and the results are not presented in a separate figure.
In the Bothnian Sea, nitrogen-fixing cyanobacteria are more relevant than in the Bothnian Bay. In this region there is a tendency of earlier bloom start (cf. Kahru and Elmgren 2014), but moderate (150–200 µg/L) cyanobacteria biomass is also found in autumn. Therefore we kept the period from June to October for this area. Starting with very low cyanobacteria biomass in the mid of the 1990s, biomass has increased more or less continuously (Andersson et al. 2015). Moreover, in contrast to earlier years, cyanobacterial blooms were also observed in the northern part of the Bothnian Sea (Lehtinen et al., 2019). In the Gulf of Finland, the highest biomass of the whole Baltic Sea occurred with single peak values from 2000 to 7470 µg/L in the late 1990s and in the beginning of the 2000s, in 2009 and again since 2013. The blooms have been mainly dominated by Aphanizomenon with the exception of the year 1999, when Nodularia contributed more to the total cyanobacterial biomass.
The Finnish coastal station “Nau 2361 Seili intens” was the only station situated in the Archipelago Sea. As it could not be combined with other stations, its data gaps could not be filled and the data could not fulfil the requirements explained in the Metadata section “Methodology and frequency of data collection”. Thus, data for Archipelago Sea is not presented.
In the Gulf of Riga, high seasonal average biomass value in year 2015 was mainly based on peak values from 4.8.2015 (1981 µg/L). In 2017, the highest biomass was recorded on 6 July, almost exclusively based on Aphanizomenon (1360 µg/L at station 165). In 2018, cyanobacteria biomass was three times lower than in 2017 and by half lower than the long-term mean.
The cyanobacteria biomass at the Landsort Deep station (BMP H3) appears relatively low for methodological reasons. This was the only station where the upper 20 m were sampled in contrast to 10 m in the other open sea regions. As cyanobacteria prefer the upper water layers, the inclusion of the lower layer of the euphotic zone reduces the depth-integrated average. The cyanobacteria biomass per m³ might be double, especially for the strongly buoyant Nodularia, if only the upper 0-10 m water layer would be considered. In 2018, the peak biomass (477 µg/L) was found on 18 June, dominated by Aphanizomenon.
Data from the Eastern Gotland Basin were contributed by Finland, Germany, Lithuania, Poland and Sweden. Nevertheless, the data basis is rather poor. The biomass peak of the genera considered was recorded on 28 June 2018 (975 µg/L). Mean cyanobacteria biomass increased compared to 2017 and significantly exceeded the long-term mean (197 µg / L). The increase in biomass occurred both in the open sea and the coastal area, where it was necessary to close the beaches even for two weeks in July. (For exemplar along the Polish coast of the Eastern Gotland Basin it was recorded around 30 such events according to the announcements of the State Sanitary Inspection https://sk.gis.gov.pl/index.php/kapielisko/112).
A similar situation occurred in the Gdańsk Basin in 2018. Peak biomass of cyanobacteria (701 µg/L) in 2018 was observed on 4 August at the station BMPL1 (Gdańsk Deep). In the BSEFS Cyanobacteria biomass from previous years, data from the Gdańsk Basin were not considered separately due to the lack of data from the 1990s meeting the criteria of the methodology (averages of at least three months June-August ), and some of them were combined with the Eastern Gotland Basin data. For the first time the Gdańsk Basin is considered in this report based on the available data series from the period 2004-2018 and single years: 2000 and 2002 (Fig. 1 and Fig. 2). Data from stations previously included in the Eastern Gotland Basin analysis have now been transferred to the Gdańsk Basin database. Cyanobacteria biomass from the stations BMPL1, BMPL5 and BMPL6 (sampled within the Polish National Monitoring Programme governed by the Chief Inspectorate of Environmental Protection, footnote 11) was combined with nearby stations sampled occasionally by NMFRI (footnote 1). Long-term mean of cyanobacteria biomass in the Gdańsk Basin is lower than long-term mean for the Gulf of Finland and higher than long-term mean for the Eastern Gotland Basin. The single peak values were observed in 2004 (1301 µg/L), 2006 (1125 µg/L), 2008 (2194 µg/L), 2009 (3361 µg/L), 2010 (6216 µg/L) and 2015 (1090 µg/L). Among genera observed in that region Aphanizomenon dominated although in some years Nodularia (2008, 2010, 2016) and Dolichospermum (2010) contribution was significant.
Cyanobacteria biomass in the Bornholm Basin was generally rather low (76% of considered data is below 100 µg/L) in comparison with the northern regions of the Baltic Proper, and did not reach bloom concentrations since 2015.
In the Arkona Basin, cyanobacteria biomass decreased strongly during the investigation period. Indeed, the lowest mean biomass was found in 2018 with a seasonal maximum of only 38 µg/L on 4 August.
In the Bay of Mecklenburg, blooms are not usual, but they may reach the coasts occasionally, e.g. in 2003 and 2006, when beaches had to be closed because of nuisance cyanobacteria blooms. Differences occurred between samplings from 0-10 m depth and samplings from the surface only. Samplings of the upper 10 m in the open sea revealed cyanobacterial biomass exceeding 100 µg/L in the years 2006, 2010 and 2011 in the series from 2004 to 2013 presented by Schneider et al. (2015). The surface samples from coastal and open sea stations showed biomass peaks in 1993, 1994, 2006, 2013 and 2016 (Fig. 2 g). In 2018, high cyanobacteria biomass of 588 µg/L was found at the Mecklenburg coast only on 17 July and was dominated by Nodularia (Wasmund et al. 2019).
Data from the Bay of Mecklenburg and Kiel Bight were considered for the first time in the BSEFS report of 2015. Data were delivered by State Agencies (footnotes 3 and 13) and from the coastal monitoring of the IOW (station Heiligendamm = “HD”; see Wasmund et al. 2019). All these data originated from surface samples (about 1 m depth); the few samples from 0-10 m depth were excluded from the analysis in order to prevent mixing of different methods.
The cyanobacterial biomass in Kiel Bight, starting in 2000, was generally low (maximum summer average 167 µg/L in 2012) and is thus not presented in a figure. The biomass peak samples were almost exclusively dominated by Dolichospermum.
Also Kattegat data are not presented because of generally low cyanobacteria biomass, which indicates that heavy cyanobacteria blooms do not occur in that sea area. Only at the end of July 2008, a bloom with biomass peaks of up to 400 µg/L occurred at the two Kattegat stations, but monthly and seasonal means were much lower.
Because of the high variability, no clear trend is visible in most areas. A decrease in cyanobacteria biomass was noticed in the Gulf of Riga and Arkona Basin until 2014, but this trend was interrupted by high biomass values in 2015. An increasing trend seems to establish in the Bothnian Sea (Andersson et al., 2015). This is in line with the results by Lehtinen et al. (2016), who showed that biomass of the class Cyanophyceae has increased statistically significantly in the Bothnian Sea from 1979 to 2014, mainly due to the increasing biomass of Aphanizomenon. Trend analyses by Wasmund et al. (2011) with data from 1979 to 2005 revealed decreasing trends in summer cyanobacteria in the Bornholm Basin and Arkona Basin but not in the Eastern Gotland Basin. Increasing trends in late summer cyanobacterial biomass in the northern Baltic Proper, the Gulf of Finland, and the Åland Sea from year 1979 to 2011 (2014) have been reported by Suikkanen et al. (2013), Lehtinen et al. (2016) and weak increasing trend for the Landsort Deep station has been reported from year 1994 to 2017 by Huseby et al. (2019). Oscillations instead of continuous long-term trends in surface blooms are reported by Kahru et al. (2018).
Large variations between different areas may occur. For example, cyanobacterial biomass was exceptionally low in the Arkona Basin and Bornholm Basin in 2004, 2005, 2017 and 2018 but high in the Eastern Gotland Basin at the same time. The basin-wide differences in bloom distribution are also known from satellite images (Kahru and Elmgren 2014, Kahru et al. 2018, Öberg 2018). This stresses the importance of dividing the Baltic Sea into sub-regions and treating them separately.
Although the satellite images give valuable information on the spatial differences in cyanobacteria abundances, numerous discrepancies between satellite observations and ship-based biomass data exist. For example, the high biomass in the Arkona Basin in 1998 and 2008 is not reflected in the number of days with cyanobacteria observed in the satellite images (Öberg 2018). Also at station Landsort Deep there is only little systematic correlation between actual cyanobacteria biomass and satellite surface data, probably because of deep maxima of Aphanizomenon which cannot be adequately recorded by satellites. Satellites may detect the blooms only under specific weather conditions (clear sky) whereas ship-based measurements are not so selective. If wind mixes the cyanobacterial biomass into the water, surface accumulations will not form even though cyanobacterial biomass was high. On the other hand, calm winds may enable surface blooms to become visible even though actual cyanobacteria biomass was not exceptionally high.
As shown in Fig. 2, Aphanizomenon is dominating in the northern regions of the Baltic Sea whereas Nodularia is mostly dominating in the southern Baltic Sea. This may reflect: (1) a north-south salinity gradient or (2) a coastal versus open sea gradient as most stations in the north are situated near the coast whereas those in the south are mainly remote of the coast. Aphanizomenon seems to prefer lower salinity than Nodularia irrespective of the coasts. Lehtimäki et al. (1997) found that Aphanizomenon from the Baltic Sea grows best at salinities of 0 to 5 psu. Moreover, Nodularia has a higher temperature optimum (20-25 °C) than Aphanizomenon (16-22 °C) according to Lehtimäki et al. (1997). Dolichospermum is of less quantitative importance.
Fig. 1: Map of the regularly sampled stations, containing one graph on diazotrophic cyanobacteria biomass per area (seasonal mean biomass in µg/L); details see in Fig.2. Stations in Bothnian Bay, Kiel Bay and Kattegat were tested but results are not presented. Sampling depth is 0-10 m, except in the Landsort Deep (0 to 20 m) and in the Bay of Mecklenburg (0 m) . “n.d.” = no sufficient data.
Fig. 2: Mean biomass (wet weight, µg/L) of the three bloom-forming cyanobacteria genera in the different Baltic Sea areas (a-i) during their blooming period (note the different scales). The long-term mean per area (all species together) is indicated by a horizontal line. “n” is total number of samples analysed for this region, “n.d.” = no sufficient data.
1. Data source: Danish, Estonian, Finnish, German, Latvian, Lithuanian, Polish and Swedish national monitoring data (see list of authors and Footnotes). Main sampling locations are presented in Fig. 1. Original purpose of the data: Phytoplankton monitoring programs in the frame of HELCOM COMBINE.
2. Description of data: Biomass data (wet weight in µg/L) in integrated samples (0-10 m; 0-20 m at the Landsort Deep; surface = 0-1 m in Bay of Mecklenburg). Sampling at the Finnish high-frequency coastal stations “Hailuodon ed int.asema”, “Suomenl Huovari Kyvy-8A”, “UUS-23 Längden” and “Vav-11 V-4” reached from surface to the depth of 2x Secchi depth (usually 0-8 m, maximum depth is 10 m); they could be integrated into the existing data series without problems. Genera included in index: Nodularia, Aphanizomenon and Dolichospermum (previously Anabaena) (see Fig. 3).
Fig. 3: Genera included in index, from the left: Nodularia, Aphanizomenon and Dolichospermum (previously Anabaena).
3. Geographical coverage: Entire Baltic Sea (see Fig. 1).
4. Temporal coverage: Summer 1990-2018 (June-August, in the Bothnian Sea June-October). Note that the years 1992-1993 are missing from the Landsort Deep station, 1994 and 1996 from the Eastern Gotland Basin, 1994-1996 from the Bornholm Basin, 1997 and 1999 from the Bay of Mecklenburg and 2001 and 2003 from the Gdańsk Basin. Even if data from one month were available, they were excluded because only one month was not representative for the investigation period. Some time series started later, e.g. from Gulfs of Finland and Riga in 1993 and Gdańsk Basin in 2000.
5. Methodology and frequency of data collection: Information based on national monitoring samples analysed and identified by phytoplankton experts, using the mandatory HELCOM methods (HELCOM 2017).
Additional explanation on the counting procedure using size classes was given by Olenina et al. (2006). Sampling frequency varies in dependency of the national monitoring cruises. At least one sample per month has to be available to allow the calculation of the seasonal average. This precondition could also be fulfilled by pooling nearby stations. Only in a few exceptions, mentioned in the Assessment section, data are presented despite missing data from one month out of three. The total number of samples is indicated in each diagram in Fig. 2.
6. Methodology of data manipulation: The precondition of at least one sample per month could be fulfilled in the representative open sea stations by combining the different national monitoring data. In coastal areas under the responsibility of only one country, many data (from Lithuania, Poland and Finland) had to be rejected because of too low sampling frequency. Other coastal data (from Gulfs of Bothnia, Finland and Riga, see Fig. 1) are included, as they were close to the open sea stations and their sampling frequency was high (Fig. 2).
From the single data, monthly means were calculated, which served as basis for calculation of seasonal mean values.
1. Strength and weakness (at data level): The main strength is the availability of comparable multi-decadal genus-specific biomass data. The main weaknesses are the low number of sampling stations and the low seasonal coverage in the sampling frequency. Monitoring cruises into the open Baltic Sea are expensive and can be conducted only a few times per year by the countries involved. This undersampling problem, occurring generally at ship-based sampling, is dramatic if high patchiness occurs. Especially the buoyant cyanobacteria are inhomogeneous in their horizontal and vertical distribution. The vertical inhomogeneity is tackled by the integrated sampling down to 10 m, or at specific stations down to 20 m depth (Landsort Deep) or 2 times Secchi depth (Finnish coastal stations). The equipment is however not designed for representative sampling of surface scums. The combining of the different national data taken at the central HELCOM stations improves the total sampling frequency to reach the minimum requiremen
2. Reliability, accuracy, robustness, uncertainty (at data level): Data on the reliability and precision are not available. A ring test of HELCOM-PEG, conducted in 2012, gave information on the precision of Nodularia countings in dependence of the counting procedure (Griniene et al. 2013). The phytoplankton proficiency test (Vuorio et al. 2015), which was participated by many HELCOM PEG members, included identification test for Aphanizomenon flosaquae and Nodularia spumigena, and counting test for Aphanizomenon sp. The uncertainties concerning sampling are discussed above; they have natural reasons. The microscopical counting is a robust method of high accuracy. In contrast to indirect methods (satellites, pigments etc.), the objects can directly be recognized, counted and measured. Moreover, the contribution of the different species can be evaluated. The calculation of biomass from the counting results is highly reliable since common biovolume formulas (Olenina et al. 2006) and a regularly updated biovolume file (http://www.ices.dk/marine-data/Documents/ENV/PEG_BVOL.zip) are used.
3. Further work required (for data level and indicator level): In order to assure a sufficient sampling frequency, the combined efforts of different countries to sample at least the central key station in each sea area have to be maintained or better to be extended. This is especially important when these data will be used to follow up the Baltic Sea Action Plan, the Marine Strategic Framework Directive and the Water Framework Directive. The basic data for this Environment Fact Sheet are integrated into a Cyanobacteria indicator, called “CyaBl”, for the implementation of the Marine Strategic Framework Directive. In order to be able to utilize the ICES database for the long-term trend analyses, the database should be updated annually, and kept harmonized concerning taxonomy and biovolume calculation formulae since the beginning of the study period (since year 1990). At the moment, data for this BSEFS has been collected yearly from the national PEG representatives.
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1 National Marine Fisheries Research Institute (NMFRI), ul. Kołłataja 1, 81-332 Gdynia, Poland
2 Leibniz Institute for Baltic Sea Research, Seestr. 15, D-18119 Warnemünde, Germany
3 State Agency for Agriculture, Environment and Rural Areas Schleswig-Holstein, Hamburger Chaussee 25, D-24220 Flintbek, Germany
4 Finnish Environment Institute (SYKE), Marine Research Centre, Agnes Sjöbergin katu 2, FI-00790 Helsinki, Finland
5 Department of Ecology, Environment and Plant Sciences, Stockholm University, SE-106 91 Stockholm, Sweden
6 Umeå Marine Science Center, Norrbyn SE-90571 Hörnefors, Sweden
7 Estonian Marine Institute, Tartu University, Mäealuse 14, 12618 Tallinn, Estonia
8 Aarhus University, Faculty of Science and Technology, Department of Bioscience, Frederiksborgvej 399, PO Box 358, DK-4000 Roskilde, Denmark
9 Swedish Meteorological and Hydrological Institute, Oceanographic Unit, Sven Källfelts gata 15, SE-426 71 Västra Frölunda, Sweden
10 Latvian Institute of Aquatic Ecology, Department of Marine Monitoring, Voleru īela 4, LV-1007, Riga, Latvia
11 Institute of Meteorology and Water Management, Maritime Branch, ul. Waszyngtona 42, 81-342 Gdynia, Poland
12 Environmental Protection Agency, Department of Marine Research, Taikos str 26, LT-91149, Klaipeda, Lithuania
13 State Agency for Environment, Nature Conservation and Geology Mecklenburg-Vorpommern, Goldberger Strasse 12, D-18273 Güstrow, Germany
For reference purposes, please cite this Baltic Sea environment fact sheet as follows:
Kownacka, J., Busch, S., Göbel, J., Gromisz, S., Hällfors, H., Höglander, H., Huseby, S., Jaanus, A., Jakobsen, H.H., Johansen, M., Johansson, M., Jurgensone, I., Kraśniewski, W., Lehtinen, S., Olenina, I., v.Weber, M., Wasmund, N., 2018. Cyanobacteria biomass 1990-2018. HELCOM Baltic Sea Environment Fact Sheets 2018. Online. [Date Viewed],
Report of HELCOM Phytoplankton Expert group (PEG) meeting
Report of HELCOM Phytoplankton Expert group (PEG) meeting 2019, 8-12 April, Daugavpils, Latvia
Cyanobacteria Biomass in Earlier Years
Cyanobacteria biomass 1990-2017 (HELCOM Baltic Sea Environment Fact Sheet 2018)
Cyanobacteria biomass 1990-2016 (HELCOM Baltic Sea Environment Fact Sheet 2017)
Cyanobacteria biomass 1990-2015 (HELCOM Baltic Sea Environment Fact Sheet 2016)
Cyanobacteria biomass 1990-2014 (HELCOM Baltic Sea Environment Fact Sheet 2015)
Cyanobacteria biomass (HELCOM Baltic Sea Environment Fact Sheet 2014)
Cyanobacteria biomass indicator (HELCOM Baltic Sea Environment Fact Sheets 2013)
Cyanobacteria biomass indicator (HELCOM Baltic Sea Environment Fact Sheets 2012)
Cyanobacteria biomass indicator (HELCOM Baltic Sea Environment Fact Sheets 2011)