Phytoplankton biomass and species succession in the Gulf of Finland, Northern Baltic Proper and Southern Baltic Sea in 2008

	Seppo Kaitala and Seija Hällfors, FIMR

Key message

 Phytoplankton biomass was in July higher than the long term average in all sea areas

Results and assessment

Fig. 1.  Annual variation of chlorophyll a (mg m-3) in the western Gulf of Finland (upper), the northern Baltic Proper (middle), and the Southern Baltic Proper (lower). The blue curve represents the average for the years 1992-2007, the black diamonds the measurements made in 2008. Image: FIMR/Alg@line.

Fig. 2. The relative cyanobacterial bloom index calculated from visual observations for 2008 and for 1998-2007 in coastal and open sea areas surrounding Finland. Data from the Finnish Regional Environmental Centres, SYKE and FIMR. For description of method see http://www.ymparisto.fi/default.asp?contentid=241484&lan=FI or contact SYKE

Relevance of the indicator for describing developments in the environment

Eutrophication is considered one of the most serious threats against the Baltic Sea. It is defined as an increase in the rate of supply of organic matter to an ecosystem, and is most commonly caused by nutrient enrichment. Chlorophyll a concentration, representing phytoplankton biomass, assesses the eutrophication-driven alterations of the Baltic Sea. More importantly, it can address with an adequate precision the intensity and occurrence of cyanobacterial blooms. It must be kept in mind, however, that although highly responsive to changes in surface nutrient concentrations, chlorophyll a is also a product of parameters not related to eutrophication, namely other biological factors, hydrography and climate.

Policy relevance and policy references

Although being a natural phenomenon per se, the algal bloom events have become more frequent, intense, and extensive due to the eutrophication of the Baltic Sea. Since the mid-90’s, the strength of cyanobacterial blooms have increased to levels to raise wide public concern. Currently, noxious and often harmful cyanobacterial blooms disrupt the functioning of the Baltic ecosystem, limit the recreational and economic use of the sea, and represent a clear and present health risk for humans and domestic animals. No signs of decrease of cyanobacterial blooms have been seen yet.

Assessment for the Gulf of Finland 2008

The spring bloom started in early April, one week earlier than  in the previous year and it reached its peak in late April. The ice-free-winter changed somewhat species composition, so the diatoms Thalassiosira levanderi, T. baltica, Chaetoceros ceratosporus, C. holsaticus, C. wighamii and  Skeletonema costatum coll. dominated the beginning of the bloom while usually very abundant species Achnanthes taeniata occurred but scarcely. The dinoflagellates Woloszynskia halophila/Scrippsiella hangoei and Peridiniella catenata became dominant during the peak and remained moderately common until late May.

The cool and windy weather prevented the growth of blue-green algae and prolonged so the summer minimum phase to early July. No surface accumulations of blue-green algae occurred during June. Nanoflagellates were dominant (the prasinophycean Pyramimonas spp., the dictyochophycean Pseudopedinella elastica and P. tricostata and the euglenophycean Eutreptiella gymnastica), while the potentially toxic haptophyte Chrysochromulina polylepis occurred only minor amounts. In July water rust red to brownish discolouring blooms of the non-toxic dinoflagellate Heterocapsa triquetra occurred in the archipelagos in the western Gulf of Finland, but it did not occur in bloom quantities in the open sea. This dinoflagellate does not form blooms as regularly and over as widespread areas as blue-green algae.

The amount of the blue-green algae Aphanizomenon flos-aquae, Anabaena spp. and chroococcalean colonies increased towards end July and when weather became warm and calm first surface accumulations were observed in the archipelagos of the Gulf of Finland. In the open Gulf large amounts of blue-green algae were mixed in the water column. In the beginning of August the recently formed blooms were scattered by strong winds. Later in August the blue green algae decreased, and nanoflagellates (mainly Chrysochromulina spp.) became dominant. No late autumn diatom or dinoflagellate bloom was observed. Nanoflagellates (cryptophytes, prasinophytes and Eutreptiella spp.) codominated with chroococcalean colonies (Woronichinia compacta) in mid October.

Assessment for the Northern Baltic Proper 2008

An exceptional mass occurence of Chrysochromulina polylepis (Prymnesiophyceae) started to develop in early winter in the western parts of the Northern Baltic Proper. It was more prominent in the Central Baltic Proper around Gotland. The spring bloom started in early April and reached its peak in late April. The species dominating the bloom were diatoms (Thalassiosira spp., Chaetoceros spp., Skeletonema costatum coll.) and dinoflagellates (Scrippsiella hangoei/Woloszynskia halophila, Peridiniella catenata and Heterocapsa sp.). Later in May nanoflagellates, especially the euglenophyte Eutreptiella gymnastica, the dinoflagellate Heterocapsa rotundata and the chrysophyte Dinobryon balticum became abundant. The haptophyte Chrysochromulina polylepis was very abundant in early May in the western parts of the Northern Baltic proper near the Swedish coast (Hajdu et al, 2008).

The blue-green algae Aphanizomenon flos-aquae and Anabaena spp. at first, later also Nodularia spumigena started to increase in mid June, but mainly they remained mixed in the water due to windy weather. When weather became calm in late July, surface accumulations of blue-green algae covered large parts of  the Baltic Proper. In early August winds dispersed the surface aggregations and the amount of blue-green algae decreased. Narrow oscillatorealean filaments (Pseudanabaena sp.), Aphanizomenon flos-aquae and nanoflagellates (Chrysochromulina spp., the cryptophycean Plagioselmis prolonga and Teleaulax spp. and the prasinophycean Pyramimonas spp.) were the most abundant taxa in August.

Diatoms (Coscinodiscus granii, Actinocyclus octonarius, Skeletonema costatum, Cyclotella choctawhatcheeana) and nanoflagellates were moderately common in mid October. Among the nanoflagellates the haptophyte Chrysochromulina polylepis has started to increase again as during the previous late autumn, but it does not yet dominate the nanoplankton fraction.

Assessment for the Southern Baltic Proper 2008

An exceptional mass occurence of Chrysochromulina polylepis (Prymnesiophyceae) developed in November 2007 in the western parts of Central Baltic Proper around Gotland. This species dominated since early winter also in the southern parts of Baltic Sea Proper and changed somewhat species succession and abundances. The diatoms Skeletonema costatum coll., Chaetoceros spp. and Thalassiosira spp. which usually occur during spring bloom started to increase in late March but they did not become dominating. Also the dinoflagellate Peridiniella catenata was observed, but only in moderate amounts.

Chrysochromulina polylepis bloom continued until mid June, when other nanoflagellates (Chrysochromulina spp. with smaller cell size, the prasinophycean Pyramimonas spp., the cryptophycean Teleaulax spp. and Plagioselmis prolonga  and the dinophycean Gymnodiniales spp.) became more abundant. The small sized diatom Cyclotella choctawhatcheeana usually occuring in late summer was observed in mid June.

Blue-green algae, particulary small colonial species (Cyanodictyon spp., Aphanothece spp.), became dominant towards the end of June and first observations of surface accumulations occurred in the beginning of July. The filamentous species (Nodularia spumigena, Aphanizomenon flos-aquae, Anabaena spp.) dominated in July, while in August the chrooccalean species became again abundant. The invasive alien dinoflagellate Prorocentrum minimum and the diatoms Nitzschia paleacea, Cylindrotheca closterium, Cyclotella choctawhatcheeana, Coscinodiscus granii and Actinocyclus octonarius became also common.

Diatoms (Coscinodiscus spp., Chaetoceros spp., Pseudo-nitzschia spp. Skeletonema costatum, Cerataulina pelagica) dominated also in mid October. The invading species Chaetoceros concavicornis occurred in small numbers. Other nanoflagellates (Pyramimonas spp., Plagioselmis prolonga, Hemiselmis virescens, Eutreptiella gymnastica) were more common than Chrysochromulina polylepis, even though it clearly has started to increase.

References

Fleming, V. & Kaitala, S. 2008. Phytoplankton spring bloom biomass in the Gulf of Finland, Northern Baltic Proper and Arkona Basin in 2007. Helcom Indicator Fact Sheet.

Hajdu,S., Hällfors, S., Gromisz, S., Skejvik, A.-T., Busch, S., Kownacka, J., Jurgensone, I., Olenina, I., Huseby, S., Andersson, A:, Wasmund, N., Jaanus, A., Hällfors, G., Rintala, J.-M., Majaneva, M., Blomster, J., 2008. Unusual phytoplankton event during winter-spring 2007-2008. HELCOM Indicator Fact Sheets 2008.  Online:
http://www.helcom.fi/environment2/ifs/ifs2008/en_GB/Phytoplankton_events/

Metadata

Technical information

1. Data provider (source): Finnish Institute of Marine Research (FIMR). Contact persons: Seija Hällfors and Seppo Kaitala.

2. Description of data: Original unit of measure: mg chl a m-3. Semiquantitative phytoplankton analysis are based on the ranks 1 to 5 describing relative sample-based abundance of an algal species. In the cyanobacterial bloom map, visual observations are included.

Original data in WGS84-coordinates

Original purpose of the data: Phytoplankton monitoring of FIMR, Alg@line project

3. Geographical coverage: Gulf of Finland, Northern Baltic Proper, Southern Baltic Proper

4. Temporal coverage: 1992-2008

5. Methodology and frequency of data collection: The data has been collected using an automated flow-through sampling system on merchant ships, sampling depth ca. 5 m, weekly sampling during the period February/March-October/November in each year. Detection device Jasco 750 spectrofluorometer

6. Methodology of data manipulation: No data manipulation

Quality information

1. Strength and weakness (at data level)

Strength: Very high both temporal and spatial sampling frequency

Weakness: Satellite images are achieved only on clear weather. Ship-of-opportunity –measurements are restricted to the ships route, and dependant on it's schedule; diurnal changes of data are not taken into account.

2. Reliability, accuracy, precision, robustness (at data level): Filtration and extraction of Chlorophyll a from samples according to accredited method SFS-EN ISO/IEC 17025. Procedure uncertainty: 5%.

3. Further work required (for data level and indicator level): More sophisticated statistical analysis

For reference purposes, please cite this indicator fact sheet as follows:

[Author’s name(s)], [Year]. [Indicator Fact Sheet title]. HELCOM Indicator Fact Sheets 2008. Online. [Date Viewed], http://www.helcom.fi/environment2/ifs/en_GB/cover/.
 

Last updated 30 October 2008