Significant blue-green algae blooms possible in Finnish marine areas during 2017 summer

Press release 2017-06-01 at 9:34
Blue-green algae
Blue-green algae bloom near shore. Photo: Niina Yliknuussi

The risk for vast blue-green algae blooms in the Gulf of Finland is greater than during previous years. The exceptional nutritional conditions are caused partially by major Baltic inflows from the North Sea in 2014 and 2016, which allowed the phosphorous deepwater to reach the Gulf of Finland. In addition, the lack of winter ice and the windy winter mixed the water layers and brought nutrition to the surface layer of the Gulf of Finland. Significant algae blooms may also be expected in the northern section of the main basin of the Baltic Sea, the Archipelago Sea and the southern section of the Bothnian Sea.

According to SYKE, the risk of blue-green algae blooms forming in Finnish open sea areas is high in the Gulf of Finland, with the exception of the eastern part of the gulf. In addition, the risk is significant in the northern section of the main basin of the Baltic Sea, the Archipelago Sea and the southeastern section of the Bothnian Sea. The risk of algae blooms in the central sections of the Bothnian Sea is moderate. The risk is low at the northern sections of the Bothnian Sea and the Bay of Bothnia.

Risk of algal blooms

Weather conditions are the most significant factor affecting the forming of algae blooms. The most plentiful blooms will occur if periods of heavy winds and high pressure systems alternate over the summer, so that the nutrients from deeper waters feed the growth of algae and the water temperature rises to a temperature that favours algae growth. Algae accumulation may occur at some shoreline locations, due to wind and current conditions. The peak of blue-green algae blooms in Finnish marine areas occurs usually at the end of July and early August. The blooms may locally occur late into the autumn, but they are not as plentiful as during the summer.

The nutrition conditions in the Gulf of Finland are currently exceptional

There are several reasons for the exceptional nutrition conditions in 2017: The strong eastern winds late in 2016 caused the water level in the Gulf of Finland to drop. This resulted in phosphorous deepwater flowing to the Gulf of Finland from the main basin of the Baltic Sea. The windy winter with no sea ice mixed the water column in the Gulf of Finland, which is apparent in the increase in phosphor in the surface water.

The major Baltic inflows that came from the North Sea in 2014 and 2016 had moved the existing phosphorous deepwaters to the entrance to the Gulf of Finland. The nutrition conditions that favour algae blooms over the summer would have also occurred without the Baltic inflows. However, they strengthened the phenomenon.

The phenomena affecting the exceptional nutrition conditions are associated with the general eutrophication of the Baltic Sea and sea currents. The nutrition loads in the eastern areas of the Gulf of Finland have decreased significantly over the past decade, which is evident as improved conditions in the areas.

In addition to the Gulf of Finland, the northern area of the main basin of the Baltic Sea, the Archipelago Sea and the southern areas of the Bothnian Sea have been subject to conditions over the winter where there is a lot of phosphor in relation to nitrogen. This allows for significant blue-green algae blooms also in these areas over the summer, if the weather conditions are favourable for the blooms. However, the nutrition conditions in these areas are more similar to that of previous years, when compared to the Gulf of Finland.

The changes in blue-green algae blooms may be rapid

The movement of blooms that have formed at open sea areas to coastal areas depends greatly on the prevailing wind and current conditions. The surface blooms of blue-green algae may move to island and coastal areas especially if southern winds prevail. Strong winds mix the algae bloom with the surface water, which makes it more difficult to detect. When the conditions are calm, blue-green algae re-surfaces quickly.

Algae bloom
Blue-green algae bloom seen from air. Photo: Riku Lumiaro

The current conditions and nutrition load sources at coastal and island areas may result in local blue-green algae blooms, especially during an extended period of calm and warm conditions.  In addition, wind may accumulate algae to coastal waters and on shores.

Blue-green algae may form different types of toxins and agents that agitate the skin. Significant blue-green algae blooms should also be treated with caution.

The winter’s nutrition conditions affect the blooms

The risk of blue-green algae blooms is most affected by the amount of nitrogen and phosphorus during the previous winter. Data on them was obtained from nutritional samples taken by SYKE and the Swedish Meteorological and Hydrological Institute (SMHI) on the research vessel Aranda during the winter of 2017. The risk of algae blooms was assessed using the Baltic Sea ecosystem model in co-operation between SYKE and the Finnish Meteorological Institute.  

The weather conditions over the coming summer, however, cannot be forecasted with sufficient accuracy, so the blue-green algae bloom prediction is based on the wind, current and temperature conditions of the five previous years. The risk prediction of blue-green algae blooms best describes the conditions in open sea areas.

The results provided by the model have been analysed by specialists. The final risk prediction included consideration of the uncertainty factors and utilised experiences from the predictions and observations of previous years. In addition, the development of nutrition concentrations during the 2017 spring was considered, using the results from Alg@line monitoring performed by merchant vessels.  

Algae communication begins

SYKE Marine Research Centre will communicate weekly on the algae conditions of Finnish open sea areas starting this week to the end of August.

Further information

Algae bloom risk analysis
Leading Researcher Harri Kuosa, Finnish Environment Institute SYKE,, tel. +358 (0)295 251 106

Conditions of Gulf of Finland and Baltic Sea
Senior Research Scientist Mika Raateoja, Finnish Environment Institute SYKE,, tel. +358 (0)50 5355709

Communications Manager Sirpa Pellinen, Finnish Environment Institute SYKE,, +358 (0)295 251 502

Full size risk map


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