Blue-green algae spread more and more in Baltic Sea thanks to human activities

The growth of blue-green algae in the Baltic Sea is a historic occurrence. However, it is thanks to human activities that the intensity of this process continues growing, explains head of Marine Ecology Laboratory of the University of Latvia Elmīra Boikova.

She says intensive growth of blue-green algae in hot weather conditions in the Baltic Sea was observed a couple of centuries ago. This phenomenon is natural for the Baltic Sea. However, it is thanks to human activities, anthropogenic load and agricultural waste water that this phenomenon has been spreading more wildly lately, causing major damages to the ecosystem.

«Blue-green algae have been present in the Baltic Sea for a very, very long time. Growth of these algae was observed as far back as the 18th century – when intensive industrial activities were not yet present. The question is scale of growth of these algae in the past?» said the researcher.

In spring, when river water carries nitrogen and phosphorus to the sea, it causes algae that feed of those substances to grow more. In summer, however, when inorganic nitrogen is close to zero, blue-green algae begin to grow. These algae are able to absorb nitrogen from the air, says Boikova.

The expert says that as blue-green algae grow they become buoyant, gathering on the surface of the water. Blue-green algae do not present a valuable source of nutrition for other organisms, and they do more harm than good – in large volumes they start slowly dividing and slowly sinking to the seabed and using up oxygen. This creates anoxic zones. Such zones were previously observed in Baltic Sea’s deepest areas, such as the Gotland Deep. Finnish researchers have been warning for decades that the spread of anoxic zones have been rapidly spreading, and one of the reasons for this is the rapid growth of blue-green algae, Boikova explains.

Aside from blue-green algae, the Baltic Sea still has a fair share of problems – oil pollution from intensive seafaring, pollution from pharmacology and cosmetics industry, sewage water containing organic substances that promote the growth of blue-green algae, the expert explains.

She adds that the sea, similar to humans, has a way of adapting to the changing environment – the sea is able to perform certain self-cleansing processes. But it is currently impossible to say when the Baltic Sea may reach its red line, after which things may very well go tumbling down.

Boikova adds that every region of the Baltic Sea has a ‘red line’ of its own. Because species variety is not large, their ecosystem is very sensitive, because each species performs its own unique function. This means – the fewer organisms live there, the easier it is to cause imbalance in the ecosystem. Although the Baltic Sea is one of the most researched seas, there are still many unanswered questions, said the researcher.

There is currently nothing we can do about the growth of blue-green algae, she added. Swedish researchers had previously tried pumping oxygen into the sea to speed up blue-green algae blowing process, but these efforts have come to naught.

To combat the problem of blue-green algae spreading more than they should, ships should not be allowed to flush anything into the sea, including sewage, the researcher recommends.

Human sensitivity to blue-green algae differs from person to person. Nevertheless, exposure to this type of algae is known to cause conjunctivitis. Blue-green algae do not live for very long, but they do grow quickly – up to five cell divisions can happen in a day. This is easily observed using satellite images. Once the heat backs off, blue-green algae will stop growing, said Boikova, adding that reduction of their concentration requires strong waves.

Latvia’s Health Inspectorate has established restrictions on swimming in several of Latvia’s bathing areas due to increased spread of blue-green algae.

Polish authorities announced closure of the Baltic Sea coast dues to increased concentration of blue-green algae on Wednesday. This week Polish television showed photos the sea taken from the air showing a wide spread of blue-green algae.

According to information from the Swedish Meteorology and Hydrology Institute, nearly the entire central portion of the Baltic Sea is covered in blue-green algae. Algae cover the Baltic Sea from the Polish coast all the way to Stockholm and Finland.

Concentration of blue-green algae is the lowest in the waters near Denmark, as well as the Gulf of Riga and Bothnian Bay. The largest concentration of blue-green algae in Latvia is found around Northern Kurzeme.

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