Cyanobacteria enabled life, now it is choking the Baltic Sea

Cyanobacteria play a vital role in the Baltic Sea, but in large quantities they have become a serious problem, Baltic Sea Action Group project manager Anna Klemelä told Yle.

Massive blooms of the bacteria, often called blue-green algae, signal poor marine health, with human-caused nutrient loading and climate change as the root causes. When the algae die, the decomposing mass sinks to the seabed, consuming oxygen and creating vast dead zones where nothing can survive. These oxygen-depleted areas also release phosphorus back into the water, further accelerating eutrophication.

While some cyanobacteria produce neurotoxins and liver toxins, it is impossible to determine by sight alone whether a bloom is toxic. Children and pets should not be allowed to swim in water where cyanobacteria may be present.

To test for cyanobacteria, use a stick: the bacteria are so fine they will not cling to it, unlike filamentous algae. A transparent jar can also help assess the situation.

Current bloom reports along the coast are typical for this time of year, according to monitoring data from the Freshwater and Marine Wiki, Vesi.fi, and the Tarkka map service. Both experts and the public can report observations.

Klemelä notes that while cyanobacteria have a place in the Baltic’s ecosystem and food web, excessive blooms disrupt nutrient cycles and carbon sequestration. Research has shown some zooplankton species do feed on cyanobacteria, challenging the long-held belief that nothing consumes them.

To reduce blooms, Klemelä advises supporting regenerative agriculture, eating locally produced food, removing fishing gear from waters and shores, practising considerate boating, and using non-toxic antifouling paints.