Image: Stefan Simis

A new toxic organism poses a growing environmental hazard in the Baltic Sea, according to a new dissertation by a researcher at the National Resources Institute Finland (Luke).

The algae Alexandrium ostenfeldii – known as merituli ('sea-fire') in Finnish – often glows blue, a phenomenon known as the milky seas effect or mareel. Alexandrium presents a threat to marine life as well as human health.

"Across the globe this glowing seaweed has historically caused the deaths of sea birds, marine mammals and even humans," says researcher Anniina Le Tortorec. "Its risks are better known these days."

The algae emits saxitocin, a neurotoxin. It causes skin prickling and numbing in small amounts, but can paralyse or cause death in worst-case scenarios. New toxins, such as gymnomidine, that have until now been unknown in the Baltic Sea also pose a challenge for researchers.

The first recorded sightings of the Alexandrium dinoflagellate in Finland are from the 1970s. Populations of the glowing seaweed are on the rise in many places in the Baltic Sea.

"The Alexandrium likes it warm. The climate is getting warmer and excess nutrients are building up in the sea, leading to the spread of the algae," says Le Tortorec.

Light detection

The Alexandrium algae is fast becoming a threat to rival the blue algae blooms that ruin beaches across Finland each year. Blue-green bacteria are still a bigger menace, the Finnish Environment Institute says.

Luke researchers have spent some ten years mapping the presence of the phosphorescent weed in the sea areas of Åland, Tammisaari and Naantali.

Image: Stefan Simis

Le Tortorec's dissertation at the University of Helsinki is a step towards early detection of the harmful bloom. Automatic measurement systems can pick up the light emitted by the seaweed, which varies depending on its life cycle. Phosphorescence tends to occur in late summer, early autumn.

"Currently we're able to detect Alexandrium activity about two weeks before the height of the growth season," says Le Tortorec.

The earlier such detections are made, the better authorities will be equipped to inform local and visiting people in at-risk areas about measures such as limiting water consumption.

The Finnish Environment Institute is calling for boaters or coastline inhabitants to report any sightings of Alexandrium in the sea. Reports will help researchers determine the extent of the algae's spread in the Baltic.