It Came From the Deep: Baltic Swarmed by Deadly Glowing Toxic Seaweed

The poisonous bioluminescent organism, Alexandrium ostenfeldii, known in Finnish as "sea fire," has been identified as a growing environmental hazard for the long-suffering Baltic Sea in a dissertation by Anniina Le Tortorec, a researcher at the National Resources Institute Finland (Luke).

According to Le Tortorec, the organisms emit a telltale blue glow known as mareel, and present a threat to both marine life and human health.

"Across the globe, this glowing seaweed has historically caused the deaths of sea birds, marine mammals and even humans," Anniina Le Tortorec told Finnish national broadcaster Yle.

Previous research indicated that the algae emit saxitocin, a dangerous neurotoxin causing skin prickling and numbing in small amounts, yet capable of inducing paralysis and even death in worst-case scenarios.

​While first recorded in the Baltic Sea in the 1970s, populations of the glowing seaweed are on the rise across the whole region. Le Tortorec attributed the proliferation of the heat-loving organism to the gradual warming of the environment, where excess nutrients are building up in the sea. In recent years, the glowing weed has grown to become a rival to blue-green algae, the traditional archenemy of Finnish beaches.

​Le Tortorec's fellow Luke researchers have spent about ten years investigating the ever-growing presence of the phosphorescent weed in the sea areas around the Åland archipelago, as wells as the towns of Tammisaari and Naantali. Luke is currently busy developing new ways of combatting the toxic luminescent weed.

Today, the phosphorescence of the Alexandrium ostenfeldii, which occurs mainly in late summer and early autumn, may be picked up by automatic measurement. However, Luke also called on fishermen, boaters and coastline inhabitants to report any sightings of the easy-to-identify algae in order to correctly determine the extent of its spread across the Baltic. Early detection of the harmful bloom allows the authorities to be better-equipped to inform locals and tourists about preventive measures.

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

​The Alexandrium ostenfeldii are part of the dinoflagellata phylum. Most of its representatives are marine plankton, yet are common in freshwater habitats as well. The bloom of certain dinoflagellata results in a visible coloration of water, colloquially known as a "red tide" or "milky seas effect" depending on the color.

Decades of overfishing and pollution have put creatures living in the Baltic Sea at extreme risk. At present, more than half of all fish species there are categorized as having reached a critical level.

In 2014, the EU-funded MARLIN study, the first of its type to monitor the level of marine litter in the Baltic Sea, concluded that Finnish shores were likely to be more cluttered with debris compared to beaches in other Baltic countries. An unsurprising 75 percent of the litter was found to be plastic.