Invasive species: Part 6 – Sargasso Snare

Sargasso snare, a brown algae, was initially discovered in 1985 in northern Bohuslän and has since become prevalent along the Swedish west coast. During the summer months, it bears a striking resemblance to regular Swedish knotweed, characterized by numerous small bubbles measuring a couple of millimeters in diameter.

The introduction of the Sargasso snare to Europe can be traced back to the importation of live giant oysters from Japan. Sargasso snare can grow up to two meters in length and thrives in shallow waters, typically found at depths of up to ten meters. What sets it apart from our native Swedish knotweed is its ability to self-fertilize, meaning that only a single plant is required for propagation.

In November, shoots begin to emerge from the plant. After about a year, these shoots detach and drift away with ocean currents before settling elsewhere. The algae exhibits rapid growth, rapidly forming dense and tall clusters that overshadow the seafloor, outcompeting other seaweed species that rely on sunlight for survival. However, the sargasso snare also has positive aspects. When it colonizes bare sandy and soft bottoms, it provides shelter for various marine organisms, leading to the creation of new ecosystems.

Reportage: Lena Scherman
Photography: Göran Ehlmé

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