But as our climate continues to change, the living conditions in many places are changing with it. Inka Bartsch has been researching the “giants” among the algae for years and is still fascinated: “Algae look so simple. Yet their reactions are highly complex, and in some cases very sensitive, when their habitat begins to change,” she explains. For example, if the water temperature remains above 20 degrees for an extended length of time, it’s a death sentence for many types of brown algae.
The depths at which macroalgae can be found depends on how clear the water is – in other words, on how much sunlight makes its way to the seafloor. Since the coastal waters off Helgoland have to date been comparatively turbid, around 1970 brown macroalgae only grew there at depths of up to eight metres. But changing water currents are now making Helgoland’s waters clearer. As a result, some algae are now expanding into several-metre-deeper waters, effectively enlarging their habitat.
However, the North Sea has also grown warmer: by an average of 1.7 degrees Celsius from 1962 to the present. This change has likely been hard on oarweed. Inka Bartsch has determined that it reproduces much more poorly at summertime temperatures above 16 degrees; at 20 degrees it can’t reproduce at all, and begins dying out when exposed to prolonged water temperatures above 20 degrees.