Mia Henriksson


A long, band-like plant that can grow up to one metre tall grows under the surface of the Baltic Sea. Common eelgrass (Zostera marina) is a seed plant of marine origin.

Eelgrass grows in extensive meadows on the sea bottom, at a depth of one to eight metres, along the coast of the Baltic. In Finland eelgrass often grows together with other seed plants of sweet water origin. This is something unique to the Northern Hemisphere, where eelgrass meadows usually consist of eelgrass only. Fields with several species are normally found only in the tropics.

In his research, Docent Christoffer Boström, lecturer in marine biology at Åbo Akademi University, studies the function of coastal ecosystems, specifically the flora and fauna of eelgrass beds.

“A considerable proportion of all eelgrass meadows in the Northern Hemisphere are found in Scandinavia. Recent estimates show that there are over 2,100 km2 of eelgrass in the Nordic region and the Baltic Sea. Probably there is much more. Eelgrass grows on open sand bottoms and sways slowly with the movements of the water. It is a very beautiful and peaceful environment to dive in,” says Boström.

The eelgrass meadows are called the ‘coral reefs’ of the Baltic Sea, and they are both important and beautiful.
“The many roles of eelgrass in the marine ecosystem make the green meadows very fascinating. At first sight the meadows might seem uninteresting, but on looking closer, you will see that they swarm with life. Eelgrass is a so-called ‘key species’ that gives shelter and nutrition to many organisms and provides humans with a number of ecosystem services, such as coastal area stabilisation, oxygen production and carbon and nutrition sinks. The ecosystems in the Baltic might not be as colourful as the coral reefs, but they are all the more interesting when you learn what to look for,” says Boström.

Eelgrass is a very important plant in the ecosystem in the Baltic Sea, but it is threatened by human activities. For example, nutrients that cause eutrophication, and dredging and anchoring at unsuitable places cause eelgrass to disappear. Globally seagrass beds disappear at a rate of 110 km2 per year, which is even faster than the pace at which coral reefs and rainforests are disappearing.

The largest losses of seagrass have been noted in Denmark, Germany and on the Swedish west coast. There are no long-term studies in Finland, but it is obvious that eutrophication, muddy waters, overfishing and drifting algal mats constitute the main threats to the meadows in the Archipelago Sea and the Åland Islands. In addition, the Finnish eelgrass beds are usually a hundred- to a thousand-years-old giant clones, which makes them particularly vulnerable. If one clone disappears in an oil catastrophe, it will never return.

Boström carries out his research using the Korpoström Archipelago Centre in Finland as his base. He has supervised several doctoral students working on seagrass themes, and he acts as an expert within a campaign of the World Wildlife Fund (WWF) which aims at making the distribution and biology of seagrass meadows better known.