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Skansen helps place Bladderwrack in the Baltic Sea

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Bladderwrack is one of the species that has significantly declined in the Baltic Sea since the 1970s due to factors such as eutrophication. However, it is now making a comeback. Skansen’s staff have been on-site in the Riddersholm Nature Reserve to assist in the placement of new bladderwrack plants in anticipation of the weekend’s full moon, which is when reproduction occurs.

Restoring the Vitality of the Baltic Sea

It is through WWF’s project “Restoring the Vitality of the Baltic Sea” that the Baltic Sea Science Center at Skansen has had the fantastic opportunity to contribute to the effort. This along with the Archipelago Foundation and the Swedish Sportfishing Association, all of whom are participating in the project. The goal is to create favorable conditions for bladderwrack reproduction.

Artificial reef to bring new life

In the bays around the Riddersholm Nature Reserve near Kapellskär, the Swedish Sportfishing Association has constructed an artificial stone reef with 300 tons of stone. This is to counteract erosion caused by traffic along the Furusund shipping lane. Intense and fast-moving vessel traffic in the Furusund has resulted in the movement of bottom materials.

Male and female plants reproduce during full moon

On the reef, efforts are being made to establish a new habitat for the species. And with a little help, the goal is to grow a new underwater forest. Bladderwrack plants are either male or female. This means that at least two plants of different genders are required for successful reproduction.

“Since the reef provides new shallow and hard surfaces, it becomes an ideal place for bladderwrack to grow. On Tuesday, we collected branches from the sea outside Riddersholm. At the same time, the reef was cleaned of fine filamentous algae that would otherwise compete with the upcoming seedlings” says Sophie Lewenhaupt at the Baltic Sea Science Center at Skansen.

First, the collected branches are bound into bundles. Then they are attached to small buoyant stones that the divers can secure to the rocks along the reef. In the Baltic Sea, bladderwrack reproduces only during a short period, either in early summer or in autumn. Fertilization is the most sensitive stage in the bladderwrack’s life cycle.

“Now, the plants hang over the reef, and hopefully, they will release their eggs and sperm during Saturday’s full moon so that new bladderwrack plants will grow there” says Sophie Lewenhaupt.

Info Box

Bladderwrack – a Keystone Species in the Baltic Sea Bladderwrack (Fucus vesiculosus) is considered one of the few keystone species in the Baltic Sea. A keystone species is particularly important and can create habitat and protection for other plant and animal species. Small algae and sedentary animals attach themselves to a bladderwrack thallus. This habitat is also home to amphipods, snails, sea squirts, mussels, and many more. Fish fry can live in the shelter of bladderwrack branches, while others find their food there.

Reproduction during Full Moon Bladderwrack consists of female plants carrying eggs and male plants carrying sperm, all found in the knobby tips that can be found on bladderwrack during the reproductive season. On calm evenings in May and June when the full moon shines, bladderwrack plants release billions of tiny eggs and sperm into the water, which unite in the water and seek a suitable rock to grow on. There, it can live for over 50 years if left undisturbed.

Curious About Bladderwrack? Participate in the citizen science project “Algforskarsommar” (Algae Research Summer), which is now in its third consecutive year. Contribute to the collection of new knowledge about coastal algae belts, when bladderwrack reproduces, and what happens to the wildlife in a bladderwrack thallus. Your contribution is valuable for understanding the Baltic Sea’s coastal ecosystems. Learn more on Stockholm University’s website.

Through the placement of new bladderwrack plants, the project aims to strengthen the species and contribute to a healthier Baltic Sea. (14.2)

Through the project, the Baltic Sea Science Center is helping to create favourable conditions for a new bladderwrack habitat in the Baltic Sea and thereby strengthen the species’ resilience. (15.5)