Free-living bladderwrack in the Baltic Sea. Photo: Susanne Qvarfordt
Free-living bladderwrack (in the foreground) and rooted vascular plants (in the background) on soft bottoms in the Baltic Sea. Photo: Susanne Qvarfordt

Bladderwrack is one of the most important species in the coastal areas of the Baltic Sea. Just like trees in a forest, they provide food and shelter for many small animals, fish and other algae at 0,5-5 metres depth.

Typically, bladderwrack grows attached to hard surfaces under water, such as rocks and boulders. It is therefore usually considered a ‘rocky shore organism’. It is therefore very interesting that free-living, unattached, bladderwrack also exist. These are found in sheltered bays, lying loose on soft sediment bottoms, where we usually find rooted vascular plants. In the Askö area in Sweden and western Gulf of Finland, free-living populations of bladderwrack have been recorded during the last 20 years. They can be extensive (100-1000m2) and seem to occur year after year at the same sites.

What role does the free-living Fucus play?

Our first aim is to compare the functional role of free-living bladderwrack from soft bottoms to that of attached bladderwrack from hard bottoms. This will be done by comparing what species of associated animals and algae we find (biodiversity) and how many of them there are (abundance). We will also compare with the rooted vascular plants, which are commonto the soft bottoms where we also find the free-living bladderwrack.

How do they grow or reproduce? 

We also do not know where these populations originate from or how they reproduce. It is possible that they multiply simply by falling apart into fragments that just keep on growing.

The second aim of this study is therefore to discover if free-living bladderwrack populations are the result of continuous supply of fallen-off material from nearby attached populations. Or whether they, fully or partly, also multiply by asexual fragmentation.

Project method

The sampling was carried out in the Askö area south of Stockholm (Sweden), and along the SW coast of Finland. Both free-living and attached bladderwrack was collected from several sites in both countries. The genetic pattern of the free-living bladderwrack samples will be compared to nearby attached bladderwrack. All sampling was done by SCUBA diving.

Researchers: Ellen SchagerströmSusanne Qvarfordt DEEP, SU & Jaanika Blomster, Roxana Preston, University of Helsinki.