The PhD thesis together with a dried specimen of Fucus radicans. Photo: Lena Kautsky.

- What is particular for F. radicans is that it can reproduce clonally through fragmentation. Small pieces of a plant can attach themselves to a new substrate and grow into a new seaweed thallus. No other Fucus species uses this mode of dispersal in such large extent as F. radicans, says Ellen Schagerström, a PhD student at the Department of Ecology, Environment and Plant Sciences.

In this way, a single female individual has spread across the Bothnian Sea and is now frequently found in a large part of the population. Since a certain genetic diversity develops through somatic mutations, there is a genetic diversity even within clones.

- Another new feature of F. radicans that we have discovered is that we can tell the difference between female and male plants with the naked eye, says Ellen Schagerström.
Along with F. vesiculosus, F. radicans builds up what we usually describe as the underwater forest, an environment which is extremely important for small fish and other creatures in the species-poor ecosystem of the Baltic Sea.

- It was long thought that F. radicans was a variant of the F. vesiculosus, its small, narrow form caused by the low salinity of the Bothnian Sea. When it was realized that it was a separate species, it was obviously important to find out more, says Ellen Schagerström.

Fucus radicans to the left is very similar to the original species Fucus vesiculosus, but has narrower thalli. Photo: Petra Nowak.

In her thesis, Ellen Schagerström investigated what role F. radicans plays in the Baltic Sea ecosystem. Which environmental factors does it tolerate better or worse than the original species F. vesiculosus, and how has F. radicans evolved? These questions are interesting both from a management perspective and as basic research.

- We have only found F. radicans in the Bothnian Sea and around the island of Saaremaa in Estonia. So far, nowhere in the Åland archipelago and no further south than Öregrund on the Swedish coast. The reason why it is not found further south is likely due to competition by F. vesiculosus that grows bigger with increasing salinity, and that it also is more palatable to grazers than F. vesiculosus and therefore gets eaten by isopods and other hungry grazers, says Ellen Schagerström.

There are three different Fucus species in the Baltic Sea with partly overlapping distribution. Fucus serratus is only found in the south, Fucus radicans is only found in the north, and Fucus vesiculosus is present along almost the entire coast.

For further information
Ellen Schagerström, PhD student at the Department of Ecology, Environment and Plant Sciences, Stockholm University, tel +46 (0)8-16 3778, mobile +46(0)73-6291812, email ellen.schagerstrom@su.se

Link to the PhD thesis: http://su.diva-portal.org/smash/record.jsf?pid=diva2:813951