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Narrow wrack

Fucus radicans

Photo: Lena BergströmPhoto: Lena Bergström

Narrow wrack formed less than 8 000 years ago from bladder wrack inside the Baltic Sea. It has since spread and established along the coasts of the Bothnian Sea, and along the coast of Estonia in the Baltic Proper.

Conservation genetic management advice

  • Maintain large population sizes and connectivity at present levels.
  • Protect populations with any sexual activity, see map. The sexually reproducing Estonian populations should be highly prioritised, as should local populations with sexual reproduction in the Gulfs of Bothnia and Finland.
  • The Estonian populations are genetically different from the Gulf of Bothnian populations, and should thus not be used to replace lost populations in Gulf of Bothnia.
  • Provide management plans for populations in Gulf of Bothnia and Estonian waters, and in Gulf of Finland – if present.

Threats to genetic biodiversity

The warming and salinity decrease predicted for the Baltic Sea over the coming 50 to 100 years could risk the loss of populations or the whole species. Due to large areas with no or very little sexual reproduction (see map) this species has a low potential for adapting to new environmental conditions. This is particularily true for the populations in Gulf of Bothnia, see below.

Knowledge on genetics in the Baltic (2017)

Narrow wrack is endemic to Gulf of Bothnia and Estonian waters. It may also be present in Gulf of Finland. Recent genetic data show that narrow wrack and bladder wrack are very closely related and sometimes difficult to separate.

Population genetic structure in wracks, Fucus sp.Population structure in wracks, Fucus sp., based on genetic data. Colours represent genetically distinct populations. Non-coloured coastlines lack data. Illustration: Elsa Wikander/Azote.

Both wracks can reproduce asexually by cloning. Females and males are separate individuals who can form new individuals by dropping adventitious branches (a few centimeter long vegetative branches) that grow to new thalli. The ratio of sexual to asexual recruitment varies among populations, from no clones to nearly all individuals being one same clone.

Clones are vulnerable
If cloning is common, diversity of genotypes is low and recombination that produce new genotypes is rare, making these populations especially vulnerable to environmental change. In contrast, populations with sexual activity have a potential for adapting to environmental change. Consequently, it is important to identify and protect sexually active populations in areas otherwise dominated by clones, see map below.

Approximate distribution of reproductive strategies for wracks, Fucus vesiculosus and Fucus radicans, in the Baltic Sea.
Illustration: Elsa Wikander/Azote.

In the Gulf of Bothnia and especially on the Swedish side, most Fucus populations are dominated by individuals reproducing clonally. In other areas, there is a mixture of populations with individuals reproducing both clonally and sexually. In the Baltic proper, cloning is rare, and at the Swedish west coast and further out in the Atlantic, cloning has never been found. 

Along the Swedish coast of Gulf of Bothnia, asexually reproducing clones of narrow wrack are very common. Most clones are locally distributed but two clones – one female and one male – have extensive geographic distributions.

The "superfemale" is found along a 550 km coastline in Gulf of Bothnia, making up 20–95 percent of individuals of local populations in this area, see map above. Due to this dominant clone, the genetic structure in narrow wrack is less fine-scaled than in bladder wrack here.

In Estonian waters, asexually reproducing clones seem to be nearly absent.

There are large genetic differences between populations in Gulf of Bothnia and in Estonia. A population in the Russian part of Gulf of Finland may also represent a genetically distant narrow wrack.



Kerstin Johannesson

Ricardo Pereyra

Additional information

Narrow wrack and bladder wrack are extremely closely related and are difficult to separate. Work is ongoing to resolve their taxonomic relationship. Ecologically, they both provide important ecosystem functions in the Baltic Sea particularly as habitat forming organisms.

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