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Bladder wrack

Fucus vesiculosus

Bladderwrack is the most dominant and ecologically important macroalga in the Baltic Sea. It provides essential ecosystem services as maintainers of local biodiversity, but also as nurseries for commercially important fish species.

Conservation genetic management advice

  • Maintain large population sizes and connectivity at present levels.
  • Identify and protect populations with high sexual activity, i.e. populations with many genotypes and thus, a capacity for future adaptations. This is particularly important in areas where cloning is otherwise predominant, and at range margins in Gulf of Bothnia and Gulf of Finland, see map.
  • Provide management plans for marginal populations, i.e. in Gulf of Bothnia, Gulf of Finland and Gulf of Riga.
  • Consider genetic monitoring.
  • Consider restoration of earlier lost populations in Gulf of Gdansk, using individuals from areas of similar salinity.

Threats to genetic biodiversity

The warming and salinity decrease predicted for the Baltic Sea over the coming 50 to 100 years may result in loss of populations in marginal areas (the gulfs of Bothnia, Finland and Riga). See future distribution.

In areas with clonal reproduction (=low levels of sexual reproduction) the potential for adaptation to new environmental conditions is low. Here, populations are particularly vulnerable, and environment sweeps could lead to potential extinction. See map below.

Eutrophication, increased turbidity or cascading effects of overfishing have historically eradicated local populations of bladder wrack. Loss of this type is likely to lead to loss of genetic variation including local adaptations. In some areas, populations have recovered.

Knowledge on genetics in the Baltic (2017)

The population structure in bladder wrack is strong in the Baltic Sea, with limited gene flow (connectivity) even among populations as little as one kilometers apart. Between some areas the genetic differences are large: Populations along the Finnish coast, from Turku to Wasa and in Gulf of Finland, are genetically very different from the rest of the Baltic.

Population structure of 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. 

Clones in some areas

In the Baltic Sea, both bladder wrack and the closely related narrow wrack reproduce sexually but also asexually, by cloning. Females and males are separate individuals and can form new individuals by dropping adventitious branches (a few centimeter long vegetative branches) that grow to new thalli.

Reproductive strageties of Fucus in the BalticApproximate 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 asexually. 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.

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.

Tolerance to climate change & potential to adapt

Experimental studies in BONUS BAMBI clearly showed that predicted future combinations of salinity and temperature represent serious challenges for the Fucus populations, particularly in the central and marginal regions of the Baltic Sea. This may lead to contractions in the species range, and a shift southwards, towards the Baltic Sea entrance.

We did find evidence for genetic variation in tolerance to future salinity and temperature, especially in the central and entrance populations. Such genetic variation may provide the raw material necessary for adaptation to a changing environment. However, our genotypic data just documents the potential for adaptation. We cannot foresee whether the speed or the magnitude of the adaptive response can match the rate of climate change.

See also results from our modelling of Fucus distribution in the future Baltic Sea.

References

CONTRIBUTORS

Kerstin Johannesson
kerstin.johannesson@gu.se

Ricardo Pereyra
ricardo.pereyra@marine.gu.se

Future distribution

Climate change and eutrophication may modify the present distribution of bladder wrack in a negative way.

More...

Additional information

Recent genetic data show that bladder wrack and narrow wrack are very closely related. In several cases, analyses fail to separate them from each other. Ecologically, they both provide important ecosystem functions in the Baltic Sea particularly as habitat forming organisms.

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