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Fucus radicans is a species of brown algae in the family Fucaceae, endemic to and recently evolved within the Baltic Sea. The species was first described by Lena Bergström and Lena Kautsky in 2005 from a location in Ångermanland, Sweden. The Botanical name is from the Latin and means "rooting", referring to the fact that this species primarily reproduces by the taking root of detached fragments. Fucus radicans L.Bergström & L.Kautsky AlgaeBase. Retrieved 2012-02-29.
Fucus radicans seems to have diverged from the closely related and widely distributed Fucus vesiculosus within about the last 400 years. It often reproduces clonally, which may have helped its rapid emergence as a new species. Genetic analysis supports the hypothesis of the recent divergence of Fucus radicans from Fucus vesiculosus as an example of sympatric speciation, with the two species presently occupying the same semi-marine territory.
Being intermediate between sea and fresh water, the Baltic Sea, and especially the Gulf of Bothnia, has a low biodiversity and supports only a small number of plant and animal species that have been able to adapt to this level of salinity. Those that are present tend to be smaller than in their main habitats, be those marine or freshwater . Bladderwrack ( F. vesiculosus) has a wide distribution and is present in quantities in the Baltic Sea where it lives side by side with the very similar F. radicans. Studies to find their evolutionary relationship using chloroplast (RuBisCO gene) or mitochondrial DNA (intergenic spacer) sequence markers have been inconclusive. Genetic analysis using microsatellite markers (short DNA sequences) suggests that a divergence between the two species occurred between 125 and 2475 years ago with a posterior distribution peak at around 400 years ago. This means the species would have diverged more recently than the transition of the Baltic Sea from a marine environment to its present brackish state. This hypothesis is supported by the fact that F. radicans is found nowhere else other than the Baltic.
An isolating mechanism between the two species may be the fact that F. vesiculosus normally reproduces sexually whereas F. radicans shows a much greater tendency to reproduce asexually, with detached fragments having the ability to take root and develop into new plants. Environmental stress, in this instance the decrease in salinity of the water, has been shown to contribute to the formation of new species. Another contributor to speciation is the evolutionary pressure applied by the change in the environment.
The genetic structure in F. radicans is complex, and the genetic differences between populations in Estonia and in Gulf of Bothnia are substantial. Some populations are almost completely sexually recruited while others are dominated by single clones. The Estonian populations are mostly sexually reproduced, and harbour large genetic variation. The populations in the Bothnian Sea mostly recruit asexually, and are dominated by two clones—one female and one male. The female is found along a 550 km coastline, making up 20–95 % of the individuals in local populations. Due to this dominant clone, the genetic structure in F. radicans is less fine-scaled than in bladder wrack in this area.
According to the Baltic Sea research and development project BONUS BAMBI, management for long-term conservation of F. radicans should aim to:
Genetic biodiversity
Fucus radicans is endemic to the Baltic Sea where it occurs along the coasts of the Bothnian Sea and in Estonian waters. It may also be present in (the Russian of) Gulf of Finland. Just like the closely related bladder wrack ( F. vesiculosus), F. radicans can reproduce both sexually and asexually.
Management
Genetic variation is fundamental for a species ability to adapt and survive in new environmental conditions. To mitigate future losses, management and conservation of Baltic Sea biodiversity should include also the genetic level. The situation in Fucus radicans, with large areas with no or very little sexual reproduction, means that this species has low potential for future genetic adaption. Thus, the warming and salinity decrease predicted for the Baltic Sea over the coming 50 to 100 years could risk the loss of populations and even the whole species.
Since the Estonian populations are genetically different from other populations, they should not be used to replace lost populations in the Bothnian Sea.
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