''Fucus radicans'' is a

species In biology, a species is the basic unit of classification and a taxonomic rank of an organism, as well as a unit of biodiversity. A species is often defined as the largest group of organisms in which any two individuals of the appropriate s ...

brown algae Brown algae (singular: alga), comprising the class Phaeophyceae, are a large group of multicellular algae, including many seaweeds located in colder waters within the Northern Hemisphere. Brown algae are the major seaweeds of the temperate and p ...

in the

family Family (from la, familia) is a group of people related either by consanguinity (by recognized birth) or affinity (by marriage or other relationship). The purpose of the family is to maintain the well-being of its members and of society. Idea ...

Fucaceae,

endemic Endemism is the state of a species being found in a single defined geographic location, such as an island, state, nation, country or other defined zone; organisms that are indigenous to a place are not endemic to it if they are also found else ...

to and recently evolved within the

Baltic Sea The Baltic Sea is an arm of the Atlantic Ocean that is enclosed by Denmark, Estonia, Finland, Germany, Latvia, Lithuania, Poland, Russia, Sweden and the North and Central European Plain. The sea stretches from 53°N to 66°N latitude and ...

. The species was first described by Lena Bergström and Lena Kautsky in 2005 from a

location In geography, location or place are used to denote a region (point, line, or area) on Earth's surface or elsewhere. The term ''location'' generally implies a higher degree of certainty than ''place'', the latter often indicating an entity with an ...

Ångermanland Ångermanland ( or ) is a historical province (''landskap'') in the northern part of Sweden. It is bordered (clockwise from the north) by Swedish Lapland, Västerbotten, the Gulf of Bothnia, Medelpad and Jämtland. The name is derived from ...

, Sweden. The specific epithet is from the

Latin Latin (, or , ) is a classical language belonging to the Italic branch of the Indo-European languages. Latin was originally a dialect spoken in the lower Tiber area (then known as Latium) around present-day Rome, but through the power of the ...

and means "rooting", referring to the fact that this species primarily reproduces by the taking root of detached fragments. Fucus radicans and vesiculosus

''Fucus radicans'' seems to have diverged from the closely related and widely distributed ''

Fucus vesiculosus ''Fucus vesiculosus'', known by the common names bladder wrack, black tang, rockweed, sea grapes, bladder fucus, sea oak, cut weed, dyers fucus, red fucus and rock wrack, is a seaweed found on the coasts of the North Sea, the western Baltic Se ...

'' 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.

Description

''Fucus radicans'' is morphologically similar to bladderwrack (''Fucus vesiculosus'') which is dichotomously branched, and has brown leathery fronds known as thalli with a prominent midrib and globular air bladders. The main differences between the two are that plants of ''F. radicans'' are smaller and more bushy than ''F. vesiculosus'' and have narrower thalli. Bladderwrack is common on the foreshore on both sides of the

temperate In geography, the temperate climates of Earth occur in the middle latitudes (23.5° to 66.5° N/S of Equator), which span between the tropics and the polar regions of Earth. These zones generally have wider temperature ranges throughout ...

North Atlantic and the subarctic. ''F. radicans'' is

to the

, where it grows alongside ''F. vesiculosus''.

The Baltic Sea and speciation

The Baltic Sea was formed by the retreating ice after the last

ice age An ice age is a long period of reduction in the temperature of Earth's surface and atmosphere, resulting in the presence or expansion of continental and polar ice sheets and alpine glaciers. Earth's climate alternates between ice ages and gre ...

, about ten thousand years ago. At first it was a freshwater lake but the sea broke through on more than one occasion. From about 4,000 years ago till the present time it has been a brackish water area, relatively isolated from the

North Sea The North Sea lies between Great Britain, Norway, Denmark, Germany, the Netherlands and Belgium. An epeiric sea, epeiric sea on the European continental shelf, it connects to the Atlantic Ocean through the English Channel in the south and the ...

with only occasional inflows of oceanic water. Over 200 rivers flow into the Baltic and this results in the surface layers being much less saline than other seas. There is a certain amount of inflow of water from the North Sea but this remains on the bottom and relatively unmixed with the surface waters.The Baltic Sea:Its Past, Present and Future
Jan Thulin and Andris Andrushaitis. Retrieved 2012-02-29. ''F. radicans'' is endemic to the Baltic Sea, where it grows in shallow water alongside ''F. vesiculosus''. It seems to be specially adapted to low salinity levels and unable to tolerate the higher levels of salinity to which other species of seaweed are habituated. Even within the Baltic, salinity levels vary and ''F. radicans'' favours the northernmost part, the Gulf of Bothnia, where the brackish water may have a salinity of less than 10

‰ Per mille (from Latin , "in each thousand") is an expression that means parts per thousand. Other recognised spellings include per mil, per mill, permil, permill, or permille. The associated sign is written , which looks like a percent si ...

(the open ocean has an average of 35‰). Being intermediate between sea and fresh water, the Baltic Sea, and especially the Gulf of Bothnia, has a low

biodiversity Biodiversity or biological diversity is the variety and variability of life on Earth. Biodiversity is a measure of variation at the genetic (''genetic variability''), species (''species diversity''), and ecosystem (''ecosystem diversity'') l ...

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

biome A biome () is a biogeographical unit consisting of a biological community that has formed in response to the physical environment in which they are found and a shared regional climate. Biomes may span more than one continent. Biome is a broader ...

s. 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 Ribulose-1,5-bisphosphate carboxylase-oxygenase, commonly known by the abbreviations RuBisCo, rubisco, RuBPCase, or RuBPco, is an enzyme () involved in the first major step of carbon fixation, a process by which atmospheric carbon dioxide is con ...

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 Any cause that reduces or increases reproductive success in a portion of a population potentially exerts evolutionary pressure, selective pressure or selection pressure, driving natural selection. It is a quantitative description of the amount of ...

applied by the change in the environment.

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. 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.

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. According to the Baltic Sea research and development project BONUS BAMBI, management for long-term conservation of ''F. radicans'' should aim to: * protect populations with sexual activity. The sexually reproducing Estonian populations should be highly prioritised, * maintain large population sizes, * maintain connectivity between populations at present levels, * provide management plans for populations in the Bothnian Sea and in Estonian waters, and in Gulf of Finland – if present. Since the Estonian populations are genetically different from other populations, they should not be used to replace lost populations in the Bothnian Sea.

References

{{Taxonbar, from=Q5507040 Fucales Biota of the Baltic Sea Plants described in 2005 Fucaceae