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  • 1. Ardehed, Angelica
    et al.
    Johansson, Daniel
    Schagerström, Ellen
    Stockholm University, Faculty of Science, Department of Ecology, Environment and Plant Sciences.
    Kautsky, Lena
    Stockholm University, Faculty of Science, Department of Ecology, Environment and Plant Sciences.
    Johannesson, Kerstin
    Pereyra, Ricardo T.
    Complex spatial clonal structure in the macroalgae Fucus radicans with both sexual and asexual recruitment2015In: Ecology and Evolution, ISSN 2045-7758, E-ISSN 2045-7758, Vol. 5, no 19, p. 4233-4245Article in journal (Refereed)
    Abstract [en]

    In dioecious species with both sexual and asexual reproduction, the spatial distribution of individual clones affects the potential for sexual reproduction and local adaptation. The seaweed Fucus radicans, endemic to the Baltic Sea, has separate sexes, but new attached thalli may also form asexually. We mapped the spatial distribution of clones (multilocus genotypes, MLGs) over macrogeographic (>500km) and microgeographic (<100m) scales in the Baltic Sea to assess the relationship between clonal spatial structure, sexual recruitment, and the potential for natural selection. Sexual recruitment was predominant in some areas, while in others asexual recruitment dominated. Where clones of both sexes were locally intermingled, sexual recruitment was nevertheless low. In some highly clonal populations, the sex ratio was strongly skewed due to dominance of one or a few clones of the same sex. The two largest clones (one female and one male) were distributed over 100-550km of coast and accompanied by small and local MLGs formed by somatic mutations and differing by 1-2 mutations from the large clones. Rare sexual events, occasional long-distance migration, and somatic mutations contribute new genotypic variation potentially available to natural selection. However, dominance of a few very large (and presumably old) clones over extensive spatial and temporal scales suggested that either these have superior traits or natural selection has only been marginally involved in the structuring of genotypes.

  • 2. Ardehed, Angelica
    et al.
    Johansson, Daniel
    Sundqvist, Lisa
    Schagerström, Ellen
    Stockholm University, Faculty of Science, Department of Ecology, Environment and Plant Sciences.
    Zagrodzka, Zuzanna
    Kovaltchouk, Nikolaj A.
    Bergström, Lena
    Kautsky, Lena
    Stockholm University, Faculty of Science, Department of Ecology, Environment and Plant Sciences.
    Rafajlovic, Marina
    Pereyra, Ricardo T.
    Johannesson, Kerstin
    Divergence within and among Seaweed Siblings (Fucus vesiculosus and F. radicans) in the Baltic Sea2016In: PLoS ONE, ISSN 1932-6203, E-ISSN 1932-6203, Vol. 11, no 8, article id e0161266Article in journal (Refereed)
    Abstract [en]

    Closely related taxa provide significant case studies for understanding evolution of new species but may simultaneously challenge species identification and definition. In the Baltic Sea, two dominant and perennial brown algae share a very recent ancestry. Fucus vesiculosus invaded this recently formed postglacial sea 8000 years ago and shortly thereafter Fucus radicans diverged from this lineage as an endemic species. In the Baltic Sea both species reproduce sexually but also recruit fully fertile new individuals by asexual fragmentation. Earlier studies have shown local differences in morphology and genetics between the two taxa in the northern and western Bothnian Sea, and around the island of Saaremaa in Estonia, but geographic patterns seemin conflict with a single origin of F. radicans. To investigate the relationship between northern and Estonian distributions, we analysed the genetic variation using 9 microsatellite loci in populations from eastern Bothnian Sea, Archipelago Sea and the Gulf of Finland. These populations are located in between earlier studied populations. However, instead of bridging the disparate genetic gap between N-W Bothnian Sea and Estonia, as expected from a simple isolation-by-distance model, the new populations substantially increased overall genetic diversity and showed to be strongly divergent from the two earlier analysed regions, showing signs of additional distinct populations. Contrasting earlier findings of increased asexual recruitment in low salinity in the Bothnian Sea, we found high levels of sexual reproduction in some of the Gulf of Finland populations that inhabit extremely low salinity. The new data generated in this study supports the earlier conclusion of two reproductively isolated but very closely related species. However, the new results also add considerable genetic and morphological complexity within species. This makes species separation at geographic scales more demanding and suggests a need for more comprehensive approaches to further disentangle the intriguing relationship and history of the Baltic Sea fucoids.

  • 3. Barboza, Francisco R.
    et al.
    Kotta, Jonne
    Weinberger, Florian
    Jormalainen, Veijo
    Kraufvelin, Patrik
    Molis, Markus
    Schubert, Hendrik
    Pavia, Henrik
    Nylund, Göran M.
    Kautsky, Lena
    Stockholm University, Faculty of Science, Stockholm University Baltic Sea Centre.
    Schagerström, Ellen
    Stockholm University, Faculty of Science, Department of Ecology, Environment and Plant Sciences.
    Rickert, Esther
    Saha, Mahasweta
    Fredriksen, Stein
    Martin, Georg
    Torn, Kaire
    Ruuskanen, Ari
    Wahl, Martin
    Geographic variation in fitness-related traits of the bladderwrack Fucus vesiculosus along the Baltic Sea-North Sea salinity gradient2019In: Ecology and Evolution, ISSN 2045-7758, E-ISSN 2045-7758, Vol. 9, no 16, p. 9225-9238Article in journal (Refereed)
    Abstract [en]

    In the course of the ongoing global intensification and diversification of human pressures, the study of variation patterns of biological traits along environmental gradients can provide relevant information on the performance of species under shifting conditions. The pronounced salinity gradient, co-occurrence of multiple stressors, and accelerated rates of change make the Baltic Sea and its transition to North Sea a suitable region for this type of study. Focusing on the bladderwrack Fucus vesiculosus, one of the main foundation species on hard-bottoms of the Baltic Sea, we analyzed the phenotypic variation among populations occurring along 2,000 km of coasts subjected to salinities from 4 to >30 and a variety of other stressors. Morphological and biochemical traits, including palatability for grazers, were recorded at 20 stations along the Baltic Sea and four stations in the North Sea. We evaluated in a common modeling framework the relative contribution of multiple environmental drivers to the observed trait patterns. Salinity was the main and, in some cases, the only environmental driver of the geographic trait variation in F. vesiculosus. The decrease in salinity from North Sea to Baltic Sea stations was accompanied by a decline in thallus size, photosynthetic pigments, and energy storage compounds, and affected the interaction of the alga with herbivores and epibiota. For some traits, drivers that vary locally such as wave exposure, light availability or nutrient enrichment were also important. The strong genetic population structure in this macroalgae might play a role in the generation and maintenance of phenotypic patterns across geographic scales. In light of our results, the desalination process projected for the Baltic Sea could have detrimental impacts on F. vesiculosus in areas close to its tolerance limit, affecting ecosystem functions such as habitat formation, primary production, and food supply.

  • 4. Florin, Ann-Britt
    et al.
    Mo, Kerstin
    Svensson, Filip
    Stockholm University, Faculty of Science, Department of Ecology, Environment and Plant Sciences.
    Schagerström, Ellen
    Stockholm University, Faculty of Science, Department of Ecology, Environment and Plant Sciences.
    Kautsky, Lena
    Stockholm University, Faculty of Science, Department of Ecology, Environment and Plant Sciences.
    Bergström, Lena
    First records of Conrad´s false mussel, Mytilopsis leucophaeata (Conrad, 1831) in the southern Bothnian Sea, Sweden, near a nuclear power plant2013In: BioInvasions Records, ISSN 2242-1300, Vol. 2, no 4, p. 303-309Article in journal (Refereed)
    Abstract [en]

    The invasive, biofouling, Conrad's false mussel Mytilopsis leucophaeata was first recorded in Sweden during spring 2011 in the cooling water system of the power plant of Forsmark in the southern Bothnian Sea. The cooling water discharge area offers a favourable environment for growth, survival, and reproduction of M. leucophaeata and may provide a stepping stone for further spread. We present three different studies in the area, revealing a rapid increase in mussels in the artificially heated area, with densities of the magnitude of thousands of individuals m-2, as well as mussels living in surrounding waters, indicating an on-going expansion in the region.

  • 5.
    Kautsky, Lena
    et al.
    Stockholm University, Faculty of Science, Stockholm University Baltic Sea Centre. Stockholm University, Faculty of Science, Department of Ecology, Environment and Plant Sciences.
    Qvarfordt, Susanne
    Stockholm University, Faculty of Science, Stockholm University Baltic Sea Centre.
    Schagerström, Ellen
    Stockholm University, Faculty of Science, Stockholm University Baltic Sea Centre. Stockholm University, Faculty of Science, Department of Ecology, Environment and Plant Sciences.
    Fucus vesiculosus adapted to a life in the Baltic Sea: impacts on recruitment, growth, re-establishment and restoration2019In: Botanica Marina, ISSN 0006-8055, E-ISSN 1437-4323, Vol. 62, no 1, p. 17-30Article in journal (Refereed)
    Abstract [en]

    Fucus vesiculosus is common both on the tidal coasts of the North Atlantic and in the Baltic Sea, where it has adapted to low salinity and nontidal conditions over the last 7000 years. During the late 1970s and early 1980s, extensive declines of F. vesiculosus populations were reported in the Baltic Proper, mainly attributed to high nutrient loads. During the past 30-40 years, considerable efforts have been made to reduce nutrient runoff to coastal areas but few successful initiatives to restore F. vesiculosus populations have been performed. In this paper, we present how substratum manipulation, i.e. clean rocky surfaces, brushing rocks, Hildenbrandia rubra cover and different filamentous algae, as well as different algal exudates, affect the recruitment and survival of juvenile F.vesiculosus. Further, we show through a 5-year field experiment that it will take at least 4-5 years to reach reproductive age for F. vesiculosus in the Baltic Sea. We also present transplantation studies from two different areas, showing that epiphytic load, light, grazing and type of substratum are some of the factors that need to be taken into consideration in order to achieve successful restoration of F. vesiculosus.

  • 6.
    Schagerström, Ellen
    Stockholm University, Faculty of Science, Department of Ecology, Environment and Plant Sciences.
    Fucus radicans: Reproduction, adaptation & distribution patterns2013Report (Other academic)
    Abstract [en]

    The Baltic Sea is considered an ecological marginal environment, where both marine and freshwater species struggle to adapt to its ever changing conditions. Fucus vesiculosus (bladderwrack) is commonly seen as the foundation species in the Baltic Sea, as it is the only large perennial macroalgae, forming vast belts down to a depth of about 10 meters. The salinity gradient results in an increasing salinity stress for all marine organisms. This is commonly seen in many species as a reduction in size. What was previously described as a low salinity induced dwarf morph of F. vesiculosus was recently proved to be a separate species, when genetic tools were used. This new species, Fucus radicans (narrow wrack) might be the first endemic species to the Baltic Sea, having separated from its mother species F. vesiculosus as recent as 400 years ago. Fucus radicans is only found in the Bothnian Sea and around the Estonian island Saaremaa. The Swedish/Finnish populations have a surprisingly high level of clonality. As much as up to 80% of the individuals on the Swedish side are clones, dominated by one female clone that has been found over a range of 550 km. In spite of this ability to asexual propagation, we do not find F. radicans further south than Öregrund in Sweden, and even further north in Finland. I attempt to find out why.

  • 7.
    Schagerström, Ellen
    Stockholm University, Faculty of Science, Department of Ecology, Environment and Plant Sciences.
    On the endemic Fucus radicans in the Baltic Sea2015Doctoral thesis, comprehensive summary (Other academic)
    Abstract [en]

    The brown macroalgae Fucus radicans is endemic to the Baltic Sea, but little is known about this newly described species. This thesis investigates the ecology and role of F. radicans within the species poor Baltic Sea ecosystem. The thallus of F. radicans had a more complex structure but was smaller than F. vesiculosus, the other important foundation species with which it grows in sympatry at several sites. The variability of the associated flora and fauna communities of these two Fucus species, however, was explained by the thallus size, not the complexity. Comparisons between the populations of F. radicans in the Bothnian Sea with those in Väinameri Sea on the Estonian coast, showed that the Estonian thalli were smaller, less complex and lacking the numerous adventitious branches which occur extensively in the Bothnian Sea populations.

    The distribution of F. radicans in Sweden is limited to the Bothnian Sea coast. The low salinity at the northern limit prevented successful fertilization, while increased salinity did not restrict F. radicans but improved its reproductive success. The southern distribution limit was instead shown to be negatively impacted by a combination of grazing and competition. The asexual reproduction through settling of detached fragments was favoured by high light levels and high temperature in laboratory conditions. Re-attachment occurred by basally formed rhizoids but settling also occurred through a calcium-rich substance, seemingly secreted by the fragment. Genetic spatial distribution of F. radicans showed a dominance of a few widespread clones both within and between sites with an intermingled rather than clustered pattern. The extensive female clone, common in most sites, is most likely old and several clonal lineages have derived from her.  Although more clearly expressed in the clonal populations, the macroscopic sexual dimorphism discovered appears to be a species specific trait in F. radicans. This thesis presents further insight in F. radicans role within the Baltic Sea ecosystem and its value as a study species for adaptation, clonality and speciation.

  • 8.
    Schagerström, Ellen
    et al.
    Stockholm University, Faculty of Science, Department of Ecology, Environment and Plant Sciences.
    Forslund, Helena
    Stockholm University, Faculty of Science, Department of Ecology, Environment and Plant Sciences.
    Kautsky, Lena
    Stockholm University, Faculty of Science, Department of Ecology, Environment and Plant Sciences.
    Paernoja, Merli
    Kotta, Jonne
    Does thalli complexity and biomass affect the associated flora and fauna of two co-occurring Fucus species in the Baltic Sea?2014In: Estuarine, Coastal and Shelf Science, ISSN 0272-7714, E-ISSN 1096-0015, Vol. 149, p. 187-193Article in journal (Refereed)
    Abstract [en]

    On rocky shores, fucoids provide habitat, shelter and food for associated biota. In the northern parts of the Baltic, the Bothnian Sea, the new fucoid species Fucus radicans (Bergstrom et Kautsky) was recently described. This study compares the thallus complexity and size as well as quantified the abundance and biomass of epiphytic algae and invertebrate taxa of the two fucoid species F. radicans and Fucus vesiculosus L. from sympatric sites in the Bothnian Sea on the Swedish coast and around the Estonian island Saaremaa. We found that F. radicans was more complex than F. vesiculosus within the whole study range, but both species had a more complex thallus structure in the Bothnian Sea compared to Estonia. The complexity of host algae did not contribute to their associated flora and fauna taxon richness; instead, the size of thalli was a good proxy for associated communities. Specifically, on a biomass basis, F. vesiculosus displayed highest species richness and highest faunal abundance in the Bothnian Sea, whereas no such differences were found around Saaremaa, probably because both Focus species had similar height around Saaremaa whereas F. vesiculosus grew much taller and larger in the Bothnian Sea. There were some unique associated macroalgal and invertebrate species that were found only on either of the fucoids, indicating the importance of separating them as species in surveys and monitoring.

  • 9.
    Schagerström, Ellen
    et al.
    Stockholm University, Faculty of Science, Department of Ecology, Environment and Plant Sciences.
    Kautsky, Lena
    Stockholm University, Faculty of Science, Department of Ecology, Environment and Plant Sciences.
    Despite marine traits, the endemic Fucus radicans (Phaeophyceae) is restricted to the brackish Baltic Sea2016In: European journal of phycology, ISSN 0967-0262, E-ISSN 1469-4433, Vol. 51, no 4, p. 378-386Article in journal (Refereed)
    Abstract [en]

    Many of the marine species that were introduced to the Baltic Sea during the Littorina stage (c. 8500-3000 years BP), e.g. Fucus vesiculosus and F. serratus, have adapted to the present low salinity. These marine species have gone from marine conditions into lower salinity environments. In this paper we ask why the recently discovered endemic brown alga Fucus radicans shows the opposite pattern. Fucus radicans is only present in the northern parts of the Baltic Sea, the low salinity Bothnian Sea (4-6 psu). Potentially, the fitness of F. radicans might be reduced in higher salinities if it is better adapted to brackish conditions. We hypothesize, however, that the southern distribution limit of F. radicans is set by biotic factors, e.g. competition with F. vesiculosus and higher grazing pressure by Idotea balthica and not by salinity. Our results show that the reproductive output of F. radicans is limited by low salinity (4 psu) but increases in higher salinities. However, the southern distribution limit, i.e. the northern Baltic Proper, is regulated by biotic factors, where the additive effects from shading by taller F. vesiculosus thalli and grazing on F. radicans by the isopod I. balthica limit the biomass production of F. radicans. We suggest that F. radicans still maintains marine traits due to its ability to propagate clonally and is restricted to the Bothnian Sea by interactions with F. vesiculosus and I. balthica. We also propose that increased precipitation due to climate change might affect the northern range limit and that the distribution of F. radicans could be expected to shift further south into the Baltic Proper.

  • 10.
    Schagerström, Ellen
    et al.
    Stockholm University, Faculty of Science, Department of Ecology, Environment and Plant Sciences.
    Kautsky, Lena
    Stockholm University, Faculty of Science, Department of Ecology, Environment and Plant Sciences.
    Macroscopic sexual dimorphism in Fucus radicans (Phaeophyceae) with implications for its reproductive ecology2016In: Botanica Marina, ISSN 0006-8055, E-ISSN 1437-4323, Vol. 59, no 6, p. 485-490Article in journal (Refereed)
    Abstract [en]

    Sexual dimorphism on a macroscopic scale is unusual within the Phaeophyceae. We report for the first time macroscopic sexual dimorphism in Fucus radicans. A set of morphological characters was measured on three dioecious Fucus species, F. radicans, Fucus serratus and Fucus vesiculosus, to determine if sexual dimorphism occurs in the endemic F. radicans in the Baltic Sea and if it also is found in the other fucoids. F. radicans was sampled from highly clonal populations of the Bothnian Sea and from populations in the Vainameri Sea where no clones have been found. In both locations, sexual dimorphism was recorded in receptacle size and weight in F. radicans. Also, the receptacle dry weight to wet weight ratio was higher in males than in females, showing that male receptacles have a lower water content than females. The dimorphism was more pronounced in the Bothnian Sea populations, where further differences between the sexes in thallus width and fertility index also were present. This has not been shown for any member of the genus Fucus before, but seems to be a species-specific character in F. radicans, as there were no differences between the sexes in either F. serratus or F. vesiculosus.

  • 11.
    Schagerström, Ellen
    et al.
    Stockholm University, Faculty of Science, Department of Ecology, Environment and Plant Sciences.
    Salo, Tiina
    Stockholm University, Faculty of Science, Department of Ecology, Environment and Plant Sciences. Roskilde University, Denmark.
    Interactive effects of temperature and light on reattachment success in the brown alga Fucus radicans2019In: Botanica Marina, ISSN 0006-8055, E-ISSN 1437-4323, Vol. 62, no 1, p. 43-50Article in journal (Refereed)
    Abstract [en]

    Fucus radicans is an endemic habitat-forming brown macroalga in the Baltic Sea that commonly complements its sexual reproduction with asexual reproduction. Asexual reproduction in F. radicans takes place through formation of adventitious branches (hereafter fragments), but the exact mechanisms behind it remain unknown.

    We assessed experimentally the importance of two environmental factors determining the re-attachment success of F. radicans fragments. By combining different light conditions (daylength and irradiance; high or low light) and water temperature (+14°C and +4°C), we mimicked ambient light and temperature conditions of winter, spring/autumn and summer for F. radicans. Fragments were able to re-attach in all tested conditions. Temperature and light had an interactive impact on re-attachment: the combination of high temperature and high light level resulted in the highest re-attachment success, while light level had no effects on re-attachment success in cooler water temperature and the re-attachment success in high temperature under low light levels was very low.

    The results suggest that rhizoid formation, and thus re-attachment success, may depend on the net primary production (metabolic balance) of the fragment. However, whether the re-attachment and asexual reproduction success simply depends on photosynthetic capacity warrants further mechanistic studies. Understanding the mechanisms of asexual reproduction in F. radicans is important in order to assess the dispersal capacity of this foundation species.

  • 12.
    Schagerström, Ellen
    et al.
    Stockholm University, Faculty of Science, Department of Ecology, Environment and Plant Sciences.
    Salo, Tiina
    Temperature and light affect asexual reproduction in brown algae Fucus radicansManuscript (preprint) (Other academic)
    Abstract [en]

    Fucus radicans is a habitat forming brown macroalgae that utilizes asexual reproduction to complement its sexual reproduction. While asexual reproduction by adventitious branches (hereafter fragments) is common in F. radicans, the mechanisms behind it remain unknown. We conducted an experiment to study if water temperature and light intensity together with day length affect the re-attachment success of F. radicans fragments by using the light and temperature average conditions of the four seasons. Fragments were able to re-attach in all tested conditions. The fragments attached mostly by rhizoids but an alternative form of attachment was also observed, where an opaque substance cemented the fragment to the substrate. Temperature and light had an interactive impact on re-attachment, and re-attachment was highest under conditions of combined high temperature and high light. Although re-attachment was observed in all different temperature and light treatments, our results suggest that re-attachment success is favoured during warm temperatures and light conditions, i.e. the summer period. Understanding the mechanisms of asexual reproduction in F. radicans is important in order to assess the future dispersal patterns of this endemic foundation species.

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