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On the endemic Fucus radicans in the Baltic Sea
Stockholm University, Faculty of Science, Department of Ecology, Environment and Plant Sciences.
2015 (English)Doctoral 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.

Place, publisher, year, edition, pages
Stockholm: Department of Ecology, Environment and Plant Sciences, Stockholm University , 2015. , 66 p.
Keyword [en]
seaweed, sexual reproduction, clonality, fragmentation, dimorphism, salinity, distribution
National Category
Biological Sciences
Research subject
Plant Ecology
Identifiers
URN: urn:nbn:se:su:diva-117584ISBN: 978-91-7649-196-6 (print)OAI: oai:DiVA.org:su-117584DiVA: diva2:813951
Public defence
2015-09-18, Nordenskiöldsalen, Geovetenskapens hus, Svante Arrhenius väg 12, Stockholm, 09:30 (English)
Opponent
Supervisors
Funder
Swedish Research Council Formas
Note

At the time of the doctoral defense, the following papers were unpublished and had a status as follows: Paper 2: Manuscript. Paper 3: Manuscript. Paper 4: Manuscript. Paper 5: Manuscript.

Available from: 2015-06-11 Created: 2015-05-25 Last updated: 2017-11-24Bibliographically approved
List of papers
1. Does thalli complexity and biomass affect the associated flora and fauna of two co-occurring Fucus species in the Baltic Sea?
Open this publication in new window or tab >>Does thalli complexity and biomass affect the associated flora and fauna of two co-occurring Fucus species in the Baltic Sea?
Show others...
2014 (English)In: Estuarine, Coastal and Shelf Science, ISSN 0272-7714, E-ISSN 1096-0015, Vol. 149, 187-193 p.Article in journal (Refereed) Published
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.

Keyword
Baltic Sea, foundation species, macroalgae, benthic invertebrates
National Category
Earth and Related Environmental Sciences Biological Sciences
Research subject
Plant Ecology
Identifiers
urn:nbn:se:su:diva-113140 (URN)10.1016/j.ecss.2014.08.022 (DOI)000346220800019 ()
Note

AuthorCount:5;

Available from: 2015-02-27 Created: 2015-01-23 Last updated: 2017-12-04Bibliographically approved
2. Despite marine traits, the endemic Fucus radicans (Phaeophyceae) is restricted to the brackish Baltic Sea
Open this publication in new window or tab >>Despite marine traits, the endemic Fucus radicans (Phaeophyceae) is restricted to the brackish Baltic Sea
2016 (English)In: European journal of phycology, ISSN 0967-0262, E-ISSN 1469-4433, Vol. 51, no 4, 378-386 p.Article in journal (Refereed) Published
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.

Keyword
competition, distribution range, egg production, fertilization, grazing, Idotea balthica, reproductive success, salinity, shading
National Category
Biological Sciences
Research subject
Plant Ecology
Identifiers
urn:nbn:se:su:diva-136955 (URN)10.1080/09670262.2016.1183234 (DOI)000387617100002 ()
Available from: 2016-12-22 Created: 2016-12-19 Last updated: 2017-11-29Bibliographically approved
3. Temperature and light affect asexual reproduction in brown algae Fucus radicans
Open this publication in new window or tab >>Temperature and light affect asexual reproduction in brown algae Fucus radicans
(English)Manuscript (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.

Keyword
Baltic Sea, clonal, fragmentation, fucoid, re-attachment, rhizoid
National Category
Biological Sciences
Research subject
Plant Ecology
Identifiers
urn:nbn:se:su:diva-117582 (URN)
Available from: 2015-05-25 Created: 2015-05-25 Last updated: 2016-01-29Bibliographically approved
4. Complex spatial clonal structure in the macroalgae Fucus radicans with both sexual and asexual recruitment
Open this publication in new window or tab >>Complex spatial clonal structure in the macroalgae Fucus radicans with both sexual and asexual recruitment
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2015 (English)In: Ecology and Evolution, ISSN 2045-7758, E-ISSN 2045-7758, Vol. 5, no 19, 4233-4245 p.Article in journal (Refereed) Published
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.

Keyword
asexual reproduction, clonality, macroalgae, microsatellites, somatic mutations
National Category
Biological Sciences
Research subject
Plant Ecology
Identifiers
urn:nbn:se:su:diva-122750 (URN)10.1002/ece3.1629 (DOI)000362523300002 ()
Available from: 2015-11-16 Created: 2015-11-10 Last updated: 2017-12-01Bibliographically approved
5. Macroscopic sexual dimorphism in Fucus radicans (Phaeophyceae) with implications for its reproductive ecology
Open this publication in new window or tab >>Macroscopic sexual dimorphism in Fucus radicans (Phaeophyceae) with implications for its reproductive ecology
2016 (English)In: Botanica Marina, ISSN 0006-8055, E-ISSN 1437-4323, Vol. 59, no 6, 485-490 p.Article in journal (Refereed) Published
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.

Keyword
clonality, fertility index, morphology, receptacles, reproductive allocation
National Category
Biological Sciences
Research subject
Plant Ecology
Identifiers
urn:nbn:se:su:diva-137611 (URN)10.1515/bot-2016-0046 (DOI)000388584400009 ()
Available from: 2017-01-10 Created: 2017-01-09 Last updated: 2017-11-29Bibliographically approved

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