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Despite marine traits, the endemic Fucus radicans (Phaeophyceae) is restricted to the brackish Baltic Sea
Stockholm University, Faculty of Science, Department of Ecology, Environment and Plant Sciences.
Stockholm University, Faculty of Science, Department of Ecology, Environment and Plant Sciences.
Number of Authors: 2
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.

Place, publisher, year, edition, pages
2016. Vol. 51, no 4, 378-386 p.
Keyword [en]
competition, distribution range, egg production, fertilization, grazing, Idotea balthica, reproductive success, salinity, shading
National Category
Biological Sciences
Research subject
Plant Ecology
Identifiers
URN: urn:nbn:se:su:diva-136955DOI: 10.1080/09670262.2016.1183234ISI: 000387617100002OAI: oai:DiVA.org:su-136955DiVA: diva2:1059346
Available from: 2016-12-22 Created: 2016-12-19 Last updated: 2017-01-10Bibliographically approved
In thesis
1. On the endemic Fucus radicans in the Baltic Sea
Open this publication in new window or tab >>On the endemic Fucus radicans in the Baltic Sea
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
seaweed, sexual reproduction, clonality, fragmentation, dimorphism, salinity, distribution
National Category
Natural Sciences
Research subject
Plant Ecology
Identifiers
urn:nbn:se:su:diva-117584 (URN)978-91-7649-196-6 (ISBN)
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: 2017-01-10Bibliographically approved

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