Origin and regeneration of free-living Fucus vesiculosus in the Baltic Sea

Biodiversity represents the variability within and between ecosystems, species and individuals and is critical for ecosystem functioning. The most basic element of biodiversity is genetic diversity. Genetic diversity is important in defining a species adaptive potential, yet is still a largely neglected aspect of biodiversity. Moreover, traditional taxonomically recognized species often conflict with evolutionary or ecologically relevant units, whilst the ecological significance of intraspecific variants are also often overlooked. Within this thesis, I assess the genetic diversity of two variant forms of the perennial, marine, brown alga Fucus vesiculosus (Fucaceae, Phaeophyceae) and their potential ecological differences within the Baltic Sea. Special focus lies on determining the processes forming and maintaining populations of the free-living form are and how this influences their genetic diversity.
This thesis consists of four papers bridging genetics and ecology at varying spatial scales. Papers I & II use molecular techniques to determine the spatial genetic structure over long and short temporal scales. I determine that the Baltic Sea free-living Fucus should continue to be taxonomically classified as F. vesiculosus, yet free-living populations are markedly different from their attached counterparts. In particular, clonality plays a major role in forming and maintaining populations yet is nearly entirely absent from the attached form. This reliance on clonality significantly reduces the genetic diversity of the free-living form, nevertheless the genetic diversity can still be considered relativity high. Papers III & IV examine the potential ecological significance of the free-living form. Paper III describes the heterogeneity of the free-living form’s phenotype in terms of morphological traits. Free-living thalli are polymorphous with phenotypic complexity varying at the population and individual level. Consequently, I conclude that free-living mats of F. vesiculosus form highly complex canopies similar to those of the attached form. Paper IV provides biodiversity estimates for the associated faunal community. The paper confirms the ecological significance of free-living F. vesiculosus as a habitat forming species comparable to the attached form.
The four papers included in this thesis highlight the heterogeneous nature of the free-living form of F. vesiculosus. Thus for Baltic Sea F. vesiculosus, it is imperative that management strategies are tailored throughout the varying scales of biodiversity, including that of the intraspecific variation within and between the two forms.