Phenotypic variation in sexually and asexually recruited individuals of the Baltic Sea endemic macroalga Fucus radicans: in the field and after growth in a common-garden

Of the nine phenotypic traits, recovery after freezing, recovery after desiccation, and phlorotannin content showed substantial inherited variation, that is, phenotypic variation in these traits were to a large extend genetically determined. In contrast, variation in six other phenotypic traits (growth rate, palatability to isopod grazers, thallus width, distance between dichotomies, water content after desiccation and photochemical yield under ambient conditions) did not show significant signals of genetic variation at the power of analyses used in the study. Averaged over all nine traits, phenotypic variation within monoclonal groups was only 68% of the variation within the group of different MLGs showing that genotype diversity does affect the overall level of phenotypic variation in this species.Our result indicates that, in general, phenotypic diversity in populations of Fucus radicans increases with increased multilocus genotype (MLG) diversity, but effects are specific for individual traits. In the light of Fucus radicans being a foundation species of the northern Baltic Sea, we propose that increased MLG diversity (leading to increased trait variation) will promote ecosystem function and resilience in areas where F. radicans is common, but this suggestion needs experimental support.In most ecosystems, increased species richness tends to support ecosystem function [1-3], but in ecosystems dominated by one or a few foundation species - such as seagrass meadows, seaweed belts, and stands of forest trees - species diversity may be less important while instead phenotypic diversity within the foundation species is likely to affect properties of the ecosystem as a whole, such as function and resilience [4]. For example, a population of a habitat-forming species in which the individuals are phenotypically different will create a more complex habitat than one in which phenotypes are all alike, and most likely the more complex habitat will attract more associated spec