Does the growth rate of drifting Furcellaria lumbricalis and Coccotylus truncatus depend on their proportion and density?

Abstract

The West Estonian Archipelago Sea hosts a loose-lying red macroalgal community dominated by Furcellaria lumbricalis and Coccotylus truncatus. The community is truly unique in European seas. In factorial field experiments we evaluated separate and interactive effects of algal density and the proportions of F. lumbricalis and C. truncatus on their growth rates in a set of monospecific and mixed communities. Our experiment demonstrated that the growth of red algae was density dependent and that increased algal densities resulted in a fall of daily growth rates. An elevated growth of the red algae was observed at their lower proportions in the community. A potential mechanism behind the observed patterns is the light availability for photosynthesis, i.e. light utilization is more efficient in mixed communities.