Dynamics of the biomass–density relationship and frond biomass inequality for Mazzaella cornucopiae (Gigartinaceae, Rhodophyta): implications for the understanding of frond interactions

Abstract

This paper examines the interactions of fronds of the clonal red alga Mazzaella cornucopiae (Postels et Ruprecht) Hommersand. An analysis of the temporal variation of the relationship between stand biomass and frond density showed that the variables are positively correlated on an annual basis for the population studied at British Columbia, Canada. This indicates that fronds (ramets) do not undergo self-thinning even at the highest natural densities. Two of the hypotheses originally proposed to explain the lack of self-thinning among ramets of terrestrial clonal plants seem to apply also to this clonal alga, e.g. physiological integration among ramets and density-dependent formation of ramets. However, the ‘ultimate biomass–density line’ hypothesis does not, because biomass–density combinations for M. cornucopiae are higher than values predicted by this hypothesis for a given density, and these are thought to constrain biomass–density combinations for the entire plant kingdom. During the growth season for M. cornucopiae, frond biomass inequality decreases as fronds grow in biomass. This suggests that the growth rate of fronds is negatively related to frond size. Frond competition most likely results from the vertical gradient of irradiance within the algal stand, but competition among fronds appears to be symmetric, as opposed to asymmetric competition among nonclonal plants. The generality of our findings for clonal red algae is discussed, and comparisons with terrestrial clonal and nonclonal plants are made.