The interspecific biomass-density relationship for terrestrial plants: where do clonal red seaweeds stand and why?

For crowded stands of terrestrial plants, ranging from mosses to trees, pla nt (or ramet, for clonal plants) density is negatively related to stand bio mass. Stand biomass and ramet density were determined for Mazzaella cornuco piae and for Pterocladiella capillacea, two morphologically distinct intert idal clonal red seaweeds, to compare them with terrestrial plants. For thes e seaweeds, ramet densities were similar to the highest values reported for terrestrial plants (mosses, specifically). Stand biomass was higher than a verage values expected from the terrestrial interspecific biomass-density r elationship, but lower than the limits expected from the terrestrial ultima te biomass-density line. These seaweeds show unexpectedly low ramet slender ness and high biomass packing per unit of volume, compared with the trend o bserved for terrestrial plants. Possible explanations for these differences are related to the particular physiology and habitat of intertidal clonal seaweeds.