Significance of macroalgal polymorphism: intraspecific tests of the functional-form model

Abstract

The functional-form model, developed for comparisons among species in a diverse macroalgal community, was used to examine the functional significance of macroalgal polymorphism (i.e., the existence of genetically distinct morphotypes within a single species). Four predictions of this model were examined along a continuum of morphotypes represented by eight clones of the red alga Gracilaria tikvahiae McLachlan. These clones had significant differences in calorific contnet, percentage of photosynthetic tissue, net photosynthesis, and specific growth rate. All of these functional attributes were a function of the surface area:volume ratios. Consistent with the predictions of the functional-form model, clones near opposite ends of the surface area:volume continuum had significant differences for these attributes. A cluster analysis of these attributes identified three clusters of clones that agreed well with their surface:volume ratios. Polymorphism in G. tikvahiae increases the ecological and physiological fitness of this species in an estuarine system where spatial and temporal changes in the environment occur. Each morphotype possesses concomitant, ecologically meaningful combinations of benefits and costs which collectively spread the risk from different sources of mortality and thus increase the overall survival of the population.