THE RED ALGAL EPIPHYTESMICROCLADIA COULTERIANDM. CALIFORNICA(RHODOPHYCEAE, CERAMIACEAE). II. BASIPHYTE SPECIFICITY1

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Abstract
The phenomenon of basiphyte specificity in the settlement and growth of the red algal epiphytesMicrocladia californicaFarl. andM. coulteriHarv. was examined by studying the interface with their respective basiphytes and by cross‐inoculation experiments.Microcladia californicaattaches only to the surface of its single basiphyteEgregia menziesii(Aresch.) Turn. whereasM. coulteripenetrates the tissue of a wide range of basiphytes. The pattern of primary rhizoid development in both epiphytes determines the mode of attachment and may influence the range of basiphytes possible for each epiphyte. Cross‐inoculation experiments show thatMicrocladia californicais not able to colonize the basiphytes ofM. coulteri, IridaeaandPrionitis, orUlva.The mechanisms by which these algae restrict the growth of epiphytes include short life‐span, “cuticle peeling” and chemical defense.Microcladia coulteri, which naturally colonizesIridaeaandPrionitis, has evolved mechanisms to counteract the antifouling effects of those basiphytes. The question of whyEgregiais the exclusive substratum forM. californicaremains undetermined. However, Egregia may provide the appropriate ecological conditions and a surface topography conductive toM. californicaspore settlement and growth.