Competitive Algal Community Organization in Exposed Intertidal Habitats from Central Chile

Measurements of cover in the field indicate that most of the lower intertidal waveexposed habitats of Central Chile are dominated by the colonial, non-calcareous, crustose chlorophyte Codjum d~rnorphum. Summer bleaching of the C. dimorphurn colonies results in reduction of cover below the 1.5 m intertidal level and disappearance from levels above the 1.5 m mark. This, in turn, results in seasonal distributional changes in mid and upper intertidal species. Field removal experiments indicate that C. dirnorphum is able to overgrow, exclude and therefore limit the lowermost extent of most other intertidal species. Recovery of C. dimorphum and the course of successional events thereafter (followed during 41 months) are affected by seasonal bleaching and grazing. Herbivore exclusion experiments indicate that grazing plays a major role i n the seasonal reduction of cover of C. dimorphum after initial summer bleaching of the colony. These results are discussed in view of presently accepted hypotheses on intertidal algal zonation, intertidal community structure, successional events and ecological adaptation of non-calcareous crustose algal morphologies.