Phenology of two Acanthophora najadiformis (Rhodophyta, Ceramiales) populations in the Ionian Sea (Mediterranean Sea)

Both an intertidal and a subtidal population of Acanthophora najadiformis near the Cheradi Islands (Ionian Sea, Mediterranean Sea) were studied in order to know the life cycle of the species and both seasonal variation in plant size and the phenology of reproduction. The proportions of gametophytes, tetrasporophytes and propagule-bearing plants were analysed. Acanthophora najadiformis proved to be a perennial alga present only with the overwintering basal system in winter and spring and well developed fronds in summer and autumn, when it is the dominant species in the subtidal community. Differences in both plant size and reproductive plant number were detected between the intertidal and subtidal levels. In the intertidal zone plants grow faster and reach greater sizes than the subtidal ones; tetrasporophytes and propagule-bearing plants are more numerous than at the subtidal level. In both zones, tetrasporophytes seem to be dominant and propagule-bearing plants are by far the most numerous.