Observations on the biology and ecology of selected macroalgae from the littoral of Sao Miguel (Azores)

The dominant benthic algal species from two sites, located on opposite coas ts of the island of Sao Miguel, Azores (Sao Rogue in the south and Sao Vice nte on the north coast) were studied over a two-year period (September 1993 -September 1995). From both sites monthly collections were made in the inte rtidal zone and in the adjacent subtidal zone down to a depth of 15 m. The algae occur under different ecological conditions, a few species being rest ricted to the intertidal zone (Fucus spiralis, Gelidium microdon, Jania cra ssa, Caulacanthus ustulatus and Chondria coerulescens), while others (Codiu m elisabethae, Zonaria tournefortii, Jania verrucosa and Sphaerococcus coro nopifolius) were exclusively present subtidally. Other species were present at both levels. Differences were observed between the two sites. A few spe cies (Chaetomorpha linum, Corallina elongata and Caulacanthus ustulatus) we re more abundant at Sao Rogue, their presence on the north being only spora dic or occasional. On the other hand, Fucus spiralis, Gelidium microdon, Sp haerococcus coronopifolius and Centroceras clavulatum were statistically mo re abundant at Sao Vicente. Seasonal changes were seen in the growth and/or reproduction of certain species, with many (Ulva rigida, Bryopsis hypnoide s, Stypocaulon scoparium, Dictyota dichotoma, Padina pavonica, Colpomenia s inuosa, Gelidium microdon, Asparagopsis armata, Chondracanthus acicularis a nd Plocamium cartilagineum) having larger plants and/or higher values of bi omass in spring and/or summer. With the exception of Dictyota dichotoma tha t was statistically more abundant in the second sampling year, no differenc es were observed on the species abundance between the two years. Reproducti ve phenology varied according to species, with many (Fucus spiralis, Ulva r igida, Gelidium microdon, Jania I rubens, Sphaerococcus coronopifolius, Cau lacanthus ustulatus, and Plocamium cartilagineum) having prolonged fertile periods. Some species were more seasonal in their reproduction, being ferti le only over two seasons: Codium elisabethae and the tetrasporophyte of Asp aragopsis armata in autumn and winter; Cystoseira abies-marina and Pterocla diella capillacea in summer and autumn; the gametophyte of Asparagopsis arm ata in winter and early spring. A few had a more restricted fertile period: Chaetomorpha linum and Jania verrucosa in summer; Chondracanthus aciculari s in autumn.