| Summary: | An appraisal of the benthic marine algal communities of the bay of São Vicente (São Miguel island. Azores) was undertaken in July 1996 and July 1997 as part of the project "Biodiversity of the archipelago of the Azores". A permanent transect was laid down across the subtidal zone. Quadrates were sampled at pre-determined intervals along the transect from the low water level, down to 30m depth. Qualitative collections were made along the transect. The relative importance of each species was determined using a semi-quantitative scale. The transect revealed the occurrence of relatively large and frondose algae establishing the transition between the intertidal and the subtidal zones. Pterocladiella capillacea was the dominant species in this transition zone and extended its presence down to 12m depth. A depth-related change in the algal flora was present in both years. Pteroclardiella, Ulva spp., Stypocaulon scoparia, Hypnea musciformis and Asparagopsis armata dominated the shallow levels; Zonaria tournefortii, together with Sphaeroroccus coronopifolius and Dictyota dichotoma dominated the deep ones.
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