Algae-based biotopes of the Azores (Portugal): spatial and seasonal variation

The increasing importance of coastal management created the need for a systematic classification and characterization of marine communities. Accurate quantitative methodologies for rocky shore algae-based biotope definition, were developed and tested on the Islands of Sao Miguel and Santa Maria (Azores). Shores of both islands were surveyed, covering all rocky substrate types. Biotopes were defined by assessing the associated habitat and species characteristics, using ANOSIM and SIMPER analysis, respectively. A total of ten biotopes were identified. Generally both islands' biotopes are characterized by the same taxa/ecological categories, in summer and in winter. However, association between these taxa/ecological categories and the shore height at which they occur differs geographically and temporally. There is a generalized gradual succession of taxa/ecological categories from upper intertidal down to deepest subtidal, although geographical differences occur. Diversity is highest at the land-water interface and decreases towards both extremes (upper intertidal and deepest subtidal level). The strongest evidence of seasonal variation occurs at the upper intertidal. The methodology used proves to be effective in broad scale shoreline assessment of biological communities in warm-temperate coastal marine environments, and thus suitable for the purpose it was developed for. As a consequence it should be applied to the remaining islands of the Azorean archipelago as well as to other macaronesian islands, e.g. Madeira and the Canaries.