Low Diversity of Intertidal Canopy-Forming Macroalgae at Urbanized Areas along the North Portuguese Coast

Abstract

Canopy-forming macroalgae are the main component in some of the most diverse and productive coastal habitats around the world. However, canopy-forming macroalgae are very sensitive to anthropogenic disturbances. In coastal urban areas, intertidal organisms are exposed to the interactive effect of several anthropogenic disturbances that can modify the community’s structure and diversity. Along the North-East Atlantic shores, many studies explored the effect of anthropogenic disturbances on canopy-forming macroalgae, but mainly focused on kelps and fucoids. However, along the intertidal rocky shores of the Atlantic coast of the Iberian Peninsula, the most abundant and frequent canopy-forming macroalgae belong to the family Sargassaceae. To explore the effect of urbanization on these intertidal canopy-forming species the diversity and assemblage structure of canopy species were compared between four urban and four non-urban shores in the north of Portugal. Intertidal canopy assemblages on urban shores were dominated by the non-indigenous Sargassum muticum that was the only canopy-forming species on three of the four studied urban shores. Canopy assemblages on all non-urban shores were more diverse. Moreover, stands of canopy-forming species on urban shores were always monospecific, while at non-urban shores multi-specific stands were common. Therefore, results suggest that urbanization reduces canopy´s biodiversity.

Keywords

• sargassaceae
• urbanization: rocky shores
• North Portugal
• Atlantic Ocean