Structure of macroalgal communities on tropical rocky shores inside and outside a marine protected area

•We studied marine macroalgal communities on six tropical rocky shores.•We examines macroalgal richness and diversity in a marine protected area (MPA) and nearby unprotected coastal areas.•The species richness, Simpson's diversity and evenness were significantly higher inside the MPA than outside the MPA.•Morpho-functional groups of macroalgae species are useful for detecting differences between outside and inside MPAs.•The results indicate that human impacts cause competitive advantage and dominance of articulated calcareous algae.

The structure of marine macroalgal communities and morpho-functional groups were investigated in a poorly characterized region on the Tropical Southwestern Atlantic coast, Brazil. The survey was conducted at six rocky shores located on the mainland and on coastal islands distributed inside a marine protected area (MPA) and outside the MPA (near a densely populated area). We hypothesized that tropical rocky shores inside the MPA and islands have higher species richness, diversity, and evenness of marine macroalgae. Results confirmed that species richness, diversity and evenness were significantly higher inside the MPA than in rocky shores outside the MPA. Only species richness was higher on islands than on the mainland. The results suggest that human impacts could lead to a competitive advantage and dominance in the articulated calcareous morphotype, resulting in community differences and lower benthic biodiversity in tropical ecosystems near urbanized sites.

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