Rapid expansion and successful recruitment of the invasive Mediterranean mussel Mytilus galloprovincialis in the main mussel farming region of Brazil

Abstract The Mediterranean mussel Mytilus galloprovincialis is one of the world’s most successful marine invaders and represents a growing threat to mussel aquaculture. Throughout 2024, we monitored nine mussel farms across Santa Catarina Island Bay, southern Brazil (27°37′10.66″S; 48°33′8.87″W), using commercial spat-collector and grow-out ropes to assess the species’ current distribution and recruitment. M. galloprovincialis recruitment occurred year-round across all monitored sites, exhibiting strong spatial heterogeneity. Recruitment rates in spat collectors revealed that M. galloprovincialis already recruits as successfully as the native mussel Perna perna . Furthermore, despite the site-specific variation during initial recruitment, M. galloprovincialis reached significantly higher overall densities on cultivation ropes. Individuals ranging from recently settled juveniles to adults were found on grow-out ropes across all sites, with extreme density events favoring the invasive species, indicating its successful establishment and persistence throughout Brazil’s principal mussel-producing region. These findings demonstrate that M. galloprovincialis is now widely established in southern Brazil and undergoing sustained recruitment, highlighting the need for continued monitoring and targeted management of this invasive species.