The article expands upon care theory in Science and Technology Studies by attending to marine spaces and practices for conservation of marine and coastal ecosystems. Examining the case of efforts to protect the Mediterranean-endemic seagrass Posidonia oceanica, which the European Union declared a priority habitat in 1992, the article evaluates the concrete impact of a 2018 decree from the Government of the Balearic Islands intended to protect the species in the Balearic Sea. In contrast to the strictly established boundaries that predominate in area-based approaches for marine governance, I analyze two care configurations around Posidonia which allow us to rethink the territorialization of marine space: care “blocks” characterize occasions in which the species-specific emphasis keeps attention away from other systems or species, while care “overflows” denote care spilling over to other systems and species. By thinking these concepts in relation to area-based and species-centered approaches to marine conservation, the article contributes to develop care scholarship, enriching its conceptual repertoire and providing tools to better understand the effects of species-centric environmental policies.