The Blue Economy concept is being embraced enthusiastically in Africa, both internally and externally. However, this new framing creates and calls for new understandings of how actors and places relate to one another, control, and create meaning and value. Thus, understanding the ocean - and its conceptual and material fabric - in this context, is a matter of political ecology, raising a number of questions that extend across geographies, spatio-temporalities, and political actors, both human and more-than-human. In this article, we flesh out these questions. An understanding of historical efforts to legally secure oceanic space can help contextualize the emergent African blue economy, one which we propose rests predominantly on the notion of 'security.' We demonstrate how resources are economically, environmentally, and politically 'secured' as they are first constructed as economic objects of accumulation, then militarized as matters of geopolitical security, and finally controlled through technologies of monitoring, surveillance, and resistance. The 'security' of the blue growth agenda and its effects operates across different temporal and spatial dimensions and are realized in different ways across the continent as explored in the six articles in this Special Section.