Along the African coast are a diversity of peoples, many of whom hold a unique cultural relationship with the sea. In the last few decades, Environmental and Social Impact Assessments (ESIA), a legal requirement in many African countries, are, in some instances, now including Cultural Heritage Impact Assessments (CHIA). In the following a discussion on the value of CHIA to ESIA is offered, as well as a discussion on human cultural relations with the sea and deep ocean in Africa. The discussion is anchored in social science theories of posthumanism (Braidotti, 2016) and pluriversal knowledges (Escobar, 2018), theoretical strands which posit that anthropocentric (human-centred) perspectives prioritise humanistic frames of world and obscure the agency of nature and inanimate things. Considering transmaterial and pluriversal knowledges, humans may be able to perceive and treat the ocean not as an asset but as a living entity that has intersubjective communication with human kind. To contextualise the discussion, two case studies are offered, one of spiritual veneration and the place of the seabed as the final resting place of ancestors in South Africa and a second case study of severed cultural relations with the sea as a spiritual entity in the aftermath of colonial rule in Namibia. The chapter begins with a brief overview of the history and anthropology of the two geographical sites and continues with a presentation of the case studies. Finally, the chapter reviews the place of ESIA and CHIA in proposed offshore development in these two countries.