Interdisciplinary marine research is pivotal for addressing ocean sustainability challenges. While interdisciplinary research brings together a diversity of disciplines, we ask: 'does it bring together individuals and groups from diverse socio-economic, cultural, or identity backgrounds or does it favour only certain groups?' This paper draws on the perspectives, experiences, and knowledge of interdisciplinary marine Early Career Researchers, stemming from a Diversity, Equity, and Inclusion (DEI) workshop hosted by the Interdisciplinary Marine Early Career Network (IMECaN). We discuss and synthesise these perspectives into three key messages: (1) Diversity is essential for developing high-quality interdisciplinary marine science, (2) Interdisciplinarity can provide additional challenges and complexity for minoritised groups, and (3) Interdisciplinary marine science may exclude minoritised groups and be associated with discrimination, prejudice, and elitism. We conclude by providing ten recommendations for fostering DEI in interdisciplinary marine science. As the health of our ocean and coastal ecosystems is increasingly under threat, fostering DEI within this scientific domain is not merely an aspirational goal but an ethical imperative.