Marine Sciences are of relevance to many societal challenges, as well as able to capture public imagination and interest. Despite that potential, we are not the leaders we could be at making all our research output publicly accessible, to allow citizen science to take place and facilitate public awareness efforts. Open Science principles not only feed the need for impact in a "publish or perish" reality, it also fully complements Ocean Literacy and the need to educate and engage the public in marine policy formulation based on sound science. So, can we afford NOT to make Marine Science open by default? Invited Presentation at the CIESM 40th Congress, Marseille 29th Oct 2013