Marine issues develop in complex social contexts, usually involving a large number of sectors, actors, and users. Achieving sustainable marine governance requires a continued and context-specific structure of interdisciplinary knowledge, inter-sectorial interaction as well as inter-institutional coordination that generates daunting challenges to government, stakeholders and civil society. In this sense, it is imperative for marine governance structures to pay close attention to social sustainability factors, such as recognition of socio-cultural diversity, representation in decision-making and distribution of ‘goods’ and ‘bads’, which have commonly been overlooked in environmental governance in general and marine governance in particular. Costa Rica’s territorial sea is an important source of income for a myriad of communities on the Pacific and Caribbean coasts. During 2019 and 2020, the Responsible Fishing Marine Area and Marine Management Area of Barra del Colorado were created under the expectation of serving the social and ecological needs of the community. Taking this into consideration, this study aims to examine how social sustainability was handled in the formation process of the two resource management areas, which involved participation of institutional and civil society actors from 2010 until 2019. This study first analyses the concept of marine governance and its relationship to social justice. The concept of social sustainability is explained and I then develop a social sustainability conceptual framework. Secondly, the methodology and methods are described. The choice of the empirical case is described in the next section and I next give a brief overview of Barra del Colorado’s social and economic characteristics and background. Further, an analysis of the process to consolidate the Responsible Fishing Marine Area and the Marine Management Area of Barra del Colorado through the social sustainability framework is conducted. Last, the results of the analysis are discussed and the main findings are presented. Through this analysis, the process of consolidation was assessed against the normative social sustainability theory, concluding that the process was found lacking regarding its social sustainability due to a series of government-related issues, that affected the representation, recognition and distribution of the process.