Marine protected areas (MPAs) are promoted as a tool to manage the world's ocean and coastal resources more sustainably. In recent years, the protected areas management paradigm - including MPA management - has started to promote inclusive and collaborative practices. At least on paper, this shift, and the multi-stakeholder engagement and partnerships that came along with it, should have led to better conservation outcomes - at the same time as ensuring that people affected by conservation measures have access to alternative or supplementary livelihood opportunities. In reality, the record of MPAs has been quite mixed. The aim of this study is to examine stakeholder engagement and collaboration in MPA management actions that have occurred in the Mnazi Bay-Ruvuma Estuary Marine Park (MBREMP) in southern Tanzania - in view of exploring whether existing collaborations have influenced conservation outcomes. Fieldwork results, arising from key informant interviews, participant observation, focus group discussions and a survey, show that contacts and interactions between stakeholders followed a bureaucratic process without clear and shared goals that could make conservation and livelihood objectives compatible. Unclear and poorly coordinated processes - both in relation to conservation activities, such as enforcement of the park's regulations, and in relation to livelihood projects - hampered the proper functioning of MBREMP and its actual and potential stakeholders. As a result, both conservation and socio-economic outcomes have been problematic. Future research needs to further investigate how dysfunctional stakeholder engagements and lack of collaborative arrangements affect environmental and socio-economic objectives in MPAs and how these can be addressed.