Territorialization and ecologization are deeply entwined processes. But what role do infrastructural actors such as ports play in governing their interconnections, especially following the liberalization of port governance? Focusing on La Rochelle in southwest France, we examined how this port developed a proactive governing strategy mutually conditioning ecological and territorial change. We applied an 'interdependency' approach to analyse port governing practice, understanding that the grasping of interdependency is a major challenge for effective transition governance. This approach drove research to investigate, of all possible interdependencies experienced by port actors, which ones were being selected and promoted by them for governance? We found that territorial interdependencies were being prioritized for governance in line with a narrative of climate, rather than biodiversity, transition. Further, by making connections between policy decisions taken at precise points along a land-sea gradient, actors greatly extended the territorial scope of port public action. But whilst political work over territorial interdependencies opened new spaces for climate governance (politicization), work over public/private interdependencies, essential for the construction of the port as a collective actor, depoliticized otherwise 'efficiency value-laden' policy choices. Consequently, our 'interdependency' approach both revealed the conditions under which a port can influence a complex territorial climate politics, and the extent to which its own internal port governance can influence certain transition choices over others and, potentially, certain territorial futures over others.