<p>Small islands in Indonesia are increasingly confronted with acute spatial saturation and ecological stress. This article examines how residents of Barrang Lompo Island—a densely populated coral island in the Spermonde Archipelago—respond to extreme land scarcity through informal, household-led expansion into the sea. Drawing on maritime ethnography, the study analyzes how everyday adaptation practices reshape spatial configurations, governance arrangements, and social–ecological resilience under conditions of severe spatial compression. As terrestrial land becomes fully occupied, families construct stilt houses and seawalls over shallow reef flats, transforming the littoral zone into a hybrid space of habitation and defense. These practices constitute a form of everyday maritime urbanism through which households secure proximity to kin and sustain social life. At the same time, the analysis reveals a resilience paradox: while seaward expansion enhances short-term household survival, it simultaneously fragments collective governance, privatizes common marine space, and accelerates coastal ecological degradation, thereby undermining long-term social–ecological resilience. By integrating perspectives from maritime urbanism, political ecology of adaptation, and social–ecological resilience, this study conceptualizes Barrang Lompo as an emergent case of urbanization at sea. The findings underscore the need for forms of community-based spatial governance that reconnect informal local adaptations with ecological integrity and institutional support, highlighting how maritime urbanism both constrains and enables adaptation in small-island contexts in Southeast Asia.</p>