Context <p>Terrestrial concepts often guide the science and management of marine systems, as exhibited by the influence of landscape ecology on seascape ecology. However, the theoretical assumptions that inform these concepts have not been sufficiently interrogated within the distinct social-ecological realities of seascapes.</p> Objective <p>We call for a ‘sea system science’ that navigates the human dimensions of seascape change to advance the study and management of ocean spaces.</p> Methods <p>We evaluate two terrestrial concepts (intensification and expansion) that underpin common approaches to marine management. We establish key dimensions of theoretical (mis)alignment across agriculture, forestry, hunting, marine aquaculture, and capture fisheries.</p> Results <p>Seascape uses are substantively different from their landscape counterparts, though there is limited alignment between agriculture and marine aquaculture and between hunting and capture fisheries. We outline opportunities for sea system science to both interrogate terrestrial management concepts and develop an alternative management ontology tailored to seascapes.</p> Conclusions <p>A sea system science that engages with the human dimensions of seascape change and co-evolves with seascape ecology offers a pathway toward management approaches that are grounded in the social-ecological realities of marine spaces. Without closer attention to these dimensions, seascape ecology risks implementing terrestrial management practices that are procedurally feasible but ecologically and socioeconomically ineffective.</p>