Marine ranching is evolving from artificial reef deployment and stock enhancement toward an integrated ocean-use system that combines ecological restoration, sustainable aquaculture, resource conservation, environmental monitoring, and marine public services. However, current marine ranching operations still rely heavily on manual inspection and fragmented monitoring, making it difficult to observe underwater habitats, quantify ecological responses, assess cultured organisms, and support timely operational decisions under turbid, low-light, and dynamic coastal conditions. Unmanned systems provide a promising pathway to bridge this gap by enabling persistent, high-resolution, and adaptive observation of marine ranching environments. This study proposes an unmanned-system-enabled framework for smart marine ranching, integrating underwater robots, unmanned surface vehicles, multi-source sensing, edge computing, and digital twin-based operation services. The framework is designed to support four major functions: underwater infrastructure inspection, ecological and water-quality monitoring, aquaculture organism observation, and intelligent operation scheduling. Underwater robots are used for net cage inspection, artificial reef observation, seabed habitat imaging, and anomaly detection, while unmanned surface vehicles support water-quality mapping, surface patrol, sensor deployment, and phenotype data acquisition. Multi-source data, including optical images, acoustic measurements, water-quality parameters, positioning information, and equipment status, are fused to construct a dynamic representation of the marine ranching system. A key feature of the proposed framework is its transition from single-device deployment to system-level closed-loop operation. Environmental sensing, biological observation, risk warning, and equipment task planning are linked through a digital operation platform, enabling the marine ranch to be monitored and managed as a coupled “environment–organism–facility–operation” system. This approach can improve the visibility of underwater processes, reduce manual inspection costs, support early warning of environmental and structural risks, and provide data services for ecological assessment, aquaculture management, and marine ranching demonstration. The study highlights the potential of unmanned systems as a core digital infrastructure for next-generation marine ranching. By integrating robotics, environmental sensing, artificial intelligence, and digital twin technologies, the proposed framework contributes to more sustainable, observable, and service-oriented marine ranching practices, and provides a technical basis for the development of smart marine ranching in coastal and offshore environments.