This study proposes a novel solution for addressing coastal erosion and ecosystem degradation worldwide. By attaching a specially designed prosthesis to the curved surface of tetrapods, common marine structures in Korea, we aim to restore vital seaweed forest ecosystems within coastal areas. Leveraging 3D scanning, printing technologies, and robotic arms, we develop a customized attachment to seamlessly integrate with tetrapods, overcoming construction area limitations. Our approach utilizes Fused Granular Fabrication, employing biodegradable plastic made from recycled seaweed waste, promoting sustainable material use and disposal in marine environments. Method of attaching to the surface of the tetrapod was divided into three methods: Foldable 3D printing, On-surface 3D printing, and Barnacle 3D printing, which improves the two preceding methods. This innovative solution offers promise for sustainable coastal management and ecosystem restoration.