Engineering Perspectives on Kelp (Saccharina japonica) Cultivation Structures in China: Nearshore Practices and Transition to Offshore Environments

Abstract

China produces approximately 91.5% of the world’s Saccharina japonica (the species denoted by “kelp” herein) and its kelp farms collectively constitute one of the largest populations of floating marine structures anywhere. This review examines them as marine structures rather than as crops, asking what their geometry, load paths and standardization status imply for mechanization and for survival offshore. Nearshore cultivation rests on a single structural family, the floating single line, whose three variants, namely, horizontal, vertical and one-dragon kelp rope raft culture, differ in how the grow-out rope attaches to the backbone rather than in load path or design basis. Of these, the one-dragon configuration is the most promising for offshore adaptation, though on qualitative rather than measured grounds. The principal barrier to mechanized harvesting lies not in harvesting machinery but in a rope geometry dimensioned for manual operation and lacking standardized parameters. Integrated multi-trophic aquaculture, treated here as a structural modification of the kelp longline rather than as an ecological strategy, substantially increases suspended loading without any reported reinforcement of backbone, mooring or buoyancy. Recent offshore projects in Fujian and Shandong prove to be seaward extensions of nearshore rafts rather than purpose-designed systems, in contrast to international programmes which, although pre-commercial, begin from a stated design environment and return verifiable outcomes. We conclude that the defining obstacle to both mechanization and offshore expansion is the cultivation structure itself, and identify mechanization-compatible, load-verified structural standards as the critical and currently unaddressed research priority.