Modeling the growth of the cultivated seaweed Undaria pinnatifida under climate change scenarios in the Seto Inland Sea, Japan

To assess the potential effects of future climate change on Undaria pinnatifida cultivation in the Seto Inland Sea, Japan, we developed an individual-based growth model for the U. pinnatifida sporophyte. Initially, we validated the model’s performance using field observation data. The simulation results replicated temporal variations in the total lengths of sporophytes at two stations with differing oceanographic conditions. Subsequently, we conducted numerical simulations of sporophyte growth in the Seto Inland Sea during the 1990s and projected outcomes for the 2090s under four emission scenarios of the Representative Concentration Pathway (RCP 2.6, 4.5, 6.0, and 8.5). The majority of areas exhibited decreased sporophyte growth in the 2090s compared to the 1990s, except for the eastern area under the RCP 2.6 scenario. This decline was attributed to delayed cultivation start times associated with ocean warming and reduced dissolved inorganic nitrogen concentrations. Interestingly, the impacts of ocean warming on U. pinnatifida cultivation were not uniformly negative. In addition to adverse effects, there were positive effects that accelerated growth rates in low-temperature winter areas. Sensitivity analyses revealed that the balance between positive and negative impacts varied geographically; moreover, the contrasts were enhanced with higher RCP scenarios. Simulations for climate change adaptation using a high-temperature tolerant cultivar indicated that yield losses could be mitigated, even under the RCP 8.5 scenario. Despite uncertainties in the simulation results, such as future management of nutrient loads and herbivore feeding damages, our projections underscore the potential sustainability and future viability of U. pinnatifida aquaculture in the Seto Inland Sea.