Predictions of kelp distribution shifts along the northern coast of Japan

Japanese kelps are important because they perform a valuable ecosystem function of coastal kelp forest formation, and they are important food resources. The present study aimed to predict future shifts in major kelp species in northern Japan under different climate change scenarios. From a database of cold temperate kelp species in Japan, we extracted 1,958 data points to estimate the distribution of 11 kelp species that inhabit the waters around northern Japan. Distributions of the past (1980s) and the future (2040s and 2090s) were estimated using a species distribution model (MaxEnt). Variation in summer and winter sea surface temperatures was the factor most responsible for the estimated distribution patterns for most species; the length of natural rocky coasts and wave height were also important for some species. A forecast of shifts in distributions based on different Intergovernmental Panel on Climate Change scenarios showed that kelp species diversity in Japan would significantly decrease. By the 2090s, their habitat range overall was estimated to decline to 30-51% of that of the 1980s with moderate warming (Representative concentration pathways [RCP] 4.5) and to 0-25% with severe warming (RCP 8.5). The model predicted that 6 of 11 cold temperate kelp species may become extinct around Japan by the 2090s (RCP 8.5). Commercially important species, such as Saccharina japonica, are also expected to decline greatly, which may affect kelp fisheries and aquaculture in northern Japan.