Planned seedling production in the distribution area of Saccharina japonica: Sorus formation through the induction of sporophyte maturation and the culture of the seedlings produced

Inconsistency in maturation of saccharinan kelp due to changes in the marine environment is a problem in terms of securing seedlings for aquaculture. In Hokkaido, the main producing area of Saccharina japonica, it has become a challenge to stably secure the parental algae of the species for aquaculture. When maturation was induced by short‐day conditions in naturally collected S. japonica sporophytes as well as in the sporophytes collected from them and cultivated, sorus formation began in approximately 3 weeks and spread to 0.4%–16.8% on the upper side area and 23.2%–41.1% on the underside area after about 5 weeks, with the highest rates, 23.2%–59.5%, observed around the base part of the underside. Sorus formation began from the base and middle parts in the top‐intact thalli and from the marginal part in the top‐cut thalli. The released zoospore germlings grew steadily as aquaculture seedlings, and the blade width and wet weight of the seedlings collected in August and subjected to mariculture in November were significantly larger after approximately five and a half months compared to those of thalli cultivated using a conventional method (i.e. thalli collected just prior to the mariculture). Seedling production through maturation induction in sporophytes would be a feasible option for seedling production facilities and would be helpful for stably producing seedlings without the effect of the natural environment.