The influences of temperature and irradiance on thallus length of Saccharina japonica (Phaeophyta) during the early stages of cultivation

Korean Saccharina japonica is highly valued, both for human consumption and abalone feed. For the stable production of abalone feed, fresh seaweed biomass is required throughout the year. However, currently, the production of farmed Saccharina is limited by environmental conditions such as temperature, irradiance, and nutrient availability between August and November. Due to shortages experienced in supply, the production of early-season biomass can be highly profitable and, therefore, some famers attempt to start their cultivation activities before prevailing, surface seawater temperatures (SST) are optimal. However, attempting to cultivate too early, can lead to total crop failure. Young kelp sporophytes are easily destroyed between 18 and 22 degrees C SST, which can occur during the early nursery period when the materials are confined to tanks. This study investigated the growth of S. japonica thalli and photosynthetic quantum yield (F-v/F-m) under five temperatures (i.e., 18-26 degrees C, at 2 degrees increments) and five irradiances (i.e., 5, 10, 20, 40, and 80mol photons m(-2)s(-1)). This was undertaken for four different size groups of sporophyte thalli (i.e., 0.25, 1, 5, 10mm). There were different responses of the initial groups of S. japonica showing different tolerances to temperature and irradiance. In general, the smaller plants (1mm) were more tolerant of sub-optimal conditions than their larger cohorts. These results indicated the optimum temperature and irradiance ranges for different size groups of S. japonica thalli which, if adopted in management protocols, could contribute to enhanced profitability and a more stable and evenly distributed production of Saccharina raw materials over an entire annual basis.