Chronological change and the potential of recovery on the photosynthetic efficiency of Pyropia yezoensis f. narawaensis (Bangiales) during the sporelings frozen storage treatment in the Japanese Nori cultivation

The chronological change of photosynthetic efficiency in a frozen storage treatment of the Japanese Nori cultivation industry was examined in the cultivated red alga, Pyropia yezoensis f. narawaensis (Saga-#5 Strain, Bangiales) by using pulse-amplitude fluorometry. During the desiccation process that was conducted after the nursery cultivation season in November, the maximum quantum yield (F-v/F-m) of the gametophytic sporelings growing on the Nori-net decreased monotonically with decreasing absolute water content (AWC), and was around 0.1 at 20% AWC. During frozen storage of the Nori-net, the F-v/F-m of the frozen gametophyte was low but stable, and ranged between 0.10 +/- 0.02 SD and 0.14 +/- 0.05 SD. The magnitude of F-v/F-m for the gametophyte of the freezing treatment, after 10min and 3h of immersion in seawater, recovered quickly. After 10min and 3h of immersion, these values were 0.29 +/- 0.12 SD and 0.47 +/- 0.05 SD during the 14days of freezing treatment, and 0.15 +/- 0.02 SD and 0.29 +/- 0.04 SD after 71days of freezing treatment, and suggest that the ability to recover gradually decreased as the storage duration increased. The response of F-v/F-m from general cultivation (i.e., directly cultivated from the nursery cultivation season) and those after 47days of freezing were almost identical, suggesting that the current Nori-net frozen storage period (6 or 7weeks) was not detrimental to the gametophyte.