Seasonal changes in the biomass and occurrence of wild sporophytes of Saccharina japonica (Phaeophyceae) on the coast of Cape Ohma, northernmost of Honshu, Japan

Abstract

Seasonal changes in the biomass and occurrence of wild Saccharina japonica (J.E. Areschoug) C.E. Lane, C. Mayes, Druehl & G.W. Saunders sporophytes were investigated at the coast of Cape Ohma, northernmost point of Honshu island, Japan. The blade sizes of marked 25 - 30 sporophytes were monitored at a depth of 14 m each month from November 1991 to December 1994. Their blade elongation was monitored by recording the position of punched holes on the blades to calculate growth rates. The data of algal standing crop, water temperature and NO₃-N concentration were also obtained at each time of sampling. The sporophytes of S. japonica occurred every year except 1992. First- and second-year-old sporophytes grew to the maximum length of ca. 0.8 m and 2 m in spring, respectively. Both of them formed zoosporangial sori from October to February. Regeneration of the blade was observed from October to March for the first-year-old sporophytes. Deterioration of the second-year-old sporophytes occurred from November to December. Annual elongation of the blades of first- and second-year-old sporophytes at the meristematic part was calculated as 1.6 m and 1.8 m, respectively. The blade growth had a significant negative correlation with water temperature, but positive correlation with NO₃-N concentration. First- and second-year- old sporophytes grew at the water temperature lower than 20 °C and 14 °C, respectively. The growth rates decreased at rates of 1.7 mm day^-1 for former and 2.8 mm day^-1 for latter per 1 °C increase.