Resource accumulation of the kelp Saccharina ochotensis based on photosynthetic rate and specific nutrient uptake kinetics

Abstract

To demonstrate the resource accumulation of Saccharina ochotensis, hatchery-raised young sporophytes collected from Rishiri Island, Hokkaido were cultivated in Matsushima Bay, Miyagi, Japan, from November 2000 to July 2001. Seasonal morphologies, carbon and nitrogen content, photosynthetic rates, and nutrient uptake kinetics were examined. The blade length of the kelp reached a maximum in May, and then decreased as a result of an increase in erosion rate. The blade weight increased gradually from January until July when the carbon and nitrogen content increased markedly at the meristem. The high photosynthetic rate in the part of the blade with the maximum width and in the apical part was maintained from January to June. At the meristem, the uptake rate of NH4–N increased significantly from May to July. The correlations between NO3–N and NH4–N concentrations and the uptake rates of the kelp were fitted to hyperbolic regressions, indicating high uptake ability at high and low nutrient concentrations, in winter and summer, respectively. These results suggest adaptation of the kelp to seasonal nutrient conditions in the northern Sea of Japan. Resource accumulation in the meristem is the result of marked expansion of the blade area from winter to spring, when sufficient carbon and nitrogen are produced by a high rate of photosynthesis, high nutrient uptake ability, and translocation of resources from the eroding apical part of the blade. This resource accumulation is likely to be essential for regrowth of the kelp the following year. The high NH4–N uptake ability of S. ochotensis shows a positive correlation between a temporal increase in nutrient concentration and thallus growth.