Physiological ecology on formation and maintenance of marine forest

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Recent warm and nutrient-stressed oceanographic condition resulted in widespread losses of marine forest in many part of the world. The significance of nutrient availability on formation and maintenance of marine forest was investigated by some culture studies and a field experiment. In the culture studies, the combined effect of high water temperature and low nutrient concentration on growth and survival in fucoid algae Sargassum yesoense and S. confusum was examined. These species in low nutrient concentration grew in 5-30℃, but could not survive in 35℃. We previously reported that the young sporophyte of the kelp Ecklonia cava withered within 12 days in 30℃ and low nutrient concentration. These results suggest that the fucoids have high-temperature and nutient-stressed tolerance compared with the kelp. In the field experiment, liquid fertilizer was continuously provided into a crustose collarine bed in western coast of Hokkaido, nothern Japan, and the growth of the kelp Saccharina japonica transplanted in November was compared with that transplanted to another site without fertilizing. The kelp with fertilizing grew until January, but the kelp without fertilizing disappeared. These results suggest that the nutrient availability has a significant role for the formation of marine forest. Further studies of the nutrient requirement of kelp and fucoids are necessary to develop the marine afforestation technique by fertilizing.