Delta Putra1, Haruka Suzuki1, Masakazu N. Aoki1
1Graduate School of Agricultural Science, Tohoku University, Sendai 980-8572, Japan
Eisenia bicyclis is a dominant stipitate understory canopy-forming kelp on the Pacific coast of Japan. The kelp is perennial with 8 years of longevity. While the blades of E. bicyclis are gradually renewed, the stipes are constantly present for supporting blades and have been observed to persist for some time after the loss of blades or the detachment of holdfast. Therefore, the stipes may function as a long-lasting carbon sink, but their contribution to coastal environment have been rarely quantified. In this study, field experiments were conducted to investigate their contribution to carbon storage. Cut pieces of E. bicyclis stipe (N = 6), ca 8 cm long were suspended at the depth of 3 m at subtidal rocky shore of Kitsunezaki, Oshika Peninsula, Japan. Changes in their morphology, wet weight and C/N ratio were recorded for two months with ca two-week intervals. The experiment was conducted in different seasons: summer (Jun-Aug, 2021; 24-27ºC), autumn (Sep-Dec, 2021; 16-23ºC) and spring (Feb-Apr, 2022; 14-22ºC) and the results were compared between seasons and analyzed. Stipe thinning was started from the core region with decreasing stipe weight at a rate of 49% (summer), 26% (autumn) and 6% (spring). C/N ratios over seasons were almost constant, but nitrogen contents were 50% lower in blades than in stipes. In conclusion, it is suggested that E. bicyclis stipes contribute to coastal ecosystem as a long-lasting carbon sink. Accelerated decomposition of kelp stipes with increasing temperature by global warming can reduce their value as dominant coastal carbon sink.