[A-CG23] Coastal Ecosystems ? 1. Water Cycle and Land-Ocean Interactions

[ACG23-P07] Comparative study of growth in Manila clam under different environmental conditions of submarine groundwater discharge

*Osamu Tominaga¹, Ryo Sugimoto¹, Katsuhiro Kitagawa¹, Makoto Yamada², Jun Shoji³, Hisami Honda², Shiho Kobayashi⁴, Makoto Taniguchi² (1.Faculty of Marine Biosciences, Fukui Prefectural University, 2.Research institute for Humanity and Nature, 3.Hiromshima University, 4.Kyoto University)

Keywords:submarine groundwater discharge, Manila clam, growth , stable carbon isotope ratio

Submarine Groundwater Discharge (SGD) is often characterized by high concentration of nutrients and documented as an important pathway between land and sea contributing to the biological productivity in coastal waters. We investigated to what extent SGD contributed to the growth of primary consumer by the field rearing experiments of Manila clam at two sites (Mega and Torisaki) along the Mt. Chokai volcanic coast in northern Japan from June to August 2015. Average Radon 222 (²²²Rn) concentration at surface layer of Mega and Torisaki for two months were 4037 Bqm^-3 and 241 Bqm^-3, respectively. The δ¹³C of shell of Manila clam (δ¹³C_SHELL) reflected the δ¹³C _DIC of the ambient water, i.e. lower δ¹³C_SHELL value at Mega than that at Torisaki. There was the positive correlation between ²²²Rn activity and DIN concentration (r=0.881 p<0.01). Contrary to expectations, the average growth rate of Manila clam reared at Mega was slightly smaller than that at Torisaki. The concentration of chlorophyll-a was almost the same at two sites. However water temperature at Mega was about 2 ℃ lower than Torisaki. Kobayashi and Toba (2005) reported that clear positive correlation between the growth rate of Mania clam and rearing water temperature. This suggested the negative effect of low temperature on the growth of manila clam. This study showed the seepage area does not always have a favorable influence on fisheries resources. The larger-scale effects of SGD on biological production of primary consumer is necessary.