Studies on biological production on lower trophic levels in the vicinity of seamount and adjacent waters

1993年6月，利用三重大学的T/S Seisui Maru在Komahashi第二海山附近进行了观测。调查了营养盐、浮游植物的分布和牧草的摄食量。此外，还建立了用培养的微藻测定DNA含量的方法，以评价天然植物生长速度。经测线处理后，高浓度硝酸盐（1 μ M）到达幼水层。在0-200米水柱的综合硝酸盐是1.6倍以上的海山比邻近的水。N/P比值随深度增加而增加，表明硝酸盐的吸收快于磷酸盐。模拟结果表明，涡动扩散使100 m处的硝酸盐浓度升高到1 μ M需要两周以上的时间，由于水柱结构和水流系统在几天内就发生了变化，因此水流系统的非平衡比涡动扩散对营养盐的供应更重要。浮游动物的湿重在80和140毫克/平方米之间<-3>（平均值（）SY. ±. ()1SD，100（）SY. ±. ()15 mg/m2<-3>）。在水柱中的叶绿素a浓度（0.12-0.22 μ g/L）<-1>：0.16（±）SY.（）0.03 μ g/L<1->），白天高，夜间低。浮游动物肠道色素在夜间高。叶绿素a /（叶绿素a^+phaeopigments）比值在1500时最大，2100时最小，与水体中叶绿素a的变化呈负相关，表明放牧控制了浮游植物的丰度。正在进一步分析数据，以了解海山地区周围低营养级的动态。

Observations were conducted in the vicinity of the Komahashi No.2 Seamount during June of 1993, using the T/S Seisui Maru, Mie University. Nutrient ynamics, phytoplankton distributions, and grazes' consumption were investigated. In addition methods to determine DNA amount were established using cultured microalgae to evaluate growth retes of natural phytoplankters.The field observations revealed upward shifted isothermal line in the vicinity of the seamount. Being paralleled with the line, high concentration of nitrate (1 muM) reaced the euphtic layr. Integrated nitrate within 0-200 m water column was 1.6 times higher above the seamount than in the adjacent water. The N/P retio increased with depth, suggesting that uptake was faster for nitrate than phosphate. Simulation based on the sequential observations showed that it should take more than two weeks when eddy diffusion could elevate concentration of nitrate at 100 m to 1 muM.Since water column structure and current system changed within a few days, non-equilibrium of the current system is morr essential than the eddy difusion for supply of nutrients.Diurnal variations of phyto- and zooplankton were investigated traching a buoy. Wet weight of zooplankton varied between 80 and 140 mg m^<-3> (mean(〕SY.+-.〔)1SD, 100(〕SY.+-.〔)15 mg m^<-3>). Chlorophll a concentration in the water colum (0.12-0.22 mug L^<-1> : 0.16(〕SY.+-.〔)0.03 mug L^<1->) was high in day and low in night. Zooplankton gut pigments were high in night. Chlorophyll a / (chlorophyll a^+phaeopigments) ratio of the gut pigments became the maximum at 1500 and the minimum at 2100, showing an inverse correlation with the variation of chlorophyll a in the water column, suggesting grazing controls of phytoplankton abundance. Data are further analyzing for understanding of dynamics in lower trophic levels around the seamount area.