Inter-individual variability of stable-isotope ratios in marine organisms

用氮和碳稳定同位素比值分析营养水平比用肠道内容物检查进行的传统食性分析更有优势，因为前者反映了个体动物的长期食物史，而后者仅给出捕获前的食物组成。本研究采用氮碳稳定同位素比值法沿着常规肠内容物分析，研究了相模湾及其邻近沃茨中上层鱼类和虾类摄食习性的个体间差异。1.7%的氮。在中层和深层虾类中，非洄游性深海物种Bentheogennema borealis的Δ ^ C值显著低于<13>两种<15>垂直洄游者，而Δ ^ N值则显著高于两种垂直洄游者。在后者中，Sergiaprehensilis在较大的个体中表现出较高的Δ ^<15>N值，与肠道内容物分析的结果一致（强食肉性）。另一种迁徙动物四棘水蚤的δ ^<15>N值与四棘水蚤相似，但大小之间的差异不太明显，这表明四棘水蚤从相对较年轻的阶段开始摄取营养级较高的食物。垂直迁徙的穆氏毛口鱼（Maurolicus muelleri）的δ ^ N值在个体间存在差异<15>。1.5结果表明，三角洲值提供了个体食物特征和食物历史的有用信息，这些特征与个体的其他生态学特征，如生长、摄食垂直迁移和分布深度。

Analysis of trophic levels by using nitrogen and carbon stable-isotope ratios is advantageous to conventional food-habit analysis by gut-content examination, in that the former reflects a long-term food history of an individual animal, while the latter gives a food composition only immediately before capture. The present studies examined inter-individual variability of food-habits of pelagic fishes, meso-and bathypelagic fishes and shrimps in Sagami Bay and adjacent waters, by applying nitrogen and carbon stable-isotope ratio method along with conventional gut-content analysis.In Japanese anchovy, the individual stable-isotope ratios of both larvae and adults were clustered into two groups, with a variation of ca. 1.7% in nitrogen. In meso-and bathypelagic shrimps, Bentheogennema borealis, a non-migrant, deep-sea species, showed significantly lower delta^<13>C and higher delta^<15>N values than the two vertical migrants. Of the latter, Sergiaprehensilis showed higher delta^<15>N values in larger individuals, coinciding to the result of gut-content analysis (strong carnivory). Acanthephyra quadrispinosa, another migrant, showed delta^<15>N values similar to S.prehensilis but difference between sizes was less marked, suggesting that A.quadrispinosa take foods of higher trophic levels from relatively young stages. Maurolicus muelleri, a vertical migrant, showed inter-individual variations of delta^<15>N of ca. 1.5 times those of the three non-migrating mesopelagic fishes of the genus Cyclothone, suggesting that the former utilizes food resources from both the epi-and mesopelagic layers.In summary, the present results demonstrated that the delta values provide useful information on food characteristics and food history of individual animals and that these characteristics are closely related to other ecological characteristics of individuals, such as growth, vertical migration, and distributional depths.