The foodweb of El Tóbari Lagoon (central-east Gulf of California) was studied for four seasons through the carbon and nitrogen isotopic characterization of primary producers, invertebrates, fish, birds and potential food sources. The range of δ13C measured was much wider for potential food sources than for consumers. Many organisms presented enrichments of δ13C and δ15N values. There was a clear trend toward increasing δ13C and δ15N from base organisms to top-predators in the four seasons. The isotopic and percentage of contribution data confirmed that suspended particulate organic matter and phytoplankton are the main organic source supporting the foodweb. Our results also imply the occurrence of a nutrient transfer from zooplankton to some invertebrates and juvenile fishes. Consumers were composed in four trophic levels, with trophic level 2 occupied by zooplankton and filter-feeders and trophic level 4 occupied by carnivorous fish and most bird species. Carnivorous fish exhibited dietary similarities by a considerable sharing of resources, which could be related to the abundance of possible prey, between invertebrates and juvenile fishes. Crustaceans and fish represented the main food sources of birds, although some birds showed more dietary variation (marine and offshore prey).

中文翻译：

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加利福尼亚湾中东部生态系统中 δ13C 和 δ15N 的时间变化：估计营养关系

通过初级生产者、无脊椎动物、鱼类、鸟类和潜在食物来源的碳和氮同位素特征，对 El Tóbari Lagoon（加利福尼亚湾中东部）的食物网进行了四个季节的研究。与消费者相比，潜在食物来源的 δ13C 测量范围要宽得多。许多生物体表现出 δ13C 和 δ15N 值的富集。在四个季节中，从基础生物到顶级捕食者的 δ13C 和 δ15N 有明显增加的趋势。同位素和贡献率数据证实悬浮颗粒有机物和浮游植物是支持食物网的主要有机来源。我们的结果还暗示了营养从浮游动物转移到一些无脊椎动物和幼鱼的发生。消费者由四个营养级别组成，营养级 2 被浮游动物和滤食动物占据，营养级 4 被食肉鱼类和大多数鸟类占据。肉食性鱼类通过大量共享资源而表现出饮食相似性，这可能与无脊椎动物和幼鱼之间可能猎物的丰富性有关。甲壳类和鱼类是鸟类的主要食物来源，尽管一些鸟类的饮食差异更大（海洋和近海猎物）。