Abstract According to the River Continuum Concept, headwater streams are richer in allochthonous (e.g. terrestrial leaves) than autochthonous (e.g. algae) sources of organic matter for consumers. However, compared to algae, leaf litter is of lower food quality, particularly ω‐3 polyunsaturated fatty acids (n‐3 PUFA), and would constrain the somatic growth, maintenance, and reproduction of stream invertebrates. It may be thus assumed that shredders, such as Gammarus, receive lower quality diets than grazers, e.g. Ecdyonurus, that typically feed on algae. The objective of this study was to assess the provision of dietary PUFA from leaf litter and algae to the shredder Gammarus and the grazer Ecdyonurus. Three different diets (algae, terrestrial leaves, and an algae–leaf litter mix) were supplied to these macroinvertebrates in a flume experiment for 2 weeks. To differentiate how diet sources were retained in these consumers, algae were isotopically labelled with 13C. Both consumers became enriched with 13C in all treatments, demonstrating that both assimilated algae. For Gammarus, n‐3 PUFA increased, whereas n‐6 PUFA stayed constant. By contrast, the n‐3 PUFA content of Ecdyonurus decreased as a consequence of declining algal supply. Results from compound‐specific stable isotope analysis provided evidence that the long‐chain n‐3 PUFA eicosapentaenoic acid (EPA) in both consumers was more enriched in 13C than the short‐chain n‐3 PUFA α‐linolenic acid, suggesting that EPA was taken up directly from algae and not from heterotrophic biofilms on leaf litter. Both consumers depended on algae as their carbon and EPA source and retained their EPA from high‐quality algae.

中文翻译：

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底栖无脊椎动物中藻碳的优先保留：来自室外水槽实验的稳定同位素和脂肪酸证据


摘要 根据河流连续体概念，对于消费者而言，源头溪流中的外来有机物（例如陆地树叶）来源比本地来源（例如藻类）更丰富。然而，与藻类相比，落叶层的食物质量较低，特别是ω-3多不饱和脂肪酸（n-3 PUFA），并且会限制河流无脊椎动物的体细胞生长、维持和繁殖。因此可以假设，撕碎动物（例如伽马鲁斯）所接受的饮食质量低于食草动物（例如通常以藻类为食的蜕皮动物）。本研究的目的是评估从落叶和藻类中向切碎的伽马鲁斯和食草动物蜕皮的膳食多不饱和脂肪酸的提供情况。在为期两周的水槽实验中，向这些大型无脊椎动物提供了三种不同的食物（藻类、陆地树叶和藻类-树叶混合物）。为了区分这些消费者如何保留饮食来源，我们对藻类进行了 13C 同位素标记。两名消费者在所有处理中都富含 13C，这表明两人都吸收了藻类。对于 Gammarus，n-3 PUFA 增加，而 n-6 PUFA 保持不变。相比之下，由于藻类供应减少，脱皮藻的 n-3 PUFA 含量下降。化合物特异性稳定同位素分析结果证明，两个消费者中的长链 n-3 PUFA 二十碳五烯酸 (EPA) 比短链 n-3 PUFA α-亚麻酸更富含 13C，这表明 EPA直接从藻类中吸收，而不是从落叶上的异养生物膜中吸收。两位消费者都依赖藻类作为碳和 EPA 来源，并从优质藻类中保留了 EPA。