Understanding the magnitude and causes of isotopic fractionation between organisms and their dietary resources is crucial for gaining knowledge on stable isotope ecology. However, little is known regarding the diet-tissue fractionation values of marine ciliates, which play a critical role in the reconstruction of microbial food webs. In the present study, we conducted experiments on two benthic (Pseudokeronopsis pararubra and Protocruzia labiata) and two pelagic (Strombidium sulcatum and Uronemella filificum) marine ciliates, where they were fed with isotopically constant foods (Chaetoceros calcitrans and Isochrysis galbana) under laboratory culture conditions to determine their carbon and nitrogen isotopic fractionation values (Δ¹³C and Δ¹⁵N). The stable isotope values (δ¹³C and δ¹⁵N) of ciliates for all experiments rapidly increased after the initial feeding, with half-lives ranging from 6.1 to 23.0h for δ¹³C and from 3.1 to 24.9h for δ¹⁵N. The Δ¹³C and Δ¹⁵N for all ciliates represented significantly positive enrichments, with overall mean fractionations of 0.6±0.2 and 1.2±0.4, respectively. Irrespective of the dietary type, both Δ¹³C and Δ¹⁵N were very similar for the same ciliate species. These results suggest that Δ¹³C and Δ¹⁵N for marine ciliates are similar to those found in common marine organisms with very little food-dependent variation. Overall, quantifying the specific isotopic fractionation of marine ciliates is expected to provide fundamental information on the trophic transfer of carbon, nitrogen, and energy flow through the microbial pathway in marine ecosystems.

了解生物体及其膳食资源之间同位素分馏的幅度和原因对于获得稳定同位素生态学的知识至关重要。然而，关于海洋纤毛虫的饮食组织分馏值知之甚少，它们在微生物食物网的重建中起着关键作用。在本研究中，我们对两种底栖动物（拟南芥 和 唇形原蟹) 和两个远洋 (梭菌 和 丝状尿囊藻）海洋纤毛虫，在那里它们被喂以同位素恒定的食物（角毛角藻 和 等鞭金藻) 在实验室培养条件下确定它们的碳和氮同位素分馏值（Δ ¹³ C 和 Δ ¹⁵ N）。所有实验中纤毛虫的稳定同位素值（δ ¹³ C 和 δ ¹⁵ N）在初始喂养后迅速增加，δ ¹³ C 的半衰期为 6.1 至 23.0小时，δ ¹⁵ N 的半衰期为 3.1 至 24.9 小时。所有纤毛虫的 Δ ¹³ C 和 Δ ¹⁵ N 代表显着的正富集，总体平均分馏率分别为 0.6±0.2 和 1.2±0.4。无论饮食类型如何，Δ ¹³ C 和Δ ¹⁵对于相同的纤毛虫物种，N 非常相似。这些结果表明，海洋纤毛虫的Δ ¹³ C 和 Δ ¹⁵ N 与普通海洋生物中发现的相似，食物依赖性变化很小。总的来说，量化海洋纤毛虫的特定同位素分馏有望提供关于碳、氮和能量流通过海洋生态系统微生物途径的营养转移的基本信息。