Methane enrichments are frequently observed in the oxic upper water column of the central Baltic Sea during summer months. However, methane sources as well as the fate of methane produced in surface near waters still remain unclear. In the present study, we conducted ship-based grazing experiments to examine the presence of methanogenic archaea in copepod faecal pellets. We quantified bacterial and archaeal 16S rRNA and the mcrA gene and transcripts within copepod faecal pellets by using droplet digital polymerase chain reaction. We showed that the pellets (< 150-µm) harbour a small number of methanogenic archaea; however, mcrA transcripts indicating methanogenic activity were not detected. This suggests that copepod faecal pellets from the central Baltic Sea, similar to analogous data on copepod guts, harbour the potential but are an unlikely hotspot for methane production by methanogenic archaea.

中文翻译：

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波罗的海桡足类粪便颗粒中产甲烷古细菌的定量

在夏季的几个月里，经常在波罗的海中部的含氧上部水柱中观察到甲烷富集。然而，甲烷来源以及在靠近水域的地表产生的甲烷的归宿仍不清楚。在本研究中，我们进行了基于船舶的放牧实验，以检查桡足类粪便颗粒中是否存在产甲烷古菌。我们通过使用液滴数字聚合酶链反应量化了桡足类粪便颗粒中的细菌和古菌 16S rRNA 以及 mcrA 基因和转录物。我们发现颗粒 (< 150 µm) 含有少量产甲烷古菌；然而，没有检测到表明产甲烷活性的 mcrA 转录本。这表明来自波罗的海中部的桡足类粪便颗粒，类似于桡足类内脏的类似数据，