ABSTRACT: Anthropogenic carbon dioxide (CO₂) emissions drive climate change and pose one of the major challenges of our century. The effects of increased CO₂ in the form of ocean acidification (OA) on the communities of marine planktonic eukaryotes in tropical regions such as the Timor Sea are barely understood. Here, we show the effects of high CO₂ (mean ± SD pCO₂ = 1823 ± 161 μatm and pH_T = 7.46 ± 0.05) versus in situ CO₂ (504 ± 42 µatm, 7.95 ± 0.04) seawater on the community composition of marine planktonic eukaryotes after 3 and 48 h of treatment exposure in a shipboard microcosm experiment. Illumina sequencing of the V9 hypervariable region of 18S rRNA (gene) was used to study the eukaryotic community composition. Increased CO₂ significantly suppressed the relative abundances of different eukaryotic operational taxonomic units (OTUs), including important primary producers, although the chlorophyll a concentration remained constant. OA effects on eukaryotes were consistent between total (DNA-based) and active (cDNA-based) taxa after 48 h, e.g. for the diatoms Trieres chinensis and Stephanopyxis turris. Effects of OA on the relative abundances of OTUs were often species- or even ecotype-specific, and the incubation selectively allowed for detection of the OA-sensitive OTUs that benefitted the most from incubation in a closed bottle, as containment effects on the community structure were evident after 48 h. Many OTUs were adversely affected by sudden decreases of seawater pH, suggesting high sensitivity to OA at the base of the tropical marine biodiversity and difficult-to-predict outcomes for food-web functioning in the future ocean.

中文翻译：

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对海洋酸化的短期反应：对热带帝汶海真核浮游生物相对丰度的影响

摘要：人为排放的二氧化碳（CO ₂）推动了气候变化，并构成了本世纪的主要挑战之一。人们几乎不了解以海洋酸化（OA）形式增加的CO ₂对热带地区（例如帝汶海）海洋浮游性真核生物群落的影响。在这里，我们显示了高CO ₂相对于原位CO ₂的影响（平均值±SD p CO ₂ = 1823±161μatm，pH _T = 7.46±0.05）在舰船缩影实验中，暴露于海洋浮游性真核生物的3,48 h后，（504±42 µatm，7.95±0.04）海水对海洋组成的影响。18S rRNA（基因）的V9高变区的Illumina测序用于研究真核生物群落组成。尽管叶绿素a浓度保持恒定，但增加的CO ₂显着抑制了不同的真核生物操作分类单位（OTU）的相对丰度，包括重要的初级生产者。OA对真核生物的作用在48小时后的总类群（基于DNA）和活动类群（基于cDNA）之间是一致的，例如对于硅藻Trieres chinensis和Stephanopyxis turris。OA对OTU相对丰度的影响通常是物种特异性的，甚至是生态型特异性的，并且通过选择性培养可以检测出对OA敏感的OTU，这对封闭瓶中的培养最有利，因为它对群落结构具有遏制作用在48小时后可见。海水pH值突然下降对许多OTU产生了不利影响，表明热带海洋生物多样性基础上对OA的高度敏感性以及未来海洋食物网功能的难以预测的结果。