Martens Nele, Russnak Vanessa, Woodhouse Jason, Grossart Hans-Peter, Schaum C-Elisa
Institute of Marine Ecosystem and Fishery Science, Olbersweg 24, 22767, Hamburg, Germany.
Helmholtz-Zentrum hereon, Max-Planck-Straße 1, 21502, Geesthacht, Germany.
Environ Res. 2024 Jul 1;252(Pt 4):119126. doi: 10.1016/j.envres.2024.119126. Epub 2024 May 10.
In estuaries, phytoplankton are faced with strong environmental forcing (e.g. high turbidity, salinity gradients). Taxa that appear under such conditions may play a critical role in maintaining food webs and biological carbon pumping, but knowledge about estuarine biota remains limited. This is also the case in the Elbe estuary where the lower 70 km of the water body are largely unexplored. In the present study, we investigated the phytoplankton composition in the Elbe estuary via metabarcoding. Our aim was to identify key taxa in the unmonitored reaches of this ecosystem and compare our results from the monitored area with available microscopy data. Phytoplankton communities followed distinct seasonal and spatial patterns. Community composition was similar across methods. Contributions of key classes and genera were correlated to each other (p < 0.05) when obtained from reads and biovolume (R = 0.59 and 0.33, respectively). Centric diatoms (e.g. Stephanodiscus) were the dominant group - comprising on average 55 % of the reads and 66-69 % of the biovolume. However, results from metabarcoding imply that microscopy underestimates the prevalence of picophytoplankton and flagellates with a potential for mixotrophy (e.g. cryptophytes). This might be due to their small size and sensitivity to fixation agents. We argue that mixotrophic flagellates are ecologically relevant in the mid to lower estuary, where, e.g., high turbidity render living conditions rather unfavorable, and skills such as phagotrophy provide fundamental advantages. Nevertheless, further findings - e.g. important taxa missing from the metabarcoding dataset - emphasize potential limitations of this method and quantitative biases can result from varying numbers of gene copies in different taxa. Further research should address these methodological issues but also shed light on the causal relationship of taxa with the environmental conditions, also with respect to active mixotrophic behavior.
在河口，浮游植物面临着强烈的环境胁迫（如高浊度、盐度梯度）。在这种条件下出现的分类群可能在维持食物网和生物碳泵中发挥关键作用，但关于河口生物群的知识仍然有限。易北河河口也是如此，该水体下游70公里的区域在很大程度上尚未得到充分探索。在本研究中，我们通过宏条形码技术研究了易北河河口的浮游植物组成。我们的目的是确定该生态系统未监测区域的关键分类群，并将我们在监测区域的结果与现有的显微镜数据进行比较。浮游植物群落呈现出明显的季节和空间模式。不同方法得到的群落组成相似。从读数和生物量获得的关键类群和属的贡献相互关联（p < 0.05）（R分别为0.59和0.33）。中心硅藻（如星杆藻）是优势类群——平均占读数的55%，生物量的66 - 69%。然而，宏条形码技术的结果表明，显微镜检查低估了具有混合营养潜力的微微型浮游植物和鞭毛虫（如隐藻）的普遍程度。这可能是由于它们体积小且对固定剂敏感。我们认为混合营养鞭毛虫在河口中下游具有生态相关性，例如，在那里高浊度使生存条件相当不利，而吞噬营养等技能具有根本优势。尽管如此，进一步的发现——例如宏条形码数据集遗漏的重要分类群——强调了该方法的潜在局限性，并且不同分类群中基因拷贝数的变化可能导致定量偏差。进一步的研究应该解决这些方法学问题，同时也应阐明分类群与环境条件之间的因果关系，特别是关于活跃的混合营养行为。
