Diatoms are one of the most abundant, diverse and ecologically relevant phytoplanktonic group, contributing enormously to global biogeochemical processes like the carbon and silica cycles. This large success has been partly attributed to the mechanical and optical properties of the silica shell (the frustule) that envelops their body. But since they lack motility it is difficult to conceive how they cope with the fast-fluctuating environment they live in and where distributions of resources are very heterogeneous and dynamical. This pinpoints an important but yet poorly understood feature of diatoms physiology: buoyancy regulation that helps them controlling their sinking speed and position in the water column. While buoyancy regulation by light and nutrients availability has been well studied, the effect of hydromechanical stress via fluid shear has been rather overlooked when considering diatoms dynamics. Here, we aim to start filling this gap by first presenting direct experimental evidences for buoyancy control in response to hydro-mechanical stress and then review recent theoretical models where simple couplings between local shear and buoyancy control always result in heterogeneous cell distributions, specific accumulation regions within complex flows and increased sedimentation times to the depths, features of direct ecological relevance. We conclude by suggesting future experiments aiming to unveil such coupling and therefore gain better understanding on the fate of these fascinating microorganisms in their natural habitat. This article is part of the theme issue ‘Stokes at 200 (part 2)’.

中文翻译：

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关于下沉硅藻的命运：海洋中活性浮力调节细胞的运输

硅藻是最丰富、多样化和生态相关的浮游植物群之一，对碳和二氧化硅循环等全球生物地球化学过程做出了巨大贡献。这一巨大的成功部分归功于包裹它们身体的硅壳（硅藻壳）的机械和光学特性。但由于它们缺乏运动能力，很难想象它们如何应对所生活的快速波动的环境以及资源分布非常多样化和动态的环境。这指出了硅藻生理学的一个重要但知之甚少的特征：浮力调节，帮助它们控制它们在水柱中的下沉速度和位置。虽然已经很好地研究了光和养分可用性对浮力的调节，在考虑硅藻动力学时，流体剪切产生的流体力学应力的影响被相当忽视。在这里，我们的目标是通过首先提出响应流体机械应力的浮力控制的直接实验证据开始填补这一空白，然后回顾最近的理论模型，其中局部剪切和浮力控制之间的简单耦合总是导致不均匀的细胞分布，特定的积累区域在复杂的流动和增加的深度沉积时间中，具有直接生态相关性的特征。最后，我们建议未来的实验旨在揭示这种耦合，从而更好地了解这些迷人微生物在其自然栖息地中的命运。本文是主题问题“斯托克斯 200（第 2 部分）”的一部分。