Ralph M. Parsons Laboratory, Department of Civil and Environmental Engineering, Massachusetts Institute of Technology, 77 Massachusetts Avenue, Cambridge, MA 02139, USA.
Nat Commun. 2013;4:2148. doi: 10.1038/ncomms3148.
Patchiness plays a fundamental role in phytoplankton ecology by dictating the rate at which individual cells encounter each other and their predators. The distribution of motile phytoplankton species is often considerably more patchy than that of non-motile species at submetre length scales, yet the mechanism generating this patchiness has remained unknown. Here we show that strong patchiness at small scales occurs when motile phytoplankton are exposed to turbulent flow. We demonstrate experimentally that Heterosigma akashiwo forms striking patches within individual vortices and prove with a mathematical model that this patchiness results from the coupling between motility and shear. When implemented within a direct numerical simulation of turbulence, the model reveals that cell motility can prevail over turbulent dispersion to create strong fractal patchiness, where local phytoplankton concentrations are increased more than 10-fold. This 'unmixing' mechanism likely enhances ecological interactions in the plankton and offers mechanistic insights into how turbulence intensity impacts ecosystem productivity.
斑块性通过决定个体细胞相互作用及其捕食者的速度，在浮游植物生态学中起着根本性作用。在亚米长度尺度上，运动浮游植物的分布通常比非运动物种的分布更为斑块化，但产生这种斑块性的机制仍然未知。在这里，我们表明，当运动浮游植物暴露于湍流中时，小尺度上会出现强烈的斑块性。我们通过实验证明，在单个涡旋中，Heterosigma akashiwo 形成了引人注目的斑块，并通过数学模型证明，这种斑块性是由运动性和剪切力的耦合产生的。当在湍流的直接数值模拟中实施时，该模型表明，细胞运动性可以克服湍流弥散作用，形成强烈的分形斑块性，使局部浮游植物浓度增加 10 倍以上。这种“混合”机制可能会增强浮游生物中的生态相互作用，并为了解湍流强度如何影响生态系统生产力提供机制上的见解。
