Ruiz Javier, Macías Diego, Peters Francesc
Instituto de Ciencias Marinas de Andalucía and Consejo Superior de Investigaciones Científicas, Area de Ecología, Facultad de Ciencias del Mar, Universidad de Cádiz, Campus Río San Pedro, 11510 Puerto Real, Cádiz, Spain.
Proc Natl Acad Sci U S A. 2004 Dec 21;101(51):17720-4. doi: 10.1073/pnas.0401539101. Epub 2004 Dec 15.
It is a well known fact that stirring keeps particles suspended in fluids. This is apparent, for instance, when shaking medicine flasks, when agitating tea deposits in a mug, or when heavy winds fill the air with dust particles. The commonplace nature of such observations makes it easy to accept that this feature will apply to any natural phenomenon as long as the flow is turbulent enough. This has been the case for phytoplankton in the surface mixed layers of lakes and oceans. The traditional view assumes that an increase in turbulence bears ecological advantages for nonmotile groups like diatoms that, otherwise, would settle in deep and unlit waters. However, this assumption has no theoretical ground, and the experimental results we present here point in the opposite direction. Phytoplankton settling velocity increases when turbulence intensifies from the low to the higher values recorded in the upper mixed layers of lakes and oceans. Consequently, turbulence does not favor phytoplankton remaining in lit waters but is rather an environmental stress that can only be avoided through morphological and/or physiological adaptations.
搅拌能使颗粒悬浮在流体中，这是一个众所周知的事实。例如，摇晃药瓶、搅动茶杯里的茶渍或者大风扬起空气中的灰尘颗粒时，这一点就很明显。此类观察司空见惯，让人很容易接受这样一个观点：只要水流足够湍急，这个特性就适用于任何自然现象。湖泊和海洋表层混合层中的浮游植物就是如此。传统观点认为，湍流增加对像硅藻这样的非游动生物群体具有生态优势，否则它们会沉降到黑暗的深水中。然而，这一假设没有理论依据，我们在此展示的实验结果却指向相反的方向。当湍流从湖泊和海洋上层混合层记录的低值增强到高值时，浮游植物的沉降速度会增加。因此，湍流不利于浮游植物留在有光照的水域，而是一种环境压力，只能通过形态和/或生理适应来避免。
