Whitman Center, Marine Biological Laboratory, Woods Hole, MA 02543.
Proc Natl Acad Sci U S A. 2013 Oct 29;110(44):17904-9. doi: 10.1073/pnas.1306983110. Epub 2013 Oct 7.
Gelatinous zooplankton populations are well known for their ability to take over perturbed ecosystems. The ability of these animals to outcompete and functionally replace fish that exhibit an effective visual predatory mode is counterintuitive because jellyfish are described as inefficient swimmers that must rely on direct contact with prey to feed. We show that jellyfish exhibit a unique mechanism of passive energy recapture, which is exploited to allow them to travel 30% further each swimming cycle, thereby reducing metabolic energy demand by swimming muscles. By accounting for large interspecific differences in net metabolic rates, we demonstrate, contrary to prevailing views, that the jellyfish (Aurelia aurita) is one of the most energetically efficient propulsors on the planet, exhibiting a cost of transport (joules per kilogram per meter) lower than other metazoans. We estimate that reduced metabolic demand by passive energy recapture improves the cost of transport by 48%, allowing jellyfish to achieve the large sizes required for sufficient prey encounters. Pressure calculations, using both computational fluid dynamics and a newly developed method from empirical velocity field measurements, demonstrate that this extra thrust results from positive pressure created by a vortex ring underneath the bell during the refilling phase of swimming. These results demonstrate a physical basis for the ecological success of medusan swimmers despite their simple body plan. Results from this study also have implications for bioinspired design, where low-energy propulsion is required.
凝胶状浮游动物种群以其接管失调生态系统的能力而闻名。这些动物具有竞争优势，并能在功能上替代表现出有效视觉捕食模式的鱼类，这令人费解，因为水母被描述为游泳效率低下的动物，它们必须依靠与猎物的直接接触来进食。我们表明，水母表现出一种独特的被动能量捕获机制，这种机制被利用来允许它们在每个游泳周期中行进 30%的距离，从而减少游泳肌肉的代谢能量需求。通过考虑净代谢率的大种间差异，我们证明，与普遍观点相反，水母（Aurelia aurita）是地球上最节能的推进器之一，其单位质量每米每焦耳的运输成本低于其他后生动物。我们估计，被动能量捕获减少代谢需求可将运输成本降低 48%，从而使水母能够达到足够猎物相遇所需的大型尺寸。使用计算流体动力学和从经验速度场测量中开发的新方法进行的压力计算表明，这种额外的推力是由游泳过程中钟形物底部的涡环在填充阶段产生的正压引起的。这些结果为水母游泳者的生态成功提供了物理基础，尽管它们的身体结构简单。本研究的结果对于需要低能量推进的仿生设计也具有启示意义。
