Coral Fertilization as a Model System for Reactive Stirring and Mixing in Free-surface Turbulent Flows

在这个项目中，首席研究员将确定自由海面海洋湍流的物理特性如何影响珊瑚和其他海洋无脊椎动物使用的繁殖策略（广播产卵）的成功。这项研究的及时性被世界范围内珊瑚礁的消亡所打断。其目标是利用基于物理学的研究来了解生命系统中的繁殖，并了解进化适应复杂的湍流物理如何揭示物理本身的微妙之处。产卵的成年雄鱼和雌鱼同时向周围的水流中挤出精子和卵子。随后的受精主要依靠湍流搅拌来混合配子。大多数造礁珊瑚释放浮力的配子，这些配子上升到自由表面，在那里它们被自由表面的湍流搅动。自由表面湍流中的浮力粒子路径是可压缩的，即使底层的三维流是不可压缩的。这就导致了浮力粒子聚集和发散的区域（对应于上升流）。这种物理现象在海洋中漂浮和近表面颗粒的结构中起作用，包括泡沫条纹、石油泄漏和太平洋上臭名昭著的垃圾带，但它对施肥成功的影响尚不清楚。这个研究项目将结合实验室实验和数值模拟来研究自由表面湍流对最初远处浮力标量聚集的影响，并预测广播产卵珊瑚的受精率。首席研究员将把研究方法整合到教学课程中，作为学习流体力学的有效工具，并利用广播产卵的主题作为使K-16学生对工程和科学感兴趣的工具。将开发一个实际操作的互动模块，展示地表湍流对浮力标量的传播和聚集的作用，并将其作为持续努力的一部分，将研究主题整合到推广活动中，其中许多活动直接针对妇女和其他代表性不足的K-16学生。

In this project the Principle Investigator will determine how the physics of free-surface oceanic turbulence impacts the success of a reproductive strategy (broadcast spawning) used by corals and other marine invertebrates. The timeliness of the research is punctuated by the worldwide demise of coral reefs. The goals are to use a physics-based investigation to learn about reproduction in the living system and to see how evolutionary adaptations to complex turbulent physics shed light on subtleties of the physics themselves. Broadcast-spawning adult males and females simultaneously extrude sperm and ova into the surrounding flow. Subsequent fertilization relies primarily on turbulent stirring to mix the gametes. Most reef-building corals release buoyant gametes that rise to the free surface, where they are stirred by the free-surface turbulent flow. Buoyant particle paths in free-surface turbulence are compressible, even when the underlying 3D flow is incompressible. This results in regions of buoyant particle coalescence and divergence (corresponding to upwelling). This physical phenomena plays a role in the structure of floating and near-surface particles in the ocean, including foam streaks, oil spills, and the infamous garbage patch in the Pacific, but its effect on fertilization success is unknown. This research program will integrates laboratory experiments and numerical simulations to study the effect of free-surface turbulence on coalescence of initially distant buoyant scalars, and to predict fertilization rates for broadcast spawning corals. The Principle Investigator will integrate research methods into the teaching curriculum as an effective tool for learning fluid mechanics, and use the topic of broadcast spawning as a vehicle for getting K-16 students interested in engineering and science. A hands-on interactive module demonstrating the role of surface turbulence on the spreading and aggregation of buoyant scalars will be developed and used as part of the on-going effort to integrate research topics into outreach activities, many of which directly target women and other underrepresented K-16 students.