Accelerational Forces in Breaking Waves: Their Nature and Biological Consequences

丹尼9313891冲浪区岩质海岸水流具有速度快、加速大的特点，对被海浪冲刷的底栖生物具有重要影响。特别是，破碎波下的加速可以超过重力的40倍，导致大量的加速力被假设为在各种潮间带生物中设定了分布限制和机械大小限制。然而，目前关于冲浪区加速度的信息不足以预测遇到给定震级的加速度的可能性。针对这些问题，本研究项目将解决四个主要目标：(1)将在具有代表性的岩石潮间带站点测量冲浪带加速度，并描述它们与同时的瞬时速度的关系。(2)决定有机体遇到给定速度和加速度时所受力的形状系数将在实验室中测量。实验将集中于测试一种具有代表性的藻类物种。(3)通过比较施加在田间实际植物上的力和根据实验室数据预测的力，来测试实验室得出的形状因子预测田间藻类所受作用力的能力。(4)通过实验室和现场测量，探讨加速力对海浪藻类的理论意义。为此，将测量几种藻类的强度分布，并将使用现有的数学模型来预测作为大小和波浪暴露的函数的生存。总而言之，这些数据将被用来估计这些物种的分布和大小限制，这一结果对潮间带群落生态学具有重要意义和适用性。此外，还将进行实验，以量化湍流诱导的剪应力对受精和早期发育的影响。大多数潮间带无脊椎动物是通过体外受精繁殖的。然而，由于破碎的海浪会迅速卷走产卵动物掉下的配子，高度动荡的海浪带中的生命对繁殖构成了严峻的挑战。最近的实验表明，由破碎波引起的湍流混合迅速稀释配子，导致受精成功率较低。但暴露在湍流中除了稀释配子外，还有其他后果：有一些迹象表明，湍流引起的剪应力可能会机械地损害配子，并可能阻碍卵子与精子的结合。此外，即使卵子受精，暴露在湍流中也可能延缓和改变发育。通过将配子和胚胎暴露于在两个旋转圆柱体之间剪切的液体中产生的高剪应力(Couette流)，将模拟高度湍流海浪带中的受精。在近岸混合层环境中发现的低到中等水平的剪切力的长期影响将使用一个水箱进行研究，在水箱中，湍流是由从振荡网格中脱落的涡流产生的。***

Dennny 9313891 Surf-zone flows on rocky shores are characterized by rapid velocities and large accelerations, with important consequences for wave-swept benthic organisms. In particular, accelerations beneath breaking waves can exceed 40 times gravity, inducing substantial acceleration forces that have been hypothesized to set both distribution limits and mechanical size limits in a variety of intertidal organisms. However, information on surf-zone accelerations is presently inadequate to predict the likelihood of encountering accelerations of given magnitude. In response to these issues, this research project will address four major goals: (1) Surf-zone accelerations will be measured at a representative rocky intertidal site, and their relationship to concurrent, instantaneous velocities will be described. (2) The shape factors that determine the force experienced by an organism encountering a given velocity and acceleration will be measured in the laboratory. Experiments will focus on testing a representative variety of algal species. (3) The ability of the laboratory-derived shape factors to predict forces on algae in the field will be tested by comparing the forces acting on actual plants in the field to forces predicted on the basis of the laboratory data. (4) Using the laboratory and field measurements, the theoretical implications of the accelerational force to wave-swept algae will be explored. To this end, strength distributions of several algal species will be measured, and existing mathematical models will be used to predict survivorship as a function of size and wave exposure. Together, these data will be used to estimate distributional and size limits in these species, results that have significance and applicability to intertidal community ecology in general. Additionally, experiments will be carried out to quantify the effect of turbulence-induced shear stress on fertilization and early development. The majority of intertidal invertebrate an imals reproduce by external fertilization. However, because breaking waves quickly sweep away gametes shed by spawning animals, life in the highly turbulent surf zone poses a severe challenge to reproduction. Recent experiments have shown that turbulent mixing caused by breaking waves rapidly dilutes the gametes, resulting in low fertilization success. But exposure to turbulence has consequences other than gamete dilution: there are some indications that turbulence-induced shear stresses may mechanically damage gametes and could hinder egg-sperm binding. Furthermore even when eggs are fertilized, exposure to turbulence may retard and alter development. Fertilization in the highly turbulent surf-zone will be simulated by exposing gametes and embryos to the high shear stresses developed in liquid sheared between two rotating cylinders (Couette flow). The longer-term effects of the low to moderate levels of shear stress found in the near-shore mixed-layer environment will be studied using a tank in which turbulence is created by vortices shed from an oscillating grid. ***