Accelerational Forces in Breaking Waves: Their Nature and Biological Consequences

岩石海岸上的冲浪带水流具有速度快、加速度大的特点，这对被海浪冲刷的底栖生物有重要影响。特别是，破碎波下的加速度可以超过重力的40倍，产生了巨大的加速度，这种加速度被假设为在各种潮间带生物中设定了分布限制和机械尺寸限制。然而，目前关于冲浪区加速度的资料不足以预测遇到给定量级加速度的可能性。针对这些问题，本研究项目将解决四个主要目标：(1)将在一个具有代表性的岩石潮间带遗址测量冲浪带加速度，并描述其与同步瞬时速度的关系。决定有机体在遇到给定速度和加速度时所受的力的形状因素将在实验室中进行测量。实验将集中于测试一种具有代表性的藻类物种。(3)实验室导出的形状因子预测野外藻类受力的能力，将通过将作用于野外实际植物的力与根据实验室数据预测的力进行比较来检验。(4)通过实验室和现场测量，探讨了波浪藻加速力的理论意义。为此，将测量几种藻类的强度分布，并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存活率。这些数据将用于估计这些物种的分布和大小限制，这些结果对潮间带群落生态学具有重要意义和适用性。此外，还将进行试验来量化湍流引起的剪切应力对受精和早期发育的影响。大多数潮间带无脊椎动物通过体外受精繁殖。然而，由于破碎的海浪会迅速冲走产卵动物的配子，因此在高度湍流的冲浪区生活对繁殖构成了严峻的挑战。最近的实验表明，波浪破碎引起的湍流混合会迅速稀释配子，导致受精成功率低。但是，暴露在湍流中，除了配子稀释之外，还有其他后果：有迹象表明，湍流引起的剪切应力可能会对配子造成机械损伤，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阻碍和改变发育。通过将配子和胚胎暴露在两个旋转圆柱体（库埃特流）之间的液体中产生的高剪切应力中，可以模拟在高度湍流的冲浪区受精。在近岸混合层环境中发现的低到中等水平剪切应力的长期影响将使用一个水槽进行研究，其中湍流是由振荡网格脱落的涡流产生的。＊＊＊

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. ***