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Biology and the Mechanics of the Wave-Swept Environment

Biology and the Mechanics of the Wave-Swept Environment

Copyright Date: 1988
Pages: 344
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    Biology and the Mechanics of the Wave-Swept Environment
    Book Description:

    This text introduces and draws together pertinent aspects of fluid dynamics, physical oceanography, solid mechanics, and organismal biology to provide a much-needed set of tools for quantitatively examining the biological effects of ocean waves. "Nowhere on earth does water move as violently as on wave-swept coasts," writes the author, "and every breaker that comes pounding on the shore places large hydrodynamic forces on the organisms resident there." Yet wave-swept coral reefs and rocky shores are home to some of the world's most diverse assemblages of plants and animals, and scientists have chosen these environments to carry out much of the recent experimental work in community structure and population dynamics. Until now these studies have been hampered because biologists often lack a working understanding of the mechanics of the wave-swept shore. Mark Denny here supplies that understanding in clear and vivid language.

    Included are an introduction to wave-induced water motions and the standard theories for describing them, a broad introduction to the hydrodynamic forces these water movements place on plants and animals, and an explanation of how organisms respond to these forces. These tools are put to use in the final chapters in an examination of the mechanisms of "wave exposure" and an exploration of the mechanical determinants of size and shape in wave-swept environments.

    Originally published in 1988.

    ThePrinceton Legacy Libraryuses the latest print-on-demand technology to again make available previously out-of-print books from the distinguished backlist of Princeton University Press. These paperback editions preserve the original texts of these important books while presenting them in durable paperback editions. The goal of the Princeton Legacy Library is to vastly increase access to the rich scholarly heritage found in the thousands of books published by Princeton University Press since its founding in 1905.

    eISBN: 978-1-4008-5288-8
    Subjects: Ecology & Evolutionary Biology

Table of Contents

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  1. Front Matter
    (pp. i-vi)
  2. Table of Contents
    (pp. vii-x)
    (pp. xi-xii)
    (pp. xiii-2)
  5. CHAPTER 1 Introduction: The Need for Proper Tools
    (pp. 3-5)

    As a graduate student in biology, I had somehow thought I was prepared. After all, I had dissected my share of pickled invertebrates, and I had thumbed throughBetween Pacific Tidesso many times that it became an old friend. With this kind of preparation, I asked myself, how many surprises could there be left in my first trip to a wave-swept rocky shore?

    I was on my way to Tatoosh Island, a small dot on the map lying about a half mile off of Cape Flattery, Washington. It is the most northwestern point in the lower forty-eight states and...

  6. CHAPTER 2 The Organisms
    (pp. 6-17)

    Throughout this book we approach the topic of wave-swept organisms from the viewpoint of a team of engineers assigned the task of designing a new, improved plant or animal. A potential difficulty is associated with this mechanistic view, in that it works exactly backwards from the process of evolution: we start with a set of design criteria and end with the mechanical structure(s). But the present structures of plants and animals are in fact the result of natural selection (a process of trial and error), not of a goal-directed design process. Natural selection starts with the mechanism (a plant or...

  7. CHAPTER 3 An Introduction to Fluid Dynamics
    (pp. 18-30)

    In this chapter we begin to explore the physics of moving fluids. In doing so, we set forth on a long and tortuous road. The subject of fluid dynamics is extremely complex, and the accurate and complete description of even the simplest of flows involves the use of mathematics. In this introduction we will take the first few steps toward understanding moving fluids and keep the mathematics to a minimum (a more mathematical approach will come in Chapters 5 to 11).

    As far as possible, the basic concepts will be explained through intuitive examples. But there is some danger in...

  8. CHAPTER 4 An Introduction to Water Waves
    (pp. 31-44)

    Waves are commonplace. It would be difficult to imagine a world that does not resound with light waves, sound waves, radio waves, and water waves. The attempt to understand wave motion fully has occupied whole legions of physicists and mathematicians for the last three centuries, and the size of the literature on wave mechanics is staggering. Much of this research has been directed toward wave forms that are not readily tangible. For instance, an electron may be thought of as a wave, but it is difficult to pick one up and examine it. In such cases, we must resort to...

  9. CHAPTER 5 Wave Theories
    (pp. 45-71)

    The simple, often qualitative approach taken in Chapter 4 provides an intuitive understanding of wave action, but its utility is severely limited. For instance, what if we need to know the water’s acceleration at a depth of 3 m beneath a periodic wave 2 m high? This simplified approach cannot provide an accurate answer. What are the pressure changes at the bottom as a wave passes overhead? These pressure changes are a useful way of measuring wave heights (Chapter 19), but the approach taken so far does not specify the relationship between wave height and bottom pressure. To be able...

  10. CHAPTER 6 The Random Sea
    (pp. 72-85)

    In the last two chapters we have considered the fluid motions accompanying water waves. This analysis has assumed that waves in deep water have a sinusoidal shape and that one wave is much like another, with wave height and period essentially the same. Such a depiction of the water surface is shown schematically in Figure 6.1a, but it is not an accurate portrait. A brief visit to the seashore will convince anyone that no two waves are exactly alike, and that successive waves can be quite different in both their height and period. A more typical picture of the ocean...

  11. CHAPTER 7 Breaking and Broken Waves
    (pp. 86-104)

    In Chapter 5 we examined waves as they exist in deep and shallow water, but we did not follow one particular wave as it moves inshore and breaks. The process of moving from deep to shallow water is known ashoaling, and a simple theory for wave shoaling is the next topic of discussion.

    We begin by examining the rate at which energy is conducted by waves. Consider a vertical plane 1 m wide lying parallel to the wave crests and extending from the bottom of the ocean through the surface. As waves move ashore, how much energy is conducted...

  12. CHAPTER 8 Tides
    (pp. 105-116)

    Tidal fluctuations in sea level have profound effects on the lives of wave-swept organisms. Certainly for those organisms in the intertidal zone, the tides are “the heartbeat of the ocean” (Defant 1958). However, in addition to their biological relevance, tides are also of economic importance, determining when waters will be navigable and when tidal currents flow. In response to this economic importance, the governments of various nations go to a great deal of trouble each year to predict the tides for the world’s shores. Unlike information about wave patterns or fluid-dynamic forces, accurate information about the tides is as close...

  13. CHAPTER 9 Benthic Boundary Layers
    (pp. 117-132)

    In our examination of linear wave theory (Chapter 5), we worked with a model of wave motion that, for simplicity, treated water as an “ideal,” inviscid fluid. By ignoring the existence of viscosity we predicted that under waves in shallow water sizable horizontal velocities extend all the way to the sea bed (Fig. 4.6). For a viscous fluid constrained to satisfy the no-slip condition, this conclusion is clearly false. But, fortunately for this model, the actual consequences of viscosity are confined to areas very close to the substratum, and they have only minor effects on overall wave motion. Linear wave...

  14. CHAPTER 10 Turbulence and Mixing
    (pp. 133-153)

    Although moving fluids and organisms often form an adversary relationship, many aspects of biology actually require the movement of water. For instance, passive filter feeders rely on water currents to bring food within their grasp. Planktonic larvae depend on water flow to disperse any substantial distance, and, once dispersed, require flow to return to the substratum. The swash of waves prevents organisms from desiccating in the high intertidal zones, and all aquatic organisms need some water movement to carry away their waste and to bring in new supplies of oxygen or carbon dioxide.

    Although water movement can be a “good...

  15. CHAPTER 11 Hydrodynamic Forces
    (pp. 154-175)

    In chapters 4 through 7 we saw how waves are accompanied by complex water flows. We now use this information in an attempt to understand and predict the forces that these water motions impose on wave-swept organisms.

    Consider the situation shown in Figure 11.1a. An inviscid fluid flows past a horizontal circular cylinder, here seen end-on. The bulk of the fluid moves at a constant velocity,u0, although, as we can see from the pattern of streamlines, the velocity varies in the vicinity of the cylinder. In particular, the velocity along the top and bottom of the cylinder is higher...

  16. CHAPTER 12 Properties of Biological Materials
    (pp. 176-194)

    What happens when a force is applied to a solid material? Imagine yourself grabbing a rubber band, pulling on it, and noting the results: the more force you place on the rubber band, the farther it deforms. If you maintain a constant force, the rubber band maintains a constant length, and when you remove the force the rubber goes back to its original dimensions. If you stretch the rubber band beyond some limit, it breaks. These simple observations embody all the concepts required to describe accurately the properties of solid materials. They are, however, qualitative. In order to make use...

  17. CHAPTER 13 Static Beam Theory
    (pp. 195-211)

    Examples of simple loading regimes are difficult to find in nature. As a rule, organisms come in rather bizarre and complex shapes, and hydrodynamic forces can cause the application of complex stresses. To tie together our knowledge of applied forces and material properties, we must first account for the role ofshapein determining the capabilities of structures. This is the province of a large body of engineering endeavor cumulatively known asbeam theory.

    Consider a piece of material loaded in tension. If the force is applied uniformly, the stress near the end is the same no matter where in...

  18. CHAPTER 14 Dynamic Beam Bending
    (pp. 212-227)

    We have assumed that the forces we dealt with in the preceding chapter act at static equilibrium. But when a force is applied to a cantilever, the beam has to bend to provide the stresses required for equilibrium. For any real beam, a finite velocity is acquired during the course of this deflection, giving the beam some inertia, and we have yet to take this factor into account. To do so we need a method for describing the dynamic responses of cantilevers.

    All descriptions of the dynamics of oscillating systems are based on the idea ofharmonic motion, and it...

  19. CHAPTER 15 Adhesion
    (pp. 228-237)

    The term “adhesion” is used here in a very general sense: adhesion is the force that tends to hold two objects together. This term could be applied to all the component parts of an organism (cell-cell adhesion, etc.), but the two objects we are most interested in are an organism as a whole and the substratum to which it adheres.

    Perhaps the simplest form of adhesion is mechanical adhesion. For instance, if a crab wants to adhere to a rock, it wraps its legs around some protuberance. To dislodge the animal one must forcibly unbend its legs. This type of...

  20. CHAPTER 16 Structural Wave Exposure
    (pp. 238-262)

    In the preceding fifteen chapters we have examined the mechanics of the wave-swept environment in considerable detail, so we are now in a position to apply our knowledge in a coordinated exploration of the biological consequences of the physical environment. These consequences are traditionally lumped together aswave exposure, a term that is a bit too all-encompassing for present purposes. In this chapter we confine ourselves to what is more appropriately calledstructural wave exposure, the environmental determinants of a plant’s or animal’s structural integrity. For example, from our knowledge of waves we can (at least in theory) specify the...

  21. CHAPTER 17 Mechanical Determinants of Size and Shape
    (pp. 263-279)

    In the last chapter we briefly examined the role that wave forces play in determining the survivorship of an organism of a given size and shape. In this chapter we extend these ideas by exploring the possibility that the wave-force environment may have been an important selection pressure in determining the shape of these organisms and the size to which they grow.

    The basic premise behind this discussion is familiar to any biologist—we measure the success of an organism by how many young it produces. The more surviving progeny an organism produces, the larger its relative contribution to the...

  22. CHAPTER 18 Whither Hence?
    (pp. 280-281)

    Our exploration now draws to a close. The previous chapters have presented a particular perspective on the study of wave-swept organisms, providing an introduction to the tools through which this perspective can be explored. Though we have not yet explored all the possible questions and answers regarding the mechanics of the wave-swept environment, we have run out of data on which to base useful speculation. It is tempting to extend this exploration out of the realm of science and into the world of “fun with numbers,” but we should resist this temptation. Before the examination of mechanics in the wave-swept...

  23. CHAPTER 19 Techniques of Measurement
    (pp. 282-308)

    In the past eighteen chapters we have discussed in detail the nature of the wave-swept environment and its biological consequences. In many places we have assumed that a certain kind of measurement can be accurately made. If we want to know the water velocity in a certain habitat, we grab our trusty, all-purpose velocity meter and go out and measure it. If we want to know the drag coefficient of a certain animal, we stick the creature in our drag meter, and voilà! This cavalier attitude toward the measurement of flows and forces, though it may be handy for discussing...

  24. APPENDIX: List of Symbols
    (pp. 309-312)
    (pp. 313-320)
  26. INDEX
    (pp. 321-329)