Exposure to wave action: Measurements of an important ecological parameter on rocky shores on Anglesey

Miller

Stokes

et al. 2003

Water velocities as high as 25 m s Ϫ1 have been recorded in the surf zone of wave-swept rocky shores-velocities more than twice the phase speed of the breaking waves with which they are associated. How can water travel twice as fast as the waveform that initially induces its velocity? We explore the possibility that the interaction of a wave with the local topography of the shore can greatly amplify the water velocities imposed on intertidal plants and animals. Experiments in a laboratory wave tank show that interactions between bores refracted by a prowlike beach can produce jets in which the velocity is nearly twice the bore's phase speed. This velocity can be further amplified by a factor of 1.3-1.6 if the jet strikes a vertical wall. This type of topographically induced amplification of water velocity could result in substantial spatial variation in wave-induced hydrodynamic forces and might thereby help to explain the patchwork nature of disturbance that is characteristic of intertidal communities.

mentioning

confidence: 99%

Extreme water velocities: Topographical amplification of wave‐induced flow in the surf zone of rocky shores

Miller

Stokes

et al. 2003

“…Direct records of wave-induced forces have been obtained at the scale of individual organisms (e.g., Jones and Demetropoulos 1968;Koehl 1977;Bell and Denny 1994;Denny 1995;Gaylord 1999Gaylord , 2000, but these measurements are difficult to conduct in this severe environment. An attractive alternative approach is to generate predictions of forces from measurements of nearshore wave height (Denny 1995;Carrington 2002).…”

mentioning

confidence: 99%

Predicting wave exposure in the rocky intertidal zone: Do bigger waves always lead tolarger forces?

Helmuth

2003

104

Hydrodynamic forces from breaking waves are among the most important sources of mortality in the rocky intertidal zone. Information about the forces imposed by breaking waves is therefore critical if we are to interpret the mechanical design and physiological performance of wave-swept organisms in an ecologically and evolutionarily relevant context. Wave theory and engineering experiments predict that the process of wave breaking sets a limit on the maximum force to which organisms can be subjected. Unfortunately, the magnitude of this limit has not been determined on rocky shores. To this end, at a moderately exposed shore in central California, we measured the maximum hydrodynamic forces imposed on organism-sized benthic objects and related these forces to nearshore significant wave heights. At 146 of 221 microsites, there was a significant and substantial positive correlation between force and wave height, and at 130 of these microsites, force increased nonlinearly toward a statistically defined limit. The magnitude of this limit varied among sites, from 19 to 730 newtons (N). At 37 other sites, there was no significant correlation between surf zone force and wave height, indicating that increased wave height did not translate into increased force at these sites either. At only 16 sites did force increase in proportion to wave height without an apparent upper bound. These results suggest that for most microsites there is indeed a limiting wave height beyond which force is independent of wave height. The magnitude of the limit varies substantially among microsites, and an index of local topography was found to predict little of this variation. Thus, caution must be exercised in any attempt to relate observed variations in ocean ''waviness'' to the corresponding rates of microsite disturbance in intertidal communities.Rocky intertidal invertebrates and algae live in a world of extreme environmental severity, and the risk of damage or dislodgment from wave-generated forces is thought to be among the most important determinants of survival in this habitat (e.g., Dayton 1971; Levin and Paine 1974;Koehl 1979; Paine 1979; Paine and Levin 1981;Sousa 1984;Denny 1987Denny , 1988Carrington 1990Carrington , 2002Bertness et al. 1991;Hunt and Scheibling 1996;Blanchette 1997). Quantifying the hydrodynamic forces acting on organisms, and how they vary in space and in time, is therefore key to understanding the evolutionary and ecological consequences of morphological design and the subsequent effects of wave-driven forces on the dynamics of intertidal ecosystems (Denny 1988;Koehl 1996;Denny and Wethey 2001;Carrington 2002).The use of engineering theory to study these issues has proven fruitful and has led to a deeper understanding of how intertidal organisms are able to withstand the rigors of waveexposed shores (e.g., Koehl 1979;Denny 1988;Carrington 1990Carrington , 2002 Bell and Gosline 1996;Denny et al. 1998;Gaylord 2000). Understanding how organisms resist damage and dislodgment, however, also requires an estima...

“…Quinn 1979;Paine and Levin 198 1;Sousa 1984). In fact, it has been standard practice for many years to correlate the assemblage of organisms present on a shore with the "exposure" (Jones and Demetropoulos 1968;Ricketts et al 1968;Lewis 1968;Newell 1979). The term exposure has generally been taken to * This study was supported by ONR contract NO00 14-79-C-06 11 with logistic support from NSF grant OCE 77-26901 to R. T. Paine. 2 Present address: Hopkins Marine Station, Pacific Grove, California 93950.…”

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confidence: 99%

“…However the action of many small forces, each presenting no physical danger to an organism, may have entirely different biological consequences from a few large forces capable of breaking or dislodging the organism. The converse problem is inherent in the method of force measurement used by Jones and Demetropoulos (1968). A recording spring scale was attached to a small disk and used to record the maximum force encountered over a series of tides.…”

mentioning

confidence: 99%

Wave forces on intertidal organisms: A case study1

1985

107

Breaking waves impose large forces on intertidal organisms, and these forces are important in structuring wave-swept communities. Here a telemetry system is used to continuously record wave forces at an exposed site; the interpretation of one such record is presented as a case study of the nature of wave forces. For waves with a breaking height of 2-4 m, water velocities of at least 8 m s-l and accelerations of at least 400 m s-~ are present near the substratum. The forces imposed on organisms by these flows depend on the size and shape of the organism. For a limpet (CoZZzkeZIa pelta) an average force is about 0.6 N, a maximum about 3 N. The magnitude and direction of wave forces are unpredictable in both time and space over periods of seconds to hours, although predictability is possible over longer periods. A quantitative exposure index, based on an organism's ability to withstand wave forces, shows that various organisms exposed to the same flow are at widely varying risks. No impact forces were observed during this study.