Wave forces on intertidal organisms: A case study1

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−1 and accelerations of at least 400 m s−2 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 (Collisella 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.